Is a 1.5mm twin + cpc ring main ok for two 2kW panel heaters??????

[super*spark]

I have been asked to carry out intial testing and inspection of a large, new commercial project and have came across a ring main wired in twin + cpc 1.5mm cable, which serves two 2kW panel heaters. The cables are clipped direct for part of the run and for the remainder they are within an insulated Gyproc partition wall. The protective device is a 20A type B and the cable run is 20 metres. I appreciate that it is normally 2.5mm csa cable used for this purpose, however I have looked at the 17th Edition regs and it appears that the rating of a 1.5mm twin + cpc ran in insulation (worst case) is roughly 10A. I would normally replace a circuit like this just to be on the safe side but this would mean lots of associated builderswork and costs for this new client and I would like to avoid if possible.

P=IV / I/PV
> I=P/V I=4000W/230V = 17.39A

i would appreciate your feedback guys, cheers.

 

[D80]

The protective device is oversized for the cable. You could downsize it to an appropriate size - most likely a 10A, which is turn isn't that likely to hold during the winter. I think you're likely to be upgrading the cable size or running in a new circuit to one of the panel heaters.

 

[D80]

Actually just reread. Are you sure its a 1.5MM ring? Seems a bit of a crazy thing to install. It's not a separate supply to each of the panel heaters?

 

[super*spark]

Would I be better off splitting the ring circuit into two radials and having two separate 10A MCBs at the distribution board? it would be easier to split the ring as the interconnecting leg between both spur's is clipped direct on the facing of the wall.

Thanks

 

[telectrix]

either that or replace the 20A MCB with a 16A.

 

[Silly Sausage]

I would say it's 'almost' OK!!!
Are the heaters equidistant from the supply (ie both legs carrying 9A), if so, and nothing else can be connected to the circuit, I'd pass it but make a note on the report.

Plus, specify that nothing else should be added to this circuit.

 

[super*spark]

i thought the same at first but belled it out and it is a ring circuit.!!!

 

[ruston]

Actually just reread. Are you sure its a 1.5MM ring? Seems a bit of a crazy thing to install. It's not a separate supply to each of the panel heaters?

I agree , I would'nt like to think they designed it to service sockets also.

 

[super*spark]

either that or replace the 20A MCB with a 16A.

Surely if I replaced the 20A breaker with a 16A then that wouldn't work???

Total circuit load is 17A+

 

[super*spark]

I agree , I would'nt like to think they designed it to service sockets also.

its only for these two heaters. Technically i believe it meets the regs but just thought i would see what everyone thought

 

[telectrix]

fig.3.4 (p 249 in the red book), shows you that a 16A type B MCB requires 23Ato break in 10,000 seconds. at 17A it's off the graph, so theoretically it will never trip at 17A

 

[D80]

fig.3.4 (p 249 in the red book), shows you that a 16A type B MCB requires 23Ato break in 10,000 seconds. at 17A it's off the graph, so theoretically it will never trip at 17A

The cables running in an insulated wall would put me off fitting a 16A MCB

That said it's a ring - not had any dealings with a 1.5MM, and not sure how to go about working out the CCC of the cable in that case.

 

[Richard Burns]

I think it meets the requirements of the regs, albeit a bit close to the limit.:helmet:
For parallel conductors (bit dicey here) carrying equal current then you add the CCC of the cables.
Since if it is buried in insulation as the worst case then the CCC total is 20A. This is the CPD installed; but I would note the situation on the report.