Question For The DNO Guys

[Oxia]

Hi,

About 7 years ago we had a brand new three phase supply to our coffee shop and until now we have never seen it as the cables etc were covered by stone (stone covered duct)

Im just a bit puzzled by what we have...

There is a cable coming from the road and it says on the sheath (3 x 70mm) then that goes in to a resin joint (along with a 25mm earth cable from a spike) from there a 16mm cable comes out of it in to our shop.

Few questions...


1. I take it we have a TT supply?
2. If the cable says 3 x 70mm where does our neutral come from?
3. Why has it been done this way?
4. why does the earth go from a spike in to the joint then join to the outgoing cable?

Sorry for all the questions, just curious.

Thanks!

 

[ericmark]

Because there is an earth rod it does not mean it's TT the PME (TN-C-S) the ME means "multiple earths" and the DNO is allowed to use same conductor for earth and neutral. I would guess earth and neutral is using outer case.

The DNO rules are different to what we are allowed to do they seem to be a law onto themselves.

 

[westie101]

More or less what eric said.

Any cable we use is labelled with the core size so that will be a 3 core & concentric neutral/earth.

Because it is terminated and a service taken from it we are obliged to fit a nominal earth rod to the N/E, which becomes part of the "multiple earth"
the rod will be connected directly to the N/E not via the service cable.

 

[Oxia]

Thanks for your replies, is there any particular reason there is a 70mm cable coming down the field and then jointed to a 16/25mm?

 

[Robin0577]

I'm no expert on DNO practices, but an educated guess would be either....

70mm is required due to the run length to keep voltage drop and/or fault loop impedance within spec.

OR

To allow for future expansion

Or a bit of both

 

[ban-all-sheds]

Or it's cheaper to just buy one size for cables, joints etc?

 

[westie101]

Or it's cheaper to just buy one size for cables, joints etc

We only have 3 sizes of mains cable, two sizes of service cable (house and street furniture).

 

[efiste2]

The DNO rules are different to what we are allowed to do they seem to be a law onto themselves.

I wish I had a pound for every time I have heard that off consumers, sorry customers