sub main

stegw353 · Sep 28, 2010

I am currently in the middle of rewiring a house and will have to run in a sub main for the consumer unit. The consumer unit has to be moved approx 10m from its current location where the electricity metre is. Am I right in asking the electricity supplier to install an isolator between the meter and the consumer unit? Then would would it be ok to run a 26mm SWA from the isolator into the consumer unit 10m in distance away and would I need to install a seperate earth or would the the outer armour be enough.

I would appreciate the help guys as I am just recently qualified.

Cheers
steven

Andyfm · Sep 28, 2010

I normally put a switch fuse in, feeding a 25mm three core armoured and earth the sheath as well

telectrix · Sep 28, 2010

yep 25mm 3 core. use one core as earth and earth the armour as well. as for the isolator, if they will, get them to do it.

malcolmsanford · Sep 29, 2010

I would contact your DNO and get some information. Unless it's changed dramtically most DNO insist that any tails over 3 metres and some DNO's it's 2 mteres will need a protection device.

If you run surface then you can use a fuse but if you fall foul in anyway of the conditions in the 17th then you will need RCD protection, which would mean either a "S" type RCD or a 100Ma one for discrimination

stegw353 · Sep 29, 2010

The steel wire armour will ne installed under the floor from the isolator to the consumer unit. this is a 10m run. Would I need a "S" type RCD instead of the isolator or in between the isolator and the consumer unit?

malcolmsanford · Sep 29, 2010

If you use a 3 core armoured, which I would use, then as per reg 7.3.1 part (ii) you will use the earthed armouring method and only need to protect the sub main with a fuse. If you use the armour as your CPC then you will need to fit an RCD.

If you use a BS 88 fuse then that can be used as isolation then just a normal switchfuse can be used.

If you have to go down the RCD route and an RCD unless is suitable for Isolation, can not be use as one, then you will need both an isolator and a RCD.

stegw353 · Sep 29, 2010

thanks for the help I will use a 3 core armour as the sub main and a 100amp fuse to protect the sub main between the isolator and the consumer unit.

cheers

Danielwareham · Sep 30, 2010

What part of the big red book covers a protective device being needed with tails over 3m's/ Can't seem to locate it! Thanks

JUD · Sep 30, 2010

stegw353 said:
thanks for the help I will use a 3 core armour as the sub main and a 100amp fuse to protect the sub main between the isolator and the consumer unit.

cheers

What size is the main cut-out fuse? If it's 100A then you will need to install an 80A switch fuse for discrimination. No good installing 100A if the main cut-out is only 80A as the main cut-out would pop before your switch fuse.....if you get my drift.