Cable between cabinet and consumer unit

[bungledlow]

Hi, this may be a case of "ask your electrician", but I was hoping I may be able provision the main supply cable to the house without connecting it to the consumer unit as we want to get all the digging done in one go.

 

We have a cabinet with a 3 phase supply, each 100 amp. The DNO used 3 core 35mm SWA (see attached) for this from the joint bay to the main fuse.

It is a PME (TN-C-S) system (see attached) so my understanding is the Neutral and Earth are essentially the same. What I don't understand is how the Neutral/Earth is supplied through the 3 core cable. Do they use the armour?

 

The house is another 50 metres from the cabinet, calculators show 35mm cable should be sufficient for this.

The question I have is how many cores are required? 3 like the supply cable, 4 to carry the Neutral, or 5 to carry Neutral & Earth?

 

Any advice appreciated

[ProDave]

That is not strictly SWA.  That is the 3 core version of "concentric".  The outer braid is the Combined Neuitral and Earth (CNE) and the 3 cores are the 3 L phases.

 

In the supply head the N and the E terminal are both connected to the outer conductor.

 

That cable is ONLY to be used by the DNO for the supply from the network to the supply head.

 

Now to answer the rest of your question, what exactly are you planning?  To leave the supply head and meter in this cubicle and run a cable from there to the house?  If so 35mm 4 core SWA will do using the SWA as earth, but you cannot use that cable the DNO left, it sadly has no use after the supply head and meter.

[Dan F]

Our electricians used 5-core 25mm SWA, but in our case the distance was closer to 25m.  I asked them about 4-core, but they weren't keen for some reason.

 

We have since moved our supply, from the site kiosk near boundary, into the house.  Given the 25m of 5-core SWA wasn't cheap, we plan to resuse it for a slightly overspecced car charging station in an optimum position on the drive to park/charge 2 cars (20m away) , rather than a more standard location near garage.  Will handle 2 x 22kW 3-phase chargers easily (if we ever have two EV's that support this!)

Edited September 10, 2021 by Dan F

[bungledlow]

Thanks, that all makes sense now.

They did not leave that cable, I just snapped it before they put it down the conduit so I could see what I was getting for my money!

 

34 minutes ago, ProDave said:

what exactly are you planning?  To leave the supply head and meter in this cubicle and run a cable from there to the house?

Yes, exactly this. I will purchase a new 4 core SWA cable then and put it in the conduit ready for the electrician.

[bungledlow]

12 minutes ago, Dan F said:

I asked them about 4-core, but they weren't keen for some reason.

I suppose I should ask the electrician then, but I think I know the answer - 5 core, the most expensive...

[gravelrash]

what size hockey stick did you use? Northern power have said I need 125mm but yours appears much smaller.

[ProDave]

2 minutes ago, bungledlow said:

Thanks, that all makes sense now.

They did not leave that cable, I just snapped it before they put it down the conduit so I could see what I was getting for my money!

 

Yes, exactly this. I will purchase a new 4 core SWA cable then and put it in the conduit ready for the electrician.

Speak to your electrician first. Some don't like using the SWA as the earth, so 5 core might be better if not too much more expensive.

[ProDave]

1 minute ago, gravelrash said:

what size hockey stick did you use? Northern power have said I need 125mm but yours appears much smaller.

SSE said something equally ridiculous to me but did not bat an eyelid when presented with 75mm ducting.

[gravelrash]

Seemingly Northern power are twats...including there own tile tape at stupid price.

[bungledlow]

3 minutes ago, gravelrash said:

what size hockey stick did you use?

54mm (2") as requested by UK Power Networks. 

Difficult to get hold of, nobody seemed to offer them, but Travis Perkins managed to get them in the end

[gravelrash]

Doesnt it piss you off that such an important thing in life like an electricity connection is not standardised to government standards...Oh shit, its just like planning and that's not even privatised.

[TonyT]

I would go for a 5 core.

or run a separate earth alongside the 4core, so back to a 5 core then?

[PeterW]

Difference between 4 core SWA and a separate 25mm earth, and 5 core SWA is about £20 over 30m - not that much to worry about other than the cost of the terminals at each end !