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Static Caravan Problems.

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I was called out to a static holiday/residential caravan today. Nuisance tripping was reported. Apparently the electrics were reliable before the van was moved to a new pitch on the same sandy site. The van's consumer unit comprises 1 30mA R.C.D., a 32 Amp socket M.C.B. and a 6A lighting M.C.B.


The pitch permanent "hook up" point comprises a 30 mA R.C.D. and a 16 Amp M.C.B.


The lady has many high powered appliances, 2kW kettle, three 2kW+ room heaters, a 2.2kW coffee machine etc. The heating is normally by bottled gas.


The two R.C.D.s tested out fine, not over sensitive. But the van owner can not remember which devices tripped off over a period of time. Once the nearby brick supply building had to be accessed to reset something, but we were not allowed even just to look inside it today by the site owners. Very unhelpful.


Anyway, all appliances tested good, no faults. I presumed that the lady had plugged too many items in at once.                                                                                                                                                                                                                                                                Guidance note 7, page 58 Fig. 7.1 it shows 4 possible separate vans being supplied via a single  100 mA R.C.D.


So, looking at the possibility of nuisance tripping if 4 vans each leak say 20 to 30 mA, the 100 mA R.C.D. could trip off blacking them all out. Should a time delayed 100mA type be used? The Guidance note says that the 100 mA R.C.D. is chosen to discriminate with the pitch socket outlets R.C.D.s. But, if say 100mA was to flow from a van fault,  both the 30mA pitch socket R.C.D. AND the 100mA brick supply building could trip off together. This would then deprive a total of 4 vans of a supply.


Comments please.


Thanks,


Z.


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    1c6e7e969920667155bec73e33fdcaa5-original-20200729_090834.jpg
  • Former Community Member
    0 Former Community Member
    To confirm some reader's thoughts of my eccentricity, I think I have a salvaged one in my stores................ But as there's so much other "tat" in there, it might take a while to find!


    Regards


    BOD


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    Sparkingchip:
    91f336dee0d852dcea5c7e59286acdea-original-20200728_110719.jpg


    One in South Wales from last year I posted a picture of before on this forum. 


    The label on it says it’s a 0.5 amp RCD, just as Bod said.



    If I saw something like that not sure ide know what to make of it thinking about it is it just a very large version of what you'd find in a normal 30mA RCD I've never seen anything like that before

     


     


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    There’s a surprising number of those 500 mA hybrid VOELCB/RCD devices still in use, as well as a considerable number straight VOELCB.
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    Sparkingchip:

    There’s a surprising number of those 500 mA hybrid VOELCB/RCD devices still in use, as well as a considerable number straight VOELCB.


    There will be many about as they were built to a very high quality standard and will work for decades. Regular testing is required.


    There was a Crabtree model P60 that looked similar. It was rated at 30mA tripping sensitivity and had a 60 Amp overload trip incorporated into it as the main switch. It was made to B.S. 4293. Grey/cream in colour with a yellow rest button. Big, bulky but beautiful. And very high quality. Made in Walsall U.K.


    Z.

    .


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    Sparkingchip:

    The big black VOELCB with the yellow test button is easy to spot as are most RCD devices. 


    However there's some hybrid devices, RCDs made up using a VOELCB.


    Try this one from Wednesday in Devon, VOELCB or RCD?
    c5f8551222043d37eb68e524b00878e2-original-20210424_213426.jpg

     


    This looks like the Crabtree L60 model.


    Z.


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    Back then  (60s/70s) B.S. 4293:1968 required that current operated earth leakage circuit breakers should operate with an earth leakage tripping current of no more than two per cent of the rated circuit current. This would correspond to a current of 1.2 Amp. for a 60 Amp circuit, or 0.6 Amps. for a 30 Amp. circuit. The values typically adopted in practice  for a 0.1 second maximum disconnection time are: 1.0 Amp. for a 100 Amp unit, or 500 mA for a 60 Amp. unit.


    The 14th Edition I.E.E. Regs. did  not normally require operating currents of less than 500 mA.


    This protection seems to be mainly about reducing fire risks.


    But regarding shock risks, and a persisting fault current of 0.5 Amps. on a 30 Amp cooker circuit,  with an Earth loop impedance of about 120 Ohms, the shock Voltage is 65 Volts. Or with an Earth loop impedance of 80 Ohms is 40 Volts. The current operated earth leakage circuit breaker would clear the fault instantaneously..


    Z.
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    the test button on the 30 mA RCD can take both of them out.


    That makes it quite unusual nowadays.

    On a modern RCD the test button unbalances the sensor by connecting outbound live back to incoming neutral, rather than connecting live to earth, so any upstream RCD sees a normal LN current rather than L-E. Only the RCD under test sees an imbalance. The presence or absence of an earth is not an issue to the test button !


    You can play the same game with the RCD tester, and use upstream neutral as the tester earth if you need to test one RCD and not trip another. Do just check the LN polarity first though before spoofing a tester CPC from the live side.

    Mike.
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    Morning guys I've re read all the posts now and realise that yesterday I was getting myself in a bit of a mess trying to understand stuff I got it now tho so my apologise for my previous confusion think its cos I didn't take my pills Lo,


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    I have found 30 mA versions, that’s why if I cannot see a rating label I put the tester on them to see what happens and some fo work.


    As to what is behind a locked door, there’s only one way to find out.

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