Pme query

Tridentsystems · Apr 23, 2013

Hi all , went to look at a job today..... Main house with PME all good bonding etc. The detached garage and workshop also has a separate PME supply. Inbetween main house and detached garage they have built a one bed granny annexe, this links the two buildings but with no access through to existing house or garage. New cu has been fitted to granny annexe supplied from garage supply. Boiler has been fitted from main house gas supply to the annexe which is main bonded to house PME. I think I should link the MET from each supply then bond new cu to boiler ? Any thoughts ? NAPIT technical didn't want to commit to an answer !

SirKit Breaker · Apr 23, 2013

Why am i not surprised that Napit wont commit!

Before i have a stab, just confirm that you have electric from one building and gas from another, all coming together in the middle bit.

Cheers...........Howard

Tridentsystems · Apr 23, 2013

Yes howard

guest119 · Apr 23, 2013

The granny flat is a separate electrical installation in its own right and so should have the normal bonding of incoming services.
The fact that the gas and possibly water come from another property is neither here or there, still an incoming service, hopefully with their own shutoffs. Therefor bonding at incoming point, after shutoff and before any tee.

Boydy

spark 68 · Apr 23, 2013

Well you are going to have to bond the boiler in the Granny annexe to the local CU in that annexe anyway.

If you have GN8 have a look at fig's 5.12 an 5.13 (pg 62 in new book), this sort of explains what you need to do.

Tridentsystems · Apr 23, 2013

Thanks guys just in process of reading bible but wanted some real world input. Just feels like an exported earth on the PME

spark 68 · Apr 23, 2013

You are going to sort of end up with a mix of these two drawings.
with two bonds (4 if water services are metal)

1) a local bond from the annexe to the local MET also in the annexe
2) a bond from the supply MET (garage in your case) also to the annexe

A further point to consider

the house is already locally bonded, and an additional bond in the annexe is not needed.

At least according to the drawings in GN8

Tridentsystems · Apr 23, 2013

Thanks spark. Can't see the attachment for some reason

spark 68 · Apr 23, 2013

I have uploaded it as a Jpeg, so you should be able to see it ?

Anyway the point is you only need bond from the electricity supply side (as if exporting as usual), not from the services supply side and of course local to the annexe MET.

The house is already bonded locally, and the house electricity supply/installation (and bonds) end there.

Edit: re-attached as a Pdf on this post

Tridentsystems · Apr 23, 2013

Thanks. Think it's an iPhone thing. Gonna hit the sack and look on PCM tomorrow. Thanks for help

spark 68 · Apr 23, 2013

There appears to be two ways of doing this, if the supply cables (from the garage) earthing conductor has a large enough csa (it may do including the armourings) to satisfy both protective and Bonding duties then you would only need a local bond in the annexe (to each service) to the annexe MET.

The drawings above show MET to MET bonds, from the electricity supply (garage) to the MET in the annexe.

I suppose it may be considered as an extra risk (of been disconnected ?) by bonding the service to the garage supply instead, which I may have inadvertently implied in an earlier post.
Sorry for any confusion caused

Tridentsystems · Apr 23, 2013

I was thinking just advise a 16mm met to met and main bond new gas to new cu. all water is poly

spark 68 · Apr 23, 2013

Tridentsystems said:
I was thinking just advise a 16mm met to met and main bond new gas to new cu. all water is poly

That may satisfy the conditions, but you need to be careful here where PME applies, that bond garage MET to Annexe MET may need to be as large as 35mm ! if it is to satisfy both bonding and protective functions.

IN GN8 showing a similar scenario they show 35mm local bonding too.

The Bonding conductors are sized against the incoming Neutral (to the garage) not the supply cable to the annexe, be careful.

Tridentsystems · Apr 23, 2013

Good point. Hate jobs that have already been done. This one was done by the plumber

spark 68 · Apr 23, 2013

Here is another pic from GN8, showing exported PME.

Pme query

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