Splitting Tails to Second CU

DublinDilbert

Hi all,

Is there any regs covering where tails are split to supply a second consumer unit in a domestic installation? Both consumer units will be located pretty much side by side. Is it ok if each individual board has its own disconnect?

Thanks

M cebee

Every db needs an isolating switch

The only way you can add a second board
is as a sub-board

in other words you have to have 63amp main overcurrent protection unless you get an increase in capacity from esbn

DublinDilbert

M cebee wrote: »

Every db needs an isolating switch

The only way you can add a second board
is as a sub-board

Thanks, this is what i was wondering. So is each DB allowed have its own isolating switch? or does there have to be one for the whole installation?

M cebee

Every installation requires a main isolating switch-to cut power totally

every distribution board requires an isolating switch(main switch) in the board

DublinDilbert

M cebee wrote: »

Every installation requires a main isolating switch-to cut power totally

every distribution board requires an isolating switch(main switch) in the board

Cool, that's pretty much what i thought.

M cebee

Basically you cant split tails coming in

you can feed sub-board from the outgoing side of main isolating switch/ocpd or an mcb assuming theres capacity for any additional loads youre connecting

Dardania

what about if the main isolating device is the 63A MCB in the meter cabinet? Can two sub boards be run from it?

M cebee

Dardania wrote: »

what about if the main isolating device is the 63A MCB in the meter cabinet? Can two sub boards be run from it?

i took it that the main ocpd was located indoors here and tails were being split before main ocpd

with the new setup -it wouldn't be standard practice anyhow

they'd have to be two separate buildings with no more than standard demand in total

i would wire from main db as normal

Dardania

M cebee wrote: »

i took it that the main ocpd was located indoors here and tails were being split before main ocpd

with the new setup -it wouldn't be standard practice anyhow

they'd have to be two separate buildings with no more than standard demand in total

i would wire from main db as normal

I'd tend to agree with that you should extend from main db to the next, if nothing more to prevent the possibility of simultaneous peaks causing trips, and in case someone not in the know knocks off one board and thinks they've isolated the house when in fact they havent, but in principle theres nothing stopping you (from what I can see in the regs) in branching at the meter cab.

If you really wanted to do it properly, surely you could fit a main MCB and two outgoing 40A MCBs in the weatherproof enclosure in the metering cab...

M cebee

suppose you could do that providing the demand was such that the main ocpd isn't going to be overloaded regularly
and one is an outbuilding


reci/ecssa would likely pull you up on it as it's a distribution board in the cabinet

2011

This is what would be normal in an industrial installation, and I would do the same in a domestic:


............................Meter cabinet
...................................⬇
.......................Main distribution board
.......................⬇..........................⬇
...........Sub Dist Board A................Sub Dist Board B





The main distribution board would contain a main switch fuse as well as switch fuses for sub boards A & B.

Sub boards A and B would not have main fuses, but main isolators instead.

I seem to need the dots to get my arrows to align! Please ignore them