Special non rcd socket for pat testing

Discussion in 'Electricians' Talk' started by tina lucinda lane, Jan 13, 2021.

  1. The Happy Builder

    The Happy Builder Screwfix Select

    Don’t even consider trying to do something with a shaver socket and a lead with a two pin shaver plug on it unless you’re really clear on the desired outcome.

    Again, to test the plug in RCD you would have to take the two core cable into 13 amp socket then link the neutral and earth, but with a two pin shaver socket you cannot guarantee getting the polarity correct, because the two pin plug can be reversed.

    So unless you are a whizz with electronics and intending to break the shaver socket up for parts rather than using as is, keep well clear of the shaver socket setup.

    Apart from that, does an isolation transformer improve safety or merely remove the protection the installation RCD is giving you?
  2. MGW

    MGW Screwfix Select

    @tina lucinda lane is a regular poster, and it seems she (I assume) is an electrician, so fully aware of the dangers, for the non electrician does it really matter? He does not need to enter tripping times or currents, he presses the button on the 10 mA MK RCD socket and it trips the socket, the 30 mA RCD in local consumer unit, and the 100 mA RCD in the distribution board so he knows he is protected. Yes that did happen where I worked, so clearly the test button was testing line to earth.

    In the main we go times 3, so 10 mA, 30 mA, 100 mA, 300mA, 500 mA 1 amp as we go board to board, plus built in delay. So a RCD tester should be able to test each device as current increases.

    But the caravan site and marina have always presented a problem, how do you test a caravan or narrow boat when the shore supply also has a 30 mA? I did use an inverter to supply the caravan or boat, I have a 12 Ah jump starter with a 300 VA output at 230 volt, however the output is simulated sine wave, so now we are looking at type AC, type A, etc.

    Also there is a problem where there are diodes in the earth to stop erosion of the hull, it seems @tina lucinda lane is more concerned than myself, I was rather naughty and I recorded tripping time shown on tester, and did not really care which RCD tripped. In the main both tripped.

    So big question, how far should we go? I have only once tested MCB's for tripping current, was on a caravan site, and we were getting the main fuse blowing when total of all MCB's was under rating of main fuse, so 5 amp supply and used a 2 kW fan heater and if MCB did not trip, changed it, that is the only time I have tested MCB's.

    So the big question is how far do you take the testing of a RCD, should you inject a 6 mA DC load to ensure the type A RCD still trips at 30 mA?

    Maybe we should? Hands up everyone with a RCD tester that can inject 6 mA DC.

    But if all sockets are RCD protected is there really any need to test the RCD on an extension lead? If @tina lucinda lane is an electrician I am sure she can work out how the test extension leads without anyone on here saying how to do it. We all at some point break the rules, be it the oven which has absorbed moisture, or fitting a new consumer unit when there is no isolator, we all know how it is done, but we would if we have any sense we would not admit we do it on here.

    So I hope @tina lucinda lane can read between the lines, if not I would say not really an electrician. We can hint, but can't really say how to do it.
  3. tina lucinda lane

    tina lucinda lane Screwfix Select

    Again thanks for the big up I'm not a spark but am an electrical and electronics engineer, software engineer, pat tester and general fixer so have a deep understanding of electrical systems however I know from experience how different rcds react in fault conditions did a garage job (full rewire I designed and sourced all materials had a spark do the actual work, I only helped) had a 30ma rcd in the house feeding the garage via a circuit in the house, not best done btw but wasn't on the remit of work so simply noted that improvements where advised, garage replacement cu had a 30ma rcd as well had done basic research and found a fault live to earth in garage will trip garage rcd 1st before house rcd unfortunately on a neutral to earth they tripped at the same time, this however unideal was acceptable as both rcds provided protection and met standards (can't remember amp rating of the rcds)
  4. tina lucinda lane

    tina lucinda lane Screwfix Select

    That's an option and the polarity problem can easily be rectifed with simple labeling via either using light engraving into the plug to mark a l and an n or pened on using metal marker in silver or gold
  5. MGW

    MGW Screwfix Select

    I am also an electrical engineer, i.e. have a degree, but the problem today is be it inspection and testing of in-service electrical equipment or electrical installation condition report you have to state if the person who did the work, did it right.

    Minor works or installation certificate is no problem I decide what I am going to do. I don't have to criticise anyone else's work. All I am doing is saying my work is compliant.

    But testing some ones else's work is not so easy, if I am fitting a induction hob, it is up to me if I fit a type AC or type A, so I can supply and fit type A, but it inspecting some ones else's work, can I really fail a type AC? with a TN supply I would say no, but with a TT supply not so easy.

    However as to inspection and testing of in-service electrical equipment it has to take into account the environment, so a building site 4 month ticket, and office a 4 year ticket for same device. So you don't need to state trip times or currents for an RCD plug, it passes or fails, and if the socket is RCD protected there is no need for a RCD on the lead, and if the item is moved to another premises then it needs retesting.

    So with a radio with a 2.5 amp fig of 8 lead in an office I would pass it, but same radio in a factory with water everywhere it will fail. If you have 10 x 30 mA RCD's as long as one trips, then the whole is safe.

    Put it this way, with all sockets RCD protected, would you fail an extension lead because it has no RCD? I am sure the answer is no, so neither could you fail it because the RCD fails to operate. OK if testing equipment in a store which could be used else where maybe you need that socket, but unless you know the environment is it really up to you?

    My worry is RCD type, with a all RCBO board not worried, even if type AC, the chances of a unit stopping the RCBO tripping is low, so my personal risk assessment is it does not matter. But 5 circuits on one RCD, that is different, a three port valve on the central heating could stop the RCD working on the socket supplies, but with a TN supply does it really matter? Likely it does not, but with a TT supply then not so sure.

    But if you started a thread is a type AC RCD permitted on a TT supply I suspect it would open a can of worms.
  6. tina lucinda lane

    tina lucinda lane Screwfix Select

    Excatly and excellent break down there I understand completely the can of worms all work can cause
  7. Lectrician

    Lectrician Screwfix Select

    There is no selectivity between upstream RCDs, either one could operate first on L or N fault. That is why we use time delayed RCDs on upstream RCDs, and never put two 30mA in series.
  8. tina lucinda lane

    tina lucinda lane Screwfix Select

    Well in this case under test the garage one tripped 1st every time on live to earth fault, and in this case it was part of the requirement that a 30ma rcd was fitted to protect users in garage and garden as also had an outside socket fitted and was requested that all sockets in garage protected by 30ma rcd as recommended supply to garage be split of meter tails insted of via socket circuit so this design provided the infrastructure for such improvements to be made, and garage was all crabtree gear in dB, while house was a bg brand dB with a suppliers earth rather than rod system, garage was given 4 metal clad double sockets, two strip fluorescent lights one sensor bulk head inside, bulk head outside for near bins and sensor flood light out front with outside double socket (as homeowner had a sports car that had to have 2nd battery kept charged up as full electronic gear box and it 2nd battery flat vehicle won't drive, and other for lawnmower use) so was a complex design and installation we where only there to do garage upgrade house had been done year before when new kitchen was fitted (so new kitchen part rewire, and new cu badly fitted with a messy configuration of existing circuit's, recommended full rewire as well as breaking garage supply from meter tails, was taken under consideration hence provision in place for that work to be done) also I'm simply stating that allow certain rules should happen between products made to same specification performance in field can be totally different
  9. The Happy Builder

    The Happy Builder Screwfix Select

    The specific job in hand is testing the plug in RCDs as part of PAT.

    Without ensuring that only the specific RCD under test trips the results are null and void.

    This can be done without removing the RCD protection from the installation socket by making a simple testing adapter.

    If you make up a test rig using a isolation transformer you will still need to wire the output the same as you would if the transformer wasn’t there.

    Using an isolation transformer would isolate the output from the installation RCD, removing the protection it gives you whilst testing the plug in RCD. Wiring the isolation transformer to allow it to be used to test RCDs would also mean it’s no longer an isolation transformer.
  10. Lectrician

    Lectrician Screwfix Select

    An isolation transformer could be used. The output from the transformer would have one side of the winding connected to earth, the test current would not flow back to the source, it would flow back to the isolation transformers winding via this connection, it has no other option. However, the simple lead made up with N used for both N and E is the simplest method, tried and tested by so many sparks. I have one in my van with 16amp plug/socket for testing RCDs within caravans without tripping the external hookup RCD. I don’t know why Tina doesn’t want to use this obvious simple approach. Installing a non RCD socket, which will end up on her bench via an extension lead is just crazy. It won’t be controllable, and you can’t say “only I’ll use it”. If it was a laboratory or something, with many skilled people, and RAMS galore, fine........but the back room of a charity shop? No.

    She could forget to put it away one day, could go to the loo, could be taken unwell. It would remain out and be used. And what protection is there for the trailing lead from the hidden socket to the desk? It’s going to be trailing and prone to damage.

    Tina, just make up the incredibly simple test lead, and keep it in your test box.
  11. tina lucinda lane

    tina lucinda lane Screwfix Select

    I have taken both as options and will consider both most likely will end up with the simple test lead you suggested I was simply exploring all the options
  12. MGW

    MGW Screwfix Select

    In the workshop I used we had a MK 10 mA RCD protected socket, this was supplied from a 30 mA RCD which was in turn supplied from 100 mA S type RCD and pressing the test button on the socket would take out all three. Rather poor design that test button took out all three, I thought MK was good stuff until then.

    When some on in a mess hut knocks in a nail for their coat and hits cable taking out the 30, 100, 500, and 1 amp RCD's I can understand, but a test button?

    I was a little surprised with 1 amp and 1 minute it still tripped, but a nail is a good conductor, lucky hammer shaft was not.

    I have looked at my older RCD's and no Type A.png or any other sign to say what type, and I do wonder what should be done in that case, up to now only tested with a TN supply so the RCD is an extra protection, so not worried if type A, but with a TT still find one 100 mA protecting whole supply with no type markings, and they have been used with Y Plan central heating for years, I say Y Plan as there is a diode in the mid position three port valve, which in theory could freeze a type AC RCD. Never had one fail, but no idea if central heating was running at the time.

    In fact it was normal to turn everything off before testing, so if there was some thing with a DC component would not know if it froze the RCD as turned off.

    I have not does inspecting and testing for years, so I suppose the new testers all can simulate DC components for the test, other wise is there any point in testing? May as well just assume they will work like we do with MCB's.
  13. The Happy Builder

    The Happy Builder Screwfix Select

  14. tina lucinda lane

    tina lucinda lane Screwfix Select

    That's useful only problem I can foresee tho may not be an issue if someone with experience of using a Robin rcd tester that uses a 3 pin iec socket connection as well as a earth reference connection as well same as the interest I have wondering if a earth to neutral adapter, as suggested may also cause problems is that part of the device requires a fully normal power connection to operate
  15. The Happy Builder

    The Happy Builder Screwfix Select

    If you look at the diagram of testing at a wall socket you will see the connection from the socket is a dotted line, as with the other diagram as the neutral connection is not required or used.

    Where you connect the earth test lead determines whether or not the upstream installation RCD will trip of not.

    Connect it to the earth and both RCDs will trip, connect it to the neutral in-between the two RCDs and only the downstream RCD will trip as the earth current from the tester will run back through the neutral of the installation RCD.

    It really is quite simple :)
  16. Lectrician

    Lectrician Screwfix Select

    Absolutely not. You’ve been given advice by so many people who have so much experience. You’re clearly out of your comfort zone.

    Either buy a two lead modern tester (your Robin is past its expected life, long past BS7671 requirements), or do as so many have tried to explain....use the neutral as a fake earth.....AS EVERY TRADING SPARK WILL DO AS NEEDED.
  17. tina lucinda lane

    tina lucinda lane Screwfix Select

    I'm not out my depth just simply adding a extra layer to the tests I can preform and I'm more than capable of doing the work just need help with the experience I currently lack, also just because my machine is a little retro doesn't mean it needs replaced, I mean the pat tester I'm chasing for my self is a seaward pac with only the rotary selector not the full on keyboard yes I know she's a big brick lump to carry around but she's a beauty and the machine I learnt on and it was love at 1st sight
    Last edited: Jan 16, 2021
  18. tina lucinda lane

    tina lucinda lane Screwfix Select

    Thanks, that clears it up fantasticly didn't want to look stupid but still managed to anyway
  19. Lectrician

    Lectrician Screwfix Select

    Using a tester which is no longer recognised as a tester by the BS isn’t great. Ignoring all the advice you’ve be given to make this tester work for you isn’t great either. Similarly with an old seaward PAT tester.
  20. The Happy Builder

    The Happy Builder Screwfix Select

    The tester is fine for what you want to use it for, testing plug in RCD adapters and the like.

    Though it will cost you more to get it calibrated than you paid for it, if you need it to be calibrated.

    Are you actually testing RCDs that will be sold or used by others?

    This is testing for PAT, not EV charger installations and the like with Type B RCDs and similar.

    Horses for courses and all that.
    Last edited: Jan 16, 2021
    tina lucinda lane likes this.

Share This Page