Consumer unit

[elektrisien]

I have seen a newly installed consumer unit in a college that are being refurbished. The thing is, this consumer unit has a lot, maybe 20, blue cables, I assume neutrals. They seem to have been pre-installed into the unit, as no circuits are as of yet connected to it. I cannot make out what they are for. Has anybody ever seen this ? ( This may be a stupid question, but I would still like to know )

 

[davelerave]

ya

a large school where i'm on call -all the sub-boards were pre assembled(merlin guerin)

 

[Sav]

Hi,
are you maybe refering to concentric cables ?? These usually have a load of blue cables which go into the neutral of the main switch .
I will try to find a link to post.
Best regards,
Sav

 

[elektrisien]

Hi,
are you maybe refering to concentric cables ?? These usually have a load of blue cables which go into the neutral of the main switch .
I will try to find a link to post.
Best regards,
Sav

Hi Sav,
Yes that sounds like it !
If you can get me a link to explain it, it would be much appreciated, Thanks.

 

[eskimo39]

Did they look like this?

 

[Sav]

Beat me to it Eskimo

Sav

 

[eskimo39]

Sorry Sav

There is some more info here : DIYnot.com > Wiki > Electrics > Cable types > Concentric type cables straight concentric and split concentric

 

[elektrisien]

Well, they are blue, but they are singles. Not part of three core etc.
I am supposed to be back on that job, on Monday.
I will take a photo with my mobile phone, and post it on the forum.
I think that would be the easiest.

I have checked the link that Eskimo39 put up.
But this is a massive consumer unit, maybe 40 mcb's plus empty space left for even more, an industrial type.

 

[m4tty]

It's not half way through installing is it with all theneutrals connected first then the din rail goes in with cpds then the lives are connected last is it by any chance?

 

[eskimo39]

Are you sure the unit hasn't had all RCBO's fitter prior to installation?? These have a blue (and usually a white earth lead) coming out of them.

 

[davelerave]

40 massive eh

 

[davelerave]

Did they look like this?

holy cow- i'd wonder about those pvc blues all paralleled like that

 

[elektrisien]

Are you sure the unit hasn't had all RCBO's fitter prior to installation?? These have a blue (and usually a white earth lead) coming out of them.

Yes, the RCBO's are pre-installed as far as I can see.
So why are they blue and white ? Why are the cables already connected ?
How do you connect your circuit then to the blue cable ? ( I suppose the blue one would be Live ? )

 

[eskimo39]

Yes, the RCBO's are pre-installed as far as I can see.
So why are they blue and white ? Why are the cables already connected ?
How do you connect your circuit then to the blue cable ? ( I suppose the blue one would be Live ? )

RCBO's have 2 outputs, so your live (phase) and neutral circuit conductors are wired directly into it.

On a standard MCB you only wire the live into it. The earth (white) flylead is connected into the consumer units earth bar along with the (sleeved) earth from the circuit cables. The blue flylead from the RCBO is directly connected into the consumer units neutral bar.

On a basic circuit, for example lighting, you would have the Brown, Blue & Green wires of the circuit entering your consumer unit. The brown would be connected to the 'L' terminal of the RCBO, the blue to the 'N' terminal. The RCBO would get it's feed from the busbar the same as a standard MCB. Then the blue flylead of the RCBO wouold be in the CU's neutral bar on it's own to supply the 'N' terminal of the RCBO. The white flylead of the RCBO would be connected to the CU's earth terminal along with the Green wire from the circuit.

Here:

Hope this helps

 

[davelerave]

RCBO's are double pole, so your live (phase) and neutral circuit conductors are wired directly into it.

On a standard MCB you only wire the live into it but in the event of it tripping, the neutral is still connected. In the event of a RCBO tripping both live & neutral are disconnected. The earth (white) flylead is connected into the consumer units eart bar along with the (sleeved) earth from the circuit cables. The blue flylead from the RCBO is directly connected into the consumer units neutral bar.

Hope this helps

i think they may be single-pole-solid neutral