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Type A rcd . EICR coding ? etc

aligarjon
Hi Guys.   Not been on for a long time, just had a bit of a search and couldn't really find anything so thought i would ask and see what you all thought.


1.  Are we or will we be coding type AC rcd's if there are LED's or induction hobs, lots of electronics  etc  present.

2. How much DC leakage does it actually take to saturate an rcd and cause  problem?

3. How much does a standard LED lamp or induction hob  leak ?

If we test an AC RCD with no load and it's fine then re-test it with all LED lights, induction hobs etc turned on and it operates correctly could we then say that it is ok with a note on EICR  OR EIC if installing any of the above.  


Obviously also on an EICR if the RCD then doesn't operate with it all on it becomes a C2 ?


Any thoughts



Gary
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    LOL.  watch your blood pressure Dave.     That is pretty much what i told the customer when he rang me.    Maybe they read the manufacturers instructions as well.  Although we only have to take account of them don't we and decide that they are useless.  :)


    Gary
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    Alcomax:
    No, but the cables in walls do.



    Not being facetious, honest ? but the boiler is not buried in the wall.


    Is this a case of a fear that new boiler manufacturers guarantee may be voided by their spurious "requirements" not being met?


    No, my fear is that the boiler may trip a type AC RCD in the same way as the VSD in my lathe does. We shall find out in due course. In the mean time, I have contacted the manufacturer (Worcester).


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    davezawadi (David Stone):

    As usual, a manufacturer's instruction Chris which is WRONG. Why does a boiler need a type A, in the case it requires additional protection? There are several points here. If bonding is in place to the gas or oil supply, why would the boiler require additional protection? Can THE BOILER introduce an external potential, which is not introduced by the gas/oil pipe? NO. Can the boiler produce a DC mains current? NO. Does it have a plug? NO. So what exactly does this instruction mean? It means that whoever wrote it has no idea about anything and providing faulty manufacturers' instructions should become a criminal offense both for the writer and the manufacturer with a prison sentence as the minimum on conviction as well as a hefty fine. In fact, this instruction was probably written in a country that does not have type AC RCDs available, and the boiler does not require anything any fancier than the minimum. Let's assume a TT installation. There is NO additional protection available except bonding or perhaps a number of RCDs in series. Most important there is no danger, so just what do they mean, and certainly no explanation of why a type AC is needed!


    Aligarjon, British gas should lose its electrical certification. This is again just plain wrong. It appears that very few persons understand RCDs, DC Current, or anything else.


    What on earth makes you assume the manufacturer got it wrong?


    Perhaps the boiler is known to "blind" Type AC RCDs for a very simple reason. The boiler doesn't have to produce a DC mains current - but it could well have a bridge rectifier on the mains - as per a lot of SMPSUs - and therefore the manufacturer considers it's possible, for some faults on the rectifier output, to generate a fault current that is simply not suitable for a Type AC RCD  - See item 4 in Figure A53.1 (Page 192 of BS 7671).


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    What about the fixed wiring after the boiler - e.g. between the boiler PCB and room 'stats and so on? - if that's concealed in a wall (it usually is) then BS 7671 will likely require additional protection by 30mA RCD - can we be sure that that wiring isn't fed by semiconductors?


      - Andy.
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    Chris Pearson:
    Alcomax:
    No, but the cables in walls do.



    Not being facetious, honest ? but the boiler is not buried in the wall.


    Is this a case of a fear that new boiler manufacturers guarantee may be voided by their spurious "requirements" not being met?


    No, my fear is that the boiler may trip a type AC RCD in the same way as the VSD in my lathe does. We shall find out in due course. In the mean time, I have contacted the manufacturer (Worcester).




    In addition to the manufacturer knowing there may be issues with Type AC RCD's, this is another possibility.


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    AJJewsbury:

    What about the fixed wiring after the boiler - e.g. between the boiler PCB and room 'stats and so on? - if that's concealed in a wall (it usually is) then BS 7671 will likely require additional protection by 30mA RCD - can we be sure that that wiring isn't fed by semiconductors?


      - Andy.


    But it could be a fault in the boiler as well ...


    We can't go assuming the manufacturer has got it wrong just because it means the job is a little more difficult.


    Engineering truism - Assumption is the mother of all muckups!


  • 0
    Looking at the Worcester 2000 combi, the MIs state " the correct type of RCD must be employed where additional protection is required that is suitable for a low energy DC modulating pump according to IET wiring regulations"

    So it seems they are more worried about the pump.

    The manufacturers' external controls use extra low voltage DC via a bus.

    Also most modern boilers use flame rectification to prove the gas is burning, which puts a DC voltage to earth.

    So a lot of DC flying about.
  • 0
    No, my fear is that the boiler may trip a type AC RCD



    But the boiler instructions said

     
    Type A RCDs must be employed where additional protection is required."



    They did not say anything about tripping an AC type being a problem. 


    However, if there is some claim that an AC will be blinded by the normal function of the boiler, so disabling Additional Protection for all or part of an installation, then that Boiler is not fit for purpose as a "replacement", unless it has been made crystal clear, by the seller or reseller beforehand, of the significant constraints regarding extra costs and warning of the alledged risk to safety of continuing to use an AC RCD.


    I expect the instructions or advertising do not advise that AC type RCDs will be disabled by the Boiler or that it will trip an AC RCD.


    Back, really, to an earlier point being these instructions have been updated to the 18th, that is all. The Boiler and its components are likely not very different now to those installed a while ago. I do not buy into the manufacturers having a sudden eureka moment, after all they would surely have many years of data of their boilers tripping AC RCDs or blinding AC RCDs, if that were the case.



    Edited as Olympus Mons just referenced some instructions

     
    low energy DC modulating pump according to IET wiring regulations



    This seems like a bit of @r$e covering by the makers, just in case. They should not be marketed as "replacements" without full disclosure beforehand of any perceived safety issue.
  • 0
    I totally agree that manufacturers are responding to new regs requirements without any thought given to the consequences of their instructions on the electrical installation their boiler is attached too.
  • 0
    Very well, Gentlemen, the boiler manufacturer cannot be bothered to correctly fuse his appliance, expects there to be faults in his electronics, safety coverings, etc. and so we must fit a type A RCD. He cannot be bothered to put an Earth terminal on the casing and expects the piping not to be bonded to Earth and the CPC open circuit. That is the biggest load of A.. covering I have ever heard. This product does not pass the LV Directive, is unsafe, has no internal protection, and is expected to fail dangerously.


    I think it would be reasonable for someone to describe what fault exactly could require a type A RCD. As you all know by now I don't believe there is a credible scenario without multiple faults which could make a type AC fail to disconnect this appliance. What is the scenario where normal thermostats (230V) could cause a DC fault? If they are special LV types they are inherently not dangerous. How could this appliance require personnel protection? Therefore WHY is an RCD required? If the reason is because of incorrect installation then that is "Someone Else's Problem", not the Boiler manufacturer or BS7671. Andy may care to check out a few boilers, the thermostats tend to drive timers/controllers that have relays, and the thermostats are 230V, they depend on that for the heater to reduce hysteresis. Just in case anyone is wondering, failure of one diode in a bridge rectifier feeding large smoothing capacitors, does nothing much if open circuit, and takes a large current if short circuit. The appliance fuse (perhaps 3A but should be 1A) pops immediately. Power isolated, no problem. No reasonable fault can cause any DC on the mains, so an RCD requirement is odd unless it is as my paragraph 1.


    I have done a lot of experiments with several makes of type AC RCDs and have yet to find one where small levels of DC (real DC not rectified waveforms) prevent operation. Some of them have somewhat reduced sensitivity at modest levels of DC (30-50 mA) which is not a problem except for personnel protection. They all work with rectified waveforms. The tests are not exhaustive but a guide. JW is not the only one who tests things!


    Note to Chris, your inverter either has a large inrush or excessive current through EMC filters. My Japanese 4kW one is fine on an RCD < 10mA and no significant inrush. It is a PFC corrected type, so no rectifier/capacitors off the mains.


    I am interested in answers to my questions above, they are not "getting at" any of the posts above, all of which are useful.

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