Would it have complied to use 2 only RCD's in my house?

[ericmark]

I have all RCBO's so not an issue in my house, however neighbours house when new consumer unit fitted had just 2 RCD's. So does this comply when both lights and sockets split into two circuits with sockets split front back and lights split up down?

To my mind it would need at least 4 RCD's so that losing a RCD would not result in both lights and sockets lost in the same room.

Also I have seen houses with 2 and 5 amp sockets for standard lamps and table lamps, considering idea is to have some lights still working if one RCD trips, should the standard and table lamps be from same RCD as ceiling lights?

 

[DetlefSchmitz]

I think you are overthinking it. Most houses probably now have 2 RCDs. As John once said: what do you do when there's a power cut?

 

[securespark]

The usual convention is to have one floor's lighting on the same RCD as the other floor's sockets, so if the lights go out, you have at least got table lamps.

 

[securespark]

Further, you could wire the landing on the GF lighting feed and a conveniently placed GF light on the FF feed. If the first floor lights go out, the landing light is still on, giving light on the stairs, conversely, if the ground floor lights go out, the chosen GF light is still on.

I have wired this way in a house occupied by vulnerable users.

 

[ericmark]

If the power is cut due to some thing out side the house, then clearly street lights and all house lights other than battery backed fail, I have a battery backed light on the stairs so I will not trip on the stuff wife leaves on the stairs.

However where the power cut is due to some thing in side the house, then some one may be injured or startled at the same time, this is the least opportune time to lose lights.

My battery backed light for stairs is also PIR controlled so if just a lighting circuit is lost, it will still light with movement, as plugged into a socket outlet.

I consider the danger other than stairs is not that high when loosing power, so else where in the house there is no battery backed lights, and should I be plunged into darkness I can likely shuffle my way to some where safe to wait for lights to return. However if for example getting stuck toast out of toaster the person gets a shock, then they are already disorientated, so to be plunged into darkness as well there is a very real danger of them touching some thing hot, or tripping over some thing.

So we have

314.1 Every installation shall be divided into circuits, as necessary, to:

(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit

I know a circuit is defined as

An assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device(s).

but a RCD does trip when the current leakage goes over a pre-set limit, so it is debate-able if a RCD forms a circuit, and it is clear that not including RCD as forming a circuit when considering 314.1 is being rather blinkered considering the explanation as to why it should be divided.

I can see with a caravan that only 1 RCD on the whole supply is acceptable, one as lights are normally battery backed, and two it is such a small area with windows all around, and with a two up, two down where the lights and sockets are split so lights and sockets in every room are always on separate RCD's considering for years the 4 fuse fuse box was used so never any more than 4 circuits, then two RCD's are likely ample.

However as we look are larger properties, then very quickly we reach a stage when capacitive and inductive linking can result in the differential between in coming and outgoing power increasing, add a few interference reduction networks, and we are sailing close to the wind with a 30 mA RCD, so having just two means both more likely to trip, and also that some areas will end up with the same RCD controlling power and lights.

The easy cure would be one RCD for lights, and one RCD for power, however should a fault happen, you want to keep items like freezers running, clearly without an extension lead running up or down stairs, so splitting sockets front/back or side to side is far better than up/down and also means the earth loop impedance is reduced as cable needed is less in most homes.

However for lighting with use of ceiling roses as junction boxes, up/down is a better split for keeping the ELI low. So it is common to find the home split up/down for lights and side to side for sockets. Pre-RCD that made sense.

So this house 13 rooms or areas, when I bought it, 4 rooms had RCD protection for sockets, rest of house no RCD protection. Needed to do something as fuse box access was through a hole in false ceiling, 13 circuits however I split them, impossible to use 2 RCD's and have lights not on same RCD as sockets is some rooms, fact I need to leave house and walk down a set of steps and re-enter house to reset any trip, and even a 16 slot wide CU is big, add just two RCD's and 20 slot required so it seemed clear RCBO was the way forward. But I know the risk, and so I am doing my own risk assessment.

However with neighbours houses, they are guided by an electrician, and I question if using 2 RCD's for whole house complies. To my mind there is a danger forcing old people to leave the house and walk down steps at night in the dark to reset power which they have to do to get heating, adding two RCD's makes the home more not less dangerous when a failure of one RCD means the home becomes uninhabitable. I can if I wish plug in a oil filled radiator and wait until morning, there is a way around any RCBO tripping, and should I need to reset the one running central heating, at least there are outside lights so I can see my way down to where the CU is located.

Adding a two RCD only CU would make this house, and most houses in the street into a death trap.

 

[John D v2.0]

Further, you could wire the landing on the GF lighting feed and a conveniently placed GF light on the FF feed. If the first floor lights go out, the landing light is still on, giving light on the stairs, conversely, if the ground floor lights go out, the chosen GF light is still on.

Sounds like a good idea, i did ours with GF circuit, FF circuit, and a separate rcbo circuit for hall/stairs/landing/understairs. That was mostly to make the two way switching simpler, but there is a safety benefit.
I think the most sensible redundant system is the torch on my phone though, if the lights go off i just get my phone out and use that.

 

[JohnW2]

I think you are overthinking it. Most houses probably now have 2 RCDs. As John once said: what do you do when there's a power cut?

Once? I'm repeatedly saying it, not the least because, for me, brief power cuts are far more common causes of my house being 'plunged into darkness' than are RCD trips. ... and even a very brief period of 'being plumnged into darkness' is long enough for one to drop the pan of boiling oil or fall off the ladder/stairs etc.!

Kind Regards, John

 

[JohnW2]

Further, you could wire the landing on the GF lighting feed and a conveniently placed GF light on the FF feed. If the first floor lights go out, the landing light is still on, giving light on the stairs, conversely, if the ground floor lights go out, the chosen GF light is still on.

Indeed - or, dare I suggest, run at least one light on each floor off that floor's sockets circuit (which ought to be on a different RCD), or maybe some other 'different-RCD' circuit (cooker, shower or whatever), via an appropriate FCU.

I have wired this way in a house occupied by vulnerable users.

I have functionally similar arrangements, even though I don't yet feel particularly vulnerable. Mind you, per what I've recently written, I can't really remember when I last lost a lighting circuit because of an RCD trip (probably a year or three ago), but we've already had a couple of power cuts (both <30 seconds duration) since Christmas.

Kind Regards, John

 

[securespark]

Agreed. If your supply suffers frequent interruption, it makes sense.

 

[ericmark]

I have one of these

at top of stairs, it is enough to remove danger in a power cut when near or on stairs, however not sure how long it lasts, and to reset a RCD must leave the house and walk down steps to granny flat under house, which when wet are a little slimy.

As an installer they could fit emergency lights of course, but unless emergency lights are fitted, I question is "Every installation shall be divided into circuits, as necessary, to: (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit." being satisfied. Clearly the writers of BS7671 feel measures are required to stop circuits being lost due to some thing on that circuit causing the trips to open.

I would say every house I have lived in we get more failures due to RCD opening than a MCB opening so in many ways it needs more circuits formed with RCD's than MCB's to reduce failures, with many times the RCD will open with no apparent cause.

With a incoming mains failure often all one can do is weight, it will return without you needing to go outside or even walk around the house, I know there are RCD's that auto reset however I am told not permitted for household use, and much more expensive so really for things like unattended de-watering pumps.

 

[JohnW2]

Agreed. If your supply suffers frequent interruption, it makes sense.

The frequent (usually very brief) interruptions to my supply are probably a fairly unusual phenomenon (I suspect related to the predominance of overhead supplies in my area, which seem particularly sensitive to lightning activity within miles!) but there is nothing about my house or its electrical installation which makes me any less likely to suffer RCD trips than anyone else - and such trips really are an extremely rare occurrence for me (particularly given that I live with around a dozen RCDs).

I therefore cannot help but wonder whether we (and arguably the regs) get unnecessarily excited/concerned about RCD trips.

Kind Regards, John

 

[JohnW2]

... unless emergency lights are fitted, I question is "Every installation shall be divided into circuits, as necessary, to: (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit." being satisfied. Clearly the writers of BS7671 feel measures are required to stop circuits being lost due to some thing on that circuit causing the trips to open.

As I keep saying, failure can result (far more commonly, in my personal case) from a power cut as well as from an RCD trip - so, if one takes your view, then I presume you are right in saying that that reg can only be satisfied by the installation of emergency lights.

However, the reg is far from specifically prescriptive. If they wanted to say that every installation must have emergency lights, they could have said so - but they don't. Instead they talk about "taking into account" the danger that may arise from the failure of a lighting circuit - which would seem to leave the designer with a lot of scope for judgement and discretion.

Kind Regards, John

 

[John D v2.0]

I therefore cannot help but wonder whether we (and arguably the regs) get unnecessarily excited/concerned about RCD trips.

I would say we probably do, but the regs probably don't, given effectively they say the minimum is 2 RCDs.
The DNO has some kind of obligation to get the power back on quickly so full power cuts for long periods are less likely, but a home owner might not be able to get an electrician so quickly, so what we're basically saying is for 20-30 quid for a second RCD, the homeowner still keeps enough power to live sensibly in the mean time.
Maybe some people would say that few tens of pounds is not worth it, but it's kind of like an insurance.

Perhaps it should be all us electrically minded people who should save the cash and go for a single up front RCD, because we can just fix any issues by isolating the relevant circuits!

 

[JohnW2]

I would say we probably do, but the regs probably don't, given effectively they say the minimum is 2 RCDs.

Doesn't that mean that the regs, as well as 'us', probably do "get unnecessarily excited/concerned about RCD trips"?

The DNO has some kind of obligation to get the power back on quickly so full power cuts for long periods are less likely ...

Very true, but from the point-of-view of safety (rather than 'convenience'), loss of power (and hence lighting, assuming that it happens during the hours of darkness) for just 15 seconds or so could be enough to result in the postulated catastrophes involve pans of boiling oil, ladders, stairs etc - regardless of the cause of that loss of power.

Perhaps it should be all us electrically minded people who should save the cash and go for a single up front RCD, because we can just fix any issues by isolating the relevant circuits!

... but not necessarily 'totally easily' in the case of N-E faults.

I have to say that, for reasons I've often discussed, I would personally be pretty comfortable with no RCDs at all. That's what I (and most other people of my vintage) lived with for the first 3+ decades of my life - and during the subsequent 3+ decades, during which I have 'enjoyed' RCD protection, I can't really think of any RCD trip I've experienced which resulted from a fault which would have represented a significant risk to life, health or property in the absence of RCDs. However, as BAS often used to point out, I could say the same about the car seat belts I've been 'religiously' wearing (since long before I was 'required' so to do) for around 50 years, which have so far not saved me from any significant harm.

Kind Regards, John

 

[securespark]

I live with around a dozen RCDs

Does that make getting into the bathroom in the morning a pain?