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 )

 

[elektrisien]

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 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

Yes, it makes sense I will have a closer look when I am on site again.
And probably have another question or two.
Thanks !

 

[eskimo39]

i think they may be single-pole-solid neutral

Cheers mate, just testing.

 

[davelerave]

no worries

what about that concentric cable then? i dunno

 

[eskimo39]

Yes, it makes sense I will have a closer look when I am on site again.
And probably have another question or two.
Thanks !

Don't worry about it, it's what we are here for!!

 

[davelerave]

no armour on the concentric- but 'automatic disconnection' is assured with the N/E outer if cable is damaged

overcurrent protection on the paralleled blues should be ok if they're all connected

 

[Spudnik]

Gotta love split con

 

[mogga]

Splits brill to work with used loads on street lighting it does confuddle a lot of guys when they see it for the first times

 

[SEC-Tom]

We had to the replace all the 16mm sub mains we had installed to the flats from the mains room, because Scottish and Southern didn't want all the meters in one place so all the meters had to go in each flat. We had to pull concentric cables in fully finished plastered and painted ceilings was a nightmare.

 

[Spudnik]

Same here. although i only had to install duct and tray work.

They needed to be able to pull in a new cable at anytime without ripping the place apart in the future.

I asked how many times they have had to replace a supply cable and the answer was, a big fat zilch

 

[eskimo39]

What is the use of this over standard 2 core & earth cables?

 

[pennywise]

You try and find 25mm T+E with a 16mm earth

 

[davelerave]

what's the magnetic field like on that cable