1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

RCD types for boilers?

Discussion in 'Electrics UK' started by ericmark, 17 Jan 2020.

  1. ericmark

    ericmark

    Joined:
    27 Jan 2008
    Messages:
    14,745
    Thanks Received:
    1,309
    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    [​IMG] On another post this was posted to show the boiler and additional components must all come from same supply, in most houses there is only one supply, so rather pointless, yes I know it is seen as being the same FCU but that is not what it says.

    However the next statement is what I am raising here, the need for a Type A RCD, looking at screwfix web site a page of 16 RCD's all are Type AC so would not comply, the RCD fuse connection unit does not say what type other than active or passive, only the RCBO's seemed to comply most being Type B and some Type C.

    So it would seem only way to comply would be to use a dedicate circuit from a RCBO in which case why have a fuse, except it says 3A fuse on next arrow point.

    Ideal [​IMG] want the isolator adjacent to boiler, easy enough with a TN supply, most FCU's will allow the fuse to be drawn and a lock put in the carrier so locked off, but it only locks off line, so with a TT supply needs a means to lock the switch, or of course the RCBO.

    Yes I know one uses a bit of common sense, but as soon as you don't comply with one manufacturers requirement then why follow any, it does say "practicable" but when wiring a new build it would be "practicable" so would one have to fit a RCBO and a FCU and interconnecting wiring between the heating control and the boiler.

    The central heating was always the most complex wiring in a house, with the introduction of combi boilers it made life easy, all the complex wiring was inside the boiler, and controls went analogue, however Part L building regulations messed up that, so we now have zones, it seems no one has really defined what needs to be controlled in each zones, some government publications seems to say using TRV in every room is enough, others want time controls as well, again easy way is the programmable TRV but they are normally battery powered, so then not all supplied from same source, my house has 10 sources, 9 x twin AA batteries and one 230 volt FCU.

    So if you are designing the wiring for a home, assuming once complete some other tradesman will fit central heating, what should be provided for the heating engineer to install the heating and ventilation and if appropriate cooling devices? My old house the supply to Myson fan assisted radiator is completely independent to boiler, as the water gets hot the thermostat turns on the fan, and the fan is also controlled by the temperature of incoming air, I really see no good reason why the radiator should come from the same plug as supplies the boiler.

    Be it a motorised on/off valve, or a motorised analogue valve (TRV), pump, or fan assisted radiator I see nothing in BS7671 to say all should be from same plug or FCU, it is only the manufacturers who seem to want all from one FCU/Plug. From what I am lead to understand we no longer need to follow manufacturers instructions.

    So what is reasonable, what is required, what is sensible, what would you do etc?
     
  2. Sponsored Links
  3. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    42,464
    Thanks Received:
    2,697
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    ... Are you sure that's what they are saying? The statement in question (in a section called "Electrical Considerations") relates to "additional components that are connected to the appliance [boiler]". Things such as you are mentioning (MVs, pumps etc.) are not usually connected (electrically) to the boiler, other than via CPCs (which I don't believe is what they meant!), are they? (and they surely aren't talking about 'plumbing connections'?!!).

    Kind Regards, John
     
  4. Risteard

    Risteard

    Joined:
    18 Jun 2010
    Messages:
    1,948
    Thanks Received:
    132
    Location:
    Derry, Ireland
    Country:
    Ireland
    I'm not sure why you've referenced Type B and Type C RCBOs in relation to Type A and Type AC RCD characteristics. The tripping curve of the circuit breaker is a completely different thing. There is no RCD Type C characteristic and Type B would be horrendously expensive.

    Essentially they are obviously claiming that there will be a DC component in the installed equipment which may defeat RCD protection.

    I'm not surprised that screwfix don't have non-Type AC RCDs (which much of the world banned many years ago). MK didn't even make non-Type AC is devices so thankfully they've gone out of production.
     
  5. winston1

    winston1

    Joined:
    11 Jan 2010
    Messages:
    5,367
    Thanks Received:
    384
    Location:
    London
    Country:
    United Kingdom
    At the end of the day manufacturer’s instructions are guidance only and frequently wrong.

    All boilers are internally fused and if wired with the right size cable don’t need an external 3a fuse. They certainly don’t get it when the same boilers are used in Europe where FCUs are non compliant and not available.
    One wonders what else they have got wrong!
     
  6. ericmark

    ericmark

    Joined:
    27 Jan 2008
    Messages:
    14,745
    Thanks Received:
    1,309
    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    I had not considered if the type B or type C refereed to the RCD or MCB part of the RCBO you are correct when I looked at advert again it states curve type so would seem to refer to MCB part not RCD part of the device, so not a clue what the RCD type is, should have realised there is no type C RCD they are type AC, A, F, B and B+ so it seems more to do with the signs [​IMG]
    Above not good enough for Worcester Bosch any of below are OK but looking at screwfix web site nothing in the spec, with the MK you can just about see on the picture that it has sign for AC type as shown above.
    [​IMG]
     
    • Thanks Thanks x 1
  7. bernardgreen

    bernardgreen

    Joined:
    3 Nov 2006
    Messages:
    22,262
    Thanks Received:
    2,079
    Location:
    Bedfordshire
    Country:
    United Kingdom
    But then they use dedicated circuits with a multitude of low current MCBs. This for a 3 bedroom family home

    [​IMG]
     
  8. SUNRAY

    SUNRAY

    Joined:
    28 Jul 2009
    Messages:
    2,139
    Thanks Received:
    108
    Location:
    Kent
    Country:
    United Kingdom
    At last someone else has realised all these comments about thin cables plugged into 16A sockets are verging on irrelevant.
    In France all of those MCB's will of course be double pole.
    We stayed in a 7 bedroom Gite in France and there were 4 CU's about 600mm wide, 9 MCB's just for the sockets in the kitchen.
     
  9. Sponsored Links
Loading...

Share This Page