HRC Fuses - Page 1
Forum section: electronics / general

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 03:50:57 am
content: I hear Dave talking all the time about HRC Fuses in multimeters he reviews and I have a few questions:I know HRC means High Rupture Capacity(or something similar), but what good is that in a meter? it not like the glass breaking on a normal meter is going to cut you until you take it apart, or am i missing something?And if they are that much better, can you just replace the glass ones in a normal meter with HRC fuses of the same size and ratings? or is there something special there that would make this not possible?This may be a bit "Noobish" but i appreciate you reading this and replying. Also if this should be in a different section(like the beginner one or the blog one) feel free to have a mod move it where it goes.Thanks

author: Psi
author_rank: Super Contributor
timestamp: January 03, 2011, 04:24:12 am
content: As i understand it... when a normal glass fuse blows under extreme load. ie, you put your meter across something that can supply 1000's of amps at high voltage. The fuse wire inside instantly vaporizes creating massive pressure and heat which explodes outwards melting and breaking the glass case. You then have a shower of molten metal and glass moving out at high speed in all directions and cutting through the multimeter's plastic case as it goes, like a shaped charge cutting through the armour on a tank. So not the kind of thing you want to happen while you're holding the meter. HRC fuses don't explode like that, they are designed to handle the pressure safely.ok, that was probably a bit overly dramatic, it's pretty uncommon for them to actually do that but you get the idea, glass fuses break easier making a mess inside your meter that you have to clean up and which may damager other parts inside or hurt you throught the case. HRC fuses are designed to prevent flashover, the sand inside them melts into glass and because glass is an insulator they stop any arcs from trying to keep the connection.

author: Unknown
author_rank: Unknown
timestamp: January 03, 2011, 04:30:14 am
content: Quote from: mitpatterson on January 03, 2011, 03:50:57 amYes you are missing something, the other thread in this forum has gone off on quite a tangent about CAT ratings and life safety, these are far from the sole reason for selecting HRC fuses.In general semiconductors and PCB tracks are an excellent means of protecting standard rated fuses in electronic devices.A HRC fuse is designed to interrupt current flow in as few cycles as possible. HRC applies as much to the ability to respond quickly as it does to the ability to ensure high fault current flow can be brokenCheap meters use the audible THARWARPPP!!! indication of this error and are reset by substituting a replacement meter with its smoke still intact. Your Fluke or better meter can generally cope with the inadvertent resistance measurement across the mains at least for a few seconds while flashing their display to indicate PEBMAC error.And of course there is the inevitable meter left on amps before a mains measurement. Try that with a standard fuse and the current shunt and PCB tracks will become a shiny patch on the back of the meter case. That is the primary reason for selection of HRC. As CAT rating increase so too do the specifications but what is stated above still applies.Quote from: mitpattersonThey are much better if the task is equipment protection, equally they are much worse if used in applications such as motor starting or capacitor charging. Can you replace the glass fuses in a multimeter with HRC fuses of a similar voltage and current rating? Of course provided you can find ones of suitable dimensions. You can find 00 and 3AG sized HRC fuses, but don't forget to top up the credit on the Visa Card before purchase. But sure you can put a $20 fuse in a $35 Dollar meter.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 04:43:37 am
content: Quote from: Uncle Vernon on January 03, 2011, 04:30:14 amoh, wow, i didn't realize there where that much more expensive. Foe example if i wanted to find some at say, Mouser(http://www.mouser.com/Circuit-Protection/Fuses/_/N-5g3l/) what would i choose to find them? i don't see a HRC catagory, is there another name for them?Oh and for the record, i got a $55 meter, lol

author: Unknown
author_rank: Unknown
timestamp: January 03, 2011, 04:56:16 am
content: Quote from: mitpatterson on January 03, 2011, 04:43:37 amThey can be that expensive one off retail in AU anyway. I'm not in the habit of stressing my meters so I don't see too much need for a bulk buy. You can often get fast acting glass fuses which are better than standard but not up to being classified as HRC.Try a google search on 3AG HRC.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 03, 2011, 05:03:28 am
content: Another thing to consider is the series resistance. If it would significantly affect the circuit voltages while testing current, it would cause a significant inaccuracy.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 05:10:32 am
content: Quote from: NiHaoMike on January 03, 2011, 05:03:28 amHmmmmm... Mouser doesn't seem to list the Series Resistance for the fuse i found. It seems that a Cermaic fuse would still be better than a glass one? am i right? even if its not HRC rated it would probaly be better than glass. Well anyways, tell me what you think of these fuses as drop in replacement's for my Extech EX330 meter(which only has glass fuses, i would probaly just get one or 2 on my next mouser order as replacements in case i ever blow the glass ones)250V 500mA:http://www.mouser.com/ProductDetail/Schurter/00011001/?qs=sGAEpiMZZMseCiJT91fwIpCS8D8NVahFjqM5t9f0yKw%3d250V 10Amp :http://www.mouser.com/ProductDetail/Schurter/00011014/?qs=sGAEpiMZZMseCiJT91fwIiiR5WGKbntkea7k9eh0bPE%3dNow the 10 Amp one mouser list as glass, but the data sheet says is ceramic, so i generally believe the data sheet... but do those both look they could be drop in replacements?(same size, the fuses in the EX330 per my digital calipers are 5mm X 20mm, well a bit different, but thats the closest standard size)

author: Unknown
author_rank: Unknown
timestamp: January 03, 2011, 05:27:23 am
content: Quote from: mitpatterson on January 03, 2011, 05:10:32 amWill it fit? Depends entirely upon the fit and quality of the fuse clips. In general the HRC cartridges are designed with a slightly smaller diameter. So in short you should be able to replace a standard cartridge fuse with a HRC one, (I did say should, not all clips are equal) but you should not be able to fit a cartridge fuse into a holder intended for a HRC fuse. (Application of sufficient force can disprove that theory too, usually with poor end results)

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 05:45:46 am
content: Quote from: Uncle Vernon on January 03, 2011, 05:27:23 amso even with the same 5 X 20 mm dimensions it might not fit?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 03, 2011, 10:23:50 am
content: Forget all of you , the forum counter ranking , and say in simple words your answer to my question .How worst are the Glass FAST blow fuses , from the HRC ?Its an simple question !!And before we get to High Voltage , I will just remind , that size in length does matters,and so lets say that my glass fuse in my question its the long one .Now you have only two things ( reasons ) so to debate about .1) How fast is the " fast " ? (quick blow )2) How safe its either type .My view ..About theNo1: there is an tremendous luck of information,every one speculates that the Fuse testing , had be made by the companies that makes multimeters,because they had to , so to pass the CAT certification , and so they know best ,and their opinion must be accepted and respected .Some people who are trying to find other answers , will get trapped in the physics rules,by ignoring the chemistry ..And some other people will turn to the manufacturers of fuses for additional info,as I did , and I found an total chaos about the measuring standard of its electrical factor.That makes impossible for my head at list, to make reliable comparisons of products among just three manufacturers .About theNo2, there many questions here too .Does all Fuses explode ?What will force one glass fuse to explode ?Is it best the fuse to explode than just burn ?In my opinion I believe that an small bang that will break some glass its no an major event at all.Does the electricity loves the glass more than the porcelain ?The burned material in the Fuse ( wire ) does it maters the chemical consistency after getting burned,to make the exterior of the fuse , as important factor ?Example if I make an fuse that uses as bridging material " toxic metal or elements " I bet that I will use as exterior body on the fuse , something that does not break !!Comparing Fuses , its an very confusing task , because every one speaks with out " Hard evidence " ,at list at my eyes , its not called as " Hard evidence " some videos that show examples of what it will happens , in an very unique situation , regarding accidents in equipment that are used by highly trained personal .... and I am saying all those , because its far from my understanding ,how those examples will become advices that will have any value to the " home users " .. and will have any relation with what they do daily.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2011, 11:41:17 am
content: Quote from: mitpatterson on January 03, 2011, 05:10:32 amIt won't list the series resistance because it varies depending on the current and ambient temperature: the higher the current and temperature, the higher the resistance will be.What is specified is the typical and maximum voltage drop at the rated current. Look at the data sheet and you'll notice that the higher the current rating, the lower the voltage drop which will only be an issue when a low current fuse is used near its rating at very low voltages. This means you won't be able to accurately measure the current drawn by a circuit connected to a couple of AA cells but it won't make a difference on a mains circuit or even one powered from a car battery.http://www.schurterinc.com/var/schurter/storage/ilcatalogue/files/document/datasheet/en/pdf/typ_SP_5x20.pdfQuote from: Kiriakos-GR on January 03, 2011, 10:23:50 amI don't see why anyone should think that.I doubt multimeter manufacturers actually make fuses, the chances are they contract that out to someone who does. All you need to do is replace the fuse with one with the correct current rating and a high enough voltage, breaking capacity and speed to protect the DVM and you. Of course, as you know, the problem is finding out the specification for the fuses supplied by the DVM manufacturer but I suspect any fuse designed to protect semiconductors with the correct rating and high enough voltage rating will do.QuoteAs far as I'm concerned, buying a fuse from a reputable supplier, with the appropriate approvals, is good enough evidence that it won't blow up.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 03, 2011, 11:48:13 am
content: Quote from: Uncle Vernon on January 03, 2011, 04:30:14 amSorry - HRC has no relation to the speed of operation of the fuse. It just relates to the fact that the fuse will interrupt the circuit without rupturing or breaking even with very high (1.5kA+) fault currents. It's easy for 10kA to flow when you put a meter measuring current over a 1000V source.It's quite likely that the HRC fuse in most high end meters will take longer to blow that a fast-acting glass fuse. But it isn't there to protect the meter - it's there to protect the use and stop them having their hand or face blown up if they make a mistake. This is entirely possible - just look for videos on youtube or read some arc flash accident reports. Some meters will have series protection - one set to blow quickly under normal fault conditions, and another to interrupt massive fault currents.Kiriakos, in answer to your questions:1. A fuse curve (I2t) will show how quickly a fuse blows in given conditions. They are widely available. In the UK at least there are standards for any fuse used in mains voltage distribution (BS88). These are easy to find but not always easy to compare - there is no single number to look at.2. Again, this is just in spec sheets. HRC fuses tend to be 1.5kA+ breaking current, and 1" glass fuses 100A (at 250V). If you short a glass fuse across the mains it will not always break the circuit.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2011, 12:22:05 pm
content: Quote from: cybergibbons on January 03, 2011, 11:48:13 amYou also need to take into account of the impedance of the meter and the test leads.For example, suppose the current setting and a cheap meter has a resistance of 1 Ohm, the resistance of the 500mA fuse is 0.5 Ohm and the mains voltage is 230V, the maximum current will be under 153.3A. Now a glass fuse might explode at that current and it might destroy the meter but it's unlikely it'll catch fire or kill you. A word of warning though: if it's the same or even a lower DC voltage it will from an arc which will cause it to catch fire.

author: Unknown
author_rank: Unknown
timestamp: January 03, 2011, 01:08:55 pm
content: Quote from: cybergibbons on January 03, 2011, 11:48:13 amBollocks! Much of the ability to not rupture in entailed in interrupting flow of fault current in the shortest possible time!!! That fault current wont just be flowing in the fuse it'll be flowing through the leads, the shunt the sockets and PCB all of which will let go spectacularly with sustained fault current! Many of the larger HRC cartridges have a rating of maximum number of cycles before interruption.Quote from: cybergibbonsFor sure! which is why interrupting fault current as quickly as possible is an essential parameter.If anyone is messing about with 1000V a high fault current capability on the bench they shouldn't be!And without wheeling out the flashing lights and the OH&S BS, some simple common sense should apply before working on LV or above. Don't work on mains alone, and if your going to work on mains on your bench invest in a RCB, the milliamps are going to kill you dead long before any fault currents based fuse explosion ever does.Quote from: cybergibbonsFor sure although we're yet to see this in anything but specialised equipment.Quote from: cybergibbonsI'll bet you $1000 and a replacement box of glass fuses that those fuses will flame-out across 415V every time. But don't try this at home, such experiments are by convention only performed on-site by small groups of unsupervised third year electrical apprentices with way too much spare time on their hands.

author: Jimmy
author_rank: Regular Contributor
timestamp: January 03, 2011, 01:24:43 pm
content: OP (ad I didn't read all post's)HRC fuses are the same as the glass ones. The current flows through a fillament once the current has exceeded the fuses rating it will blow. If it is over buy a large amount eg putting 4000amp on a 1 amp fuse the fuse blows creating an air gap that will arc like an arc welder, the granular "stuff" inside the fuse is there to extinguish the arc. This means that less electricity is passed onto the rest of the circuit.

author: Chasm
author_rank: Regular Contributor
timestamp: January 03, 2011, 02:16:54 pm
content: Quote from: cybergibbons on January 03, 2011, 11:48:13 amIt is also easy to get kA currents in industrial installations of the "normal" 230/400V net.An real world accident from the nineties of the last century.Part of the completion certificate is the input voltage of the machine. So the electrician grabbed the meter from his box and began measurements. 230/400V only. Nothing fancy, right?The problem is that the certificate calls for a measurement at -but in front of- the input breakers. This machine drew current in excess of 1000A, so the substation was close.Again, the electrician grabbed the meter from his box, switched it from off to voltage and took the first reading. The meter leads were in the Amps sockets. This is the "minor" mistake.The fuse (or circuitry) did not break the current quickly. The leads got hot, very quickly. The electrician took quick look at his meter and knew what was happening. Now he made a second, the "major" mistake. He panicked and drew the test leads back, in doing to he managed to draw a three phase arc.It took a while until the closest fuse tripped, that it was on the other side of the substation in the 20kV net did not help too much. Not seconds, but long enough to turn most of the massive copper busbars into vapor phase copper and plasma, at literal arms distance from the electrican.Since that accident the company only uses meters which have automatic socket covers like the Gossen Meters Dave has reviewed. Their job is not so much to prevent you from plugging the test leads into the wrong sockets, but to prevent you form turning it to the wrong range while the leads are plugged in, especially when taking it out of the tool box and turning it on.The electrician survived badly burned. Wearing glasses helped his eyesight a lot.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 03, 2011, 04:20:51 pm
content: Nice story Chasm = interesting .For four years, I had an contract working in the heavy industry as electrician,in the factory that I was , yes we had 20KV transformers , fat bars and all .Yes I had even see the remaining s , of an large power box with melted fat bars ...The arc that caused the complete melting of this box ( explosion and all ),caused by loose bolts and nuts , that the cables attaches at those bars ..No one was even close when it happened that big bang.Another Interesting reference of yours , are about the number one scenario that the fuses needs to engage.That is .....To protect some one if he try to measure volts , by having the selector to Amperes.The Gossen Meters found the foolproof design , the FLUKE ones beep like crazy and the screen notify you too.Plus the range switch is always at Zero , otherwise it does not turn on from off !!!And so its not possible to have the selector forgotten at the wrong spot from the preview measurement .. But even if it was on sleep mode , as soon you turn the range switch at the wrong setting it will beep and nag with visual indication again.foolproof design for fool electricians , its only the one part of the story.foolproof design for every one ?? Yes those meters of Gossen and Fluke at 400-500 dollars or Euro,they do offer that.But the story gets interesting , because the Fluke ones looks unable to stop you (mechanically ) of keep doing your own mistake , even if it beeps and having the notification on the screen.And so at this point , Fluke looks to worry more about this matter (Fuses) than Gossen .And if Fluke worry about that , explains why they promote those fuses with such passion.Simply because those Fuses are capable to protect the user and the brand name it self from getting negative comments.Lets go to the Gossen camp , they have the foolproof design , why then they need HRC fuses ?At every time that I had to do an direct amperes measurement , the multimeter leads was bolted on the live contact areas or I had the " crocodiles " crock clips engaged ..Such in-line measurements never ever was risky , even if the measurement was made by old style analog instruments.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 03, 2011, 04:38:57 pm
content: Quote from: Kiriakos-GR on January 03, 2011, 04:20:51 pmcount uni-t in too! it does the same to fluke... beeps like crazy.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 04:42:59 pm
content: Quote from: Uncle Vernon on January 03, 2011, 04:30:14 amWow, i see what you mean, mine has gone of as well, lol, if some kind sole would just tell me if those fuses from mouser that i linked to should drop in and fit, they measure the same 5mm X 20mm, will they fit? someone mentioned they miight not. And do the ratings look good? Thanks

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 03, 2011, 05:37:07 pm
content: Quote from: mitpatterson on January 03, 2011, 04:42:59 pmPost an link or a picture of the product that you own ...Or post an picture of what you have at hand.To all ..Those are pictures of my own old in age Gossen ( Metrawatt) ... 80sShould I worry that it has an 8A fuse for the 7.5 Amperes range,an 4A Fuse for all the lower ranges , and the 25A range Not-fused.Or should I worry about the fuse size and type.No I am not trying to be ironical or fishy, I am trying to get some clear answers,so to be able to share them in the future with my self , and any one who cares about.Ifthere is legal maters ( new electrical regulations) that opposes the solution namedBover the old solution named asA,I need to know about it .Ifany manufacturer are able to use what ever he likes as fuses ... I need to know about it .Ifthere is a better product , in comparison with the past .... I need to know about it .( But I need details that verify this superiority, and the theory of the Amperes arc in DC does not works as evidence, at list to me) .But I can not hide one information that it came to me as an advice from other experienced technicians,the fact thatwe alwayssecure by Fuse the AC part of one device , and never the DC ...One golden rule , that it does not stand at cars - motorcycles - Trucks, and vehicles in general.(Click on the pictures for larger image )

author: Neilm
author_rank: Super Contributor
timestamp: January 03, 2011, 05:53:22 pm
content: Quote from: mitpatterson on January 03, 2011, 04:42:59 pmSimply put - an HRC fuse is designed to quickly break a high current. They are superior to normal glass fuses as they tend to have better voltage ratings and contain something to douse the arc created when the fuse melts. A glass fuse does not have anything like this and so under extream conditions the metal in a glass fuse will vapourise and turn to plasma. This will continue to conduct and will essentally act as a short circuit and bypasses the protection the fuse should have offered.HRC fuses are found in higher rated (more expensive) meters. I personally wouldn't trust a meter that didn't have HRC fuses. My view is that if they have skimpt with the fuse, what else have they missed? I have been involved in testing multimeters to see if they met the IEC61010 safety specifications. The best result was a cheap meter that claimed 300V CATIV. The test involved putting a high voltage spike superimposed on the 300V. The idea is that the high voltage (4kV?) causes an arc and the 300V continues it. The cheap meter exploded and marked the opposite wall of the test chamber, it also blew the 100A supply fuse.In answer to your specific question you should be able to replace a glass fuse with an equivilent HRC fuse. Just check that you can get one the same shape / size and the same rating.YoursNeil

author: ziq8tsi
author_rank: Regular Contributor
timestamp: January 03, 2011, 06:01:01 pm
content: Quote from: Chasm on January 03, 2011, 02:16:54 pmI do not regard that as a particularly good safety feature. Certainly not as useful as would be a working fuse.Perhaps if someone makes the mistake of having both the leadsandthe switch set for current and then connecting a voltage, they will mandate meters with no current sockets at all? Fused test probes are worth considering too for such obviously dangerous CAT IV live working.Maybe if someone who does not wear prescription glasses makes a similar mistake, the company will consider providing proper face and eye protection as well. And gloves, and flash-resistant overclothing. If anybody dies, they might even like to consider how much it really matters which side of a circuit breaker you measure voltage at.For an electronics engineering forum, the rare dangers of CAT IV arc blasts do seem to get a lot of press here, though, rather than the much more realistic CAT II/III dangers, such as electrocution.

author: Neilm
author_rank: Super Contributor
timestamp: January 03, 2011, 06:39:45 pm
content: Quote from: Kiriakos-GR on January 03, 2011, 05:37:07 pmThat appears to be quite an old meter. I believe that it predates the publication of IEC61010 which is the safety standard for test and measurement equipment. As such it would not be permitted to sell this (new) in the EU.QuoteIEC61010 details the tests to be done on the meter prior to it going on sale. This includes reviews of the documentation, tests on the creepage / clearances on the terminals (corrected for altitude), mechanical construction (impacts, drops, extream temperatures), risks of fire and explosions, fluids (cleaning or used in the system), interlocks, and misuse (including trying to measure volts on amps range ect).If someone is injured using a meter issued to them that has not been tested or does not pass the tests theymaybe able to claim compensation from their employer. I don't know for certain but it does seem vary likely.IEC61010 was first published in the 90's. Issue 2 was published in 2001. Currently we are in a transition period between issue 2 and issue 3 which was published in June last year. This is the first version that includes ratings of solid insulation, for example multilayer PCBs.QuoteThe manufacturer can specify any fuse they want. After they have, they will test it to the requirements of IEC61010. I believe that one of these requirements is that glass fuses are not used in certain areas. I don't know if this is a general ban or if it is only in applications that might get high currents. To pass the requirements for markings and documentation, the fuse type and rating must appear in both the documentation and be marked on the instrument near the fuse.QuotePersonally, working on a 600V DC system is as dangerous as working on a 420V AC system - possibly worse if the source of the 600v is a bank of batteries. If you short out the batteries with your meter on the (unfused) 25A setting something will get very hot.Quote from: ziq8tsi on January 03, 2011, 06:01:01 pmThe only advantage of that feature is that the test house does not have to do the failure test of switching range with the leads connected.QuoteYou can still get arc and blast from a CAT III installation. (it is just a lot harder) Also the hobbyist is more at risk of poor meters bought cheap. Dispite the efforts of some of the international commuinity, there are still manufactures who fake labels and ratings, either deliberatly or by not correctly understanding the regulations. These meters are OK for low energy low voltage applications, but can be very dangerous in the wrong situation.YoursNeil

author: Chasm
author_rank: Regular Contributor
timestamp: January 03, 2011, 07:11:25 pm
content: Quote from: ziq8tsi on January 03, 2011, 06:01:01 pmBy itself? No, or course not!But in conjunction with an actually working fuse.The mechanism prevents single fault accidents. It will not prevent you from switching the meter to amps and then proceeding to measure voltages.I can't check on it, but as far as I remember the DMM that failed to break the current in the accident was of the well yellow brand.Quote from: ziq8tsi on January 03, 2011, 06:01:01 pmOf course much of it is ...well I won't say the w word but it is overdone.You don't need a CAT IV meter, but even my old CAT II meter uses a 32mm ceramic fuse.Most people in this forum get told to keep their fingers of mains voltage. Especially when it comes to the modification of PC power supplies and similar stunts.Still, high current accidents are quite possible at low voltages and not something you can simply disregard. Say the good old car battery. Brushless motors are also quite popular. LED lighting on larger scale may also involve high currents.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 03, 2011, 07:38:54 pm
content: Quote from: Kiriakos-GR on January 03, 2011, 05:37:07 pmI have the Extech EX330 meter that won Daves $50 multimeter shoot out(actually $54.95 most places) just has standard glass fuses in it, i measured a fuse that was in it, it measured 5mm X 20mm, here are the 2 fuses in Ceramic that i beilve might work(i just want to confirm with you guys) the meter has a 500ma and a 10amp fuse(both 250V):500 ma:http://www.mouser.com/ProductDetail/Schurter/00011001/?qs=sGAEpiMZZMseCiJT91fwIpCS8D8NVahFjqM5t9f0yKw%3d10 Amp(the mouser pages list it as glass, but the data sheet for the product number says ceramic):http://www.mouser.com/ProductDetail/Schurter/00011014/?qs=sGAEpiMZZMseCiJT91fwIiiR5WGKbntkea7k9eh0bPE%3d

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 04, 2011, 02:18:14 am
content: Quote from: Chasm on January 03, 2011, 07:11:25 pmI still have a scar on my arm from 8 or so years ago when I tried to measure a PC power supply with a cheap meter set to amps. An unfused input can be dangerous even on some "safe" CAT I circuits.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 04, 2011, 08:30:10 am
content: Quote from: mitpatterson on January 03, 2011, 07:38:54 pmYes the fuses are up to the specs , I just checked the manual of your DMM and your links.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 04, 2011, 08:46:47 am
content: Too much references about theIEC 61010-1since 1.1.2004 ,but the discrimination between CAT I - II - III - IV , by it self it does not force any one to use HRC,especially at CAT I & II .And so even the cheapest meters can look as legal , if they wrote on them the true specs.Neilm, you had said that you had participate at multimeter testing.Well this is " Internet " , and every one can say even that he is an astronaut .Tell me something, at your testing at 4KV , how long time the voltage stayed at 4KV on the tests ?

author: Neilm
author_rank: Super Contributor
timestamp: January 04, 2011, 07:00:30 pm
content: Quote from: Kiriakos-GR on January 04, 2011, 08:46:47 amThe high voltage is a pulse not a level. The peak of the pulse is dependent on the CAT rating of the instrument. 300V CATIII is (from memory) 4kV, 300V CATIV is 6kV, 600V CATIV is 8kV. The pulse is only a few microseconds long (I don't remember the exact length now but 60us rings a bell) with the rise and fall times specificed by another IEC standard. The pulse is superimposed on the 300V / 600V with a supply rating determind by the test you are doing. I will note that when we upgraded our facility at work the sub-station required upgrading.The idea behind the test is that the pulse would cause a breakdown in the unit under test. This breakdown would then produce an ionised path of low resistance. This low resistance would then act as a short circuit to the mains supply that would then provide the energy to do damage. This test highlights problems with insufficient clearance within a unit, or with design problems with the protection circuit. For instance, if the protection circuit relys on a fuse the effect of that blowing can cause a very large voltage spike due to the inductance of the leads. This can bypass the protection if not clamped and cause a failure.YoursNeil

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2011, 09:12:15 pm
content: Quote from: Neilm on January 04, 2011, 07:00:30 pmYou're right about the high voltage pulse arcing and causing a short circuit but I think the pulse itself could be dangerous.An 8kV pulse linearly ramped up and down into 1k is is 1.92J which is pretty dangerous, think of a 33µF capacitor charged to 341V

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 04, 2011, 09:52:03 pm
content: I have awareness about the high voltage pulses , and I agree that mainly on the test are the PCB design problems ..By supplying high voltage , you do not test fuses , but the PCB flaws and the complete design ,if it survives or not.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 05, 2011, 12:45:10 am
content: Quote from: Uncle Vernon on January 03, 2011, 01:08:55 pmSorry, this simply isn't true.Most HRC fuses take a long time to blow at normal fault currents between 1 and 50 times rated as compared to a fast-acting fuse. There is a huge difference between operation under low current fault conditions (1-50 x rated current) and massive fault currents (10kA).

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 09:40:29 am
content: Quote from: cybergibbons on January 05, 2011, 12:45:10 amThen I don't know how the hell your selecting your fuses but I'd suggest you buying something very sub-standard. perhaps your confusing ceramic bodied fuses or Motor-Start cartridges with HRC ones.Quote from: cybergibbonsSo there is, but that does nothing to suggest that a HRC fuse by design should be slow to respond! To suggest there is, is insanity!Where is the safety margin from extending the duration of a fault current condition? That's right there is no reason!When you purchase a quality HRC fuse your not just buying arc quenching you are buying a device that has overall superior parameter. You're (or you should be) paying for a fuse with a superior element material one that will rupture quickly albeit not spectacularly.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 05, 2011, 10:34:35 am
content: The first time that I have seen HRC fuses , was on Fuse box that secures motors ...Its known that in motors you do not expect instant Cut off !!Even so , the shape looks to have nothing to do with the speed .I bet that at 3 phases 380V , the HRC design is used , because it is high voltage " friendly " .high voltage " friendly " = 500V ( industrial use )If the HRC can stand up to 1000V or more , its an extra benefit of this design ( shape ).And actually of how long they are , that is related with the PCB clearance , by using the resistance of air as isolator.And so if we could make the first list ofbenefits of using HRC, it could be :1)Safe design to used for 380V installations and above.2)Space saving design .. for low current up to 25AThe HRC fuses boxes that I have see , its made by plastic !!And in multimeters we have the open type metallic PCB base.3)Space saving design .. for aluminum panel boxes ( if you plan to build an AC stabilizer )or an portable industrial device.

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 11:00:37 am
content: Quote from: Kiriakos-GR on January 05, 2011, 10:34:35 amIn Australia those were always know as motor starts. Which were specifically designed to endure a reasonable number of over-current start cycles. What we'd always regarded as standard HRC came in the exact same physical format. And plenty were sacrificed by being used instead of motor starts.Quote from: Kiriakos-GRIt does and it doesn't. As fault current control requirements rise you ultimately have to settle for a physically larger device.But yes you are quite correct in the sense that for a given fuse size you can get a number of different ratings of a number of different applications.Quote from: Kiriakos-GRIt's of particular advantage if your trying to secure or maintain CAT ratings for your device. These topics started around multimeter fuses and make no mistake the speed of the fuses such as those you've pictured previously is one of the reasons better meters do not let the smoke out very often.IF HRC fuses were routinely as slow as has been claimed do you thing Fluke etc would have risked not adding some 15c fast acting fuses to supplement the HRC ones used? The don't add them because they don't need them, the fuses selected are lightning fast when they need to be. I've seen plenty of cheapo meters with intact glass fuses and vapourised PCB current tracks, You'll seldom if ever see a quality HRC fused meter with the same outcome.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 05, 2011, 11:25:23 am
content: Well every conversation about HRC fuses and multimeter's so far,it had the fate to not lead anywhere .That's why I had bring industrial examples about the usage of HRC,so to make this one more wide as conversation.Its good that we agree on the " HRC as motor starts ".The 95% of the HRC fuses that any one will easily locate on the market ,it will be the slow ones for motors.And if we start thinking , as the only known as Fast Fuses ( HRC type ) manufactures the BUSS and SIBA,this conversation will end prematurely too.Because we end up, at the two known brands that they monopolize the market ,and control the pricing too .What I am trying to do with all those conversations , are to investigate if there is another one player at the Fast Fuses ( HRC type ), that we do not know about him !!

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 11:43:44 am
content: Quote from: Kiriakos-GR on January 05, 2011, 11:25:23 amI don't agree with the 95%, I've always had to specifically order Motor-Starts. There are any number of suppliers for industrial ones. Flag ended, offset flag ended. Screw fit for those rotten old Red-Spot frames.Back to a replacement suitable for meter fitment, I use so few it's hardly been a concern. I treat it like a $20 "you wont do that again for while tax".Not lending your meter will solve most instances of need!EvenEspecially to other techs or Sparkies, they know fuses are expensive so they'll seldom own up to blowing one of yours.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 05, 2011, 11:56:52 am
content: Quote from: Uncle Vernon on January 05, 2011, 11:43:44 amMore Fuses on DMM gets burned when the meter are new , common mistake = of using the wrong Amperes input ..At my 24 years on the field , I must have burn about four fuses on several meters,I bet that my " Burning rate " are minimum .But I have not yet burn an Fluke one , on this I am still" virgin ".

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 12:09:29 pm
content: Quote from: Kiriakos-GR on January 05, 2011, 11:56:52 amI've had a fluke of some description since the mid 80's, cannot say I've ever destroyed one in use. (Having your meter run over by a fork-lift or bumped into a brine bath cannot really be described as in use.) As for fuses over all those years I'd say my count was about 6. Two of which I'll own up to being the perpetrator of the dumb act. I've lost count of how many $100 meters I've seen blasted over a similar time frame.Long before the days of OH&S (save them from themselves) nonsense, most employers learnt that providing Flukes (or equivalent) was the better option from a purely economic perspective.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 05, 2011, 09:41:52 pm
content: Quote from: Uncle Vernon on January 03, 2011, 01:08:55 pmNo, the ability to interrupt at massive fault currents is partly due to quickly stopping the flow of current. There are a lot of other factors. But at normal fault currents the time that it takes to interrupt doesn't matter - the fuse isn't going to exploded anyway.Quote from: Uncle Vernon on January 03, 2011, 01:08:55 pmI'm saying that the bulk ("It's likely") of HRC fuses are slower to blow than a fast-acting glass fuse. Look at the data sheets - you'll be hard pushed to find a HRC fuse as sensitive as a the best fast-acting glass fuses, especially if you walk into a standard electrical supplier. The two commonly available types in the UK are gG (general purpose) and gM (motor), and both are pretty slow acting compared to say, the input fuse on my audio amplifier, which is a normal glass type.Quote from: Uncle Vernon on January 03, 2011, 01:08:55 pmBy design, a HRC fuse is a tube packed very tightly with quartz sand. This hugely increases the amount of heat transferred away from the fuse element, as compared to wire in air fuses. Because a fuse element breaks using heat, this in turn means that the element takes longer to break as it is harder to make it hot. It really is the case that HRC fuses, by design, would be slower to respond. They need to use careful design to make them faster again - mainly by material selection and element notching.Quote from: Uncle Vernon on January 03, 2011, 01:08:55 pmSo why aren't all fuses quick blow then? A number of reasons:Anything with a start surge requires a slower response timeDiscrimination in a distribution system requires that upstream fuses take longer to blow than downstreamFuses blowing repeatedly means that fuses need replacing more often, in turn meaning more maintenance, and then opening up maintenance workers to higher risk of an accident.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 05, 2011, 10:05:08 pm
content: all i have to say is WOW, only like 6 replies or so in direct regards to the original questions, the rest.... a bunch of people refuting others point's..... well i guess is what happens when i ask on a engineering forum ehh?, anyways, carry on, its interesting, and for someone who knows a bit more than i do probably interesting, lol.

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 10:25:13 pm
content: Quote from: cybergibbons on January 05, 2011, 09:41:52 pmIn our multimeter scenario the speed of response is everything, how many half cycles of fault current will the components of the device sustain before something gives way explosively. We are talking a hand held device here.Quote from: cybergibbonsThe bulk of ? Now that is somewhat different from your prior statement that my reference to fast action simply saw not true! It appears the goal post are being shifted now. And then we add terms "standard electrical supplier" and "commonly available types" we were after discussing the application of a specialist fuse and its use in a specialist device! HRC fuses by application will seldom be a retail commodity. A great many of the HRC fuses used particularly those used around semiconductors will be fast acting.Quote from: cybergibbonsNo it doesn't make the case that HRC fuses are slower by design. There is considerable effort placed into the design characteristics of the fusible element in terms of it's dimensions, material selection and tolerance. That sliver of wire in a good HRC is not the same random chunk of nichrome you'll find in hardware store glass fuses. And yes that careful design is applied and yes it's another contributor to the comparatively higher prices of HRC fuses.Quote from: cybergibbonsAnd the start-up surge of a test instrument is? - Not applicableUpstream systems? we are talking multimeters remember, what has upstream systems got to do with it?Risks due to fuse replacement? Why not have all our fuses replaced with nails then or spent rifle cartridges, that'll be much safer, for sure. If a correctly sized fuse is blowing repeatedly then it is doing it's job meaning other aspects of the design or installation require attention. I've seen more than a few contactors blown of the gear tray of a switchboard because some maintenance person decided motor start fuses would be a good idea and in doing so exceeded the duty cycle rating of the electric controls. If a fuse blows on a regular basis you need to ascertain why.

author: Unknown
author_rank: Unknown
timestamp: January 05, 2011, 10:43:38 pm
content: Quote from: mitpatterson on January 05, 2011, 10:05:08 pmTrue, to answer you original question. Fuses ain't necessarily Fuses . If a meter has glass cartridge fuses it's unlikely the manufacturer paid much concern to safety in use or misuse of the device.Would you gain advantage fitting your meter with better fuses? Perhaps? However you will need to check the spec sheets to make sure your better fuse is better in all the relevant parameters.My advice for what it is worth is be careful, which you should be doing anyway regardless of the meter you use or it's fusing. Don't use general purpose meters for serious applications which require a Cat III or Cat IV device.Would I do the occasional mains presence test with a cheap meter? Yes at a pinch and with a lot of respect for the situation.Remember no meter, lamp, buzzer, volt-stick will confirm a conductor as safe to touch! They can only confirm it is not so.Working with anything that is above ELV (32V maximum) or anything capable of more than a few hundred milliamps requires a healthy degree of respect and understanding.To summarise, if it was my meter and I was in a similar situation I'd leave the glass fused meter as the manufacturer intended, and remain mindful of this when deciding where i used it. A HRC fuse will by no means guarantee you meter is now invincible, only careful design can achieve anything close to that.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 06, 2011, 12:52:58 am
content: Quote from: Uncle Vernon on January 05, 2011, 10:43:38 pmMy main concern/question is basically, when and if I blow a fuse(which i blew the 10 amper 2 days ago while testing the current draw of a UPS(under no load) so yah, lol) should i replace it with a HRC/ceramic fuse or just buy another glass one?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 06, 2011, 12:55:06 am
content: @ cybergibbonsHas some good points about Glass Fuses ,They are fast and easy to find , and they are in use for lots of years.The HRC it could be called as " New " player ..But , the design of the porcelain fuse with the sand in it ,its the older and well known.Does the HRC mimics, the old classic design ?And why?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 06, 2011, 12:57:57 am
content: Quote from: mitpatterson on January 06, 2011, 12:52:58 amThe HRC fuses are larger in diameter than the Glass type , you can not install them in a Glass fuse holder.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 06, 2011, 01:00:18 am
content: Quote from: Kiriakos-GR on January 06, 2011, 12:57:57 amI've asked this before, WHY, my glass ones measure 5 x 20mm, and the HRC/cermaic ones i found are the EXACT same size, granted even if they aren't HRC they are ceramic and fast acting, so probaly closer to HRC then the glass ones

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 06, 2011, 01:13:31 am
content: Quote from: mitpatterson on January 06, 2011, 01:00:18 amOhh I see , yes ceramic 5 x 20mm and fast acting are an great choice ...HRC its nothing magic , its just an specific size and shape of fuse.sample..

author: Chasm
author_rank: Regular Contributor
timestamp: January 06, 2011, 06:52:06 am
content: Fuses have a whole set of parameters, the current is only one of them.current ratingcharacteristic (how fast)voltagerupture currentphysical size / form factor...and some more less obvious ones, like contact residence or resistanceHRC, high rupture capacity, says nothing more than that they can (safely) rupture a high fault current. BUT, this current is very much dependent on the both the form factor and voltage.Form factor, no SMD fuse will ever rupture 10kA. (Without being ruptured itself.)Voltage dependeny, say the BUSS ABC20 type, a 20A 32mm ceramic tube (non HRC) fuse like the one in the middle of the picture above, has a rupture rating of:125V DC: 10000A125V DC: 1000A250V DC: 400AThe difference is that the HRC fuses usually give their rupture rating at their maximum rated voltage.You can also buy HRC fuses with different acting characteristics. (fast vs. slow)Speed does not affect how much current they can rupture.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 06, 2011, 08:28:17 am
content: Quote from: Uncle Vernon on January 05, 2011, 10:25:13 pmOne of my meters is 10A continuous rated, but can measure 20A for 30s. I'm sure it could take 50A in a surge without damage. I certainly wouldn't want to replace my fuse due to a half cycle of 20.01A going through my meter!HRC fuses are generally slower to blow than glass fuses at low fault currents. Take the Cooper Bussman DMM-B 11A fuse that is used in some Fluke meters (a fast-acting HRC). At 1s, it's taking approx 7I to blow. Compare to a Schurter FSF-5 glass fuse (just a random selection), which at 1s has blown at 3I. Then go to 0.1s - the HRC fuse is at 10I, and then at 7I.This is the fuse that Fluke specify, and it costs over 20 times more than the glass fuse. It blows more slowly from 2I to 10I.If, and only if, you end up in a situation where the current is greater than 10I, will the HRC fuse blow quicker. Putting 100A+ through a meter at mains voltage isn't an everyday occurrence. I'd say most meter fuses are blown at much lower currentsThe same is true for the Littelfuse FLU fuses, HRC fuses designed specifically for multimeters.So, you have said:* The fuses on meters must be quick to blow to protect the meter* The quicker the better, as that is everything in protecting the meterSo, by extension, the HRC fuses specified by the manufacturers would be some of the fastest available if this were the case? So why aren't they? Why can I find quicker glass fuses?Quote from: Uncle Vernon on January 05, 2011, 10:25:13 pmYou stopped referring to HRC fuses in meters specifically a long time ago and started making general comments about HRC fuses.Quote from: Uncle Vernon on January 05, 2011, 10:25:13 pmA lorry is slower by design than a car. Put a huge engine, nitrous, and modify the gearbox in a lorry and it can beat most cars. But it's taken a lot of extra effort, and it still doesn't go round corners as well.It's very difficult to make a HRC fuse quick, mainly due to the additional effort required to heat the fuse element. This is as a result of their design. You've pretty much backed up what I'm saying here.Glass tube fuses aren't a random chunk of nichrome at all - take a look at some with a magnifying glass and you will see blobs and crimps to tune the response, coils to pull apart the fuse etc.Quote from: Uncle Vernon on January 05, 2011, 10:25:13 pmYou deny that there is a risk involved with replacing fuses? Even in a multimeter, there are risks. What happens if the replacement is incorrect?

author: Unknown
author_rank: Unknown
timestamp: January 06, 2011, 10:04:43 am
content: Quote from: cybergibbons on January 06, 2011, 08:28:17 amCurious! I'd rather replace a fuse than a meter. Pump 50A through a 10A range and your calibration certificate isn't valid anymore.Quote from: cybergibbonsWow a sample of two, conclusive indeedy. As for most fuses extinguishing at low currents, I'd say no. Most are sacrificed when the leads aren't rearranged and a voltage reading is attempted via the current shunt. Which of your two sample fuses is going to be the first to pop under that scenario meets 240V mains?Quote from: cybergibbonsAre your glass fuses quickest to interrupt the current in the most typical scenario of incorrect lead placement? Don't think so!Quote from: cybergibbonsPerhaps in response to your erroneous generalisation that all HRC fuses were slow to act. Which was clearly not correct.Quote from: cybergibbonsI've done no such thing! More difficult does not equate to impossible! There are plenty of ultra fast HRC available with a whole plethora of different characteristics. The generalisation that every HRC fuse will be slower is incorrect.Quote from: cybergibbonsSure those 4 for 50c packs of fuses are made to the most exacting tolerances. I don't think so it's minimum cost large scale manufacture all the way. Hell your flat out buying soldered ended ones. Most have the end cap just pressed across the ends, relying on that ultra high tolerance glass envelope for a decent connection.Quote from: cybergibbonsNot at all, hell I could be struck by meteors or bitten by a poisonous snake while replacing a meter fuse in a safe manner. There are risks from eating strawberries and from sleeping but lets try to keep to some kind of reality. If you've ever had to operate a pole side air-break switch switch under load you'd consider live fuse replacement relatively tame. But yes there are risks entailed with simply breathing.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 06, 2011, 03:20:32 pm
content: Quote from: Uncle Vernon on January 06, 2011, 10:04:43 amOh, that's a shame because it doesn't make a blind bit of difference what fuse you are using - the 50A will pass through the meter regardless of the fuse blowing or not, it's just the length of time. How do you dictate when it is damaged?Quote from: Uncle Vernon on January 06, 2011, 10:04:43 amThose are the fuses used in nearly all Flukes and the Agilent meters. Then take the SIBA 5019906.11, used in the Chinese flukes and Gossen meters... again it's slower across the entire range than any fast-acting glass fuse I can find. Without a counter example of a DMM fuse faster than a fast-acting glass fuse, your case doesn't have much behind it, does it?Quote from: Uncle Vernon on January 06, 2011, 10:04:43 amReally? I can count the number of times I've done and seen anyone take a mains short across a meters on no hands. Yet I've lost count of the number of people who have "measured how much current is in their power supply" or a Ni-Cad racing pack, or misjudged the current draw when performing motor load tests, or as you say, leads on A when measuring V, but rarely on mains. Casual users don't tend to mess with mains, and professional users are careful (and should have tested the meter against, a safe, known source before hand anyway). How many people on here have blown fuses with a dead short across mains?Quote from: Uncle Vernon on January 06, 2011, 10:04:43 amIncorrect lead placement against most ELV sources, the glass fuse is likely to be quicker. Against mains, you aren't guaranteed to interrupt the current with most glass fuses. You've totally avoided the question though - you say that a fuse has to be as quick as possible to interrupt a fault current. There are many levels of fault current, and the HRC fuses recommended by the manufacturers are slower to act at many of these levels. Why is that the case? You say they can be fast, why not make them as fast as possible?Quote from: Uncle Vernon on January 06, 2011, 10:04:43 amIn general, HRC fuses are slower to react. This is as a result of their design and also the intended application (most HRC fuses are used in power networks). It's true, get over it.Quote from: Uncle Vernon on January 05, 2011, 10:25:13 pmUsing irrelevant hyperbole doesn't really add much to the argument does it?The DoE identified that a disproportionate number of accidents occurred as a almost direct result of fuse replacement. This was a combination of serious (i.e. worker doesn't correctly de-energize circuit and is killed) through to minor (general purpose fuse used instead of a motor fuse, causing a motor to single phase). So since then they have tried to ensure that they evaluate every fuse replacement to minimize the chance of unwanted blowing, including replacing with circuit breakers and making fuse replacement safer if need be. They also found several accidents where improperly maintained test equipment was the direct cause. Why take those risks when you don't have to? They also found that live working was almost entirely unnecessary...However, complacency has been proven time and time again to be a major cause of accidents...

author: Unknown
author_rank: Unknown
timestamp: January 06, 2011, 09:43:08 pm
content: Quote from: cybergibbons on January 06, 2011, 03:20:32 pmSo length of time is the dictator? You could be starting to get this!Quote from: cybergibbonsFuse you've already acknowledged that will be faster to act and more capable of interruption than your 25c glass jobbies. Me thinks your doing a pretty good job of shooting out your own argument. Why would I bother to start trolling through spec sheets.Quote from: cybergibbonsYes things must be really safe back there in cotton wool land! And sure because you've seldom been near the mains precludes all those techs and tradesman never go have meters near the mains, or a UPS or other substantial source of supply. All those electricians across the planet never near the mains? All those phone techs never near a huge DC supply? Yes the real world is almost all involved in Ni-Cad racing packs? Be serious. If the world was all bench supplies and ni-cad pacs you'd have to wonder why manufacturers even consider building Cat III, Cat IV or flameproof models.Quote from: cybergibbonsNever mess with the mains? So no non professional user ever touches the mains? Makes you wonder why so many of the hobby electronics shops sell open frame transformers and high voltage triacs doesn't it? Professionals are always careful, eh? You cant have seen too many then in action then. Cavalier being the description of attitude that comes readily to mind! You have to wonder again why we suffer all the OH&S blame shifting if all professional are careful? Don't we? Your statement is even accurate as a generalisation!Quote from: cybergibbonsThere is a massive chasm between "should have" and reality, hell if should have happened all the time they wouldn't ever need to consider adding fuses to multimeters. It not like they add any benefit to the device in terms of accuracy!Quote from: cybergibbonsAt many levels of fault current? Yes I guess if you are desperate you could consider the single digits as many levels. How many of the instances between one and a thousand times do they represent?Quote from: cybergibbonsIn general? So your sure the fuses Selected by Fluke etc are slower to react in all the situation most likely to damage the meter or the numb-skull applying the overload? Curious you'd choose to believe that, but hey it's a free world, your free to believe whatever crackpot theories you wish to.Quote from: cybergibbonsWhat like the gem? "Casual users don't tend to mess with mains, and professional users are careful" That's a classic, but it did give me a good laugh for the morning. So thank you.Quote from: cybergibbonsThey identified mobile phones as a real risk near petrol filling stations too. By current definition you can identify risk is most everything.Quote from: cybergibbonsAnd of course all those meter with blown fuses were a direct result if unsafe testing of Ni-Cad race-packs? Weren't professionals always careful?As for live work being unnecessary that is simply bollocks dreamed up by scheming unions and clueless oxygen starved knobs in far cubicles. What did they propose? Isolate the grid for a few hours each day?Ever tried to repair a live chassis television with the power off? There is no alternative but to work on live systems in a variety of situations.Quote from: cybergibbonsHow could such complacency occur? Casual users never go near risk and professional are always careful? Not much scope for complacency at all?

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 07, 2011, 12:10:00 am
content: Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmCan you answer a question directly? How do you decide how long 50A can flow before the meter is damaged? Because both fuses will allow it to pass for a length of time. My point is that a fuse doesn't have to be fast with low fault currents as it doesn't matter - the rest of my meter can take these for short periods of time. I also don't want my fuse to blow all the time with short surges.So what point are you making? It seems that, because you are countering my points, you believe that it needs to be interrupted as fast as possible, even at 50A on a 10A range?Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmThe glass fuse is quicker to act from 1 through to 10 times rated current in the spec sheet. It will likely interrupt way above it's max rated interruption current, and still do it quicker. The glass fuse will act quicker in all these situations. Do you disagree with that, as it's in the datasheets, plain to see.I don't disagree the HRC fuse is designed to interrupt larger currents.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmSo these guys short their meters across supply all the time then? I don't think "tradesmen" can really be a good name for them. I've spent years working with LV and MV and not seen or heard a genuine story of anyone shorting their meter across supply.My example with racing packs is down to the number of people who are inexperienced at using a meter and also don't realise the massive currents these packs can supply.I don't disagree that the risk of shorting mains is there, especially in a professional setting, but that doesn't mean it happens all of the time.So I stand by my point that most multimeter fuses are blown at much lower currents than dead shorts across the mains. If you work in the industry and do this frequently, you'd quickly make a name for yourself and no one would want to work with you. They guy who blows up his Fluke twice a year is the same guy who doesn't check circuits are dead before working on them.This doesn't mean that I think glass fuses are safe in multimeters, but that in most overload situations, the glass fuse will blow quicker.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmI don't see how you can read "don't tend" and change this into "never". The vast proportion of hobbyists will stick to ELV, maybe checking mains voltage with their meter to make sure it works... Even if they do work with mains it won't be multiple times a day. Hence, they don't tend to mess with mains.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmWhere did that "always" come from? Are professional users not careful, either through familiarity or training? Who do you work with that are so reckless to repeatedly short their meters across supply?Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmThat probably explains all the accidents that happening around you all of the time then. How hard is it to test a meter against a known source? I'm guessing you have people regularly contact energised circuits as well.It's not about removing all risk, it's about minimizing it. So if 9 times out of 10 you check the meter, you are less likely to have an accident. The fuses are there for the times that minimizing risk doesn't work.A lot of electricians, household, commericial and industrial have switched to using voltage testers only, as there is no room for error and they are a lot cheaper when you break them.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmYes, it's only a subset of the possible levels. But over those ranges, why don't the multimeter manufacturers specify a HRC fuse that is quicker than a glass fuse? I think it's because:* It's really hard to make a HRC fuse faster than a glass fuse (you dispute this, despite plain evidence to the contrary)* It doesn't make a blind bit of difference if low fault currents are interrupt in 0.001s or 0.1s (you've stated the meter needs to interrupt fault currents as quickly as possible though, so I guess you dispute this as well)It would appear that the meter manufacturers are with me, as they specify comparatively slow HRC fuses.Can you answer (it seems that you can't), why don't they specify HRC fuses that are as fast as fast-acting glass fuses?Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmI can't really say it any more clearly. The first HRC fuses made were very very slow to blow as they had not worked out how to design out the problem if the heat being sucked away from the element. Over time they have improved it. But the standard, cheapest design of HRC fuse is quite slow to blow. They can be made quick, but even then they tend not to be any quicker than fast-acting glass fuses.It's also the case that the number of HRC fuses produced for distribution networks and motor protection vastly outweigh those produced for meters. These are designed to blow slowly. By extension, on average, HRC fuses are quite slow.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmI've got no idea where you got the impression I said this.I said in most situations, which I believe to be low fault currents, the fast-acting glass fuse will blow quicker.I can see how you can disagree with the "most situations", but not the speed of the fuse blowing.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmHow is that hyperbole?Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmIt seems you are unable to make a point without pushing it right to the limit. It has to be "always", "never", "all", "none". It seriously weakens any point you are trying to make.Who is to say that one of the meters didn't have a blown fuse due to measuring a low voltage source like a battery? People are less careful with low voltages, but a Ni-Cad in an emergency light is perfectly capable of taking out a 10A meter fuse.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmYou (and seemingly those around you) have an attitude that I've seen in a lot of older people I've worked with, that believe the way things have always been done are the way they should always be done, and those risks always have to be there and can't be avoided, minimized, or better still, designed out of the system. They are generally the same people who think that testing their meter each morning against a known source is a waste of time.I have friends who work on both the maintenance and design of HV distribution systems in the UK. When performing maintenance, live working is avoided as much as possible, because:* It's very dangerous* It's very slow, tying up work teams on jobs for far longer than if the circuit was de-energized* They are generally quick fixes that need a full repair* It involves lots of expensive equipment* It involves lots of paperwork* It takes lots of trainingFrom the design perspective, modern grids and distribution boards are design to minimize exposure.Quote from: Uncle Vernon on January 06, 2011, 09:43:08 pmIf you are doing it regularly in a professional capacity, there is no reason that this needs to be risky of involve kA fault currents. The use of an ELCB, reasonably sized breaker, and isolation transformer reduces the danger massively.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 07, 2011, 07:10:20 am
content: Wow this atmosphere reminds me theBattlefield Bad Company 2Lots of smoke and adrenaline all over the place ..Currently the only argument that stands in favor of the HRC , are the size - clearance ,that makes them theoretically " better " for voltages above above the 380 Volts .The truth is that also, I have not seen yet an glass Fuse to have any marking other than 220V.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2011, 11:06:06 am
content: Quote from: cybergibbons on January 07, 2011, 12:10:00 amFault current must be interrupted quickly as possible.Quote from: cybergibbonsThat is somewhat of a change from your original assertion that HRC fuses cannot act quickly.Quote from: cybergibbonsI sure don't consider many with qualifications as tradesman. Electrical work is filthy dirty and not the place for Rhodes Scholars when employing staff you often have to take what you can get. Lot's of them cannot walk without grazing their knuckles, and yes these same buffoons still flash meters and no amount of tedious work method statements are ever going to make a difference. I've seen plenty of Britain's finest and can confirm they are no different. That's not to say there aren't truly electrical tradesmen out there but they are very much the exception.Quote from: cybergibbonsClearly your not doing the repair inventory for teams of electrical tradesmen.Quote from: cybergibbonsYou can stand by whatever you want, it doesn't make it any less incorrect than the first time it was uttered.Quote from: cybergibbonsMost of these wage slaves consider it funny. Pop out of perfect world for a while and you'll soon realise that lots of crazy stuff happens in building and industry.Quote from: cybergibbonsThe vast majority of hobbyists are very poorly prepared or equipped for mains even if they don't encounter it on a daily basis. While they may not have the complacency of the professional they are more often than not ignorant of the implications. It's not till that casual brush with a live terminal or the unknowing connection of a CRO probe clip to something hot that the respect needed really sinks in.Quote from: cybergibbonsI could write a book about the stupid thing you see on job sites. And it wouldn't be a little book. They aren't paying for the fuses or the meters what do they care?Quote from: cybergibbonsNot my accidents, and nowadays not my employees or those I'm responsible for. But go ahead make your slur if you think it'll help your argument.Quote from: cybergibbonsTheoretically you can dig a huge hole with a screwdriver, wont make it the right tool for the job though. No room for error? your joking. aren't you?Ever tried to use a volt stick within a switchboard? Good luck. Voltage testers while handy will never be a replacement for a multimeter. And as I have stated previously no will give you a guarantee of absence of supply.Quote from: cybergibbonsBut not impossible. Police cars aren't as quick as F1 cars, does that make them slow?Are you seriously suggesting that the fuses Fluke and similar use are slow to break fault current. Do a ring around the meter manufacturers and see how many actually subscribe to your theories.Quote from: cybergibbonsYour saying a glass fuse will be quicker to interrupt fault current likely to damage the meter or the numbskull holding it. It is certain the manufacturers don't agree with you.They have selected what they see as the best compromise and selected some fairly expensive fuses in doing that.Quote from: cybergibbonsWhat in blue blazers has that got to do with the fuses that Fluke etc currently using. The first cars assembled barely made walking pace. I guess by the Cybergibbon Metric all cars must therefore be slow.Quote from: cybergibbonsUnless I'm very much mistaken that $20 fuse for a fluke is far from the cheapest standard design.Quote from: cybergibbonsTried plugging these into your meter? There is plenty of application other than meters that require a rapid HRC fuse.Quote from: cybergibbonsIt seems you are so hung up on generalisations that you are missing the fact that there is no such thing as one size fits all.Quote from: cybergibbonsAnd you hold that clueless attitude that thinks all risk can be eliminated with paperwork and procedures. Another member of the procedure will save us all set. You have no knowledge of how go about my work or how i manage safety. Reliance on paperwork and the generalised procedures is not and will never be a safety measure.Quote from: cybergibbonsThat's nice for them, when you all wake up to real cost you can realise why your country,and mine, have ruined any chance of having the thriving industry they once did. It's not a perfect world, and in reality there are any number of reason why it is necessary to routinely work on live circuits.You can quote generalisations till the cows come home and cite all manner of antiquity, and text book theories, but none of that go any way towards substantiating the suggestion that HRC fuses are all slow. I'm bored with this now but feel free to continue arguing amongst yourself if the need remains.

author: Neilm
author_rank: Super Contributor
timestamp: January 07, 2011, 04:06:16 pm
content: The only way of settling the argument is by checking the datasheets for a couple of fuses.Most HRC fuses are larger than 5 x 20 so I tried to find a HRC of that size and an equivelent glass one. The fuses were selected by going onto the Farnell website and doing a search of either "glass fuse" or "HRC fuse". The first fuse of each type that had a decent datasheet giving rated voltage, breaking capacity and breaking time curves was selected. I decided to look at 500mA fuses as a comparison as this is the type of fuse you might find on a multi meter.Lets firstly look at a glass fuse.http://www.farnell.com/datasheets/70287.pdfA quick look at the datasheet shows that the important figures are rated voltage 250VAC; breaking capacity is 35A and with a 4 times overload it will go in between 10 and 300ms.Now for a ceramic HRC fuse.http://www.farnell.com/datasheets/19206.pdfImportant figures rated votlage 250VAC; breaking capacity is 1500A and with a 4 times overload it will go in between 10 an 300ms.Now imagine the situation. You are testing a 250V mains circuit with a loop impedence of 1.0 ohm and accidently short it out through the meter - so the maximum current is 250A. Given that, which fuse would you prefer in your meter?As a note of interest going slightly off topic most instruments designed for mains measurement will be rated at greater than 300V CATII, probably 600V CATIII. As glass fuses are not available at those voltages they will use fuses like this.http://www.farnell.com/datasheets/606768.pdf. It is a 6.3 x 32mm fuse rated. The figures on the 500mA fuse are rated votlage of 1000V; breaking capacity of 30,000A and with a 4 times overload it will go in less that 60ms.YoursNeil

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 07, 2011, 07:27:59 pm
content: Thanks Neil, that's pretty much what I was asking Uncle Vernon for a long while ago.My examples are the 10A or 11A fuses that are used for the protection on a lot of electricians meters.The Littelfuse FLU series are recommended by Gossen for use in their meters:http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_Fuse_FLU.pdf:1000V, 20kA, and at 4 times overload the time to blow is about 1s (sorry, no range, it's average).The Cooper Bussman fuse used in Flukes:http://www.farnell.com/datasheets/35154.pdf:1000V, 20kA, and at 4 times overload, time taken to blow is about 5s.The SIBA fuse used in the Chinese Flukes:http://www.farnell.com/datasheets/606764.pdf:1000V, 30kA, and at 4 times overload, time taken to blow is just over 1s.Compare to a 10A glass fuse:http://www.farnell.com/datasheets/68853.pdf:250V, 100A breaking capacity, and at 4 times overload, time taken to blow is just under 0.2s. A lot of the glass fuses are rated 100A@250V, but 10kA@125V. So can still take a dead short across, say, a bank of batteries in a telephone exchange.I'm not saying that the glass fuse is safer by any means. I want HRC fuses and a CAT rating in anything I put across mains. But I still stand by the fact that if I put two meters directly across my 20A power supply, my Fluke (HRC) and my Uni-T (glass), the Uni-T fuse would be the first to blow.Your other fuse proves that a HRC fuse can be fast, but it's still only as good as a fast-acting glass fuse with a similar rating.If I put the Uni-T across 3-phase bus bars, I would expect to end up in hospital.I think we're going to have to agree to differ on the number of fuses blown by direct shorts.And responding to someone who quotes you saying one thing, adds "all" or states something entirely different, then counters it, seems rather futile, but here are some choice selections anyway:Quote from: Uncle VernonAs quickly as possible, but making a compromise? How does that work? I can find HRC fuses faster and cheaper than the ones Fluke recommend.Quote from: cybergibbonsQuote from: Uncle VernonLOL, good comprehension skills.Quote from: cybergibbonsQuote from: Uncle VernonROFL. Average != all.Quote from: cybergibbonsQuote from: Uncle VernonVoltage tester != volt stick. Fluke T50s are everywhere over here and are fine in a switchboard.Quote from: Uncle Vernonreally hard != impossible. It's much easier to make a police car than an F1 car, and there are certainly more of them about. What is the average top speed of the two then?

author: Unknown
author_rank: Unknown
timestamp: January 07, 2011, 08:50:56 pm
content: Quote from: cybergibbons on January 07, 2011, 07:27:59 pm20A for 5s (or whatever the time is at 2 times overload) is unlikely to blow up a meter designed for 10A, since many meters allow 20A for 30s or so, although it may influence calibration. So I think the HRC fuse will protect the meter just fine in this case. At 20A, both fuses will probably be fine. At 10kA, the HRC will be faster (it will blow properly) and certainly safer. Somewhere in between (20-100A), there may be a range that can be safely interrupted by a glass fuse, but will damage the meter in the time it takes to blow the relatively slow HRC fuses. But the meter manufacturers apparently consider this unlikely, or at least not a safety hazard.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2011, 11:02:21 pm
content: Quote from: cybergibbons on January 07, 2011, 07:27:59 pmA flash and loud bang will prove conclusively that you are wrong!Quote from: cybergibbonsDoesn't matter if you try it across active and neutral or active and an earth terminal the results will be similar. Curious how you believe that this fuse will blow first and yet you'll still require hospitalisation? Which law of physics explains that one?Quote from: cybergibbonsIf you are insisting on being wrong then indeed you will have to disagree.Quote from: Uncle VernonMy comprehension skill will always be better than your interpersonal skills. Refer back to your initial reply, a sweeping generalisation rolled into a personal attack! A generalisation which your ensuing argument has proven to be incorrect.Quote from: cybergibbonsAnd the current measuring capability of the T50 is? But then given your minimal understanding of mains supply this may be of safety benefit to you. Another of your sweeping generalisations accompanied by hurried revision. First we had "A lot of electricians, household, commericial(sic) and industrial have switched to using voltage testers only" and then somehow the term voltage tester now mysteriously only applies to one device from the Fluke corporation. Test lamps are still in common usage, at least till apprentices realise their technical collage project isn't such a good idea in the 21st century. Volt sticks are just as if not more common than the T50 Fluke lists theirs under the category "voltage tester" but they must be wrong as its not a T50. My you do take a lot of differing positions in retreat! Don't you! As for the patent nonsense that with voltage testers "there is no room for error" that is a statement bordering upon being dangerous misinformation. But there still is hope sunshine you are correct in the assertion that they are cheaper than a good multimeter. They are cheaper than a Volvo estate or a good set of insulated tools too. But hey I wont shoot down the few slim traces of an argument you have remaining, your quite capable of doing that yourself.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2011, 11:07:17 pm
content: Quote from: alm on January 07, 2011, 08:50:56 pmSpot on !

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 07, 2011, 11:49:58 pm
content: Quote from: Neilm on January 07, 2011, 04:06:16 pmThey do not have larger than 2 Amps !! ( info from the PDF )And the new question are : Does size matters ?Does only the HRC fuse body , can offer fuses with the same characteristics over the 2A at 1000V ?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 08, 2011, 12:13:41 am
content: Quote from: Uncle Vernon on January 07, 2011, 11:06:06 amI am dying to be informed about such examples !!Because currently , I think that some one had set up an conspiracy by having as center the multimeter,and the HRC Fuses as cheese , and the silly mouse will pay the what ever cost so to get them,because of fear mostly.Like the sales men who trade health insurance contracts , that if you do not sign ,all the disasters of the world , it will happen to you , the next day .( This is what their propaganda says at list )

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 12:22:21 am
content: Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmThere are datasheets above for the HRC fuses specified by the major multimeter manufacturers for use in their meters that show that they are slower than fast acting glass fuses at all currents from 1 through to 10 times rated. Neil provided ones showing at lower current ranges they are par. You can't provide any counter examples.I'm beginning to think you are a troll - where does a 10A fuse overloaded to 20A on a power supply blow with a loud bang?Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmNo really, can you understand what I'm saying here, or are you not able to read? This has been stated so many times, by myself and others, but I'll try again:At low fault currents, the fast-acting glass fuse will blow first. You'll continue to ignore the datasheets linked to earlier and just keep on saying this isn't true.At kA faults currents at mains voltage the glass fuse may not interrupt the current at all.At no point have I said that using the glass fuse is safe with a mains short.These are two different situations that you seem to be unable to differentiate.Also, you do realise a phase to phase short is worse?Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmThis has to be a wind up. The whole point is that they can't measure current. A jobbing electrician measures voltage much more frequently than current. If you can't make the mistake of putting the probes in the wrong position, you won't. Where is there room for error to leave the probes in the current jacks? If you go out on a job, knowing that all you intend to do is measure the presence of voltage, then this is all that you need.Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmHaha, what? "only applies to one device from the Fluke corporation"? Where did I say that? You keep on adding these words "only", "always", "all". You could ask for clarification on the point, but assumed I meant a volt stick. People here tend to mean a contact voltage/continuity probe when they say voltage tester, and volt stick for non-contact voltage probe. I can understand why it could be ambiguous. If you'd asked me the question instead of assuming, I would have answered. I also used the word "only" too strongly, and should have said "mainly".The one thing, regardless of what particular device we're talking about, is that they both have the inability to measure current and hence cannot be shorted across the mains.To be more clear, a lot of electricians use the contact voltage/continuity probes as their primary measurement tools now. There is no room for error in probe/socket placement.But I've not said that it only applies to a given Fluke device.Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmThe argument is in the datasheets as linked. Do something to counter them and maybe someone will think you are talking sense.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 12:38:12 am
content: STOP PRESS! News fresh in.I just put my spare 10A SIBA fuse from the Fluke 17 across the power supply set to 20A/20V!I also did the same with a no-name 10A glass fuse!I used a 0.5 Ohm shunt to measure the response!Neither made a bang! The glass fuse looked like a light bulb blowing!Oh my god! The glass fuse blew quicker! 8s for the glass fuse!The HRC fuse, what a drag, how slow, almost 2 minutes, exactly as the spec sheet!I wouldn't have bothered with the current shunt if I'd known it would be so different. I'm also highly disappointed by the flash and bang I was promised.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 12:41:13 am
content: I can see the response now though.What I said was "all power supplies", not "my power supply". I totally forgot about about that 20MV, 1000MA power supply that will be invoked now.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 08, 2011, 12:45:05 am
content: cybergibbons .. Sorry mate , but you have to edit and remove from your message words like .. Troll ... talking sense.. etc etc ..Currently me and many members , we are trying to understand due this Naval battle of yours ,the technical strong points of its side ..No one of you both will get any metal of honor as winner .And so there is no need to prove your self's.I have awareness that both of you , are smart people and normal persons with an kilo of ego at list.In my eyes you are both valuable , even differential as characters ..My opinion is that Uncle Vernon started it with the " bollocks " as comment ,but in the name of the international friendship - between technicians , all this it must end here.Why I stuck my noose , in this small dog fight, because I care to have you both as regulars in this forum.I feel very lonely by knowing that the most participants , are young ones with out experiences in anything, and so there is no audience for interesting conversations such as this one.

author: Unknown
author_rank: Unknown
timestamp: January 08, 2011, 01:09:33 am
content: Quote from: Kiriakos-GR on January 08, 2011, 12:13:41 amHigh power triac lamp dimmers are just one application that comes to mind.

author: Unknown
author_rank: Unknown
timestamp: January 08, 2011, 01:14:20 am
content: Quote from: cybergibbons on January 08, 2011, 12:38:12 amYour comprehension skills missed the terms mains did they?Your rudeness, ignorance and sheer stupidity serve no purpose here or in any sensible debate!Get a clue and perhaps some manners while you are at it!You sir are the weakest link. Good-bye!

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 01:22:54 am
content: Quote from: Uncle Vernon on January 08, 2011, 01:14:20 amPlease, really, you are joking? Read the quote, this is what I said, then what you said.Quote from: Uncle Vernon on January 07, 2011, 11:02:21 pmMains... mains... no, can't see mains there. Can anyone else?

author: Unknown
author_rank: Unknown
timestamp: January 08, 2011, 01:33:29 am
content: Quote from: Kiriakos-GR on January 08, 2011, 12:45:05 amMy statement of bollocks was in response to a suggestion that a comment I made was wrong, something which has proven even by Cybergibbons own argument to be inaccurate. I apologise to you or other for any volleys I have returned to someone whose insecurity has them needing to attempt to point score.Kiriakos please don't feel you are the older participant in the forum by any measure, I'd guess I have a few years on you and I can see more than a few participants that have years on me. I have hands experience in the fields you work in but am placing myself further from that and back to a more R&D role with my own products over recent years.You're correct that there is a place for a variety of views and experience, it's only the fools that refuse to accept the input of newbies or those from other areas of expertise. Sadly a few see it as their mission to refute without consideration any input not subscribing to their own narrow focus. It is such people that I have very little time for. In respect for yourself and others I'll choose to ignore any further nonsense and bad manners from same.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 01:41:57 am
content: Quote from: Uncle Vernon on January 08, 2011, 01:33:29 amI've provided several datasheets for multimeter HRC fuses, and one for a glass fuse. The glass fuse blows faster at currents between 1 and 10 times rated. You deny this, despite the datasheets showing it. This is a very, very simple point that you could easily disprove, but for some reason won't.

author: tom66
author_rank: Super Contributor
timestamp: January 08, 2011, 02:43:49 am
content: QuoteI wish to disclaim I did this accidentally with my cheap £20 multimeter and it still works, on 230Vac mains. I initially set it on ohms while switching ranges then I got curious and I tried all ranges, volts AC, volts DC, ohms, continuity, diode, capacitance, frequency (which actually measured mains frequency of 50.02 Hz). It does weird stuff when you do it, for example, on ohms it switches between 40.00 ohms and OL, on continuity it beeps at twice the mains frequency, and on cap mode it shows "0.00pF". I left it on for about 5 minutes with no apparent loss of functionality or change in specifications. It still works today.I didn't set it on amps that time, but I did that before with another meter and it just tripped the breaker box, there was a big spark from the plug but not much else, meter still worked, needed to replace the 10A fuse though. Maybe with industrial settings the breaker wouldn't trip and the meter would melt.

author: Unknown
author_rank: Unknown
timestamp: January 08, 2011, 03:03:13 am
content: Quote from: tom66 on January 08, 2011, 02:43:49 amJust tripping the circuit breaker is the luckiest outcome. The breaker trip and the big spark should be telling you that it's not a clever thing to do. Yes as the sizes of conductors increases the potential for pyrotechnics increases, but make no mistake there is enough energy in a typical 16mm 80A supply to cause real damage. The fault currents possible even at that level are immense.Please don't ever deliberately flash things across the main sand please do your best to avoid accidentally doing so. In the right situations the risk of fire and or explosion are very real.

author: tom66
author_rank: Super Contributor
timestamp: January 08, 2011, 03:42:12 am
content: Quote from: Uncle Vernon on January 08, 2011, 03:03:13 amAccidents/mistakes happen, you take precautions but you don't notice that you're measuring amps not volts AC. That's why there's a fuse and a breaker, and far stupider things have been done by me with meters. I was a distance away from the meter when I set it up (I make sure to do this at all times when I am dealing with high voltage and cannot be sure everything is okay.)

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 08, 2011, 04:06:36 am
content: Quote from: cybergibbons on January 08, 2011, 01:22:54 amI love practical facts as proofs , and so the trillions of electrical devices that we all have plugged on Mains 24/24 with glass fuses , does not explode .. does not receive dangerous 8000V pulses ... does not cause disasters and waves ...And the permanent problem of mains its not the over-voltage ... the opposite bothers us !!And so I am less passionate about the ultimate standards , because I do not see them to have any effect in the real life !!I have exchange lots of burned fuses from all sort of devices , there is nothing tragic in a burned fuse.Some they will burn just the wire , and the glass stays clean.Some they will burn and they will become smokey .And that's it .Lets take a breath and speak a bit about human ages and advices.The parents as grownups they usually enlarge the risks , so the fear to protect the Kids ,because they are unable to understand the details.In this specific forum the members age are not viewable , and so its common most people to think that they communicate with smaller persons in age , and they doing the known " parents example " so to protect them .Recently we had even an example of one young kid who tried to measure an electrical fence !!And so I suggest to all to define their communication protocol .Father to son ?Technician to Technician ?Chef Technician to Technician ?Master God of technicians to every one ?I am more confused than all of you as an non natural English speaking person,because i am unable to detect easily at list , irony - flames - sarcasm - black humor ..And I do have hard times to follow this conversation.And so I will say so far what I have understand.cybergibbonsyou have right the glass fuses are faster ...Uncle Vernonyou are overreacting about how the fuses die , usually they die with not that's much noise.To allI believe that all those multimeter's that had become fireworks ,had internal issues on the PCB , that's why they had turn to carbon that easy.The PCB lines had less clearance than the clearance of an single glass fuse.Or the PCB was bad quality , and by the heat become cont-active.And so only the multimeter that lives on industrial environment needs to offer the " maximum " protection.(what ever that is )

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 08, 2011, 04:34:57 am
content: Quote from: Kiriakos-GR on January 08, 2011, 12:13:41 amI still expect one reply , because this is the only portable example with HRC fuses that I have see so far !!And as example that demands fast HRC only the Fluke DMM.

author: Unknown
author_rank: Unknown
timestamp: January 08, 2011, 10:09:07 am
content: Quote from: Kiriakos-GR on January 08, 2011, 04:06:36 amIn this part of the world over-voltage can be a real problem. Our 240V mains (which are supposed to be now reduced to 230V) are routinely well above that figure 8pm Saturday and I'm seeing 250V. Certainly well out of a safe range for all the 220V equipment sold here. I Western Australia and remote parts of NSW it's not uncommon to see the mains reach 275V. And yes our neglected and quasi-privatised grid experiences plenty of brown-outs too. But non of this has too much bearing upon the results in a dead short situation.Quote from: KiriakosBut that is not always it, sure it's the most common outcome but there are plenty of times it is not the case. Hell more than a few of those garbage $50 meters don't even have fuses in-line with the current shunt. And I sure as hell don't want to be holding a meter inadvertently flashed across the mains with only a cheap glass fuse as any sort of safety margin.Quote from: KiriakosNothing has been presented to suggest that a glass fuse will be the fastest thing to interrupt potentially huge fault currents or that one would be capable of interrupting it at all.Quote from: KiriakosNo ever-reaction at all, the Cat III and Cat IV devices are designed to be as safe as possible during use and potential misuse. This includes using appropriate fuses for the application. All the guff about overloads of a few times has no bearing on what happen during situations where fault currents can be massive and where arcs are easily created. The HRC fuses selected by the manufacturer will be the best cost compromise solution that meets all the required ratings.Quote from: KiriakosAgreed they are garbage that aren't suitable for even hobbyist use.Quote from: KiriakosNot just in industrial environments, in any environment where mains or high energy sources are involved, however infrequent, and I'd advise hobbyist working with anything more than a couple of AA cells to consider using the same protection.You can weld your probes onto conductors under a short! Any test instrument not rated for the environment can let go violently under severe overload. Those HRC fuses in a quality meter ARE the quickest way of ensuring operator and device safety under in situations likely to cause fire or physical harm.No amount of namby-pamby work method statements and procedures are going to help when the inevitable mistakes are made. Appropriate equipment with appropriate internal protection affords at least some protection when things go wrong. Whether it's to protect their users or to protect themselves from litigation, manufacturers of rated equipment have gone to a lot of effort to ensure minimisation of risk in the shortest possible time. On that basis, I will trust their judgement ahead of any random or selective reading of device specification under entirely different conditions.The risks remain, call it over reaction if you wish.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 10:32:20 am
content: Quote from: Uncle Vernon on January 08, 2011, 10:09:07 amNo one has claimed it would be the fastest to act under huge fault currents. It's faster to act from 1 to 10 times overload.

author: tom66
author_rank: Super Contributor
timestamp: January 08, 2011, 11:38:33 am
content: Would it be possible to upgrade a multimeter's glass fuse and replace it with a HRC?

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 08, 2011, 11:52:17 am
content: Quote from: tom66 on January 08, 2011, 11:38:33 amYes, if you can find one in that size. It's not guaranteed to make the meter any safer though - if the meter manufacturer has skimped on the fuses, it's quite likely the PCB and rest of the design may not allow interruption of large fault currents.