secondary 2 way ccu

Hi

just after some clarification, just had a secondary 2 way RCD protected ccu installed for a new kitchen extension.
The electrician has run 16mm tails too the new unit from the supply. My question is, the earth he has run in is 10mm is this big enough or should it be 16mm? The unit is supplying sockets and a cooker (32A & 40A.)

Some clarification would be appreciated

Thanks in advance

Sounds fine.

Did he install a main switch which isolates both of your consumer units (single point of isolation)?

Thanks for the reply.

No it just looks like he's took the 16mm tails off the 100A terminal blocks after the meter, if that makes sense?

Cheers

Yes it does make sense. Most people (not me) do just that and don't correctly install a main isolator before the two boards.

It should be MAIN FUSE > METER > MAIN ISOLATOR > 100A HENLEY BLOCK > BOTH CONSUMER UNITS.

Is it worth me dragging him back to put one in? Does it go against the regulations, cos he's given me paper work to say it's all correct.

GaryMo although I agree that it is good to have a single point isolation I can’t find any regulations saying this should be the case.
Who or where does it recommend single point isolation?
Eric

I'll asume everything is ok, i was just wondering about the earth but as loing as the 10mm is big enough, i'm happy.

Cheers

ericmark said:

GaryMo although I agree that it is good to have a single point isolation I can’t find any regulations saying this should be the case.
Who or where does it recommend single point isolation?
Eric

Click to expand...

Have a read of 537.1.4

I have read 537.1.4 and there is nothing about single point. Yes I know it says “A” which is singular but if we say “A door must be provided for access” that does not mean you can’t have two doors and to me I read as at least one linked switch or circuit-breaker shall be provided not only one shall be provided.
Don’t get me wrong I do think a single isolator is a good idea and looking at the standard configuration on the new consumer units with isolator and two RCD’s it seems the manufactures also like that idea. But of course they may have also configured them that way so you can change the RCD’s?
Doing a search on BS7671:2008 for single point in the main section only reference is to supply to a ring main. There is a reference 531.4.1 which refers to use of a single RCD but this does not really fall into what we are talking about and 537.4.2.2 maybe? but again is the main isolator really considered as emergency switching? Neither do I think 537.6.3 comes into play as in most homes nothing exceeds low voltage. 705.537.2 seems to say you need a single point isolation but only with agricultural and horticultural premises and of course this really proves the point that it is not required else where or it would have been included in general section instead .
I think someone has been scanning through the regulations and has read 705.537.2 without realising they were in the agricultural and horticultural premises section and has quoted it in error and the Chinese whispers have done the rest.
I again repeat I do think a single point isolation is a good idea but not required by the regulations.
Eric

Eric, read it again.

A main liked switch (singular) shall be provided an near as practicable to the origin of every installation as a mean of switching the supply on load and as a means of isolation.

Definitions - Origin of installation
The position at which electrical energy is delivered to an electrical installation.

So, we need a main switch (singular) as near to the main intake as possible to switch the supply on load or isolate the installation.

It's pretty much black and white to me what's required to comply with BS7671:2008.

ericmark said:

I have read 537.1.4 and there is nothing about single point. Yes I know it says “A” which is singular but if we say “A door must be provided for access” that does not mean you can’t have two doors

Click to expand...

If a door was to be provided for lock-down of an area and this door would provide total security then how could you have a second door which could possibly compromise the security of the first door?

Anyway, should this be in the Wood / Woodwork / Carpentry forum?

“A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation.” This statement is a continuation and points out at least one switch must switch both line and neutral in a TN-S or TN-C-S supply if they meant “The electrical installation of each building or part of a building shall be isolated by a single isolation device” then they would say that as they do in 705.537.2
Eric

I don't agree Eric but to add a little more weight have a read of 537.4.1.3

"Means for emergency switching shall act as directly as possible on the appropriate supply conductors.
The arrangement shall be such that one single action only will interrupt the appropriate supply."

We will have to agree to differ although as I say I think single point isolation is a good idea I can't see except for agricultural and horticultural premises that it is required under BS7671:2008 and as a result I would not take another electrician to task for not providing it.
Eric

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