Mains protection  - Page 1
Forum section: electronics / testgear

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 08:59:25 am
content: What are people’s views on the best way to protect yourself.I have a large isolation transformer, large variac and bulb current limiter.What order?Which devices?I work on guitar amps and currently messing with valve amps. My current protection method involves discharging caps and attaching leads etc before turning the device on. Sometimes checking things with the power on is useful. It would also be helpful to protect the device as well.What are people’s views? At the most the isolation transformer goes into the bulb limited and I have just bought a job lot of variacs.

author: madires
author_rank: Super Contributor
timestamp: October 25, 2019, 09:23:56 am
content: That's a reasonable setup for messing with valves. If you have a scope also get differential probes as the scope's ground is connected to earth/PE.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 09:52:12 am
content: Too much wide question...You must split your targets in (at least) 2:= protect the DEVICE UNDER TEST= protect you bench hardwareFirst is kinda what you have - isolation transformerwhich should have proper fuse or tripping devicesThe variac is essential on faulty devices andthe bulbs are essential too. You just can not afford topower dead short DUTs adhoc.The second problem is what sort of installationyour bench use... complex thing to setup.You need to consider a list of things regarding yourmains, type of hardware for test and devices under testMy personal setup uses individual isolation transformersfor DUT and for all my bench hardware. And YES I am awarethat some folks advice to not isolate scopes and meters...But the benefits far outweighs the risks...Nevertheless some specific faulty devices will need specialcare.. for that galvanic isolated meters (BAT POWER) andmay be compatible proper generation (aka use TUBE bench tools)will solve a lot of issuesPaul

author: Electro Detective
author_rank: Super Contributor
timestamp: October 25, 2019, 10:15:16 am
content: Add gloves, eye protection and rubber soled shoes to PKTKS setup/s above(which roll very similar to mine)and it's as safe as safe can be....that only a collapsed ceiling due to plane crash, obese termitesor fatass neighbors above, earthquake, tsunami,alien invasion/saucer crash or zombie apocalypse can stuff it up

author: nctnico
author_rank: Super Contributor
timestamp: October 25, 2019, 10:54:37 am
content: Quote from: cowasaki on October 25, 2019, 08:59:25 amThe best way to protect yourself is to use a CAT rated differential probe when working with high voltages (including mains). I advise against the isolation transformer to create a floating mains. There are a gazillion ways to ground the circuit again. Better use a low current GFI (which you test before doing a measurement).

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 11:11:32 am
content: Thanks so far. Lots to consider. I have several variacs but only one large isolation transformer. I could make another using two transformers or buy another. Would all the equipment on the bench be ok through one isolation transformer? If so I could use my existing one which is capable of supplying 13a at mains voltage.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 11:26:51 am
content: Quote from: cowasaki on October 25, 2019, 11:11:32 amNO NEVER PLUG YOUR DUT ISOLATOR in your bench tools isolation unit.Depending on what kind of devices you will work the setup will change.For tube based devices IDEALLY you would use TUBE based scopesand meters... kinda proper devices to suit the measures...You will never use for example an USB scope (5V rated pretty much masx 35V)with that sort of hardware... got it ? match things is also important.For SMPS last decade power ranges were more sane.. below 500W is more simpleBut present days SMPS have gone insanely dangerous.Power ratings of 1000W or 1200W are common with AMPERAGE inrushratings of 100A or 200A on MOBOs. The kind of ISOLATOR for that is not trivial.As said above - differential probes are becoming more important.. but neverthelessthey are WAY TOO MUCH EXPENSIVE... unless you make a living of them..So a couple or 3 ISOLATION UNITS for your bench - ONE SEPARATED UNIT w/a properVARIAC for DUTs... - should be a reasonable and affordable setup.. last but not least - yourself protection pretty much depends on the sortof work - being solder, HIGH VOLTAGE... and other stuff..a PROTO BOARD with ARDUINO definitely will not need much...while DESOLDERING OLD CRAPPY CORRODED AMPS...will require eye and lungs and skin/nail protection..NASTY STUFFPaul

author: BravoV
author_rank: Super Contributor
timestamp: October 25, 2019, 11:50:44 am
content: Quote from: cowasaki on October 25, 2019, 08:59:25 amMy view ... as I had been thru the same path in the past using isolation transformer, bulb trick and etc, and then I realized all of these are prone to mistake when swapping or reconnecting mains wirings and etc.As working with dangerous voltage, one mistake, say 0.01% mistake or just once, out of 99.99% correct, is enough to toast your scope, your limb or your life. Think about it, is it worth the risk ?Consider to save money for HV differential probe, even cheap one is better than none if you do this alot.Once you owned it, probing mains related devices will be much-much less riskier, an example a scope was probing the mains line that powered the scope it self using HV diff. probe.

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 11:59:51 am
content: I think a differential probe is likely my next purchase but everything I have I’ve had for a while. Just have my new PSUs to pay for at the weekend then that’s likely next. I’ve designed some valve based effects so quite like the idea of a HV probe. I’ve been looking for a suitable scope for a while. I currently have a decent spec UNI-T scope which was ideal for the computers and other stuff. I have a novascope which only cost £10 which I use for audio as I is very quick to setup and adjust. I see mr carlsons lab and the number of valve scopes he gets but not sure what happened to them all in the uk!

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 12:05:26 pm
content: Quote from: BravoV on October 25, 2019, 11:50:44 amTrue but indeed this risk is UNAVOIDABLE.Even having ALL OF THIS STUFF... all.. put ISOLATOR VARIAC BULB..and use DIFFERENTIAL PROBE...We are still prone to touch (with the probes or fingers ) parts whichshould not be touched while servicing..A small fraction of a second is enough to spark and TOAST EVERYTHING.With a simple probe in the wrong place.Same with the hand and fingers.. touching some parts is necessaryand BEING GROUNDED (pulse ground) may be deadly.So always consider if the setup is really safe per si - regardless the measuresThis is the hard part.. and mistakes still happen...Part of the thing.Experience does help however it will not save you from mistakesPaul

author: BravoV
author_rank: Super Contributor
timestamp: October 25, 2019, 12:35:26 pm
content: Quote from: PKTKS on October 25, 2019, 12:05:26 pmYeah, example of touching the tiny portion of the exposed metal at the probe tips ... both hands ... mains voltage connected... thats different story, no matter how good the protection is, it wont help.

author: nctnico
author_rank: Super Contributor
timestamp: October 25, 2019, 12:37:40 pm
content: Quote from: PKTKS on October 25, 2019, 11:26:51 amBad advise. Differential probes cost less than an isolation transformer nowadays (MicSig sells a very economic one). Using isolation transformers is just dangerous. There are too many ways to ground stuff. Better keep everything grounded while protected with a low current GFI. That way you can minimise the danger area to the DUT and the probe leads which is much easier to keep an overview on and thus have less chances of a mistake.

author: madires
author_rank: Super Contributor
timestamp: October 25, 2019, 12:51:39 pm
content: Quote from: nctnico on October 25, 2019, 10:54:37 amI'd prefer an isolation transformer when working on a hot chassis.

author: madires
author_rank: Super Contributor
timestamp: October 25, 2019, 12:56:25 pm
content: Quote from: PKTKS on October 25, 2019, 12:05:26 pmRubber gloves

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 01:01:44 pm
content: My isolation transformer is 3.6Kv but no current limiting. I have the bulb limiter plugged into the isolator. There is a 13a fuse in the lead to the transformer and another between the transformer into the limiter. I could get an isolation transformer for a single device and swap it as required if that would help WITH the dif probe!

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 01:02:17 pm
content: And I have rubber gloves. The floor is wooden and carpeted.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 01:04:10 pm
content: Quote from: nctnico on October 25, 2019, 12:37:40 pmNO not here in Braziland may be other places and other budgets.Almost 100% stuff in Brazil is now IMPORTED.TAXES OF EVERYTHING ... are pretty much 100% - AT LEAST!sometimes may be more due to extra shipping costsPrices are for sure the DOUBLE at least may be 3x timesEVERY STUFF YOU SEE on EBAY ALIX and BANGOOD...3x times of EVERYTHING is not a good bottom line to live withPaul

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 01:08:12 pm
content: Quote from: cowasaki on October 25, 2019, 01:01:44 pmFor costing issues I have replaced the FRONT END TRIPPING FUSEwith a zing-ear ZE-800http://www.zingear.com/e/proDetail.php?id=6735&cateid=29571Several advantages and so far so good every issue wasnicely handled. The real fuses are on the secondary sidePaul

author: AVGresponding
author_rank: Super Contributor
timestamp: October 25, 2019, 01:21:27 pm
content: OP is from the UK, not Brazil.You most likely have an RCD, maybe even RCBO protected mains. These trip at 30mA earth fault currents. You can buy ones that trip at lower currents.In my experience, isolation transformers and variacs have their place, but can lead to complacency. To be absolutely, 100% clear:AN ISOLATION TRANSFORMER WILLNOTPROTECT YOU FROM ELECTRIC SHOCK IF YOU TOUCH BOTH OUTPUTS SIMULTANEOUSLY.Its primary function is to prevent a line-earth short when connecting two line powered devices, ie probing your DUT with your scope.If you touch both outputs (call them Line and Neutral if you like), it will happily cook your arse with the full current it can supply. Since I believe you mentioned 3.6 KVA, which is 15 amps at 240V. Would you like fries with that human-burger?By all means use an isolation tranny and variac to protect your DUT and scope, but run your scope off an RCD/RCBO protected, earthed supply, to protect YOU.

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 01:34:09 pm
content: Thanks. I think that that resettable fuse looks good. Any other alternatives?

author: AVGresponding
author_rank: Super Contributor
timestamp: October 25, 2019, 01:55:40 pm
content: Limit the self-tanning effect with one ofthese.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 02:01:03 pm
content: Quote from: cowasaki on October 25, 2019, 01:34:09 pmnop haven't seen better for this purpose.I can find them easily right here or even from AliEx.They are cheap (cheaper than equivalent fuses) and hassle freewith BONUS .. they have the PANEL mounting alreadyCombine them with a regular NEON you have a cost effectivetripping wired on the mains front endSave your money for the secondary side.. more complex.piece of cakePaul

author: nctnico
author_rank: Super Contributor
timestamp: October 25, 2019, 02:22:05 pm
content: Quote from: PKTKS on October 25, 2019, 01:04:10 pmYour family will agree that it is better to pay 100% tax rather than taking a chance to die. Besides that an isolation transformer will be imported too so the tax also applies.

author: nctnico
author_rank: Super Contributor
timestamp: October 25, 2019, 02:26:18 pm
content: Besides that... how about powering the amplifier using a lab power supply which can provide the 300V (or so). Lab power supplies have very well behaving current limiting and the fancier ones will discharge the output when the output is switched off.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 02:41:50 pm
content: Quote from: nctnico on October 25, 2019, 02:22:05 pmI started my journey in electronics way back in early 70sBy that time I had obsessive fixation on a TELEFUNKEN B&W TVALL TUBES which I have spent significant time watching cartoonsand crappy stuff...From time to time it went dead .. technicians were rare and whenthey come to "FIX" I was almost inside the tube watching...Well guess what? Very soon the tech was no longer neededand I have lost the count how many times I zapped myself onthat smelling hot tubes.. about 8 tubes with 400 ~600 DC voltsalmost 80C at least..Any usual child would have just gave up that pile of hazard away..Some folks instead thinks that is a good laugh - and for my case..Those 600V DC zaps just made me more and more interested..Some neurons I am sure are lost.. but as soon as the cartoonsappeared again they went back..Well 70s TELEFUNKEN B&W TV was indeed quite a starting ride.Today a 1200W SMPS or 3000W inverter does not scary that muchMy neurons healed watching cartoons....Paul

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 03:44:17 pm
content: Quote from: PKTKS on October 25, 2019, 02:01:03 pmHow do you adjust the trip current on the adjustable version? I can’t find an image.

author: PKTKS
author_rank: Super Contributor
timestamp: October 25, 2019, 04:00:59 pm
content: Quote from: cowasaki on October 25, 2019, 03:44:17 pmI only use the FIXED version carefully matched tothe isolation transformer primary winding VA.And that transformer should meet at least thepower of the device I will isolate... otherwisei will try another method.And some of them are poorly marked ...it depends on the fabrication batchFor example I have a batch without good markings..nevertheless the minimum specs still fits safely margins.It works pretty well on the primary sideand is cheap as wellPaul

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 04:03:01 pm
content: Quote from: PKTKS on October 25, 2019, 04:00:59 pmThere is an adjustable one which looked like a good idea. I have a resettable fuse board that I made maybe 30 years ago from a kit but I'm not sure what the connections are. I'll have to reverse engineer it

author: AudioFile
author_rank: Contributor
timestamp: October 25, 2019, 05:50:40 pm
content: Everyday Practical Electronics (now just Practical Electronics) had a project for a differential probe a short while ago. I built it and it works very well. Quite cheap too (a few tens of pounds I recall).If anyone interested and can't find it, just shout and I'll dig out the reference.

author: Monkeh
author_rank: Super Contributor
timestamp: October 25, 2019, 05:59:19 pm
content: Quote from: PKTKS on October 25, 2019, 04:00:59 pmSo what you're saying is they're so cheap and nasty they can't even manage to mark the case properly, but you trust them as overcurrent protection?

author: BravoV
author_rank: Super Contributor
timestamp: October 25, 2019, 08:57:12 pm
content: Quote from: PKTKS on October 25, 2019, 01:04:10 pmBefore giving such advice, you have to know which country the OP lives, as standard of living is different, say UK vs Brazil. So does affordability in "general".What if this discussion about welding, and someone from poor African country, so proud and keep insisting that is just fine using cheap & effective welding transformer, that was salvaged & re-winded as below example.C'mon, technically with much safer equipment, "IF" its affordable is much better right ?

author: AVGresponding
author_rank: Super Contributor
timestamp: October 25, 2019, 09:12:14 pm
content: Quote from: BravoV on October 25, 2019, 08:57:12 pmI would give this guy 11/10 for improvisation!

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 25, 2019, 11:08:12 pm
content: Quote from: AudioFile on October 25, 2019, 05:50:40 pmThanks I would like that.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 26, 2019, 02:31:16 am
content: Quote from: ThickPhilM on October 25, 2019, 09:12:14 pmMeh..5 out of 10from meHe should have buttoned up the shirt sleevesWorn gloves or oven mittens, or wrap something around the electrode holder/stingerhe's too close to the welder and has a cable that would offer an extra meter or two of distance.isolate both the welder and himself from the ground with wood, cardboard, anythingnot sure if he's got a helmet or gogglesand since I can't see anything else in the picture, the local Fashion Police can add or subtract improvisation pointsfor whatever style of PPE shorts and flip flops he's sporting..

author: vk6zgo
author_rank: Super Contributor
timestamp: October 26, 2019, 02:49:34 am
content: Quote from: cowasaki on October 25, 2019, 08:59:25 amValve audio amplifiers will normally use a built-in power transformer.The only circuitry on the primary side of such a transformer are the incoming Active, Neutral, & Earth wires, an On/Off switch, a fuse, & perhaps a Mains filter.There is not much there that needs to be probed with an Oscilloscope, & a DMM will pretty much tell you all you need to know about the primary circuit.On the secondary side, isolated from the Mains you will find the High voltage & heater windings.Classic transformer power supples use a centre-tapped high voltage secondary, & a "Fullwave rectifier"circuit.https://www.google.com.au/search?source=hp&ei=1aizXZTxHZnZz7sP46uU0Ao&q=full+wave+rectifier&oq=full+wave&gs_l=mobile-gws-wiz-hp.1.0.0l8.2516.5907..8088...0.0..0.285.2271.2-9......0....1.......0..0i131j46j46i275j0i7i30.WtjN4zEIBl8#imgrc=CUBL-vAcbmvdzM:Here is somewhere you can probe, but two things come to mind.(1) Your probe needs to be rated for the voltages you are probing.Tektronix x10 probes are usually adequately rated, but "El Cheapos" may not be.I find the best probes to use for valve stuff are the big old "clunky" ones that Tek supplied with their old 500series CROs.A x100 probe would be nice but it is not really essential.(2) Don't try to hang your 'scope across the entire high voltage secondary, as you will short out half the winding (note how the centre tap in the drawing I linked goes to common, which is, in this case, the amplifier chassis.)Your probe and/or 'scope will suffer, the transformer will get"red in the face", & the fuse will probably blow.You are unlikey to suffer anything other than being dazzled by the spark.D1 & D2 in the drawing may be solid state, or they may be valve rectifiers.In the case of the latter, there is "trap for young players"Some larger or older valve rectifiers have directly heated cathodes, so require a separate better insulated winding ( almost always 5 volts).This winding will be floating at the DC HT voltage, sodon't touch!.Also, don't try to measure across the winding.All the rest of the amplifier circuitry will be referenced to Earth , or Common, most likely the ampifier chassis.After all this someone will probably pipe up that their Great Uncle found a transformerless audio amplifier in a hayshed in deepest Hampshire, but such things are as rare as hen's teeth!For good reason, too!Amplifiers, unlike domestic radios, where with a transformerless design, all the " bities"cab be corralled up inside the cabinet, an amplifier is messy!It has wires leading all over the place, such as audio inputs & speaker leads.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 26, 2019, 03:31:15 am
content: I too got zapped good and proper from an early agewhich sort of 'sparked' my interest in electronicals later on,learning how zaps happen and how to avoidTransformer isolation and grounding etiquette aside,justhow reliable are these differential probes ?and what's the worst case scenario when they fail and or pushed past their peak voltage/frequency limits,or just begin to exhibit intermittent or unreliable behaviour?Surely there are some cons with these and not just the safety pros?

author: AVGresponding
author_rank: Super Contributor
timestamp: October 26, 2019, 06:58:02 am
content: Quote from: Electro Detective on October 26, 2019, 03:31:15 amModern ones use opto-isolators to completely electrically isolate the signal from the scope, and are powered by an internal battery.As for intermittent or unreliable behaviour, that would be due to either low battery voltage, or low quality. You get what you pay for.Cons would be a false sense of safety, and a lower usable bandwidth (unless you have cash to burn anyway lol).

author: trobbins
author_rank: Frequent Contributor
timestamp: October 26, 2019, 08:38:16 am
content: Valve amp testing can be done without a lot of hoopla. AC mains requires continuity and insulation testing first., and then a cheap power meter can give volt and current readings to confirm no adverse levels during amp operation.Scope or soundcard probing doesn't need to access HV levels in a valve amp, but should use at least a 10:1 probe to avoid loading. Absolutely no need for diff probe.

author: nctnico
author_rank: Super Contributor
timestamp: October 26, 2019, 09:24:14 am
content: Quote from: Electro Detective on October 26, 2019, 03:31:15 amIf they are CAT rated then they are constructed to be safe for use on high voltages and mains up to the specified voltage limits.Quote from: ThickPhilM on October 26, 2019, 06:58:02 amWrong. Differential probes use a high voltage divider to bring the voltages down to low levels (and thus limit any current to safe levels) and then use a differential amplifier to feed the single ended input of the oscilloscope. The battery is in there to supply the differential amplifier. Constructing a good CAT rated differential probe is a bit if an art and the MicSig one is pretty good.

author: PKTKS
author_rank: Super Contributor
timestamp: October 26, 2019, 11:19:29 am
content: Quote from: Monkeh on October 25, 2019, 05:59:19 pmNop.. you can pick some Zing-Ear just fine.the material and finish is very good.They also are reliable and durable, more cost-effectivethan fuses for the purpose of using them on the primary sideThe specs are ABOVE 95% of usual bench setups sothe markings are irrelevant. I have some for quite sometimewith so far no problems.I would like to see some stress tests or comparisons...either way my transformers are very good qualityand OVER DIMENSIONED for the bench.No worries so far. They do a very nice fit therewith a simple NEON.Paul

author: AVGresponding
author_rank: Super Contributor
timestamp: October 26, 2019, 12:25:38 pm
content: Quote from: nctnico on October 26, 2019, 09:24:14 amEhhh... my bad, I thought they were isolated.Looking at the theory of operation, they seem pretty specialised, and pointless for measuring mains waveforms.May as well just use the 2 passive probe with channel maths method (making sure your probes and scope V/div combine to the correct signal magnitude), and save some cash, or a proper battery operated and double insulated scopemeter.

author: nctnico
author_rank: Super Contributor
timestamp: October 26, 2019, 01:00:02 pm
content: Quote from: ThickPhilM on October 26, 2019, 12:25:38 pmQuite the opposite. CAT rated differential probes are designed to measure mains like voltages.

author: madires
author_rank: Super Contributor
timestamp: October 26, 2019, 02:24:09 pm
content: The real fun starts when you're monitoring multiple signals with your scope. As you know, all channels of a standard scope have a common ground connected to earth/PE. So all the ground clips of the probes are connected to each other. If you like to monitor signals referenced to ground and one signal not referenced to the same ground you need differential probes. Otherwise the ground clip of that channel's probe would short something in your DUT. Another classic example is monitoring waveforms on the primary and secondary side of an isolated PSU.

author: 001
author_rank: Super Contributor
timestamp: October 26, 2019, 02:45:56 pm
content: Do You protect mains from You? Why You place fuse in primary windings only?Is it best way to add two fuses after variac for 100% and 50% range?

author: AudioFile
author_rank: Contributor
timestamp: October 26, 2019, 05:11:43 pm
content: Found it. It was in the January 2016 edition.It uses opto-isolation and the spec includes:Input-output isolation >10G OhmMax working isolation voltage: 1.4kV peak, 1kV RMSInput resistance: 2M Ohm / 10pFLinearity: +/-0.05%It cost me 50AUD for the 'hard to get' parts including the pcb.I guess the copyright police will have me if I post a photocopy here, but back numbers are available I believe.BTW, you can access lots of back copies of EPE on Issuu for free:https://issuu.com/search?q=everyday%20practical%20electronics, though sadly not the most recent ones.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: October 27, 2019, 05:48:13 pm
content: Thanks Audiofile for the hint. Just ordered the PCB and most of the components.From GBof all places.The only component I need to hunt down is the power switch.The usual suspects Mouser, RS, Farnell are out for cost reasons.Maybe I will fit two separate power switches to the side of the box.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 27, 2019, 09:17:39 pm
content: Quote from: 001 on October 26, 2019, 02:45:56 pmI have fuses everywhere and PPEwhen playing with suspect electronicalsIt's a lot cheaper and less stress blowing a fuse and learning a lessonrather than toasting equipment and learning the same lesson..Popping a question here:shouldn't variacs be fused on their output as well as the input to protect them?It's recently dawned on me the manufacturers rate them for the output current, yet never provide fuse protection either way,or put an inline fuse on the input, which may not pop soon enough in a low voltage high current 'burn baby burn' windings satay style scenarioor they put a totally wrong value fuse = NO BLOW ratedFor the money they charge, they could include some form of switch on surge tamer circuit toocold or bitchy mood variacs can pull in some serious breaker trip power on turn onIs there some sort of 240 volt surge thingie (that actually works) that can be installed in a variac or via external box ?I think I saw something posted at EEVblog ages ago somewhere

author: PKTKS
author_rank: Super Contributor
timestamp: October 28, 2019, 01:18:56 pm
content: Quote from: madires on October 25, 2019, 12:56:25 pmYES Definitely by far the best advice on top of others.Everything passing 120 VAC I am always protecting myselfwith some sort of touching aids.With my bench ISOLATED, ground is out of equation andI can touch things just fine.This will not save you from making the classic mistakesbut with your equip ISOLATED and you wearing glovesthat death sarcasm is ruled out.best comment so far.Paul

author: madires
author_rank: Super Contributor
timestamp: October 28, 2019, 03:16:15 pm
content: Quote from: Electro Detective on October 27, 2019, 09:17:39 pmI think it's not absolutely necessary but would provide additional protection. I've seen some commercial isolation transformer and variac combos with a circuit breaker at the output (and fuse at the input).

author: Electro Detective
author_rank: Super Contributor
timestamp: October 28, 2019, 09:20:47 pm
content: Rubber Glovesmay not be that safe with sweaty hands and lots of salt in your food,but a way better bet than exposed handsBest to have a few pairs, and flip the moist ones inside out to dry and reusein the event you like being cheap like meRubber gloves with thin cotton gloves underneath are the way I roll in any -ZAP!- scenario

author: AudioFile
author_rank: Contributor
timestamp: October 28, 2019, 09:58:46 pm
content: Quote from: Messtechniker on October 27, 2019, 05:48:13 pmGood luck with the build. I used a switch like this, but a cheaper, I think £2.79.https://bit.ly/32WnXgP

author: vk6zgo
author_rank: Super Contributor
timestamp: October 29, 2019, 05:34:37 am
content: In the valve era, rubber gloves were conspicuous by their absense.Commonsense working procedures reduced the likelihood of dangerous contact with high voltages to a miniscule level.Rubber gloves which are thin enough not to be an encumbrance don't withstand mechanical damage well, & a breach may compromise any insulating capabilities.Thicker gloves may increase the risk of personal injury or damage to the equipment during mechanically handling.

author: nctnico
author_rank: Super Contributor
timestamp: October 29, 2019, 07:16:28 pm
content: Quote from: PKTKS on October 28, 2019, 01:18:56 pmAnd this is exactly why the advise to use an isolation transformer without this context is so bad. Experienced people forget how much they have learned and what the underlying principles are of a certain approach. Your way of working goes way beyond just an isolation transformer. Your entire work environment is setup to work relatively safe with floating mains voltages. This isn't true for an ordinary bench or maybe even a kitchen table which may even have a metal frame and sit next to a grounded heater. A typical home/commercial environment is (very) likely designed to be protected by a GFI due to modern building regulations. You'd need to adapt the design of an entire room (or at least a significant part of it) in order to use an isolation transformer safely.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 30, 2019, 12:41:52 am
content: Quote from: nctnico on October 29, 2019, 07:16:28 pmOr have a functional brain!

author: PKTKS
author_rank: Super Contributor
timestamp: October 30, 2019, 11:22:52 am
content: Quote from: vk6zgo on October 30, 2019, 12:41:52 amUnless you have gone through all the fast changes in themid 70s/80s when "SOLID STATE" became available andreally fast the VLSI was introduced...Unless you had lived that changes forcing you to adaptyour methods and procedures and instruments... you willnot realize how easy is to take for granted the thingsavailable today.By the late 70s early 80s most OSCILLOSCOPES andvast majority of instruments were ISOLATED by design.Like it or not we lived and changed methods and the BRAINfor that.. LINEAR PSUs (there were no SMPS "supervisors")were norm and mostly FULLY ISOLATED.My old archive still have dozens of scopes and instrumentswith LINEAR ISOLATED only mains..so.. unless you have lived with that .. taking these SMPSand "differential probes" and fancy scopes of today andthinking they are safe by default...just will not fit the kind of hard methods old school forces youAttached a typical OSCILLOSCOPE FROM 70s MAIN PSU.FULLY ISOLATED by default CHASSIs NOT GROUNDEDthat kind of care was left to the technician as much asthe methods to touch a 600V HOT tube with their instruments...Not an easy time to start... lessons learnedBTW this was my first scope... w/a COLINE 100x probebest and safe enough to goPaul

author: 2N3055
author_rank: Super Contributor
timestamp: October 30, 2019, 12:14:09 pm
content: Quote from: PKTKS on October 30, 2019, 11:22:52 amWHAT was isolated from WHAT?You think floating equipment without grounding it anywhere makes it safe ?Grounding chassis became the norm EXACTLY because it is NOT safe...I made a lot of pocket money as a kid converting stupid tube guitar amplifiers from 2 wire floating to 3 wire grounded chassis wiring to mains because people were getting shocked touching microphones with their mouths while playing a guitar....It is called "protective ground" because it prevents chassis to become energized to dangerous voltages..

author: PKTKS
author_rank: Super Contributor
timestamp: October 30, 2019, 12:50:37 pm
content: Quote from: 2N3055 on October 30, 2019, 12:14:09 pmNever said an ISOLATED (aka floating) is "SAFE"as a matter of fact even having the so called "SAFE" ground pinYOU ARE STILL PRONE .. to the same mistakes.and they do happen.I will say again just 2 cents of jambo..:- an isolated DUT is a very clever option.- on the lack of a "much" better alternative...an isolated equipment will do as fine as battery one.- concerning things like common ground (BNCs) andmeasures between spots not "related" ...you are still required to think of that...And you are still required to use yourbest methods to do safe choices.Always bounded to what you have.Summary? Use what you got and get best results.Bottom line? The isolator transformers are a cheapaffordable and very good method.Proper gloves (not that crappy silly ones used by mobile techs)are a very clever option for anything above 100V.last not least. Mistakes still happen and a BRAND $1000will not prevent that. Assuming you have a 3rd pin groundedis some sort of safety may prevent you some reasoningPUDIM? I have used them isolated more than 4 decades just fine.Paul

author: 2N3055
author_rank: Super Contributor
timestamp: October 30, 2019, 02:50:27 pm
content: Quote from: PKTKS on October 30, 2019, 12:50:37 pmI will repeat this one more time.Every time this pops up, there are at least few oldtimers that do this for 40 years that say : IF YOU KNOW WHAT ARE YOU DOING IT IS SAFE..THAT IS CRETINOUS STATEMENT!!!!People that ask those questions in a first place DON'T KNOW WHAT THEY ARE DOING !!That is why they are asking....So answer to a general population on the Internet is : NO, IT IS NOT SAFE, you will kill yourself...You do whatever you think is safe for you. Don't give advice to people how to kill themself.P.S. : Make note this is not addressed to you, but to this general approach... It's not meant to insult YOU personally, but to make statement..

author: PKTKS
author_rank: Super Contributor
timestamp: October 30, 2019, 02:58:47 pm
content: 100% agreed - no insults taken.I have learned the hard way however.I would say that some folk that would fuss arounda 380V or 600V around without knowing ...well ... the world is full of insane ones.no matter how much you advice...That sort of folk fussing around without the skillswill find it sooner or later...I hope my comments will reach a proper brainThe comments are target:- a SANE interested in budget alternatives tech- a clever folk eager to find new alternatives.Some will do that with the comments just fineothers.. the odds varyPaul

author: 2N3055
author_rank: Super Contributor
timestamp: October 30, 2019, 03:30:50 pm
content: Quote from: PKTKS on October 30, 2019, 02:58:47 pmTake care!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 31, 2019, 02:40:06 am
content: Quote from: PKTKS on October 30, 2019, 11:22:52 amSorry, but this comment doesn't make sense.Yes, the internal "guts" of 1970s/'80s Oscilloscopes & other instruments was isolated from the Mains, but this wasn't at all new---my old 1930s General Radio VTVM used a power transformer to provide power to the internal parts.Over many years of experience, I have never seen an old-style "transformerless" PSU (like in AC/DC radios), used in any test equipment at all.SMPS used in test instruments also fully isolated the internal components, (outside the PSU itself), from the Mains.QuoteThis wasnottypical of Oscilloscopes of the 1970s, or any other era, for that matter!The vast majority of 'scopes did, & do, have a power cord with a Protective Earth connection to the chassis, cabinet & common side of all the internal voltages on the non-Mains side of the transformer.Other versions of the HIOKI you show in your schematic probably also used a PE connection.Quote

author: vk6zgo
author_rank: Super Contributor
timestamp: October 31, 2019, 03:40:29 am
content: Quote from: 2N3055 on October 30, 2019, 12:14:09 pmBefore "protective ground"(more commonly called "PE"), it was quite possible for several domestic appliances (& they all pretty much had metal bodies back then) to develop shorts between "Active"(A) & the body, or between "Neutral"(N), & the body.(I'm using the modern terms, even though they are not quite appropriate to the case of a fully floating Mains supply).Both A & N shorted to the body is OK, as that would blow a fuse in the building "fusebox".One device with the case shorted to A & another with the body shorted to N is a deathtrap.Example would be a toaster & a metal bodied electric kettle:-"What's for breakfast dear?""Electrocution!" came the stern reply!By providing a PE linked to the N at the building power entry, & connecting the metal bodies to PE, if A is shorted to the body, the Mains fuse will blow.iIf N is shorted to the body, it will not blow a fuse, but the metal body will not be above PE potential,so personal protection is provided.in this second scenario an RCD if fitted, will operate isolating the circuit

author: Electro Detective
author_rank: Super Contributor
timestamp: October 31, 2019, 07:51:25 am
content: Quote from: 2N3055 on October 30, 2019, 12:14:09 pmMore than likely most of those stage zaps and unrehearsed barbeques were also or mainly due to flipped polarity extension cables (stoner muso DIY kamikaze power cords)and everyone including the gunja/coked/cranked sound and lighting crews plugging into scattered power points from a three phase source,with blunder potentials of 440 not 240, assuming the Neutral was not wonky or a bootleg neutralThis was in the daze before RCDs were installed, I doubt having 2 wire or three wire would have made much difference back then,musos and tradies would have got zapped regardlessStill happens today, a lot of places don't have RCDs in their switchboards, or they are sort of bypassedand musos and tradies will always do stupid sh!t to make an easy setup task difficult and dangerous that isn't necessaryi.e. if you're a muso or tradie that loves life, buy a proper RCD/MCB orange cube, test it before each gig, and avoid suss DIY cablesIt's not really that simple, but a good start

author: nctnico
author_rank: Super Contributor
timestamp: October 31, 2019, 09:25:18 am
content: IMHO it is not very wise to rely on properly wired extension cords and outlets. And what if you are connected between 2 phases where both 'neutral' and 'live' are hot?

author: 2N3055
author_rank: Super Contributor
timestamp: October 31, 2019, 09:41:57 am
content: Quote from: Electro Detective on October 31, 2019, 07:51:25 amIn EU there is no defined which one is Live and Neutral on a single phase socket. You can freely rotate schuko socket, and both conductors are potentially dangerous. You never know which one is which. Only ground is known. What you said about 3-phase is correct, I'we seen things go boom because Neutral went wonky or lifted and you got inter-phase voltage ... And yes RCDs are godsend....

author: PKTKS
author_rank: Super Contributor
timestamp: October 31, 2019, 12:32:55 pm
content: Quote from: vk6zgo on October 31, 2019, 02:40:06 amThat HIOKI is actually (like 99% of instruments in Brazil) arebranded clone.. with some minor adjustments for local stuff.Vast majority of instruments here are just "rebranded" clonesAnd still today most rebranded clones like ICELwww.icel.com.bror MINIPAwww.minipa.com.brand some others - just have minor adjustments.That particular HIOKI and all others of that line are housed inFULL METALLIC CASE CHASSIs - with a GROUND screw provided.Well.. grounding that housing and touching the panel whileattached to some hot tubes (even w/a 100x probe) is not clever.Today vast majority housing is ABS based or some sort of plastic.While SMPS are indeed "ISOLATED" flybacks the voltages and powerratings are rather different from those cheap CRTs.Never trusted to ground such metallic housing while puttingthe probes on tubes horizontal drivers or flybacks...some bad things could happen.... isolating stuff and thinking a bench gig setup always helpbut will never prevent you from making the classic mistakes however...Paul

author: Black Phoenix
author_rank: Super Contributor
timestamp: October 31, 2019, 12:53:07 pm
content: Quote from: 2N3055 on October 31, 2019, 09:41:57 amTrue and False. Yes you can rotate the plug and it will work, although by norm (I'm citing the Portuguese Electrical Norms, because is the ones I learned on my degree) the Neutral is on the left and the Live is on the right. You can always check of course but no electrical installation is approved and allowed to enter production if they are exchanged, even if it is one plug only. Same way as you can make an ethernet cable anyway you want, just have the colours be equal in both ends if you want a straight cable, but the norm have 2 different methods, EIA/TIA 568A or EIA/TIA 568B. It sure helps a lot to diagnose.That doesn't happen with the UK Norm, were the Plug only fits one way and only that way. Of course if the socket is incorrectly wired, well nothing can't be done against it. IMHO the UK Electrical Norms are way better, a switch per plug and the plug is always fused. But that's my opinion.

author: 2N3055
author_rank: Super Contributor
timestamp: October 31, 2019, 01:13:14 pm
content: Quote from: Black Phoenix on October 31, 2019, 12:53:07 pmYou are correct, socket is standardized, but since you can rotate plug, devices can receive whatever.And if you use extension cords, those can be any combination...I agree that UK plug is better, it is indexed, and it has built in high break capacity fuse...

author: madires
author_rank: Super Contributor
timestamp: October 31, 2019, 02:43:03 pm
content: Quote from: Black Phoenix on October 31, 2019, 12:53:07 pmIn Germany it can be both ways. Some sparkies have a preference for left, some for right, and other don't care. There's no requirement for L being left or right. As 2N3055 already has explained, it doesn't matter anyway because we don't have indexed plugs (besides 3 phase connectors).

author: nctnico
author_rank: Super Contributor
timestamp: October 31, 2019, 04:56:19 pm
content: Quote from: Black Phoenix on October 31, 2019, 12:53:07 pmThat is all nice and dandy in theory but in practice you won't know if a socket is wired correctly or not. A single phase device will work just fine with live/neutral reversed or even 2 phases. Nobody cares about the wiring. So the best way to deal with single phase mains is to assume both wires are dangerous.

author: Black Phoenix
author_rank: Super Contributor
timestamp: November 01, 2019, 06:03:04 am
content: Quote from: nctnico on October 31, 2019, 04:56:19 pmTotally agree with it... When for some reason I need to check some socket I always assume it is energised even if It was me who turned off the circuit breaker. I always check with a DMM to be really sure.

author: madires
author_rank: Super Contributor
timestamp: November 01, 2019, 10:26:42 am
content: Be aware that a DMM without low-Z mode is the wrong tool for mains because the meter's high input impedance and capacitive coupling between wires can screw up the measurement. The best tool for that is a Duspol or a similar tester.

author: Black Phoenix
author_rank: Super Contributor
timestamp: November 01, 2019, 11:44:47 am
content: Quote from: madires on November 01, 2019, 10:26:42 amI'm sure that between my 87V and my 289 I have one with it. But thank you anyway for the info.

author: Electro Detective
author_rank: Super Contributor
timestamp: November 03, 2019, 08:59:28 am
content: Quote from: Black Phoenix on November 01, 2019, 11:44:47 amno Low-Z mode for 87V, but 289 has it (the first far left switch setting)It's a fixed 0 to 1000 volt range only (no auto or manual range) with both AC and DC readouts, and gets it doneTake note that in Low-Z mode with any meter, you will trip the RCD/GFCI if probing between a line and earth groundwhich may score you nil readings and some nasty vibes from others on the premises,how do I know this...?

author: madires
author_rank: Super Contributor
timestamp: November 03, 2019, 01:45:25 pm
content: It's not a bug, it's a feature called RCD test.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 03, 2019, 02:54:09 pm
content: Quote from: Electro Detective on November 03, 2019, 08:59:28 amI found that out with an Avo Model 8.On one particular piece of equipment, the Mains wiring was a bit overgrown with other components, so as a rough check for the presence of Mains, it was easier to just measure between Active & Earth.(chassis).Unbeknownst to me, the bench circuit breakers had been upgraded & now included RCDs.The breaker tripped, I reset it & re-measured------ the breaker tripped again.I then checked the logbook, which I should have done before---sure enough, the breaker upgrade was logged!

author: HalFET
author_rank: Frequent Contributor
timestamp: November 03, 2019, 07:51:37 pm
content: A large piece of polycarbonate is my main advice when you're going to be messing with power stages, I still have a scar from an IGBT that decided it didn't belong in this world. It could have been a lot worse if I didn't have a polycarbonate shield in front of my face. Also good to have around is a few PTFE stand offs to put the chassis on, that way if the chassis goes hot it at least won't be in contact with your bench (and ESD protection).

author: Electro Detective
author_rank: Super Contributor
timestamp: November 03, 2019, 09:50:40 pm
content: Quote from: madires on November 03, 2019, 01:45:25 pmIt's a 'FREE' RCD test with a 3k resistance, I forget what the actual mA trip current is at 240 voltsbut close enough for a quick and dirty go/no go test, as I don't trust nor assume anything with the RCD onboard TEST button,Low-Z comes in handy when the proper bells and whistles RCD tester is in the wrong tool bag.. miles awayI can also relate to a similar experience to vk6zgo with an AVO 8, using it to find out why the 'not so faulty' Fluke with Low-Z tripped the powerHey, you gotta do these things at least once to learn not to rush about and be overconfident..Though the experience is loads better, if no one is around to share it with you at the time..

author: Monkeh
author_rank: Super Contributor
timestamp: November 04, 2019, 12:24:45 am
content: Quote from: Electro Detective on November 03, 2019, 09:50:40 pmThe test button does exactly the same thing. Neither the test button nor your meter is a reliable test of an RCD.

author: Electro Detective
author_rank: Super Contributor
timestamp: November 05, 2019, 11:28:31 pm
content: Quote from: Monkeh on November 04, 2019, 12:24:45 amAs stated previously, it's just a convenient go/no go test to see if the unit actually trips from various locations,rather than having faith that just hitting on the TEST button is enough, and assume the premises have perfect wiring and no dramas at all the outletsFWIW I've replaced 4 pole RCDs, used in 3 phase and single phase apps, that tripped fine from the outlets, yet the onboard TEST button failed to trip the unit,and vice versa with other units. And no, it wasn't a Neutral mis-wire, which I always check.Merely replacing those units with the same type/model, and wired in exactly as they were, fixed all issuesand passed any/all testing procedures with correct specified mA/Time/Polarity specsi.e. a Low-Z meter, AVO 8 or 7or Duspol rig or tacky taped up DIY globe poker thingiecan get you started good enough on a job to diagnose a faulty or suss RCD/GFCIYes it's bestto have a proper working RCD tester (or two) to test and check actual performance,but if it's not there in a surprise situation, the other alternatives can get you started,or at the least to verify a new replacement RCD/GFCI works

author: Messtechniker
author_rank: Frequent Contributor
timestamp: March 20, 2020, 10:35:25 am
content: Quote from: AudioFile on October 25, 2019, 05:50:40 pmJust on the last leg of putting two together. Since the TLE2022 is not available any more I now use an AD 822 AN as the output opamp. Also tried a TL 072, NE 5532. However, the AD 822 gave the best match with respect the published frequency response curves..Btw: it was great to have a lab power supply with 3 separate outputs (HMC 8043). Two 9 V outputs for the isolating high voltage probe and one 12 V output for the XR 2206 frequency generator. Had to use itsince I am still waiting for the UNI-T UTG962 to become available on the market.