Split consumer unit replacing one RCD with an switch/isolator if necessary

Strategy is perfectly reasonable, albeit potentially non-compliant.


AFAIK you could simply swap an ordinary main switch for the second MCB.


If you are doing a complete rewire, I don't see why it should comply until you have finished. For example, I am currently replacing a lighting circuit, which is not RCD protected. When I have finished the CU will be changed, but until then the new circuit will not comply (at least with the 18th Edn, but it did with 17th+3).

Or go for an all-RCBO approach - if you do then have problems with certain circuits you can swap just those on MCBs temporarily - it doesn't then have to be all or nothing for the old circuits and should have a more resilient system in the end.

  - Andy.

AFAIK you could simply swap an ordinary main switch for the second MCB.

What I have in my recently purchased holiday home is the main switch replaced with an RCD.  What slightly bothers me is that so far as I can see, one RCD has just the sockets and the second has both sockets, lights and cooker (actually there is no cooker connected).  Does this contravene any regulations, and should I be concerned?


David

Nearly all split load consumer units can be tricked to link out either or both RCDs, and they are the same form factor as the incoming switch,  but as noted to do so is not to current regs. Arguably it is a reasonable intermediate step, being no more dangerous than what was there before, you are OK so long as you don't go backwards in safety at any point.

In the past when tidying a very tangled installation I have dangled the old CU and all its wiring as one 40A circuit on the new board, and then next day come back and to moved one circuit at time on to the new CU, until the old one was empty.


For  smaller buildings and flats, it is quite common to have the whole lot  on a single 30mA  RCD, there is no hard and fast rule about how the load must be divided across more or less devices. There is advice from vendors of consumer units but you are free to take that with a pinch of salt. However, it is sensible to think of what happens if too many essential things all pop off at an inconvenient time - is it always accessible to reset, (the wrong end of a long unlit garden path for example is a bad idea ) is emergency light or any kind of alarm affected or required,  would  anything be damaged (frozen food for example) by loss of power - an extension lead to another room or floor is the sort of thing most folk can manage, even if they cannot trace the fault, and becomes more relevant with houses with outdoor power or lights, and more rambling wiring and more than one socket circuit.

If you buy what is sold as a “Hi integrity consumer” you can have MCBs split between two RCDs and a couple of non-RCD ways that you can connect a potentially dangerous circuit with failed insulation to.


?

A local qualified electrician will be able to advise you and undertake the work.


Z.

Many thanks everyone for replying, always good to have such expert opinion on hand.


Mike's point about everything going off together was my main worry, but I can manage the situation so that it is not too much of a problem.


Zoom - I already have an electrician on board (sub to a builder who will be doing some work in about 4 months), and he will do a complete rewire.  His reaction  on seeing the CU was "Curious" and he thought  the rest of the installation was "odd".  I have looked at it myself and think although unconventional it seemed safe.  I just wanted to be sure about the CU in the interim.


David

Hi thanks for the comments and opinions.

AFAIK you could simply swap an ordinary main switch for the second MCB.

That sounds like the simplest initial option giving new circuits RCD cover, and allowing the connection of potentially leaky 'old' circuits via a main switch without, say, one leaky circuit causing tripping out.

If you buy what is sold as a “Hi integrity consumer” you can have MCBs split between two RCDs and a couple of non-RCD ways that you can connect a potentially dangerous circuit with failed insulation to.

The  Hi-Integrity option seems a further refinement I hadn't thought of allowing an intermediate step between All-old-circuits-on-a-switch and All-old-circuits-on-a-RCD. As would use of RCBOs.

To do it for a customer really requires the electrician to get a written acknowledgment from the customer that there is a dangerous situation.

The customer does recognise this, and acknowledges this in an email I have.

Nearly all split load consumer units can be tricked to link out either or both RCDs, and they are the same form factor as the incoming switch,  but as noted to do so is not to current regs. Arguably it is a reasonable intermediate step, being no more dangerous than what was there before, you are OK so long as you don't go backwards in safety at any point.  

Having an "reasonable intermediate step" is one thing I wasn't certain of regarding wiring . In the auto-industry I've often given the aim for application of older products as "to be as safe as or safer than the existing item" - the existing item being an application already out there with an accepted safety-case. I do note you (mapj1) say "arguably" on this point, It would be useful to know if there is anything in the regulations on making an existing circuit safer then it was but perhaps not as safe as current regulations require.

The main aim of this question is to come up with a scheme whereby I can convince the customer to have RCD protection installed for the 'new' circuits with an eye to dealing with the old leaky circuits in the future. Thanks for the comments.

Jonathan