Electrical
I am having some solar PV panels fitted and the electrician is putting in 2.5mm cable to the only spare way on the consumer unit which has a 30A MCB. The consumer unit is old so getting a lower rated MCB is not an option without fitting a new consumer unit. Whilst the current rating to and from the PV inverter is well within the current rating of the cable, if fitted to a 30 amp MCB should the cable be rated higher, eg 4 mm? Does this comply with the wiring regs?
homeowner
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4 Answers from MyBuilder Electricians
Best Answer
Homefront Electrical & Security Systems
Manchester • Member since 29 Jul 2015 • 15 jobs, 100% positive feedback
The Current Carrying Capacity of the 2.5mm cable is 27A and therefore only a 16A or 20A breaker should be used. The current carrying capacity of the cable must be at least the same if not higher than the breaker used. Either down rate your breaker to a 20A or increase the cable size to 4mm (provided you are clipping direct or burying in plaster and not going through thermal insulation)
Answered 25th Jan 2016
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Wellington • Member since 21 Oct 2015 • 1 job, 100% positive feedback
The only way a 2.5mm cable can be used on a 30A breaker/fuse is if it's wired as a ring final socket circuit. Agree with the above either downrate the fuse or upgrade the cable. Presumably we are talking 2.5mm Twin & Earth cable? 2.5mm SWA cable is rated at 35A if it's in free air.
The fuse/MCB is rated lower than the cable so that in the event of a short circuit it's the fuse that breaks the circuit, if the fuse is rated higher than the cable there is every chance the cable can become overheated and cause a fire and the fuse/MCB won't open the circuit. It's very important!!!
Answered 25th Jan 2016
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Northampton • Member since 18 Jan 2016 • No feedback yet
If it is a single 2.5 , it's normally on a 16 or 20 amp
But 4mm is normally the standard cable size for solar Pv
Answered 25th Jan 2016
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