TNS or PME?

[wiggles]

I’m confused as to if my supply is TNS or PME. I’m guessing TNS as it appears to be formed from the sheath of the supply cable? I’ve attached a picture for a professional opinion. Also, is there any significance to the red dot stuck to the left of the inside of the box?

Thanks.

EDIT to correct image

 

[Lectrician]

PME. Straight-concentric feeding service head.

here is the bottom of the service head gone?

Wider shot would be good.

 

[wiggles]

Ah, I think I’m beginning to see the light! For some reason I had assumed that with PME, the supply cable would have insulated live and neutral conductors within it and be surrounded by an armoured sheath to protect the cable but with only the live and neutral connected at the cutout. Does this type of cable only have one insulated live conductor surrounded by an armoured sheath which is both the neutral and earth?

Anyway, I’ll get a better photo. The box is very narrow (there is not much that is out of shot) but I’ll try and get one from a bit lower where the supply cable enters.

Not sure what you mean about the bottom of the service head being gone. I don’t think any things missing – but will clarify with another photo later.

 

[RF Lighting]

//wiki.diynot.com/electrics:ca...bles_straight_concentric_and_split_concentric

 

[ColJack]

red dot probably indicates which phase your supply is on.. next door one side will have a blue dot, the other side will have a yellow dot..

 

[wiggles]

Thank you all for the clarification, very informative as always.

I can now clearly see that my installation is TN-C-S/PME. As I know you love em, I've attached the pictures.

Lectrician the bottom of the service head looks to be complete, at least in the sense that there is no copper showing from the live!

RF, thanks for the link to the wiki. I now know what concentric cables are having seem them mentioned many times. As with many things electrical, a very clever design.

Incidentally, the tails disappear into the cavity wall running sideways before emerging near the base of the garage wall then running up to the consumer unit. Probably around 5 meters. In mitigation, it’s possible that the tails may run just below the floor level – I won’t know until we replace the kitchen which shares the wall with the cutout.

On this picture of the TN-S cable with it’s sheathing stripped back:

//wiki.diynot.com/_detail/elec...bles_straight_concentric_and_split_concentric

It looks like there is a single green wire? Presumably part of the earth, does it have a special significance?

Wider shot of cutout.

Closeup of concentric cable splitting off into the live and neutral terminals.

 

[RF Lighting]

The green 'wire' in Lectricians picture of a split con cable is just a plastic packing piece, and is cut off and discarded when the cable is terminated.

Your cutout looks as if it is missing the bottom cover. You should not be able to see the innards of the supply cable. It should be all enclosed like this:

 

[wiggles]

Thanks for pointing that out. I'm going to ask the DNO to install an isolator in any case so I'll get them to look at this while they are out. I emailed my supplier Southern Electric about the isolator and they have given my DNO as North Eastern Electric. Does anybody know what they charge for an isolator or is it by any chance free?

 

[Roo]

If the DNO charge your supplier for an isolator then I would imagine they'd pass that on to you.

My DNO fit isolators for free, but I know of a supplier in our area who charge £60 to have an Isolator fitted (£60 pure profit).

If your lucky you may be with a decent supplier who will only charge if the DNO do.

 

[securespark]

Sometimes TN-S has the earth leaving the side of the cut-out, in which case it's difficult to gauge which. But the split-con cable (for TN-S) is fatter than its equivalent straight con cable.

 

[plugwash]

Sometimes TN-S has the earth leaving the side of the cut-out, in which case it's difficult to gauge which. But the split-con cable (for TN-S) is fatter than its equivalent straight con cable.

But since you probablly don't know for sure what size the cable was in the first place that is of limited usefullness.

Also i don't think its unheared of to use split con and tie the neutral and earth cores together if for example the engineer has run out of straight concentric.

 

[Adam_151]

Heard of 3+CNE down the street and then houses off it in split-con

Can get confusing where the destinction between TNS and TNC-S falls!

(P.S. If you get lucky they'll actually connect the earth of the split con with the neutral and not with the phase )