10mm T&E for Consumer unit supply

Sav · Mar 22, 2014

Morning everyone,

Hope your all well.

Just a a quick question. We have been asked to quote for a HMO conversion, in a domestic property. So basically, the developer buys these houses and makes rooms out if them.
Leach room is basic, small ensuite shower ( not electric ), lights and a few sockets. There is a communal kitchen and each room is supplied by its own consumer unit.
There are 2 circuits, lights and sockets.
What I'm asking is, the consumer units are fed via 10mm T&E that go down to 60A isolators, which in turn go into a big Henley block.
There are about 5 rooms, so five isolators.
I would have thought that the consumer units for each room , from the isolators had have 16mm earth ?
Obviously things like communal smokes and fire alarm system etc are fed from landlord board.
The supply is a TN-S single phase

regards,
sav

Zebra Stripe · Mar 22, 2014

Re: 10mm T&E for Consumer unit supply

sparksburnout said:
No, I didn't make myself very clear I admit. I was initially suggesting only one RCD in a CU that would then feed each individual CU, but I now realise after giving it more than 10 secs thought that this would be crap. However, could you not use the method i suggested in my reply to D Skelton? I was not advocating having a buried T&E with no RCD protection!

Well thanks for the offer of your method, Im sure its a very good method, but its not my job or thread.

Zebra Stripe · Mar 22, 2014

D Skelton said:
That only applies to fuses. What you don't want to have is a situation where a circuit tripping a downstream device causes the upstream fuse to have to 'prepare to trip' to use a phrase. Pre arcing is a state where the fuse is subjected to the fault current but has not yet tripped. The more this happens the more damaged the fuse becomes.

Say for example you have a DB where the highest rated MCB is 50A and you plan to supply this via a sub main. If for example you choose a 63A fuse and it has a prearcing current of 45A (it won't have, this is purely an example) then this is bad design. You would need to uprate the supply fuse or, if possible, downgrade the downstream device.

A very simplistic explanation I know.

I think I shall do some reading up, if I ever get some time and can stay off the booze. Do you know of any good reading material in relation to this? No worry's if not, its just I tend to get a bit side tracked when researching something on the web. (Im mean Im lazy)

D Skelton · Mar 22, 2014

Zebra Stripe said:
I think I shall do some reading up, if I ever get some time and can stay off the booze. Do you know of any good reading material in relation to this? No worry's if not, its just I tend to get a bit side tracked when researching something on the web. (Im mean Im lazy)

http://www.cooperindustries.com/con...-datasheets-a/Bus_Ele_DS_4131_HRC_Form_II.pdf

sparksburnout · Mar 22, 2014

D Skelton, iv'e just noticed your signature, it's fantastic. I know this is going off topic but i saw a program revisiting the miners strike the other night. I had forgotten they even took benefit off their families. Lower than vermin indeed......