PME Supply Advice

[bilbo_88]

Afternoon All,

Just pricing up a job and thought I'd pick your brains.

Quick run-down, Block of Flats with an underground car park. In the mains room each individual flat has a supply ran up to the flat (picture for reference) with a split concentric. The PME connection is provided within the flat via a connection at a Solid Link Fuse (typical house service fuse block) via the N.

So I need to install a sub mains next to the fuse in the mains cupboard (downstairs) supplying a socket for a hybrid car within the underground car park. My question is can I supply the submains with a TNCS supply via the Henley Block or a link within the Consumer Unit itself, or will I have to contact the DNO directly to provide me with a connection? Not something I have had to deal with before. I have noticed that other contractors have done the same but was unsure if it is the correct way to do it.

Thanks!

 

[bilbo_88]

Bloody hell did a kid do that drawing or are you drunk. Lol
CU in, earth's back to the Ads. That probably needs doing.
That's going to cost some pennys.

Both lol

Thanks for the advice, client will be chuffed lol

 

[buzzlightyear]

Thanks for the advice, client will be chuffed lol

What with the drunk drawing or drunk kid
Doing it.

 

[bilbo_88]

What with the drunk drawing or drunk kid
Doing it.

Just reading some regs and need to make sure I am not misinterpreting it. If a ran an earth back to the earth bar by the Ryefield board, would I not be contradicting 543.4.3? And in that case would I link CPC to Neutral at the Henley block in the mains room (as it seems other have done) as to not contradict it?

 

[mhar]

You do not link the E to the N, we are not allowed to do that.
Whole thing sounds unusual, first port of call should be a call to the dno with an earthing enquiry. In my area they are extremely helpful

 

[davesparks]

Lots of confusion here it seems.

That looks to me like a block of flats which had it's electricity supplies installed by a regional electricity board in the days when they existed and before anyone realised that distributing PME internally in a building is a very bad idea.

These days the individual services to each flat would be TNS with only the incoming main possibly being TNCS.

So what you have there is a concentric/CNE (combined neutral and earth) cable coming in to the cutout, then the meter and outgoing from that another CNE cable coming out of there and presumably going to a redhead isolation link in the flat.

In this arrangement the consumers supply terminals are at the outgoing side of the redhead isolation link and not at the meter as they would normally be.

So the consumers installation begins and the flat and everything before that is the property of the DNO, except the DNOs have washed their hands of internal wiring a n blocks of flats and it magically became the property/problem of the BNO (which may not even exist for the building)

 

[davesparks]

Just put in a second CU for the car charger.
There is a Henley blocks at the cut out.
Looking at you pics.

There are henley blocks yes, but they are not part of the consumers installation, they belong to the DNO/BNO and the consumers installation begins at the isolation link fitted in the flat.

This is not the usual supply arrangement where the meter is the final part of the DNO equipment, in this installation the meter is further upstream and the isolation link in the flat is the final part of the DNO equipment.

 

[davesparks]

And in that case would I link CPC to Neutral at the Henley block in the mains room (as it seems other have done) as to not contradict it?

No, don't copy what other people have done as what they have done is incorrect.

 

[bilbo_88]

Lots of confusion here it seems.

That looks to me like a block of flats which had it's electricity supplies installed by a regional electricity board in the days when they existed and before anyone realised that distributing PME internally in a building is a very bad idea.

These days the individual services to each flat would be TNS with only the incoming main possibly being TNCS.

So what you have there is a concentric/CNE (combined neutral and earth) cable coming in to the cutout, then the meter and outgoing from that another CNE cable coming out of there and presumably going to a redhead isolation link in the flat.

In this arrangement the consumers supply terminals are at the outgoing side of the redhead isolation link and not at the meter as they would normally be.

So the consumers installation begins and the flat and everything before that is the property of the DNO, except the DNOs have washed their hands of internal wiring a n blocks of flats and it magically became the property/problem of the BNO (which may not even exist for the building)

Yes, the issue with the DNO washing their hands of the internal wiring is what leaves everything in limbo. I daresay if I contact them they will want nothing to do with it.

Practically, it is impossible to get a feed back down from the flat (5th floor) therefore this seems to be the only option to provide them with the socket. It's just the earthing situation that has thrown a spanner in the works.

 

[bilbo_88]

No, don't copy what other people have done as what they have done is incorrect.

Are you in agreement that a run back to the earth bar is the only feasible option?

 

[davesparks]

Yes, the issue with the DNO washing their hands of the internal wiring is what leaves everything in limbo. I daresay if I contact them they will want nothing to do with it.

Which DNO is it? You might be lucky and find they accept their legacy issue.

Practically, it is impossible to get a feed back down from the flat (5th floor) therefore this seems to be the only option to provide them with the socket. It's just the earthing situation that has thrown a spanner in the works.

I think hunk you've misunderstood my earlier point. Those service connector blocks and the outgoing cable are almost certainly not part of the customer's installation, they will be the property of the DNO/BNO.

The customer's installation begins at the cutout in the flat.

 

[davesparks]

Are you in agreement that a run back to the earth bar is the only feasible option?

A run of what to which earth bar?

This is an interesting situation which needs some careful thought. For one the internal PME services are going to be causing all sorts of diverted neutral currents to flow through the services and structural steelwork of that building, the last thing you want to be doing is making that situation any worse!

 

[bilbo_88]

A run of what to which earth bar?

This is an interesting situation which needs some careful thought. For one the internal PME services are going to be causing all sorts of diverted neutral currents to flow through the services and structural steelwork of that building, the last thing you want to be doing is making that situation any worse!

In an earlier post I mentioned there was an earth bar in another mains room, the earth bar is connected to the Ryefield that, in turn, supplies these fuses. Would it be possible to run an earth from here to the new CU?

 

[davesparks]

In an earlier post I mentioned there was an earth bar in another mains room, the earth bar is connected to the Ryefield that, in turn, supplies these fuses. Would it be possible to run an earth from here to the new CU?

No, that is part of a different earthing system, don't mix the different earthing systems unless you have given proper engineering consideration to the implications of this. If you are going to mix the earthing systems then you will probably need to install a much bigger CPC than you first expect, but that is beyond my abilities so I would leave that up to an engineer to specify.