Laws, Regulations, and Conventions

[ericmark]

When wiring up a house we follow:-
Laws
Regulations
Conventions
These also vary between an original and retrospective wiring the latter for example may include fused connection units to power lighting but we would hardly use that method for an original wiring system.
In the last decade, it has been the convention to include multi lighting and power circuits and in some ways, this is linked to regulation 314, which has been clarified now to include RCD divisions.
However when moving away from the house for example regulation 708.553.1.13 it is apparent that the provision of multi RCD protection is not always required for domestic premises. However the convention suggested by the manufactures and this has the support of 134.1.1 seems to be to provide two RCD’s in a normal house.
Again the manufactures seem to suggest that the lights from one area should be combined with the power outlets to another area.
But I can’t find any Laws or Regulations other than following manufactures recommendations to say we must split either the lighting or the power in domestic premises. Neither can I see anything which says when using duel RCD’s that lights in one area can be combined with power from another area.
With all the Part regulations M, L, P etc. It is likely that the requirement is not part of the wiring regulations but included in one of the many other laws and regulations which cover the supply of electricity within a dwelling.
But reading 314.1 (iii) I would have thought combining lighting with sockets would have broken the regulation? Unless some form of emergency lighting is included.
Other than volt drop I can’t see any regulation which says I must have two lighting circuits and with the move to low current lighting devices with non interchangeable holders so the old tungsten lights can no longer be fitted I can see very little point in splitting lighting between the floors. If each adjoining room and an alternating supply so failure of one supply would not plunge a whole area into darkness then I could see some point.
The same applies to splitting the power circuits. Separate kitchen supply makes sense but to split between floors has very little benefit as the two floors tend to be used at different times of day. A side to side split would make more sense both for loading and cable length.
However once one leaves convention danger is introduced because those working on the system tend to assume it will follow convention and may take short cuts in health and safety procedure and end up working on a live circuit.

So question:-
1) Is there some black and white rule I have missed or is the method of splitting circuits only controlled by convention?
2) Assuming I have not missed some black and white rules what are peoples thoughts as to using non conventional splits, and/or single supplies for all lights. The latter maybe with, or without, emergency lighting units, so maybe two answers are required.

 

[bernardgreen]

All lights on single RCD is not good based on the need to have lights in at least some rooms and on the stairs when an incident has occured that tripped some of the lighting.

Whether or not an automatic emergency light is installed splitting lights onto two separate RCDs is sensible.

On the subject of emergency lights if there is one in or near the kitchen then plug it into a socket (or FCU ) on the same circuit as the fridge freezer. If it lights then it is time to check the power to the fridge freezer.

Regulations change.

28 years ago we self built this house. To have two RCDs after the meter was forbidden and the meter installer refused to install the meter when the supply was bought to the site. I explained to his desk bound boss that one RCD was for the caravan and one for the building site. I pointed out that if there was only one RCD then any accident on site could leave us without lights in the caravan when first aid or a 999 call was needed. Miserable faced meter fitter returned the next day and fitted the meter. He would have a fit now, there are four.

Think and plan for safety if any RCD tripping event happens.

Two RCDs are sensible.

Power in a room one RCD and the lights in that room on the other RCD.
Especially for the kitchen where a toppled jug kettle could both scald the user and soak the base and thus trip the RCD. Scalded and then left in sudden darkness will delay the application of cold water to the injury.

Lights at the top of the stairs on one RCD, lights at the bottom on the other RCD.

Lights on each floor split between the two RCD so there is always some working light on each floor.

 

[ericmark]

My house was not planned as well as yours. I realised I needed more circuits so fitted second consumer unit and when my son started playing with electricity I fitted two RCD's one to each consumer unit. I also fitted emergency lights in garage where the consumer unit is located and top of open plan stair case. All well before any regulations required them.

But I have seen one post where because the lights were on one RCD and Power on another the guy wanted to fail it.

I have also seen posts where it has been found the lights when split have ending up causing a borrowed neutral and the easy method is of course to put both lighting circuits back to being controlled by one MCB and RCD.

I think in the main we would all like to see RCBO on all circuits but often this is not possible.

As a result we need to make a snap decision as to what route to take. Often then in hind sight we realise this was not the best option.

What I hope is people will consider the options and talk about them here so when we do need to make the decision we already have the options to hand.

As yet I can find no rule that says supplying a small house as with a caravan with one power and one lighting MCB of a single RCD breaks any rules although it is not what I would suggest doing. There are some houses which are no bigger than caravans.

If there is some hard and fast rule that says we can't do it then we need to know it. As some one will at some point ask us to do it.

Lets face it far easier to say that does not comply with BS7671 than to try to persuade someone its not a good idea. And I like the easy life.