Neutral Earthing up the pole

[LeeCage]

This question is mainly for academic interest - my neon screwdriver isn't rated for 11kV

A colleague recently asked about neutral earthing so I explained all about TT, TN, -C, -S, -C-S, etc. Shortly afterwards, I happened to be staying at a place fed by overhead power lines, so, perfect opportunity to look at a "real-life" installation. (Yes, some of us do lead very sad lives

).

Incoming 3-phase 11kV, feed down to transformer - check.
4 LV terminals, labelled a2, b2, c2 and yn for the lives and neutral - check. Earth wire coming up the pole, connected to the casing and other metal parts - check. (Interestingly, the barbed wire wasn't earthed, guess people deserve what they get if they climb that far).

Then, on the LV side, 5 wires running off to feed the handful of local houses, each fed from a live selected from L1, L2 or L3 plus N & E - check.

But, hang on. No apparent connection between N & E anywhere. I traced the wires very carefully and have photos to prove it! [Now just waiting for the knock on the door from MI5]

So, to the question(s). I presume this isn't IT? Is there a connection, maybe high impedance, inside the transformer casing? Is it relying on distributed conductor to E impedance? Or what?

Hope someone can explain before I drive into a hedge craning my neck to squint at every transformer that I pass.

 

[Knobhead]

The neutral – earth connection will be on the next pole away from the pole-mounted transformer.
As you say all the HV metalwork is earthed at the 1st pole. The 2nd pole will have it’s own LV earth point. 5 cores leaving the transformer pole, but how many leaving the 2nd

This is to stop a HV earth fault being transmitted in to the LV network due to the ground resistance between the 2 poles.

 

[Spudnik]

Overhead lines, which make PME available, the poles are normally staked every three.

 

[nickblake]

my neon screwdriver isn't rated for 11kV

Sledge hammer springs to mind

 

[ian.settle1]

my neon screwdriver isn't rated for 11kV

Sledge hammer springs to mind

******* things should be made illegal most dangerous things ever made

 

[UNG]

When will these people see the light that neon screwdrivers are a shockingly dangerous invention that should have been destroyed before it was manufactured

 

[LeeCage]

Hehe, thought that remark might stir some comment . Survived 30 odd years using neon testers, but must admit I use a Volt Stick these days. Interestingly one of the first screwdrivers I owned could be opened up - you could make the neon a lot brighter by removing that stupid resistor . Strange they are banned for professional use, but still available to the amateur. But then the Volt Stick isn't rated for 11kV either ...

Thanks for the info on the wiring - I'll take a closer look at a subsequent pole in my photos.

P.S. I am joking about removing the resistor. But it was perfectly possible. At the top end was a "biro" spring, so all you had to do was stretch the spring and it would connect directly to the neon. Or if you were really lucky, all the way to the shaft. And since an amateur might not realise what it was for ... Crazy.

 

[LeeCage]

OK, some photos here:

C_Transformer_conns.JPG - Windows Live

From the right of the transformer pole, all phases N & E are taken to the next pole (photo G). Here, two phases appear to be taken underground (there were houses across the road). The third phase (red I think) continues to the next pole (photo H), and thence to another underground cable. E seems to be connected to the cable armour (?). Can't see any extra N connections here.

Across the road, the cable re-emerges with the supply split to two nearby houses (photo I). But I just noticed there is a bare wire disappearing behind the pole which I hadn't seen before. Unfortunately the angle makes it hard to see where this goes, but could this be the missing link running down to an earth stake? Or is it just grounding the (limited) metalwork.

Of course, I didn't follow the other two phases taken off the left of the transformer pole, so maybe something happens there too.

 

[Spudnik]

The cable armour, is more than likely the N&E.

The supply companies use a straight concentric cable to supply the houses, overhead, or underground.

They combine the N&E on the copper "armour" of the cable at the transformer, and then split it out at the customers end.

 

[LeeCage]

That makes sense, but in this case, tracing the wires it seems that (i) the earth taken to the second and third poles and then to the cable armour (Tony's comment) is the same as the one grounding the transformer and iron work, and (ii) the neutral from the transformer seems isolated, at least to the final pole before it dives underground and re-emerges at the other side of the road. Whether it's linked there I can't quite tell (bad photo angle).