Equipment where manufacturer asks for better than type A RCD.

Discussion in 'Electricians' Talk' started by MGW, Jun 21, 2021.

  1. MGW

    MGW Screwfix Select

    When looking at the instructions for fitting a domestic AC unit I found
    This would as I read it mean a type B RCD, which presents some problems, one is you can't get a single module width RCBO better than type A for most consumer units. So to fit a type B in the main means a separate enclosure, and the consumer unit would need a MCB fitting and no RCD protection to the auxiliary enclosure which means either a high integrity consumer unit or all RCBO consumer unit to be able to convert to have a non RCD protected supply to the auxiliary unit.

    It seems type B RCD's are often three module width, and very expensive, between £120 and £700, and even then are often only rated at 40 amp, to retain type testing it needs to be same make as consumer unit it is being installed in, which also presents problems.

    The The AC in question installer reference guide this is fortunately not my problem, it is not my AC or my job to fit it. However it is possible any one of us could come across this in the future, so seems good idea to talk about it before the event so we can advise a customer.

    To my mind no domestic appliance should require over a type A RCD, simply down to you can't get better than a type A RCBO for a consumer unit, commercial not limited to using type tested consumer units so not the same problem, but an electric car charging pod can have everything built in so can be supplied from a type A RCBO, so no reason why any other appliance should not be the same.

    I have heard the Tesla charging pod does not have the equipment built in to be able to be supplied from a type A, personally I would say in that case not fit for purpose.

    But what does the team think?
  2. The Happy Builder

    The Happy Builder Screwfix Select

  3. MGW

    MGW Screwfix Select

    Yes I know the four types, AC, A, F and B. The big problem is single module width RCBO's seem only to be available as type AC or A. As soon as you move to F or B then it seems one has moved out of domestic, and the type tested distribution unit known as a consumer unit.

    So in most homes it type A is not good enough one is looking at henley block and a enclosure to hold the type F or B and that enclosure since in domestic needs to be type tested, i.e. suitable to be under the control of an ordinary person.

    Type B upload_2021-6-22_14-13-2.png is a big lump, nearly £500 and 40 amp rating, type F upload_2021-6-22_14-8-25.png are smaller but still seems 63 amp limit, and still expensive £170 and really not what you want to pay for a supply to an AC, or for that matter electric car, with the electric car the charging pod often has a 6 mA DC detection module which will auto disconnect allowing the use of a type A RCD and a voltage detection unit so if out of range 207 to 253 volt also auto disconnects first lives then earth, if some one want to fit a pod without that protection then clearly they can opt for type B RCD and TT earth, but it is up to them, there is another option.

    But the instructions for the AC
    would need a type F, [​IMG]and many consumer units simply don't have the option of fitting a type F.

    I note it say "unnecessary opening of the earth leakage protector" where as the DC component is really the reverse, with it freezing the earth leakage protector, so one could suck it and see, but if it does cause it to trip, then with a all RCBO consumer unit the cost to fit a type F and MCB with an enclosure is a lot of extra cash, in fact it could easy double the installation cost.

    So how would you deal with the problem?
  4. ElecCEng

    ElecCEng Screwfix Select

    What does the industry in general do? Nothing. Wait until the callout to ‘nuisance tripping’ and get another paycheque.

    What would I do? Probably take a sub main and small enclosure next to the unit with isolator and protection. If you’ve bought an AC unit you A) Don’t have the common sense not to buy an AC unit and B) Enough money to buy and run an AC unit. So the additional cost of protection isn’t really an issue.

    Maybe i’m just cynical...
    Squashrobinson likes this.
  5. spinlondon

    spinlondon Screwfix Select

    The problem is not nuisance tripping.
    The problem is, that Type AC and Type A RCDs may not operate due to to d.c. leakage from whatever device is in question.

    So apart from non-compliance with the requirement to provide RCD protection, you would be leaving what could be a fatal fault.
  6. MGW

    MGW Screwfix Select

    I have seen how DC can freeze a RCD, but high frequancy I was lead to undertand does reverse and causes the RCD to trip when no real fault.

    I am not too worried about DC freezing the RCD with TN supply, only with a TT is it the primary protection. But with high frequancy tripping the RCD clearly this is a problem.

    Also using RCBO the fault is limited to a small amount of items, using a general RCD is more of a problem. But the use or RCBO is claimed to be better, but simply can't buy a type F or B RCBO single modular width.
  7. Teki

    Teki Screwfix Select

    Haven't seen any singular module ones. Doepke do double module Type B ones but are very expensive and on long lead times.
  8. MGW

    MGW Screwfix Select

    Thank you for thoughts, all noted, I am lucky, I can simply say no.

    But it is still a problem where we as electricians are asked to connect an appliance and to provide a type F or B RCD is going to require a lot of work and clearly expense.

    If you don't fit the correct RCD then your leaving one self wide open for a claim, with a Bosch boiler asking for a type A not a problem, but asking for F or B is clearly more of a problem.

    The electric car charging point often uses a 6 mA disconnection unit. Not sure if you can get these for other circuits? This may be a way to use type A instead of type B, but type F I am really unsure what the result is if a type A is used instead, from what I have read it may trip when it should not, so fails safe?

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