2 bed flat - how should circuits be split?

[benjiman]

Hi All,

Got a 2 bed flat, with lounge, kitchen and bathroom.

Currently there is only one circuit for sockets to cover both bedrooms and the lounge on a 32a mcb. Is this adequate or should they all be seperate?

The lights for the bathroom, lounge and both bedrooms are also on one mcb.

The kitchen has its own mcb for sockets and seperate lighting mcb.

What should the ideal split be for a 2 bed flat for both sockets and lighting?

 

[sparkwright]

Sounds good enough as it is.

 

[ericmark]

For years 3 or 4 circuits was the norm. 32 amp for cooker if electric, 32 amp ring final, 16 amp immersion heater if fitted, 5 or 6 amp lights. No reason why a small flat should have more than 2 circuits. Only real reason for 2 is lights incorporating B15. B22. E14. E27 or E40 lampholders are limited to 16 amp.

The arrival of the RCD and the problems with one fault causing multi circuits to fail means many houses are today limited to 2 circuits anyway, they may be then sub divided using MCB's but the rules say:-

Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.

So two RCD's it seems is acceptable so also two MCB's must also be acceptable.

 

[JohnW2]

... Only real reason for 2 is lights incorporating B15. B22. E14. E27 or E40 lampholders are limited to 16 amp.

I'm not sure I really understand that. Even with incandescent lighting in a large house, it's surely unlikely that the total lighting load would have got anywhere near 16A (best part of 4,000 W), would it?

... The arrival of the RCD and the problems with one fault causing multi circuits to fail means many houses are today limited to 2 circuits anyway, they may be then sub divided using MCB's but the rules say: .... - So two RCD's it seems is acceptable so also two MCB's must also be acceptable.

I don't really understand that, either - could you perhaps clarify what you are saying? The OP has not mentioned RCD(s), so we're nor sure whether ther is one or not

It would certainly seem (to me) that to 'split circuits' in a 2-bed flat, just to satisfy a perceived regulatory requirement, would probably be a bit silly.

Kind Regards, John

 

[333rocky333]

I'm not sure I really understand that. Even with incandescent lighting in a large house, it's surely unlikely that the total lighting load would have got anywhere near 16A (best part of 4,000 W), would it?

That reg has changed now to 16amp, back in the 16th edition B15 and E14 lampholders were only allowed on maximum 6 amp Mcbs, so a house back then with chandeliers fitted with 60watt lamps, would i quess be limited to 20 lamps per circuit

 

[JohnW2]

That reg has changed now to 16amp, back in the 16th edition B15 and E14 lampholders were only allowed on maximum 6 amp Mcbs, so a house back then with chandeliers fitted with 60watt lamps, would i quess be limited to 20 lamps per circuit

Yes, but eric presumably knows that, since he was talking about "the 16A limit" and seemingly was offering that as 'the reason' for needing two lighting circuits - which made little sense to me ....

... and, in any event, I would not have thought that '20 x 60W lamps, in chandeliers' was something one came across in any 'normal house' even back then, was it?

Kind Regards, John

 

[plugwash]

Hi All,

Got a 2 bed flat, with lounge, kitchen and bathroom.

Currently there is only one circuit for sockets to cover both bedrooms and the lounge on a 32a mcb. Is this adequate or should they all be seperate?

Seems perfectly normal to me. Indeed I would say it's generous compared to many flats, the 2 bed flat I lived in before my current place only had one lighting circuit and one socket circuit (plus shower and cooker circuits) for the whole place.

Have you been watching/reading American content? The combination of the lower voltage and the lack of fused plugs means that each socket circuit over there provides about three times less power than ours do, so they need a lot more of them (OTOH they don't tend to have separate lighting circuits like we do).

 

[plugwash]

... and, in any event, I would not have thought that '20 x 60W lamps, in chandeliers' was something one came across in any 'normal house' even back then, was it?

Probably not, but when I count up the fittings fed off the lighting circuits in my parents 4 bedroom house I get

3 fittings (two single bulb, one circular flourescent) in the downstairs extension.
1 flourescent strip in the kitchen
2 fittings with 3 bulbs each in the lounge"
1 circular flourescent fitting in the dining room
1 fitting in the downstairs toilet, it's currently a LED fitting, but it was until-recently a flourescent strip so lets count it as that.
1 single bulb fitting in the hall
1 single bulb fitting each in three of the bedrooms
1 flourescent strip in the fourth bedroom
2 single bulb fittings on the landing
1 single bulb fitting in each of the two bathrooms

So that is 5 fluorescent strip/circular fittings, lets say 60W each for those for a total of 300W.
2 three-bulb fittings, if they were fitted with 60W bulbs that would be a total of 360W if they were fitted with 40W bulbs then 240W
10 single bulb fittings, if they were fitted with 100W bulbs that would be a total of 1000W, if they were fitted with 60W bulbs than 600W

So with incandescents in all the fittings that took traditional bulbs, that would be 1140W to 1660W depending on what bulbs were fitted at any given time, granted probably closer to the lower than the higher end of that range (and I suspect not all the single bulb fittings were rated for 100W bulbs). And I wouldn't regard my parents as especially posh, only a handful of rooms had more than one fitting.

So in the pre CFL/LED era I would say a single 5/6A circuit would be pushing it for a 4 bedroom house two was probably ample.

You can in theory go higher than 6A, but even with the SES/SBC rule removed, there are still potential difficulties. I checked two reputable brands of ceiling rose and both only listed a current rating of 6A. Cables run through lofts may also be subject to serious derating due to thermal insulation. There is also the question of manufacturers instructions on light fittings.

It does leave the question of what we should do when designing circuits now though, should we still allow the traditional 100W per point or should we allow lower based on the efficiency of modern lights. If so how much lower?

 

[JohnW2]

Probably not, but when I count up the fittings fed off the lighting circuits in my parents 4 bedroom house I get ..... So that is 5 fluorescent strip/circular fittings, lets say 60W each for those for a total of 300W. 2 three-bulb fittings, if they were fitted with 60W bulbs that would be a total of 360W if they were fitted with 40W bulbs then 240W ... 10 single bulb fittings, if they were fitted with 100W bulbs that would be a total of 1000W, if they were fitted with 60W bulbs than 600W.
So with incandescents in all the fittings that took traditional bulbs, that would be 1140W to 1660W depending on what bulbs were fitted at any given time .... So in the pre CFL/LED era I would say a single 5/6A circuit would be pushing it for a 4 bedroom house two was probably ample.

Yes - but, if you want to be sensible, you need to take into account (one of the manifestations of) 'diversity'. Even if the totted up total of bulb/lamp/tube ratings were 1660W, there is no way that anything like that total would be used at the same time - I would doubt that the total 'in use' at any one time would often, if ever, get as high as the 'totted up total possible'.

You can in theory go higher than 6A, but even with the SES/SBC rule removed, there are still potential difficulties. I checked two reputable brands of ceiling rose and both only listed a current rating of 6A. Cables run through lofts may also be subject to serious derating due to thermal insulation. There is also the question of manufacturers instructions on light fittings.

There are various things that I could say about that, but I won't bother, since (in terms of the present and future) I think it's moot - since (as below) I really don't think that we now need to even consider lighting circuits >6A.

It does leave the question of what we should do when designing circuits now though, should we still allow the traditional 100W per point or should we allow lower based on the efficiency of modern lights. If so how much lower?

I think we can now forget incandescents and, in terms of domestic installations, assume that there are not going to be (m)any fluorescent tubes. On that basis, the total load on any normal domestic lighting circuit (primarily LEDs, maybe some CFLs) is not even going to be anywhere near 6A - 1,380W of LEDs would be an awful lot of light!!

I therefore don't think that there is really any design consideration in terms of the power requirements of a domestic lighting circuit - if (as we will usually do) we decided to have two or more lighting circuits, that will now be for reasons other than the power required, since one lighting circuit would almost certainly be adequate (power-wise), even in very large houses.

Mine is a very large house, much larger than your parents' one, and I hate to think how many 'lamp holders' there are - probably at least around 60, since many are fittings with 3 or 5 candle or golf ball bulbs. Almost all are now LED (with a few surviving CFLs).

If I guess that there are about 30 x 5W candle/golfball and about 30 x 12/15W bulbs, that would be at most about 600W if I had the whole lot on one circuit and all switched on simultaneously (none of which would ever happen!) - leaving plenty of spare capacity (on a single 6A circuit) for the few, only very occasionally used, fluorescent tubes (maybe even an incandescent or two!!) in cellar, storerooms, garage and workshop! In reality, I have many (all 6A) lighting circuits but, power-wise, just one circuit would be more than enough, power-wise!

Kind Regards, John

 

[winston1]

Have you been watching/reading American content? The combination of the lower voltage and the lack of fused plugs means that each socket circuit over there provides about three times less power than ours do, so they need a lot more of them (OTOH they don't tend to have separate lighting circuits like we do).

Can’t see what difference fused plugs make. US sockets are rated at 15 amps, 120 volts which equates to 1800 watts, less than our 3000 watts, but not 3 times less. Anyway most loads are very much less than this so it is irreverent. US code requires that sockets are required at a regular spacing (can’t remember what it is) around a room so that is the reason they have more.

 

[plugwash]

I said socket circuits, not individual sockets. Fused plugs allow the socket circuits to have a significantly higher current rating without compromising the overcurrent protection for the appliance flexes.

US socket circuits are normally 15A or 20A at 120V. So 1.8KW or 2.4KW

UK socket circuits are normally 20A or 32A at 230V. So 4.6KW or 7.36KW

 

[winston1]

I said socket circuits, not individual sockets.

OK, fair enough.