Electricians: measuring an single appliance's earth leakage current? - Page 1
Forum section: electronics / general

author: Howardlong
author_rank: Super Contributor
timestamp: December 23, 2022, 11:28:51 am
content: As per the subject, really.The symptom I have is that sometimes, my central consumer unit's RCD/GFE will _sometimes_ trip when I turn on some older test equipment. Anecdotally, it does seem to be humidity related, for example if it's foggy outside.This started happening since I moved from an apartment in the the city to a rural house, and this is the first time I've encountered it with this TE. I've had both units for ~20 years.The TE is an HP 8753A VNA and an HP 8565A spec an.I tried measuring the leakage at the consumer unit using a UT210E clamp meter simultaneously around both Live & Neutral, that has a resolution down to 10s of mA, but it was inconclusive, as it proved difficult to get a stable reading.I measured the DC resistance on the two appliances, and it's up in the 10s of megohms. They do have Y caps of the order of single digit nF that I can measure.I do have an inline RCD, but its trip current is the same as the consumer unit's central RCD.It's kinda difficult to measure when the circuit trips.So my question is, how best can I measure earth leakage of an appliance out of circuit? Does a PAT tester measure AC impedance for example, or is it just DC resistance?I have both a variac and an isolation transformer if that's any good.

author: themadhippy
author_rank: Super Contributor
timestamp: December 23, 2022, 11:45:35 am
content: QuoteGot any outside lights ? Maybe your installation has a fault else wear that's normally not a problem,but the additional leakage from your test equipment is the final straw.If you've got a pat tester that does proper 500v insulation tests you could try an insulation test of the individual circuits to see if anything is amiss.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 23, 2022, 11:49:05 am
content: Sounds to me like it's time to start replacing the RIFAs in the mains filters of your TE, before they let the (very smelly) magic smoke out!Increased leakage current is a symptom of impending failure.

author: Gyro
author_rank: Super Contributor
timestamp: December 23, 2022, 01:59:01 pm
content: RCDs can get old and start tripping at a lower current, especially if they have already tripped a number of times.From your OP, it sounds as if your consumer unit has a single RCD, maybe two if it is a (slightly misnamed) 'high integrity' one. If so, you may find that the combined leakage current on that RCD from increasing number of appliances has built up to the point where there is very little headroom before it trips, i.e. your TE may be fine, but just pushing the combined leakage on the RCD over the edge. Individual RCBO consumer units tend to be better as the number of Y caps in the installation increases.Old Kewtech KT35 (or the equivalent Robin KMP3050DL) insulation and continuity testers often come up very cheaply on ebay in the UK. They will test at 250V,500V, and 1kV and can be used to perform general insulation and appliance PAT testing (be careful where you use the 1kV setting). These will be out of official calibration, but there are no adjustment pots inside and it is very easy to verify that they are functional and within spec with a DMM and a few low and high value resistors. It's well worth picking one up for these sort of problems.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 23, 2022, 02:11:57 pm
content: @Gyro, yes, agreed, but remember the OP said the fault also seems to vary according to humidity; it's cracks in the RIFA resin casing that allows water in that causes the failures for these.

author: themadhippy
author_rank: Super Contributor
timestamp: December 23, 2022, 02:23:58 pm
content: QuoteA second hand pat tester maybe a better bet as not only do you get the 500v insulation test,but also a 25A low resistance tester

author: niconiconi
author_rank: Frequent Contributor
timestamp: December 23, 2022, 03:00:36 pm
content: Quote from: Howardlong on December 23, 2022, 11:28:51 amSpecial Earth-leakage current clamp meters can be purchased on AliExpress for $80. I've used one to solve a RCD tripping problem at home with great success. They're basically just normal AC current clamp with very low measurement range but high sensitivity, down to 1 mA.Simply clamp the meter across L and N, if there's no leakage, ideally there's no net magnetic flux across the core. Any Earth leakage causes a residue common-mode current, which is measured by the meter.First, run with all instruments on. Then disconnect them one by one while watching the meter reading. You'll find the culprit when you see a large change. I simply clamped it across the mains entry at the main electrical panel and started turning off downstream circuits one by one.If you already have a sensitive AC current probe for lab use, just run L and N across the probe, you don't even need to buy anything (they're small and you probably cannot use it across the AC mains panel entry, of course, but you can do it at the power strip).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 23, 2022, 03:52:28 pm
content: For individual appliances, simply break its earth connection and measure the AC current through it.For whole installations, a high-res AC current clamp is the easiest option.

author: Gyro
author_rank: Super Contributor
timestamp: December 23, 2022, 06:45:56 pm
content: Quote from: themadhippy on December 23, 2022, 02:23:58 pmYes, possibly so, they just seem to be more expensive / more in demand when they are listed. Personally I like the displays on the two testers I mentioned, the cheaper PAT testers tend to be a bit more go-no go. Mine gets used for general electronics insulation measurement so I find the 1kV range useful - but then I've got a 10kV one too!

author: Howardlong
author_rank: Super Contributor
timestamp: December 23, 2022, 09:10:20 pm
content: Quote from: AVGresponding on December 23, 2022, 02:11:57 pmHmm, yes, that is quite possible.

author: Howardlong
author_rank: Super Contributor
timestamp: December 23, 2022, 09:14:50 pm
content: Quote from: mikeselectricstuff on December 23, 2022, 03:52:28 pmThe problem is that it trips before I can measure it.Any thoughts on cobbling together something with an isolation transformer and/or variac?QuoteYes, however I found the readings I was seeing to be unstable. Maybe I need a better meter.

author: Howardlong
author_rank: Super Contributor
timestamp: December 23, 2022, 09:26:43 pm
content: Quote from: themadhippy on December 23, 2022, 11:45:35 amAlready I isolated some outside sockets which I believe has improved things to quite some degree, but I still get occasional trips. I'm wondering if it's accumulated leakage of several appliances and possibly the installation itself. There's no evidence of damp in the house, but it is 150+ years old.If PAT testers measure actual AC leakage impedance then I don't mind investing on one, but if it's just DC, then I can do that without a PAT tester.If I can measure the actual individual appliance leakage current in some way then I can have some degree of certainty: the electrician I had in just said it was the appliances, but he neither measured the system earth leakage nor the appliances. Furthermore, he seemed to think to measure system earth leakage you just measure the earth wire at the consumer unit (rather than L+N together}, thus ignoring any other possible earth paths, so I wasn't impressed.

author: Howardlong
author_rank: Super Contributor
timestamp: December 23, 2022, 09:32:43 pm
content: Quote from: Gyro on December 23, 2022, 01:59:01 pmYes it's a single RCD on the main ring only (lighting isn't protected).Do PAT testers actually measureACearth leakage current? Or are they DC only? I don't mind investing in one if they do. I'd much prefer actual leakage reading than pass/fail so I can see if it's a cumulative effect.

author: Gyro
author_rank: Super Contributor
timestamp: December 23, 2022, 09:47:41 pm
content: No, they're DC, otherwise the leakagecurrent[Edit: resistance] would get swamped by capacitance.

author: Someone
author_rank: Super Contributor
timestamp: December 23, 2022, 10:08:48 pm
content: Quote from: Howardlong on December 23, 2022, 09:32:43 pmSome do, the ones I'm familiar with can pass through the mains and measure the current through the earthing pin showing it in engineering units on the display. $500 ish range second hand as these things tend to be pretty long lasting in applicability/use/life.

author: niconiconi
author_rank: Frequent Contributor
timestamp: December 23, 2022, 10:25:43 pm
content: Quote from: Howardlong on December 23, 2022, 09:14:50 pmThis $100 "CEM DT-9810 Leakage Current Tester" I got here allows me to resolve 0.3 mA and measure 1 mA. Here are some photos to show its resolution. I connected a 60 Hz sine wave from the signal generator to a 47 Ω resistor. The oscilloscope shows the voltage across the resistor, and the clamp meter shows the current. It was what I used to successfully fix my RCD problem. A similar meter can likely solve your problem too.Before buying this meter, beware that I did a quick search and saw a negative review on Amazon.QuoteI never noticed this problem during my troubleshoot attempt, but it's probably somewhat suspectiable to high-frequency noise or stray field.

author: themadhippy
author_rank: Super Contributor
timestamp: December 23, 2022, 10:27:19 pm
content: Quotemore expensive models will,but as its not a requirement for pat testing you'd have to double check the particular models specs

author: AVGresponding
author_rank: Super Contributor
timestamp: December 23, 2022, 10:29:51 pm
content: Quote from: Howardlong on December 23, 2022, 09:26:43 pmThat would only give you a whole installation figure rather than an individual appliance reading. Sounds like he doesn't have the proper equipment, these things areexpensive. Here's a pic of my whole house leakage, with a meter that costs the best part of £1k new. I paid, shall we say, somewhat less, as it was in need of repair. Yes, that is 1 micro-amp resolution:As Mike suggests, break the earth (at the appliance) and measure it with a DMM, use a Safeblock or Cliffe Quicktest or similar.

author: langwadt
author_rank: Super Contributor
timestamp: December 23, 2022, 10:50:04 pm
content: Quote from: Howardlong on December 23, 2022, 09:14:50 pm

author: amyk
author_rank: Super Contributor
timestamp: December 24, 2022, 11:39:27 am
content: Break the earth, insert a (preferably logging, but one with a max function would also work) ammeter inline.

author: m k
author_rank: Super Contributor
timestamp: December 24, 2022, 11:49:03 am
content: Quote from: Howardlong on December 23, 2022, 11:28:51 amMaybe you should make your own meter.MCU boards and small current modules are cheap and then you could do some longer time tracking.But first I'd follow AVG, since finally you can't escape that anyway.

author: Gyro
author_rank: Super Contributor
timestamp: December 24, 2022, 12:38:27 pm
content: Be very careful disconnecting the Earth on a live installation, it's not a recommended procedure. You have several non RCD protected circuits that, for all you know, might have high leakage currents to Earth. At least pull the fuses / MCBs on the non protected circuits.P.S. What kind of instalation is it, eg, TN-C-S, TT etc:https://en.wikipedia.org/wiki/Earthing_system#IEC_terminology(IEC Terminology section).A photo would help.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 24, 2022, 01:26:28 pm
content: Quote from: Gyro on December 24, 2022, 12:38:27 pmTo clarify what I personally meant about disconnecting the CPC/earth,DO NOTdisconnectANYof theFIXEDwiring, unless you are a qualified electrician. As well as the safety implications, there are issues around insurance, and if it's rented accommodation, you'll be in breach of your tenancy agreement.What I meant is this: if the plug on the equipment is a rewireable type, remove the plug and in conjunction with a Safeblock or Quicktest, connect a DMM in series with the earth. It should not be necessary to state, but I will anyway:DO NOTdo any of this while connected at the wall outlet. Once you have everything connected as it should be, only then plug the Safeblock in.If the equipment has a moulded plug and you don't want to cut it off, you'll have to make an adapter, such as a trailing socket with the plug removed that can be connected to a Safeblock.If you wanted something you could keep and use in the future without a Safeblock, you could make something like this:Plug on a flex to aPLASTICadaptable box, stuffing gland into the box. Inside the box, break out the conductors and wire them individually in flex out of the box and back in, making a small loop. Use stuffing glands. Then connect to a flex out through a stuffer to a trailing socket. With this, you can measure with a clamp the individual currents on each conductor, and all the exposed wiring is double insulated, so is reasonably safe.DO NOTuse a metal adaptable box, it will effectively become a shorted transformer winding.

author: Kean
author_rank: Unknown
timestamp: December 24, 2022, 02:06:51 pm
content: Measuring leakage through the earth wire may not tell the full story unless the product is double insulated and not connected to anything else.As nico suggested above, you should use a leakage clamp meter to measure both L & N wires together and see if there is any imbalance.Uni-T make the UT251A AC clamp meter which has 1uA resolution for smaller currents, but can read up to 60A.

author: Howardlong
author_rank: Super Contributor
timestamp: December 24, 2022, 03:46:47 pm
content: Quote from: Kean on December 24, 2022, 02:06:51 pmCorrect, that is my understanding. I was quite taken aback when the electrician discounted my measuring of L&N together in the clamp in favour of just measuring the earth at the consumer unit. Measuring just the earth at the CU isn't taking into account any other possible paths to earth. Furthermore, the RCD measures L&N together, and that's what I'm trying to fault find.QuoteThat is what I have been doing but the meter I have (UT210E) gives unstable results.QuoteOK, I'll see if I can source one.

author: Howardlong
author_rank: Super Contributor
timestamp: December 24, 2022, 03:48:52 pm
content: Quote from: AVGresponding on December 23, 2022, 10:29:51 pmI'd be quite happy to do so... if it didn't trip the darned RCD while trying to measure it!

author: Howardlong
author_rank: Super Contributor
timestamp: December 24, 2022, 03:59:16 pm
content: Quote from: niconiconi on December 23, 2022, 03:00:36 pmActually, I do have one, a TTI i-Prober: I'll give it a go, but it might be a challenge getting both L&N through the closed loop clamp.

author: nightfire
author_rank: Frequent Contributor
timestamp: December 24, 2022, 04:34:39 pm
content: PAT testers do measure AC currents down to 0.1 mA.So there are 2 possibilities to do that without buying/renting some tester:- get a leakage current clamp and measure l+N together and then the PE alone (differential vs. direct measurement)- Put a multimeter in the PE pathDo NOT do rewiring unless you are a experienced electrician and know how to build appropriate adapters, because if the PE is severed and therefore the leakage current wants to escape via shielded chassis, one wrong touch and you will be hurt.Probability is high that the powersupply is going old, or that there is some humidity buildup between the windings of a motor or transformer causing leakage.What type is the RCD? How old is it? In this case, I would have that RCD tested with an installation tester/by an electrician to confirm the current that causes actuation.But usually RCD get slower by age, not more sensitive.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 24, 2022, 05:24:07 pm
content: Quote from: Howardlong on December 24, 2022, 03:48:52 pmDoes the meter you are using not capture the peak current? Most meters have a Min-Max recording mode at least.

author: Gyro
author_rank: Super Contributor
timestamp: December 24, 2022, 05:50:39 pm
content: Quote from: Howardlong on December 24, 2022, 03:46:47 pmI'm a bit surprised that your UT210E isthatunstable. Yes they are very sensitive to movement on DC but they are normallly reasonably stable on AC. Are you sure the clamp is able to close completely around the L & N conductors? Instability that doesn't let you distinguish between single and double digit mA might be an indication of a problem in itself. You might try turning off the RCD protected circuits one at a time. I just tried it and mine is showing a solid44mAoops 24mA AC at the meter tails.

author: ejeffrey
author_rank: Super Contributor
timestamp: December 24, 2022, 07:44:40 pm
content: I took apart one of those cheap clamp meter adapters with the 1x and 10x turn branches for measuring line current and rewired it so that I could measure either ground pin or live+neutral difference. I ended up using a smaller wire gauge to get ~8 turns of both live and neutral but I was only using it for low power devices. Just make sure it's labeled to show what the branches mean and that it's for low power devices and intermittent use.I tried one of the cheaper low current clamp meters and wasn't impressed with the repeatability.

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2022, 07:41:48 am
content: Easiest fix is to add in extra RCD units, either upgrade the board to use AFCI breakers, which makes each circuit (ring or spur) into a independant system as far as RCD and AFCI protection, or at the least simply add in an AFCI breaker in place of the one supplying your TEA room, removing it's neutral from the RCD system and connecting to the main neutral bus, and supplying it from the non RCD supply terminal.That will allow your TEA to be protected still, and will also allow you to see if the old installation still has errors, plus a bonus is you do not have a single fault making you all dark. Done that to a few boards, splitting the loads so that each critical outlet set had individual protection, instead of all being on one like the normal install is. Yes RCD devices are a lot more expensive than a simple breaker, but there is nothing in the regulations about only having a single one per installation, just that all devices, from socket outlets, lights, water heating, pool and cooking appliances must be protected. Not that you only have one, though because it saves cost in wiring the house, smaller board, no disconnect needed either as RCD can act as disconnect, you often find this is done. Put in extra and you allow still having power with a fault.

author: mendip_discovery
author_rank: Super Contributor
timestamp: December 25, 2022, 10:43:41 am
content: Not sure if it's already been mentioned but if you buy a multifunction tester they have a mode for testing RCD units. They seem to test if it trips with ×1/2, ×1 and ×5 amounts of current. I assume the ×1/2 is the check it's not over sensitive, this maybe your issue. The humidity might just be a chance thing and you are thinking of it more than needed.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 25, 2022, 11:14:50 am
content: Quote from: SeanB on December 25, 2022, 07:41:48 amI was thinking the same - here in the UK we call them RCBOs.Having the whole house on one or two RCDs can be a pain as one fault affects multiple circuits.Easy update to a typical dual-RCD board, just need to link the two neutral bars. As a bonus you free up some slots.To comply with current regs the RCBOs need to be type A, not AC

author: AVGresponding
author_rank: Super Contributor
timestamp: December 25, 2022, 12:32:21 pm
content: Also bear in mind if you can't get RCBOs that fit your existing board (meaning a board change), you'll also have to upgrade to include (almost certainly) SPDs and (potentially) AFDDs.18th Edition wiring regs amendment 2

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 25, 2022, 12:59:22 pm
content: Quote from: AVGresponding on December 25, 2022, 12:32:21 pmAfdds are only required in a few cases which are unlikely in a normal house.

author: themadhippy
author_rank: Super Contributor
timestamp: December 25, 2022, 01:21:29 pm
content: Quoteuntil the manufacturers bung enters the iee's pockets,then they'll be required everywhere.

author: Howardlong
author_rank: Super Contributor
timestamp: December 26, 2022, 11:23:04 am
content: Quote from: Gyro on December 24, 2022, 05:50:39 pmIt’s tight getting it around the tails due to the stiffness an circumference of the wires, but yes, it is completely around the wires. I leave it there to settle down for a few seconds, but come back to it a few minutes later and it’s a significantly different reading despite nothing else changing.The circuit that’s tripping is a single ring, every other circuit is switched off.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 26, 2022, 11:28:08 am
content: Quote from: Howardlong on December 26, 2022, 11:23:04 amBear in mind that the other breakers are usually only switching off the live, so if there is a neutral-earth fault, that may still be contributing to leakage even if the breaker is off.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 26, 2022, 11:34:28 am
content: Quote from: mikeselectricstuff on December 25, 2022, 12:59:22 pmThat's why I said potentially. The OP doesn't specify except to say the house is ~150 years old, but if it has communal areas for cooking, washing, etc, it's quite likely to be classed as a multiple occupancy property and therefore require AFDDs. This would not be as uncommon as you might think, people with large old houses that rent out rooms or suites of rooms because they need the money for maintenance costs, for example.Quote from: mikeselectricstuff on December 26, 2022, 11:28:08 amThis is a very good point, and falls into the "traps for new players" category.

author: Howardlong
author_rank: Super Contributor
timestamp: December 26, 2022, 11:45:05 am
content: Here’s a pic of the consumer unit.

author: Howardlong
author_rank: Super Contributor
timestamp: December 26, 2022, 11:47:01 am
content: Quote from: mikeselectricstuff on December 26, 2022, 11:28:08 amVery good point.

author: Howardlong
author_rank: Super Contributor
timestamp: December 26, 2022, 11:58:30 am
content: Quote from: themadhippy on December 25, 2022, 01:21:29 pmAs far as I can tell from my casual Youtube viewing, there’s quite an industry around continuous updating and amendments of IET BS 7671 wiring regulations, and keeping current (excuse the pun), especially now private rental properties need regular inspections.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 26, 2022, 12:16:33 pm
content: Don't forget it could also be the RCD itself. Tolerance on these is wide - they can trip between 50% and 100% of their rating and be in spec.Should be easy enough to test by introducing a known leakage current with a resistor or two.

author: themadhippy
author_rank: Super Contributor
timestamp: December 26, 2022, 02:16:07 pm
content: Quoteid call it more a con,too many so called sparks are quick to quote a reg condemning an installation under the latest regs and insist remedial work is carried out to bring it up to standard while conveniently overlooking one of the first paragraphs in the book, you haven't got rcd protection you need a rewire, your cables are the wrong colour you need a rewire,your consumer unit is plastic you need a rewire,you aint got an spd you need a rewire,coming soon you aint got afdd's you need a rewire.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 26, 2022, 11:01:19 pm
content: Quote from: themadhippy on December 26, 2022, 02:16:07 pmYes, Big Clive has denounced the IET on these grounds (sorry, not sorry) on a few occasions, and it's something of a running joke amongst the sparks that I know that the IET release a new amendment every time their retirement funds run a bit low.None of the conditions you mention there merit anything more severe than a C3; it's not to current (again...) regs but isn't dangerous, and definitely should not result in an "unsatisfactory" EICR. It comes down to greed and trustworthiness, and, sad to say, I've never seen a trade body I'd trust to recommend a tradesman. It's usually best to go off word of mouth, in my experience.

author: Howardlong
author_rank: Super Contributor
timestamp: September 15, 2024, 01:39:54 pm
content: Here's a further update.While I discovered that an external socket was the cause of RCD trips some time ago, which I isolated, after over a year I've occasionally started seeing RCD trips again.I managed to get a semi-reproducible scenario, where various combination(s) of appliances at the bench plus a couple of rack mounted servers would trip it.It turns out the tripping has nothing to do with any of these appliances directly:it was a surge protectorelsewhere on the same circuit that was causing the central RCD to trip when a certain semi-random combination of these appliances was turned on, while the surge protector happened to be in circuit.Presumably when the SMPS inside these appliances is plugged in or turned on, it's enough to send short spikes enough to wake up the surge protector, and for it to cause an RCD fault. Possibly over time these MOVs degrade to some degree as they absorb repeated stresses.What wasn't of any use in diagnosing this was using clamp meter around both L&N.What was useful in tracking down these faults was an insulation tester with variable voltage: the one I have does 50, 100, 250, 500 & 1000V.These surge protectors show 80MΩ at 250V, but only 300kΩ at 500V, while all of the other appliances, splitters and power strips were tens of MΩ if not into the GΩ.Furthermore, the schematic that I reverse engineered shows three MOVs across L-N, N-E and L-E.Any thoughts from those in the power electronics world on the schematic, and if it's a reasonable solution for a "surge protector"?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 15, 2024, 01:50:20 pm
content: On a related subject - this cheap (£27 Uk delivered) clamp-meter is excellent for investigating earth leakage -0.1mA resolution on AC, 1mA on DChttps://www.aliexpress.com/item/1005006582824997.html

author: madires
author_rank: Super Contributor
timestamp: September 15, 2024, 02:32:11 pm
content: Quote from: Howardlong on September 15, 2024, 01:39:54 pmIt could be both, i.e. the surge protector triggered by surges from switching inductive loads and the leakage current of all the EMI filters (in SMPSUs) added up. If you have plenty of larger SMPSUs it would make sense to distribute them across multiple RCDs to keep each group's leakage current below the RCD's trigger current. Having multiple RCD zones also prevents a totally dark house/lab/workshop.Quote from: Howardlong on September 15, 2024, 01:39:54 pmThat's a standard design for simple and inexpensive surge protectors, often used in power strips or adapters.

author: Howardlong
author_rank: Super Contributor
timestamp: September 15, 2024, 05:38:09 pm
content: Quote from: mikeselectricstuff on September 15, 2024, 01:50:20 pmDo you have one?The two I have that go down to 1mA resolution work fine for load currents, but when I put both L+N in the clamp to measure leakage, they're both useless: I find it impossible to get consistent readings.Edit: looks like the 268B might only go down to 1mA resolution on the clamp as far as I can tell from a spec page on this YT video (1:48)https://youtu.be/cKRZNER7Gjs?si=3Y1X4e6tRI3RBlKO&t=108Edit 2: scrub first edit, spec was for DC.

author: Howardlong
author_rank: Super Contributor
timestamp: September 15, 2024, 05:57:34 pm
content: Quote from: madires on September 15, 2024, 02:32:11 pmThe consumer unit only has a single RCD for all socket outlets.QuoteOK, thank you.

author: nightfire
author_rank: Frequent Contributor
timestamp: September 15, 2024, 06:27:39 pm
content: Quote from: themadhippy on December 23, 2022, 10:27:19 pmHere in germany, if you do appliance testing according to VDE 701/702, it is AC+DC you have to measure also.Therefore may depend on model of PAT tester you get which modes it supports.

author: Monkeh
author_rank: Super Contributor
timestamp: September 15, 2024, 06:49:44 pm
content: Quote from: Howardlong on September 15, 2024, 01:39:54 pmWhat were you expecting a 470V MOV to do at 500V other than become conductive?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 15, 2024, 08:44:14 pm
content: Quote from: Howardlong on September 15, 2024, 05:38:09 pmyes ( actually two, one kept in car as emergency DMM).

author: Howardlong
author_rank: Super Contributor
timestamp: September 15, 2024, 10:56:35 pm
content: Quote from: Monkeh on September 15, 2024, 06:49:44 pmEr, think about it. How would I have known it had a 470V MOV in there? I'm not telepathic, perhaps you are.I'd identified the surge protector was behaving substantially differently to the dozens of other tests I'd done on other appliances and PDUs. The tester I have tests at a variety of discrete voltages, including 50, 100, 250, 500 and 1000V.When I removed the surge protector, the trips stopped happening.It was only then that I took the semi-potted surge protector apart to see what was inside.

author: Howardlong
author_rank: Super Contributor
timestamp: September 15, 2024, 10:58:22 pm
content: Quote from: mikeselectricstuff on September 15, 2024, 08:44:14 pmHow well do they behave when tracing earth leakage with both L+N tails in the clamp? Are the results consistent?

author: amyk
author_rank: Super Contributor
timestamp: September 16, 2024, 01:40:29 am
content: Quote from: Howardlong on September 15, 2024, 10:56:35 pmWhat do you expect a surge protector to do when subjected to a voltage much greater than normal mains?

author: Andy Chee
author_rank: Super Contributor
timestamp: September 16, 2024, 02:22:21 am
content: Quote from: Howardlong on September 15, 2024, 01:39:54 pmProperly functioning RCDs normally trip at 30mA.300kΩ at 500V is only 1.66mA.So logically it must be something else.

author: Monkeh
author_rank: Super Contributor
timestamp: September 16, 2024, 02:48:49 am
content: Quote from: Howardlong on September 15, 2024, 10:56:35 pmYou didn't mention any other surge protectors. Yes, many lesser types will have 560V or greater MOVs, but it's quite expected to see things start to conduct on a 500V IR test.It sounds far more like you're hovering on the threshold of an overly sensitive RCCB with too many circuits on it.

author: Howardlong
author_rank: Super Contributor
timestamp: September 16, 2024, 12:06:06 pm
content: Quote from: Monkeh on September 16, 2024, 02:48:49 amI did, and I put it in bold.

author: Howardlong
author_rank: Super Contributor
timestamp: September 16, 2024, 12:07:27 pm
content: Quote from: Andy Chee on September 16, 2024, 02:22:21 amIt may be a combination of things, or an accumulated combination of things, however, a previously repeatable trip scenario no longer happens.

author: Howardlong
author_rank: Super Contributor
timestamp: September 16, 2024, 12:08:49 pm
content: Quote from: amyk on September 16, 2024, 01:40:29 amI don't expect it to trip an RCD when a combination of other appliances are turned on.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 16, 2024, 12:35:21 pm
content: Quote from: Howardlong on September 16, 2024, 12:07:27 pmIn which case, I think it more pertinent to measure the earth leakage of your system, rather than the MOVs in one particular device.

author: themadhippy
author_rank: Super Contributor
timestamp: September 16, 2024, 12:49:22 pm
content: Quote30mA is the point at which it must trip,it may trip at less than that,anything down to 15ma is acceptable.

author: Monkeh
author_rank: Super Contributor
timestamp: September 16, 2024, 02:12:13 pm
content: Quote from: Howardlong on September 16, 2024, 12:06:06 pm.. that's you mentioningthissurge protector (and from another post, others of thistype). Notothersurge protectors.Even if this device is leaking slightly at normal operating voltages, it's not significant enough to be a root cause.Have the circuits protected by the RCCB undergone insulation resistance testing, not merely the appliances?Has the RCCB been tested to ascertain its tripping characteristics in practice?Have all factors been accounted for with these trips, such as routinely connected appliances which are not double pole isolated or are operated by other members of the household who may not recognise the relevance of them? (I don't drink hot drinks - nobody else in the household grasps electricity. Imagine how long it took me to figure out a kettle was the cause of nuisance trips when the answer to "what were you doing when the power went off?" was "nothing".)

author: madires
author_rank: Super Contributor
timestamp: September 16, 2024, 02:21:24 pm
content: BTW, the usual leakage current of an ATX PSU is roughly 0.5 mA (at 230 V). Some have 1 mA. And the max limit is 3.5 mA based on IEC 60950-1.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2024, 03:15:52 pm
content: Quote from: Howardlong on September 15, 2024, 10:58:22 pmNot bad, but it is a bit sensitive to external fields, like if you have 32A charging the car on a nearby breaker, so ideally need to turn off other breakers & test leakage on one circuit at a time.

author: AVGresponding
author_rank: Super Contributor
timestamp: September 16, 2024, 05:34:46 pm
content: Quote from: Howardlong on September 15, 2024, 01:39:54 pmYes, they do degrade over time.Quote from: Andy Chee on September 16, 2024, 02:22:21 amQuote from: themadhippy on September 16, 2024, 12:49:22 pmTypically 18-25mA is the goal the manufacturers shoot for. These can also degrade over time, and become inconsistent.With the plethora of things that use bloody class Y caps, it's no surprise that an older installation with one main RCD could be pushed a bit hard.Quote from: mikeselectricstuff on September 16, 2024, 03:15:52 pmYou just need to get your clamp over the main earth to measure your total earth leakage current. And as Mike says, you should test one circuit at a time when chasing down issues.

author: Howardlong
author_rank: Super Contributor
timestamp: September 16, 2024, 06:58:12 pm
content: Quote from: AVGresponding on September 16, 2024, 05:34:46 pmThe problem with this approach is that it doesn't catch any earth leakage that doesn't come down the "main earth". That's why it's recommended to clamp both L and N at the same time.Another problem is that I believe that the MCBs I have in my CU are single only pole.Legally speaking, ISTBC, but I believe that anything inside the CU needs a qualified electrician here in the UK.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 16, 2024, 07:10:28 pm
content: Quote from: Howardlong on September 16, 2024, 06:58:12 pmNot a problem.If your MCB only switches L and omits the N connection, then that MCB is NOT an RCD/RCBO, and can be ignored insofar as measuring earth leakage is concerned.Can you highlight the breaker that is "tripping" from your surge protector? Is it even in the photo?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2024, 10:13:12 pm
content: Quote from: Howardlong on September 16, 2024, 06:58:12 pmIt's a complicated mess of building regs and "competent" persons schemes, (where "competent" is defined as paying a sub to one of the cartels like NIC/IEC or NAPIT).In reality, if you actually know what you're doing then it's highly unlikely to ever be an issue unless you ever sell the house & get asked for paperwork, in which case you just claim ignorance about any work that may have been done in the past by some electrician who's now long-gone, and just offer to get an EICR done to show that the installation is safe.Historical aside - they changed wiring colours from red/black to brown/blue around the time they brought in the Part P regs on domestic electrical works (though there was some overlap, about a year or so ISTR). There's a reason there's plenty of ebay listings for "old colours" twin & earth cable.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2024, 10:18:35 pm
content: Quote from: Andy Chee on September 16, 2024, 07:10:28 pmI think there may be some confusion between both L+N physically passing through the RCD/RCBO, vs. 2-pole switching of both L+N.Most RCBOs (at least in UK) only switch the Live, with Neutral just passing through for residual current measurement. This means that any neutral-earth leakage will still be there when it's turned off, and a N-E short on that circuit will trip any upstream RCD

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2024, 10:26:56 pm
content: Quote from: AVGresponding on September 16, 2024, 05:34:46 pmUnless some of that leakage isn't leaking to the mains earth wire.

author: themadhippy
author_rank: Super Contributor
timestamp: September 17, 2024, 12:08:56 am
content: Quoteyour not replacing the consumer unit,nor adding or making changes to the existing installation and the rules do sayQuote

author: Andy Chee
author_rank: Super Contributor
timestamp: September 17, 2024, 02:48:24 am
content: Quote from: mikeselectricstuff on September 16, 2024, 10:18:35 pmIndeed. When I Googled the manufacturer of the breakers shown in the posted image above, the breakers I found only had a single physical screw terminal on the line and load sides.So unless I Googled the incorrect model breakers, the ones shown in the posted image above CANNOT be RCD/RCBOs because they do not have both L+N.In other words, RCD/RCBOs must have L+N physically passing through them. They may switch L only, or switch both L+N, but they MUST have both L+N physical connections.I have attached a photo; this is NOT a RCD/RCBO.In contrast this is a RCD/RCBO. Note the extra neutral connection. Also the big tell-tale is the TEST button that all RCD/RCBOs have.

author: Howardlong
author_rank: Super Contributor
timestamp: September 17, 2024, 07:00:04 pm
content: Quote from: Andy Chee on September 17, 2024, 02:48:24 amYes, as I mentioned, they're just the circuit MCBs, they're not the RCDs. There is only one RCD, and that is only on the socket rings and cooker (and the Joker, a 16A circuit that, as far as I can tell, only supplies the masthead amp on the TV antenna... I'd left it turned off for weeks, and only finally realised what it was for when I turned the TV a long time afterwards and there was no signal).The RCD is either a GE 604241 or 604243, can't tell the last digit as it's hidden by the switch, but they're the only 80A RCDs starting with 60424#.The way I've seen sparkies sniff out leaking circuits is to open up the CU, remove each L & N connection from each of the MCBs, and test the insulation resistance of each. Now I could do that with the high voltage tester designed for the job, but frankly I think this would probably be the time to get a proper sparks in. Unfortunately the last sparks I had in when this originally happened was a come-and-go guy, he wasn't interested in actually trying to resolve the problem as it wasn't tripping when he turned up.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 17, 2024, 11:25:22 pm
content: Quote from: Howardlong on September 17, 2024, 07:00:04 pmTo apply this strategy to your scenario, turn off all MCBs, leave RCD on, measure L+N of your 80A RCD. Should be zero imbalance.Whilst continuing to measure L+N of your RCD, turn on each MCB one by one until leakage is observed.

author: Howardlong
author_rank: Super Contributor
timestamp: September 18, 2024, 07:04:24 am
content: Quote from: Andy Chee on September 17, 2024, 11:25:22 pmYes, this depends on me having a clamp meter that gives anywhere near consistent and reliable results: the two I have with milliamp resolution don't (UT210E & ACM81). Mike convinced me enough to purchase the WinApex 268B, so we'll see what happens there. It's not tripping at the moment since I removed the surge protector.One further bit of information that I didn't think was relevant, but in retrospection it might be: on about 1 in 5 of the RCD trips, one of the 32A MCBs protected by the main 80A RCD tripped too, as well as the RCD itself. Can I infer anything from that?As I understand it, the problem of using the strategy of "turn on each MCB one by one until leakage is observed" while measuring the L+N is that, as only L is switched on the MCB, any N-E fault won't be isolated.Thanks for your input.

author: adam4521
author_rank: Regular Contributor
timestamp: September 18, 2024, 07:26:20 am
content: You’re right, don’t discount N-E faults, they can happen all over the place. Check your cooker, immersion heater, toaster. At my parents house years ago, the electrician fitted a new consumer unit and discovered a latent N-E fault in a ceiling rose, been there for decades probably, really hard to find.I think your original idea of using your isolation transformer is a useful avenue for ‘individual appliance’ test. It will stop your house RCD from tripping while you are trying to measure. You’ll need to ensure/know that the secondary winding is earthed and connected to the DUT CPC to recreate the protective conductor return path, and to keep your equipment enclosures safe. Take all the measurements you want on that local system. Note that unless your transformer is one of the medical grade ones that has an interwinding screen, there will be a small but not negligible amount of leakage current through the transformer.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 18, 2024, 09:03:43 am
content: Quote from: Howardlong on September 18, 2024, 07:04:24 amIt takes quite a lot to trip a 32A MCB so maybe indicative of something more serious - an intermittent short to earth - things likeoven or immersion heater elements are common culprits. Current sufficient to trip the 32A could well have blown out what was causing the short, at least temporarily.The problem going away by removing a surge protector could simply be that the leakage was already close to the limit and the surge protector pushes it over the edge.

author: Monkeh
author_rank: Super Contributor
timestamp: September 18, 2024, 05:03:06 pm
content: Quote from: Howardlong on September 18, 2024, 07:04:24 amWas it always the same MCB?

author: themadhippy
author_rank: Super Contributor
timestamp: September 18, 2024, 05:19:17 pm
content: if its the 32A device next to the rcd id consider swapping the circuits around to see if the fault moves,its rare ,but occasionally the magnetic field in one device can interfere with its neighbor .

author: Howardlong
author_rank: Super Contributor
timestamp: May 21, 2025, 10:40:12 pm
content: Well I risk tempting fate, but after spending hours on this trying to diagnose what combination of devices caused the nuisance tripping, I bit the bullet and put the entire electronics bench room on a 1.5kVA continuous (3kVA peak) isolation transformer about six months ago, and haven't had a trip since.So I still don't really know what was causing it, as nothing individually caused the trip, although damp weather and a combination of appliances I believe exacerbated the problem.Sometimes life's too short, and I'll live with the isolation transformer, without knowing why these things happen.I read somewhere that in data centres they put in RCDs every 8 PDU outlets or so as a rule of thumb, which seems reasonable. Nuisance tripping in a data centre isn't what you'd want to experience.On the downside, the isolation transformer eats up 47W under no load, and makes a bit of a hum, mitigated by mounting it on a bit a bit of foam. I turn everything off anyway when the equipment's not in use. I have a couple of rack servers in there, but they're for testing purposes, so not on 24/7 unless it's a very occasional long test.The isolation transformer for reference is a Carroll & Maynell part no CM3000/230, purchased from Screwfix, £130.I'd already spent more than £130 of diagnostic kit like clamp meters and insulation resistance testers. This seems like a black art TBH, probably where experience plays a large part.

author: DrijSkij
author_rank: Contributor
timestamp: May 22, 2025, 10:33:30 am
content: Too many acronyms that I don't know. Not sure if it's a European thing, or because I'm not a tradesman. Sorry, but I can't keep up.

author: JoanBS
author_rank: Contributor
timestamp: May 22, 2025, 11:16:58 am
content: Try replacing the RCD with a superimmunized model with the same characteristics. This will probably solve the problem.