Can you have two downstairs ring final circuits?

[PaulCornell'sTeeth]

I've recently built a server/network rack into the corner of one of my downstairs rooms. It is currently powered through the standard downstairs final but I would like to move everything in the rack over to its own ring in order to isolate it from the general house electrics and be able to keep the network live when I switch the downstairs ring off to do other work etc.

As the rack resides in a room where everything else will be powered from the downstairs ring this will result in a room with two rings active in it and some sockets that will not isolate when the downstairs ring is switched off.

Is this acceptable according to the standard regs? Is it advisable? My worry is that the next person comes along to do some work on those sockets, not realising they're on another ring and thinking they're isolated with the other sockets in the room.

What options do I have if this is not a recommended solution?

Thank you.

 

[sparkwright]

Yes, if you label the consumer unit accordingly, it's ok.

 

[oldbutnotdead]

You'd be better putting a radial in to a single point (FCU or DP isolator) at your Comms rack and do any multiplugging either with 13A blocks in the rack or (much better) IEC distribution units, obvs via the UPS.
If there are no 'spare' sockets on this dedicated radial it'll prevent the kids/wife/cleaners killing the normal RFC with a dodgy appliance and then repeating the trick with your dedicated supply. Which should of course be on its own RCBO in the CU ..

 

[ericmark]

I think my house has 4 ring finals, one for upper kitchen, one for bottom floor, one for front of house top two floors, and one for rear of house top two floors. And this is not unusual. In the main we try to arrange a number of ring finals so each one takes a fair proportion of the load.

Splitting side to side rather than up/down means more even load, and also less cable so less volt drop and better earth loop impedance. However around 2008 there was a thought that we could get away with two RCD's as long and lights and sockets not on same RCD in any room. There is no rule to say that, but it seems designers felt they could get away with that.

Today the cost of all RCBO is very little more to twin RCD and so this penny pinching exercise has in the main stopped. But the lights are hard to split side to side, so the sockets were split up/down to match the way the lights were split.

However it means in real terms you always test, in an ideal world in the consumer unit there would be a plan showing all cable runs, but we don't live in an ideal world.

 

[JohnW2]

In the main we try to arrange a number of ring finals so each one takes a fair proportion of the load. Splitting side to side rather than up/down means more even load, and also less cable so less volt drop and better earth loop impedance.

In reality, all that really matters is that every final circuit has an adequate capacity to serve the loads it is likely to be asked to supply - there's nothing wrong with having some circuits which rarely, if ever, carry an appreciable proportion of the total load (as usually happens with the very common up/down split) - I certainly have plenty of those in my house, even though no final circuit serves more than one floor.

Kind Regards, John

 

[ericmark]

In reality, all that really matters is

I would say you can split the home to suit your needs, anyone working on the system should test for dead.

 

[JohnW2]

I would say you can split the home to suit your needs, anyone working on the system should test for dead.

Indeed - that's essentially what I was saying - i.e. that there is no electrical reason for spreading/balancing loads across circuits (which is what you suggested), provided that no circuit is likely to be loaded beyond its capacity.

Whilst there is a limit to how far one can/should design in anticipation of the behaviour of the foolish/idiots, but it makes sense to avoid, whenever possible, sockets and lights in one room being on more than one circuit. However, there are always going to be some lights fed via focus from 'sockets' circuits and, for example, sockets in a kitchen fed from a 'cooker' circuit.

Kind Regards, John

 

[ericmark]

it makes sense to avoid, whenever possible, sockets and lights in one room being on more than one circuit.

I would say the reverse, however I think there is a comprehension problem rather than electrical here? Also what forms a circuit.

I would say a RCD does form a circuit, it is an over current device, but current differential not total current, so the MCB's form sub circuits, and any FCU a further sub circuit. But depending if looking at IET or government definitions it varies on meaning.

However what ever name it does not really matter, we want the lights designed in a way so any problem with sockets will not plunge one into darkness. However we as ever must do a risk assessment, so very likely with a 300 mA RCD it will not trip very often, and to have a TT supply with a single 300 mA RCD is not a problem, and even with a 30 mA in a narrow boat or caravan with battery backed lighting and very little area served double 30 mA RCD's in series is unlikely to be a problem.

Having sockets in a room from different phases needs to be avoided, however my kitchen has a socket from cooker supply and sockets from kitchen ring final and this is common, so really one can expect sockets in one room to be from different overload devices, my old house the cistern was removed, and the original feed to the immersion heater was made into a socket, including the isolator down stairs in kitchen, my kitchen was extended so half was also on a different ring final, so my old kitchen had 4 socket circuits, and this is not unusual.

In fact it was very handy as also from 2 separate RCD's so I could swap freezer supplies if there was a problem.

There are dangers we try to avoid with our risk assessment, for example occupants needing to run extension leads up or down stairs to keep essential equipment running when one circuit fails. Also I was lucky that the freezers in last house were on different RCD's as when one failed I only lost one freezer full of food.

Very early I learn to test for dead, empty house, so switched off main isolator, lucky was using a neon screwdriver, the socket I came to move was fed from next door, so since that always test for dead. This house again turned off main isolator, found whole of main house still had power, there was a fuse box hidden in the space between original ceiling and false ceiling.

So really no reason why every socket should not be on it's own circuit, in fact pre-war that was often the case.

 

[JohnW2]

I would say the reverse, however I think there is a comprehension problem rather than electrical here?

It depends upon what is being considered. From the point-of-view of "user convenience", it is obviously prefereable to have sockets on different circuits within a room (in case one circuit 'fails'). However, from the point-of-view of misunderstandings as regards 'what was dead'(when doing any work on the installation), it's equally obviously 'safer' for all sockets in a room to be on the same circuit - so that there is a 'single point of isolation' for all of them. Judgement has, in any particular situation, got to decide on the balance between those two points-of-view.

Also what forms a circuit. .... I would say a RCD does form a circuit, it is an over current device, but current differential not total current ...

With respect, and as has often been discussed, that is a silly argument that I doubt that (m)any people other than yourself would subscribe to

... we want the lights designed in a way so any problem with sockets will not plunge one into darkness.

As I always say, if one is concerned about people "being plunged into darkness", then the only solution is (battery powered) 'emergency lighting' - since, as I also always say, at least in my house "being plunged into darkness" is far more commonly due to a power cut than to the opeation of any protective device (or other problem) within my installation.

Having sockets in a room from different phases needs to be avoided ...

Why? I think there used to be regs about this (e.g. proximity of sockets on different phases), but it's never made a lot of sense to me.

Kind Regards, John

 

[ericmark]

I think being plunged into darkness due to general power cut is very different to being plunged into darkness because a fault which may have given you a shock as occurred. If some thing has given you a shock the last thing you want is lights to fail as well.

 

[JohnW2]

I think being plunged into darkness due to general power cut is very different to being plunged into darkness because a fault which may have given you a shock as occurred. If some thing has given you a shock the last thing you want is lights to fail as well.

Whilst I do not disagree with your second sentence, at least speaking personally, it is decades since I last experienced a significant shock (probably before the days of RCDs!) yet we must have, on average, at least a couple of 'power cuts' (usually very brief) every month.

In any event, I would suggest that the vast majority (I would actually say "almost all") RCD trips are NOT due to person experiencing an electric shock.

However, the person 'plunged into darkness' (even if due to a power cut) whilst up a stepladder or whilst holding a pan full of hot oil/whatever, may not totally agree with the implications of your first sentence!

Kind Regards, John