Circuit Dilemma...

[essexjohn76]

I have just begun to explore, and map out the electrics in a house we have bought. These are the circuits attached to the CU:

1. 15A - unused
2. 15A - attached to only 1 socket next to CU
3. 30A - cooker
4. 45A-downstairs power shower
5. 15A - ALL LIGHTS – whole house including 1 in loft and in Ground
floor utility room & lean-to. (total 14 lights). Also exhaust fans in DS
& US bathrooms, and scale inhibitor in DS bathroom.
6. 30A - ALL PLUG SOCKETS. Including supply to summer house, lean-
to, and loft power socket. + BOILER. Covering an area of about 100m2

Firstly, I am concerned about the number of lights on the 1 lighting circuit. Although I am also a little confused as, from all I have seen, lighting circuits are usually only 4/5A, whereas ours is 15A. Does this mean I don’t have to worry about only having 12 x 100W lights on the circuit? If I use energy-saver bulbs (which are only 20W each) does this solve the problem?

Secondly, the 30A circuit supplying all sockets + the boiler is very close to it’s maximum area allowance (and would exceed it with 1 simple spur socket I would like to add upstairs). I plan to have an electrician get rid of all of the old and poorly installed summer house wiring, as well as the downstairs power shower (this 2nd bathroom is to be converted to utility room). I then thought he could use the existing 45A circuit (formerly for the power shower) to supply power to the summer house and garden. Does that sound feasible?

 

[holmslaw]

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[sparkyspike]

There's nothing wrong with 15A lighting circuits as long as the wiring is 1.5mm.

Trouble is though, you will have derating factors such as the length and installation method of the cable and the fact that you are using BS3036 fuses. This will limit your cable to 10A, if it is 1.5mm. You haven't said how many lights are on your circuit, so don't know if you're overloaded. If you have less than 24 lighting outlets, you should be ok for a 10A fuse.

 

[GaryMo]

There's nothing wrong with 15A lighting circuits as long as the wiring is 1.5mm.

Trouble is though, you will have derating factors such as the installation method of the cable and the fact that you are using BS3036 fuses.

My thoughts exactly.

The design current of the circuit should be less than or equal to the rating of the protective device which should be less than or equal to the current carrying capacity of the conductors in their particular installation conditions.

 

[holmslaw]

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[essexjohn76]

we have rewireable fuses

 

[GaryMo]

So, without any other correction factors, all cabling on your lighting circuit must be capable of carrying 20.7A (15/0.725) which is greater than the current carrying capacity of 1.5mm t&e even when using reference method C (clipped direct).

 

[holmslaw]

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[GaryMo]

Sorry I assumed that you did'nt have rewireable fuses.

Or thermal insulation which may or may not be surrounding cables.
You can't really assume when giving out advice which could potentially create a fire risk.

 

[holmslaw]

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[holmslaw]

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[GaryMo]

Please correct me then after reading Section 5.1 (5.1.1) p256 BS7671:2008

I would like to add that when I said all cables were required to carry a minimum (without any other de-rating factors considered apart from Cc of 0.725) of 20.7A I wasn't including pendant flexes (just in case you're feeling a little anal).

 

[RF Lighting]

That's it holmslaw, just bludgeon you way through, without a thought to ask for more information.

Would a 15A fuse be acceptable if there were SES lampholders present on the cicuit, or 5A / 2A table lamp sockets?

How many houses have you worked in that is running on rewireable fuses have anything other than 1.0mm² (or imperial equivalent) for the lighting?

 

[essexjohn76]

we have rewireable fuses

Then you must derate as advised by sparkyspike. Sorry I assumed that you did'nt have rewireable fuses.

Because you have rewireable fuses this means that your wiring is over 40 years old. You should consider a complete rewire.

i don't think we need a complete re-wire (but i could be wrong!). i did have the place checked by an electrician before we bought it.
although we do have the old-fashioned BS3036 fuses, we definitely do not have wiring over 40 years old.
there is much evidence of rewiring, and i haven't as yet uncovered any evidence of older-style rubber-sheathed cables. the lighting circuit appears to be all on 1.5mm, and the socket circuit on 2.5mm cable.

 

[essexjohn76]

That's it holmslaw, just bludgeon you way through, without a thought to ask for more information.

Would a 15A fuse be acceptable if there were SES lampholders present on the cicuit, or 5A / 2A table lamp sockets?

How many houses have you worked in that is running on rewireable fuses have anything other than 1.0mm² (or imperial equivalent) for the lighting?

Just to be sure - (although it really does appear to be 1.5mm cable on the lighting circuit), is there a sure-fire way to check?
there doesn't seem to be anything written on the lighting cables installed here to indicate their size. on the ones in the loft - i can clearly see:

600/1000 VOLT C.M.A (REGD) A.C.I ENGLAND

i have some new 1.5mm cable here, and it appears the same, but it's hard to be sure! anyone have a solution?