10A MCB for 1.5mm radial to sockets?

[1Justin]

CU job for a customer on a bit of a budget so little room for alterations.

Part of the job, I find a small single garage conversion to ground floor bedroom (ie a small room), converted in 1980’s. Found to have it's four sockets supplied via 1.5mm ring.

Anyhow, reconnecting into new CU, I measure a low insulation resistance on one jump of the ring. I have isolated that part, and converted remaining circuit into two radials, (IR measures up OK now), still using the existing 1.5mm, and fitted new CU with 10A MCB with label “10A Max”, and will also note it in EIC. Customer will never require much current in there since it's bedside lamps and a computer, and it's only the one little room.

Does a radial to sockets on 10A MCB in 1.5mm classify as “Departure form BS7871” as far as EIC is concerned? I can’t find anything which specifically says this can’t be done. I will be recording ref method A for the ex cables, hence 10A max.

 

[Guest55]

im gonna jump in with its fine before all the hand-wringers turn up lol.
and because the EIC only covers your work , not the existing wiring , no need to record as a departure
;-)

 

[kingeri]

Whilst not a standard circuit, if it is safe and complies with the regs, then I can`t see an issue. 1.5mm2 is the minimum for power circuits. It is not a departure unless you can find a reason for it not being compliant.

 

[Harryb]

Agree with above responses breaker is rated appropriately for CCC of cable. Note it down as irregular but not a deviation

 

[Guest55]

the departures section only covers the parts of your own work that has been designed / selected with methods outside bs7671 , its not to record defects already present.

 

[1Justin]

Thanks, It's nice not to feel like a deviant.

 

[Darkwood]

Need to know reference method and approx length of the 1.5 and is it a single or twin socket on the end of the 1.5mm.

What im getting at here is if its in a stud wall in insulation and not touching either surface then this set-up can be a fire hazard although as you state its an old conversion and unlikely to be this method in the eighties.

 

[kingeri]

I am going from memory here, but ccc of 1.5mm is 19.5amps ref. method C so even if this is halved it would be fine if in insulation, bearing in mind it is wired as a ring and is on a 10amp breaker. Don't know if I need it but, tin hat on just in case.

Edit: Just re-read OP and seen he has split the ring into two radials. Ignore what I just posted! Would not be OK in insulation.

P.S. Dont drink and post.

 

[Darkwood]

Yes just had a thought ref method 103 would make it 10amps now with a 10amp mcb on it it is possible to put a small overload on the circuit for a long duration... should never assume its only going to have small items plugged in what if the boiler failed and they plugged in a 3kw heater in at approx 13amps which is less then 1.45x mcb rating and below its trip threshold on overload.
Now dont we have a reg' that says all circuits should be designed to ensure a small overload is not likely for a long duration.

Yes probably not an issue for the OP but food for thought next time he comes across this set-up and as he has altered the circuit he becomes responsible for it.

 

[Knobhead]

Unconventional YES!

Is it wrong? I can’t see a reason why.

 

[AndrewMgan1976]

Maybe it was originally for 5A lighting sockets and these have been changed through time.

 

[1Justin]

Hi Andrew,
The wiring was DIY'd in the 1980's. I found a kitchen sockets wired as an interesting set of branching spurs also in 1.5. - Also needs to be got rid of as soon as the owner clears the place out.
The kitchen is genuinely ref method C, so I downgraded it to 16A. (The garage conversion was conduited in foam insulation, somewhere between 102 and A, hence 10A).

 

[Outspoken]

CU job for a customer on a bit of a budget so little room for alterations.

Part of the job, I find a small single garage conversion to ground floor bedroom (ie a small room), converted in 1980’s. Found to have it's four sockets supplied via 1.5mm ring.

Anyhow, reconnecting into new CU, I measure a low insulation resistance on one jump of the ring. I have isolated that part, and converted remaining circuit into two radials, (IR measures up OK now), still using the existing 1.5mm, and fitted new CU with 10A MCB with label “10A Max”, and will also note it in EIC. Customer will never require much current in there since it's bedside lamps and a computer, and it's only the one little room.

Does a radial to sockets on 10A MCB in 1.5mm classify as “Departure form BS7871” as far as EIC is concerned? I can’t find anything which specifically says this can’t be done. I will be recording ref method A for the ex cables, hence 10A max.

In essence OK so long as the circuit protective conductor is at least a 1.0mm², and is the circuit afforded the additional protection of an RCD? I would suggest you take a read of Reg 433.1 and Chapter 15 of BS7671 as these are the sections that cover radials and rings from memory.