Power point in external glasshouse

[cliffed]

Client wants 2g socket in greenhouse, obviously IP rated,will be supplied from Rcd, the greenhouse consists of metal frame work on the ground.
Does this require MPBC

 

[Julie.]

Client wants 2g socket in greenhouse, obviously IP rated,will be supplied from Rcd, the greenhouse consists of metal frame work on the ground.
Does this require MPBC

I would say so because the metal frame does represent an extraneous conductive part. (411.3.1.2 item v)

At least now the bonding doesn't have to be 10mm^2

 

[cliffed]

I would say so because the metal frame does represent an extraneous conductive part.

At least now the bonding doesn't have to be 10mm^2

With that in mind that Power point will need its own earthing system ie:TT

 

[Julie.]

With that in mind that Power point will need its own earthing system ie:TT

Why?

Just bond the metal structure.

 

[cliffed]

Why?

Just bond the metal structure.

What with & where from, its either MPBC or supplementary

 

[Julie.]

What with & where from, its either MPBC or supplementary

Neither, the equivalent of MPBC as detailed in 544.1.1

So 6mm^2

 

[cliffed]

Neither, the equivalent of MPBC as detailed in 544.1.1

So 6mm^2

Which is 10mm from a Tncs supply.

 

[Julie.]

Which is 10mm from a Tncs supply.

Why, what size cable are you taking to the glass house???

If you take 6mm^2 then that would meet the minimum x section.

Use the CPC of 6mm^2 as bonding for the seperate building.

 

[cliffed]

Deemed as a Special location this Power Point now becomes an expensive item.
To comply it will need a TT earthing system for the greenhouse to accommodate MPBC

 

[Julie.]

Deemed as a Special location this Power Point now becomes an expensive item.
To comply it will need a TT earthing system for the greenhouse to accommodate MPBC

Why?

 

[cliffed]

Why, what size cable are you taking to the glass house???

If you take 6mm^2 then that would meet the minimum x section.

Use the CPC of 6mm^2 as bonding for the seperate building.

It‘s a 2.5mm from local ring main
The MPBC size relates to the existing earthing system isnt it

 

[cliffed]

Why?

Why?

Extraneous conductive parts

 

[Julie.]

It‘s a 2.5mm from local ring main
The MPBC size relates to the existing earthing system isnt it

No, it's not the MPBC, it's extraneous conductive part in a remote building therefore the bonding size is dependent upon the circuit to that building.

 

[Julie.]

Extraneous conductive parts

In a seperate building, therefore sized on the circuit characteristics - check 544.1.1

 

[Julie.]

The key part is the second paragraph:

"Where an installation covers more than one building, a main protective bonding conductor shall be selected in accordance with the characteristic of the distribution circuit protective conductor for that particular building."



(Min 6mm^2; max needed 25mm^2 of course)

 

[loz2754]

A week last Sunday it would have to be done in 10mm²

 

[loz2754]

Well done for spotting that one Julie!

 

[cliffed]

Agree to disagree here, you say use the cpc of the 6.0mm for the bonding, cpc & bonding are 2 different functions.

 

[Julie.]

Agree to disagree here, you say use the cpc of the 6.0mm for the bonding, cpc & bonding are 2 different functions.

You can use the cpc for the supply to the remote building as both a cpc for that sub board and bonding provided it meets the minimum cross section for both aspects.

You could use 2.5mm^2 for the circuit, but as it wouldn't meet the minimum for bonding, would require an additional 6mm^2 for bonding; or use a 6mm^2 combined circuit and bonding conductor.

Edit

Third choice would be a 2.5 or 4mm^2 - 3 core swa, which combined with the swa armour would give a combined x section greater than 6mm^2

Haven't got tables to hand, but pretty sure both sizes will give more than 6mm^2 combined.

Edit 2:

Even a 2 core 1.5mm^2 swa has an armour of 15mm^2 so would actually be ok for both the CPC and bonding (though I prefer 3 core for a "proper" cpc)

 

[cliffed]

The key part is the second paragraph:

"Where an installation covers more than one building, a main protective bonding conductor shall be selected in accordance with the characteristic of the distribution circuit protective conductor for that particular building."



(Min 6mm^2; max needed 25mm^2 of course)

You can use the cpc for the supply to the remote building as both a cpc for that sub board and bonding provided it meets the minimum cross section for both aspects.

You could use 2.5mm^2 for the circuit, but as it wouldn't meet the minimum for bonding, would require an additional 6mm^2 for bonding; or use a 6mm^2 combined circuit and bonding conductor.

In many cases we’ve been told that supplying a remote garage from a Tncs supply a 10mm bonding must be installed if there are extraneous conductive parts in that area.
In many cases the easiest option would be to convert to a TT System & install a 6.0 mm