Safety? Dave loves safety issues with equipment. How about safety in design? - Page 1
Forum section: electronics / general

author: Lightages
author_rank: Unknown
timestamp: August 16, 2011, 04:44:03 am
content: I think with all the emphasis that Dave puts on the safety of equipment design, it's time for a video blog on the basics of designing in safety into projects and products. Information on fusing, wiring to mains, track sizing and spacing for voltage and current, grounding in design and in measurement, safety procedures during troubleshooting and testing, chemical safey during preparation and cleanup, safety category standards and their applications (ie CAT3), and last of all static electricity safety for the electronics too.This seems to be a good time for this given the number of newer members on the forum.

author: saturation
author_rank: Super Contributor
timestamp: August 16, 2011, 10:24:33 am
content: I agree. Safety practices are easy to find, just use UK's HSA or USA OSHA. But safety in design involves many issues regarding electrical work than electronics. Design guidelines can be found in UL or CE or IEC directives [since in order to pass their safety testing, these requirements must be met], but they don't explicitly say how to accomplish these goals.

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: August 16, 2011, 11:33:34 am
content: While I don't doubt Dave's expertise in electrical safety, I think covering such topics probably needs a bit more thought and careful planning. Particularly when working with mains power. You really don't wanna screw up or inadvertently pass on the wrong message. Still, I think it is a good idea and would be an interesting topic.

author: EEVblog
author_rank: Unknown
timestamp: August 16, 2011, 11:53:49 am
content: I think I'd rather have my teeth extracted than contemplate such a blogThere are so many issues involved it would be hard to know where to start.And then if you are talking mains safety and compliance alone, then there are potentially different rules and standards for different countries, it can get messy really quick.Grounding alone can be a whole can'o'worms, with so many design/system specific things to consider.Use AA batteries for everything and make your life much easierDave.

author: Time
author_rank: Frequent Contributor
timestamp: August 16, 2011, 03:57:09 pm
content: Safety is important but a blog on it sounds terribly boring.

author: Lightages
author_rank: Unknown
timestamp: August 16, 2011, 05:43:23 pm
content: OK, then if the scope of covering it all is too daunting perhaps a blog on some bad designs and the reasons they are bad and the possible consequences. A badly designed multimeter example would be a good start. Show specifics and explain the dangers. Then blow it up and show how it can fail dangerously.Perhaps cover the concepts of trace width and spacing for higher voltages and currents.Definitely do something on the proper procedures for testing and troubleshooting so that some of the "young players" don't zap themselves when starting out. Capacitor discharging, proper grounding when testing, and electrical safety category standards for test equipment would be good subjects.C'mon Dave, you are always going on about how things tried to kill you and how shoddy some things are for safety. Put your money where your mouth is and show the newbies some pointers to save themselves injury.

author: Neilm
author_rank: Super Contributor
timestamp: August 17, 2011, 08:29:24 pm
content: Quote from: EEVblog on August 16, 2011, 11:53:49 amWe use AA batteries is some of our stuff at work - it outputs 1kV.Allow me to give a few thoughts on safety and safety standards. For background info on myself - I have spent the last 7 years designing and qualifying electrical test and measurement equipment. The company I work for self certifies their designs - and we do have someone who sits on TC66 (the committee that writes 61010)The general requirements for IEC61010 (electrical equipment for test and control) runs to some 160 pages. Then there is a standard for testing and measurement equipment (-030) it's another 30 pages. Then, there is a standard for test leads (031) another 60 pages. If you are making a simple voltmeter you have to go through all of those and ensure that the product complies to each line and clause of those standards before you say it can comply.When a new designer starts at the company I work for they are taken in excruciating detail through the process used to meet these standards. It takes all day and (hopefully) the victim comes out from it knowing that meeting these standards is very complex.As a for instance, to calculate the clearance required at a voltage requires looking numbers up in a table, interpolating those numbers (you never hit one of the values in the table) calculating the effect of transients then multiplying it by a figure for your rated altitude then using the result to give you a value for your functional clearance (single insulation). Depending on the application, the safety distance to the user (called double insulation) involves going back through your calculations and increasing some of the numbers by a specified factor. (not just doubling the result of the single level).Then you have to test the above, so you have to calculate the test voltage. This is done from yet another table but you can't just use that number, you have to compensate for the altitude of your test site. And so it goes on.All the above is a quick summary of what a designer has to do to calculate functional clearance, safety clearance and the test voltages for them. That is summed up on just 2 pages of 61010 (excluding the tables). Certain situations have these predefined (i.e. ordinary CAT II mains inputs) but many more are not.It hasn't covered documentation (yes this is a part of 61010), markings, enclosure materials, radiation, sound, mechanical hazards, stability and many many more.I hope this give you an understanding of the depth and scope that is encompassed by safety standards.As for what might happen see this. I believe that it was shown to TC66 by one member complaining that 61010 did not go far enough. It later turned out that the multimeter in the explosion did not meet 61010, even though it claimed it did.Pointers for newbies - don't mess with high voltage. If you do have to, find out about safety distances. Lastly, don't complain if the mains circuit you designed blew up even though you had protected it with a MOV because you put a metal screw head between the MOV legs. (I did see that when given a product we were looking to factor. Needless to say I immediately threw it out)YoursNeil

author: Unknown
author_rank: Unknown
timestamp: August 17, 2011, 08:56:02 pm
content: Aren't Safety Videos traditionally done by someone from the 1950's who speaks in monotone?Besides safety has been made entirely redundant and become superceded by OH&S where the demise of a worker can be fully documented and any blame duck-shoved towards those least able to compensate his widow?

author: ciccio
author_rank: Frequent Contributor
timestamp: August 18, 2011, 07:15:01 am
content: I understand Dave's concern about the difficulties that such a blog will present.Why not suggest some books?In my bookshelf are sitting these two, both published by Newnes:"Electrical Product Safety" by Tzimenakis and Holland"Practical guide to the Low Voltage Directive" by Kervill.They are old editions, both around 2000.Don't know if they are still available or if an updated edition has been printed.Every forum member that is professionally involved in electrical and electronic design should read them.I don't know if it is possible, due to copyright reasons, but maybe it could be a good idea to have some extracts from the books published in the forum.EDIT: I've searched Amazon, and both are available (still the first edition) at the absurd price of 118 USD for the first one and at a more reasonable 78 USD for the second.Didn't know I had such a treasure in my bookshelf

author: Psi
author_rank: Super Contributor
timestamp: August 18, 2011, 11:26:11 am
content: yeah, safety is a bit of a boring and broad topic to try and do a blog on.What might be interesting though, is some info on what you need to do before selling your project, does it need to be certified? or tested? or can you just start selling it?Lots of hobbyist make stuff but who here actually knows what they need to do before they can legally sell it?eg..If a project only uses low voltages and the power supply is done using an off the shelf 230v -12v adapter does that mean the device is legal for sale without needing any 3rd party testing?Of course its impossible to go into much detail as the laws will be different all around the world.

author: ciccio
author_rank: Frequent Contributor
timestamp: August 18, 2011, 01:26:02 pm
content: Quote from: Psi on August 18, 2011, 11:26:11 amAt least in Europe, if you are selling an electrical or electronic device, does not matter if battery powered (1) or mains powered or solar powered or whatever, and does not matter if you are selling one piece or thousands of pieces, and does not even matter if you are getting money or giving it away for free (2) you are obliged to CE mark it and, at least, compile a CE declaration of compliance and have a copy of a Technical File which includes all the design data and all the tests and measurements you have made to show that it complies with all the relevant technical standards.1) : if powered by less than 50 V dc or 75 V ac, it does not need to comply to the Low Voltage Directive, but other standard ( Electromagnetic compatibility, fire safety, mechanical security, etc) still apply.2) : CE marking and all the relevant activities are needed if the product is "put into the market", so it does not only mean it is sold (for money) , but also it is loaned or sent to a customer for free, etc.This is the legal point, but many people are still (after more than 15 years) making a living from single piece, custom made devices, and the CE sticker can be bought on ebay....I don't know what could happen to an hobbyist that sell his projects, but my suggestion is to play it safe, sticking to low voltage, low power designs, and use batteries or a CE marked mains adapter.This leaves you with electromagnetic compatibility issues and mechanical (personal injury) issues.The first one does not harm people, the second one is easily assessed.Edited after reading Neilms response (following message).I also forgot fire safety: your product should not fail and burst in flames or release smoke or toxic gases...

author: Neilm
author_rank: Super Contributor
timestamp: August 18, 2011, 07:34:45 pm
content: Quote from: ciccio on August 18, 2011, 01:26:02 pmTwo points - firstly there is a story of one Chinese company selling mislabelled and non complient equipment claiming that CE stood for China Export.Second, threre have been incidents of non complient equipment causing incidents that could have compromised safety. The first instance that sprung to mind was a CB radio that had very high out of band emissions. It caused the ABS system on a bus to fail (not the brakes, just the ABS system).Neil

author: ciccio
author_rank: Frequent Contributor
timestamp: August 18, 2011, 08:34:55 pm
content: Quote from: Neilm on August 18, 2011, 07:34:45 pmThat's true. Touchè.Best to stay away from RF power.We must take in account that sometimes the electronic systems (even those made by important manufacturers) installed on vehicles have shown being not compliant with immunity to real-world signals, even if they have passed the relevant tests required by standards.I live at about the center of Italy's "motor district" : 25 km from Ferrari plant, 15 km from Lamborghini's, 15 km from Maserati's, 22 km from Ducati's, 4 km from Pagani's, and I know some engineers working there or for some of their suppliers.They, sometimes, after a drink, will tell real-world tales.

author: Neilm
author_rank: Super Contributor
timestamp: August 18, 2011, 08:55:14 pm
content: Quote from: ciccio on August 18, 2011, 08:34:55 pmIt doesn't just have to be RF power - I have seen even small battery powered devices cause all sorts of problems due to poor EMC techniques.In regards test standards, as far as I am aware all EMC immunity standards are attempts to duplicate the real world with repeatability. The ones I have seen only deal with one frequncy and one method of propogation at a time. You don't get test doing radiated immunity with multiple frequencies, harmonics on the mains and conducted RF with noise burst all at the same time. As such, they simply give a guide to how susceptable they are. They also have usually unrealistic setups.At least safety regulations tend not to be open to debate on how they are implemented.Neil

author: Jimmy
author_rank: Regular Contributor
timestamp: September 08, 2011, 12:18:38 pm
content: Quote from: EEVblog on August 16, 2011, 11:53:49 amDaveGood choice just close that can of worms and move on as there are also the legal ramifications of "on the EEVBLOG they said do this and it will be safe"In Australia you shouldn't be playing with anything over 50v ac or (I think its 110v dc) unless you have an electrical license, are a REGISTERED electrical engineer, Supervised Apprentice or Student. It doesn't matter how the electricity is generated eg Battery, mains transformer, your own generator at your house, Rubbing a electrode against a cat or solar.In QLD it is Illegal to work live unless it is life threatening not to work live (having a Mcdonnalds manger tell you to work in a live switchboard to get the chip fryer working at 6pm or he will KILL you is not considered life threatening ) Testing is not considered working but you have to have a trained safety observer or a self employed contractor.If you want to know how to build your hobby stuff safely AA batt as Dave suggests and maybe a small fuse. I would say rip some old crap apart have a look around at what others have done and when designing your own stuff you will know what to look for. If you want to interface with mains voltage go buy one of those remote controlled power boards and rip the transmitter apart and interface with the low voltage side.This is lawAS/NZS 3820:2009QuoteQuoteIf you make an electrical appliance and plug it in it becomes part of the installation. An insurance company may not pay out if you burn your house down if you have installed your own designed home automation system. That is all that matters in my opinion. If you stuff up or your pcb manufacture makes a mistake that you don't pickup and 6 months down the track a small fire is started while you are not home and the Insurance man no pay. Many of the local people here in Ipswich west of Brisbane are still fighting to get paid from the Jan flood.

author: Unknown
author_rank: Unknown
timestamp: September 08, 2011, 01:15:58 pm
content: Quote from: Jimmy on September 08, 2011, 12:18:38 pmActually it's 33V, ELV has a threshold of 32VQuoteNOPE! The lunacy of our legislation prohibits those most educated in things electrical from actually doing electrical installation.Quotewith the description of supervision being somewhat vagueQuotewell actually it does, fixed wiring is heavily regulated. Even a fully licensed electrician should never be working live alone. But once you get to a domestic situation and you are not installing fixed wiring or working for payment or reward things change.There is no law that says you cannot stick your tongue into the toaster should you choose to do so. No matter how foolish that action is.Those loons from the ACMA have even made it illegal for a skilled engineer to install data cable in his own home. Yet any vandal with a white van,a dumb look and a certificate from a few hours of cablers course can do so.QuoteThey are a little strange in QLD, the legislators there particularly so.QuoteThe recommended solution to electrocution still being to beat the subject with a piece of dry timber.QuoteAs long as its on a cord from a plugtop there is no restriction on individuals regardless of the risks they may or may not understand. If you plan to use your creation in a public place or offer it for sale there are lots of regulations to say you cannot do so.QuoteMaybe yes maybe no. I'd say that is poor advice in isolation. Common sense says don't mess with stuff you don't understand or stuff that can kill you that you think you may understand. Get someone skilled to check and test your work, you may still have a set of eyebrows left after initial power-up if you do. If you cannot do this stick to batteries and approved ELV supplies.QuoteSee above the same risks apply when you interfere with any mains powered device!!QuoteAS3000 is Law for fixed wiring.QuoteNo it doesn't your electrician will not be liable for your actions. The installation is his responsibility his insurance.QuoteLiability from you own insurance depends entirely on your policy and wether or not you are covered for your own negligence and/or stupidity. Results will vary.QuoteSee above policy and cover will vary.A safety blog would be about as exciting as watching grass grow. If anyone wants to see hours of preachy video that will assume you are an idiot then they can contact workcover or do site inductions for as long as it takes for a coma to set in.Common sense things to do.Make sure you work and user space has it's power circuits protected by RCD ELCB or other protective device.Get yourself an RCD protected lead or power board.Don't mess with stuff you don't understand or that you just think you understand.Get your stuff checked by someone else (this applies to anything that draws more than a few mA too even at extra low voltage).Get an isolation transformer if you do a lot of mains work but leave it in the box until you understand how it can kill you too.Check you Insurance policy and seek advice if unsureDon't touch any fixed wiring even ELV wiring without a qualificationUnfortunately the whole subject of safety has been absorbed up by OH&S rubbish and other bureaucracy, don't for a moment think these have anything to do with safety regardless of some having safety in their titles. These are about duck shoving responsibility and are there to protect governments, large companies and insurance providers.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 08, 2011, 01:46:35 pm
content: QuoteThis is such excellent and too frequently ignored advice. If you are working on anything that might have exposed mains voltage you should have a good high sensitivity RCD for your bench.QuoteLike the fact that unless you set it up properly it will prevent an RCD from operating.

author: Jimmy
author_rank: Regular Contributor
timestamp: September 08, 2011, 02:47:34 pm
content: Uncle VernonYou are a trooper with a like mind with more knowledge I love it33v ok I was not sure because I can work at any voltageQuoteI think you will be surprisedQuoteI do like to reference the whole chunkQuoteIt depends on the IP rating of a toaster i guess it would be IP30 ( cant touch live parts with finger and no protection from water) I cant stick my tongue out longer than my finger.loons from the ACMA they approached me I said I was an supervised apprentice so go away.beat the subject with a piece of dry timber is not recommended currently to date you need to put on 1000v gloves, Isolate supply, Use Crook to move body. I would prefer the timber option and the new breed of sparkies are too scared to work live.QuoteWas aimed at a skilled audience not for total newbs. sorry it was poor advice to the hobbyistYou can buy power boards with batt operated rf remotes so no mains modification is required and I added as3000 for any engineer that wanted to build there on home automation lighting or something like that. If you have a extension lead that goes through a wall and you sheet around it and you cant pull the plug through it is classed as fixed wiring.Insurance Rant just something people should know.You say buy rcd every residential property needs to have a rcd installed on their lights and power. Its law in some parts of Australia and if you are selling a house it has to have them or at change of rental contract.If you use more than one rcd it can cascade. I have had the problem that a circuit had a 30ma rcd in switchboard and 10ma rcd at point and the 30ma would trip before 10ma. A RCD does not work between Active and Neutral it is between either and earth so make sure your earthing system is up to scratch as well. Operate you rcd atleast every 3 months buy pushing the test button because the mechanical component can get stuck.People are going to keep doing there own electrical wiring and in remote rural areas it is legal to do so. The trick is don't become dead

author: Chasm
author_rank: Regular Contributor
timestamp: September 08, 2011, 06:12:26 pm
content: Quote from: Jimmy on September 08, 2011, 12:18:38 pmThe obvious out is to blog about safety fails as encountered in real life instead. =)There have been quite a few of them in the episodes so far, there will be more in the future.

author: ivan747
author_rank: Super Contributor
timestamp: September 10, 2011, 12:30:42 am
content: Quote from: ciccio on August 18, 2011, 08:34:55 pmAwesomeI like stories about unsafe products. And I like telling my findings too, as some of you may find on the forum. I often talk about unsafe practices here in the DR.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 10, 2011, 02:19:41 am
content: Like I said in another posting,Australia is a big place!Although they are all based on the AS/NZ Standards,Electrical Licencing is a State responsibility,& the rules differ between States.In WA,for instance,there is an "Restricted" licence which enables people who are not Licenced Electricians to do limited work on mains equipment,& here are the weasel words:-"As required in their occupation"--so a plumber may have one for replacing the booster on a solar hot water system,& so on.For instance, mine says that I am "authorised to carry out restricted electrical work in association with Communication/Computing Equipment"For many years,anything to do with Radio Broadcasting & Communications was regarded as a Federal responsibility,& those that either worked for a Commonwealth authority like the PMG's Dept,& later,Telecom Australia,& on pretty much a de-facto manner,working for the private sector in positions requiring a Federal licence were left alone by the State regulators.With "deregulation" back in the 1990s the Feds backed away from the whole area,leaving a vacuum for the States to move into.The WA Licencing authority discovered that "shock,horror",Radio & TV technicians didn't just work on transistor portable radios!"Something had to be done about this state of affairs",so a bunch of us Techs from the private sector had to go & do the "R" licence!Apparently since that time,an Australia wide "R" licence has been devised,but whether it works in Queensland,I don't know--they're a bit strange up there!Meantime,I've still got my original WA "R" licence!Many thousands of people work with Electricity every day in Australia,& the number of people injured is extremely small,testifying to the widespread application of commonsense!VK6ZGO

author: Zero999
author_rank: Super Contributor
timestamp: September 10, 2011, 08:35:46 am
content: Quote from: Uncle Vernon on September 08, 2011, 01:15:58 pmRegulations vary from country to country.The British IEE classify ELV as below 50VAC or 120V ripple free DC and the IEC say it's below 25VAC or 60VDC.In the UK the regulations for voltages under 120VDC or 50VAC are less stringent than low voltage: exposed metal parts don't need to be earthed but the live parts still need to have basic insulation from the user. Basic insulation is not required in dry areas at voltages below 25VAC or 60VDC. Insulation is required at lower voltages when there's a large exposed area in contact with the human body or in wet areas: i.e. outdoors it's 30VDC or 12VAC.