T&E Sub Main

acestu · Jul 22, 2014

Hi,

I have a commercial property with several consumer units that are the old split type ie half rcd protected and half not, the boards need replacing but on some of the boards they have a breaker on the unprotected side feeding another consumer unit, ie a sub main in T&E , so when I replace the boards do I protect the sub main with an rcbo or would it be ok on an rcd protected rail of the new consumer unit ?.

Thanks In Advance
Stu

Andy78 · Jul 22, 2014

Will you be placing 2 RCDs in series at any point ? Does the t&e need rcd protection due to installation method ?

telectrix · Jul 22, 2014

what he asked^^^^^. if the T/E is surface, it probably won't require RCD protection.

Farmelectrics · Jul 22, 2014

what size is the t e supplying the other boards

acestu · Jul 22, 2014

Hi guys,
Thanks for the speedy reply, this is an old property and the t&E is under floorboards and in walls etc, at the moment there is just a breaker on an unprotected side of a split load board supplying the sub main (another consumer unit).

when the consumer unit is replaced would i have to protect it with an rcd or rcbo at the feed end with 100ma trip so as to discriminate against the rcd in the consumer unit that it is feeding ?.

cheers
Stu

telectrix · Jul 22, 2014

it's only the kit that you install that needs to comply with current regs. if the feed to your new sub-main complied when installed, and readings are satisfactory, then it's fine to be left as is.

acestu · Jul 22, 2014

telectrix said:
it's only the kit that you install that needs to comply with current regs. if the feed to your new sub-main complied when installed, and readings are satisfactory, then it's fine to be left as is.

Hi,

I am replacing the consumer unit (old split load) with a current fully protected board with 2 x rcds , this would mean that the breaker that used to feed the sub main would have an rcd on it, as would the board that it is feeding so that is my question it would have 2 x rcds in line no discrimination so would I have to use a full rcbo board and use a 100ma rcbo to supply the sub main ? sorry if this is a little confusing

stu

telectrix · Jul 22, 2014

is it just the sub that you are replacing, or the main DB as well?

D Skelton · Jul 22, 2014

You cannot use a 100mA s-type to provide additional protection to a buried cable in a wall. Only 30mA or less can be used for additional protection. If the board supplied by the submain needs RCD protection, this would have to be via a 30mA RCBO in the main board feeding its supply. If this is not a workable solution, the only way round it would be to somehow provide protection for the T+E in the walls and stick it on an MCB instead.

All this being said, how do you know that the T+E isn't protected in the walls with galv conduit? Normally, if I have to run a T+E submain and bury it in a wall at any point then it will be run in a length of galv.

May I ask why the boards need replacing??? You haven't gone in all Electrical Trainee style and told 'em that "coz they ain't 17th edition boards, they gotta come out!" have you?

trev · Jul 22, 2014

What Damian said.
If these things are 16th compliant why do you want to go to the time, trouble and expense of replacing them? As long as everything is testing out ok then they're good for continued service.

Octopus · Jul 22, 2014

Why don't you replace the MCB's on the non protected side with RCBO's?

Guest77 · Jul 22, 2014

Sounds to me like a domestic 50 quid off the shelf split DB is going in, I hope I am wrong, this could be the beginning of Electrical Trainee entering the commercial side of the trade.

Knobhead · Jul 22, 2014

MDJ said:
Sounds to me like a domestic 50 quid off the shelf split DB is going in, I hope I am wrong, this could be the beginning of Electrical Trainee entering the commercial side of the trade.