House probably not earthed

[ban-all-sheds]

Won't be PME as the neutral/earth connection mentioned will be the only one, rather than multiple points

I know it won't be PME (well - it might be - maybe he should go and find the nearest pole), but I asked about PNB vs TN-C-S......

 

[JohnW2]

However to reduce the risk of voltage appearing on the LV system from an HV fault (voltage gradient etc.) they MUST be separated by at least 10m. So if you are building an overhead network, to excavate a minimum 10m trench at each transformer becomes an issue in a lot of ways. So to counter this, it is common and the norm to earth the neutral at a point remote from the transformer.

Maybe I misunderstood the OP, but I was envsioning the overhead feed to the single house being fed coming directly from the transformer/pole. If that were the case, then presumably there would be no choice but to provide an LV earth at the pole, even if it did mean a 10m trench?

The above is why it is unlikely to be PME and more likely to be PNB when supplying a single customer. (PME requires an earth at the transformer position, so in this case if the customer provided their own rod connected to the neutral it could still not be PME)

Fair enough, but does that not apply to all overhead supplies? Even if there were an overhead network supplying multiple properties (with PME earths at some of the poles), from what you say there would still be a need for an earth at the transformer pole (hence a 10m trench) for it to be PME? ... yet I thought you'd told me in the past that overhead PME (like I think I am soon to be offered, even if I 'decline' it!) was quite common.

Kind Regards, John.

 

[JohnW2]

I know it won't be PME (well - it might be - maybe he should go and find the nearest pole), but I asked about PNB vs TN-C-S......

It's TN-C-S, by definition, isn't it (assume that it's earthed somewhere!) - since we have a 'C' and then an 'S'?

Kind Regards, John.

 

[westie101]

Sorry my bad, this is a quote from the COP, so that for PME we could connect at the first pole of a network.

6.2.2 In 8 (3)(b) it states that any distributor, in respect of any low voltage network he owns or operates, shall ensure that every supply neutral conductor is connected with earth at, or as near as is reasonably practicable to, the source of voltage except that where there is only one point in a network at which consumer's installations are connected to a single source of voltage, that connection may be made at that point, or at another point nearer to the source of voltage. This latter part contains the relaxation necessary for the application of Protective Neutral
Bonding (PNB).

BAS in terms of the effect on an installation they are the same

 

[clifford1]

I've just been out to look at the transformer pole.
There are in fact two poles, which I'd forgotten about.
At the first one, carrying the transformer underneath the main grid wires, there are two earths - one from the transformer casing, one from the neutral/earth wire.
The wires then cross into my property at a second pole, where there is another earth. Then on to the second leg to the house, where the 2 wires divide into 3.
There is no earth at that point, nor anywhere inside the house.

So the conclusion is that this is satisfactory, no house earth is required, it relies on the earths provided at the poles?

 

[westie101]

Yes that is a PME system so sounds to be correct

 

[clifford1]

Many thanks.

 

[Paul_C]

It is an isolated house supplied by overhead cables from a transformer in an adjoining field. The transformer is on a pole carrying cross-country power lines, which I believe are 500 volts. Higher than 230 anyway.

Much higher - Probably 11,000 volts, or at least 6600 volts.

 

[securespark]

I've just been out to look at the transformer pole.
There are in fact two poles, which I'd forgotten about.
At the first one, carrying the transformer underneath the main grid wires, there are two earths - one from the transformer casing, one from the neutral/earth wire.
The wires then cross into my property at a second pole, where there is another earth. Then on to the second leg to the house, where the 2 wires divide into 3.
There is no earth at that point, nor anywhere inside the house.

So the conclusion is that this is satisfactory, no house earth is required, it relies on the earths provided at the poles?

You need to ensure your CU is connected to the earth terminal. OK, so your water pipe is plastic, but have you got LPG coming into the house?

Does that need a PEB?

 

[clifford1]

You need to ensure your CU is connected to the earth terminal. OK, so your water pipe is plastic, but have you got LPG coming into the house?

Does that need a PEB?

Yes, the incoming earth wire connects to the CU.


LPG from a bottle has a copper pipe running through the door frame. There are no buried metal pipes.

 

[ban-all-sheds]

Where is the bottle?

 

[JohnW2]

Where is the bottle?

Wherever the bottle was, it would presumably be connected to the metal pipe via a non-metallic (probably rubber) hose - but one would need to check to see whether it was conductive rubber.

Although one's first reaction may be "if in doubt, bond", as recently discussed here, there's also a good argument for not bonding an outdoor LPG or oil tank/cylinder/pipework to a PME earth unless it's definitely necessary.

Kind Regards, John.

 

[clifford1]

I'm a bit lost by this. The gas bottle sits outside, it connects via a rubber/copper pipe to a free-standing gas cooker just inside the door.
Are you saying the cooker and or the bottle ought to be earthed? Why? How?

 

[ban-all-sheds]

Wherever the bottle was, it would presumably be connected to the metal pipe via a non-metallic (probably rubber) hose.

Ah - I guess it would.

A bit like this one we found in a holiday property rental a few years ago:

Quality work....

 

[ban-all-sheds]

I'm a bit lost by this. The gas bottle sits outside, it connects via a rubber/copper pipe to a free-standing gas cooker just inside the door.
Are you saying the cooker and or the bottle ought to be earthed? Why? How?

No, it shouldn't.