New CU, suit you Sir

[Risteard]

added 10 x 50W halogen down lights onto 1 of the lighting rings effectively doubling its load to 1415W

It also ignores diversity, as did his nonsense about voltage drop. (Incidentally, he was also wrong to claim that above 3% isn't allowable on a lighting circuit - he referenced an INFORMATIVE appendix.)

In fact he is an absolute pillock.

 

[ban-all-sheds]

Put your money where your mouth is, Mr Arrogant and post a picture of your work.

And all of the test results, and an EIC signed by someone credible, and a Building Regulations compliance certificate.

 

[scousespark]

2) In the main reason for not using 10A MCB with lights is the ceiling rose is only rated 5A.

That's not true. The breaker is sized for the load, not the rating of individual points in the circuit. In the majority of cases 6A is adequate.

 

[Taylortwocities]

The breaker is sized for the load

THAT is not true!!

We did this a while ago. The breaker is primarily there to protect the cable.

 

[bernardgreen]

The breaker is there to prevent :-

(1) the load taking more current that the cable and any connections can safely carry for a prolonged period
(2) the current due to a fault flowing long enough to cause the overloaded cable and connections from becoming hot enough to create a fire

 

[ericmark]

2) In the main reason for not using 10A MCB with lights is the ceiling rose is only rated 5A.

That's not true. The breaker is sized for the load, not the rating of individual points in the circuit. In the majority of cases 6A is adequate.

BS7671:2008 states we can use up to a 16A supply for lighting. But items within the circuit may not be able to take that load.
The bulb holder is often rated at 2A however since the maximum size of bulb will only draw in excess of 2A when there is a fault with the bulb this is not a problem.
Fluorescent fittings often have a fuse inside the fitting so being supplied with 16A again is not a problem.
But the ceiling rose is not an end of line item like the bulb holder or fluorescent fitting it is used as a junction box so the first ceiling rose could take the full lighting load what ever that is up to the point when the supply fuse of MCB opens. I am sure a ceiling rose can take well over 6A, however the manufacturer has rated it at 6A and until amendment 3 we had to follow the manufacturers recommendations. So to have a lighting circuit with all fluorescent fitting until the last one which is a ceiling rose then 16A supply would be OK. But reverse that and have a ceiling rose then a load of fluorescent fittings then it would not be OK.

We are told to consider every lamp as being 100W in the on site guide, however again for fittings of a design where large bulbs can't be fitted then that is not really required. The GU10 has a max of 75W although in the main 50W is the largest found, and the special with the dimple to take only energy saving bulbs I would consider is unlikely to exceed 10W. Same as using the special BA22d lamp socket with three lugs likely 30W is the largest bulb. But with a standard house with 3 or 4 down stair rooms we should be looking at no more than 500W or around 2A, the same with up-stairs 500W is again around 2A so whole house only needs around 4A. So a 5A fuse or 6A MCB is ample.

However some people do go daft, I have seen 10 x GU10 lamps in one room, no real reason to use so many, but people do daft things, then we are looking at 500W for just one room, when this was done then as one might expect the whole house raises above the 6A and some method is required to stop the 6A MCB from tripping, common method was to split up and down stairs but this can only be done when the two way wiring uses three core and earth cable.

With the introduction of RCD protection some method was required to ensure the lights don't fail with the power outlets, and this further complicated the wiring and also often highlighted pass errors where borrowed neutrals resulted in the splitting of the lights, it left a number of methods from RF switching to re-combining upper and lower floors.

So the electrician has to decide how, there is no clear cut method, using a RCBO for all lights, or a RCBO for all sockets would in real terms do the same thing, it means lost of one circuit will not effect the other. In the main the other circuits don't matter in the same way, lights is a safety circuit the loss of lights can result in danger, and the socket circuits are likely to fail far more than any other circuit in the house, so as long as them two are split the risk is low enough to be acceptable.

On a personal note I used a 16A MCB for an outside lamp, an Ikea bulb was fitted 6W CFL and when it failed it went short circuit, the 16A MCB did trip as it should but before it tripped enough current flowed to cause the bulb to weld into the holder, so whole lamp needed renewing not just the bulb, I have learnt my lesson and lights have just a 6A MCB, OK it may have still welded but likely hood would be less, so don't care what rules allow, I always use 6A MCB for lights. I also use emergency lights on stair well so does not cause danger if lights trip.

 

[scousespark]

The breaker is sized for the load

THAT is not true!!

We did this a while ago. The breaker is primarily there to protect the cable.

I never mentioned the reason we have breakers, just that the sizing calculation is based on the load and that the rating of a ceiling rose is not a factor in this calculation.

 

[ban-all-sheds]

Maybe Iz should apply to all current carrying components of the circuit, not just the cables.