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

 

[Julie.]

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

Why TT, just run a 1.5mm^2 swa including the armour as CPC and bonding and it meets the regs.

Cheapest option

 

[westward10]

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.

I have heard of this new Reg but not perused it does it apply to all TN systems.

 

[Julie.]

I have heard of this new Reg but not perused it does it apply to all TN systems.

Yes, it basically means you don't need to size the extraneous conductive part bonding on the incoming supply, but on the supply to the particular building with a minimum of 6mm^2

The rest is the same other than a bit of clarification on what is extraneous - ie not just where a bit of metal passes through the wall!

 

[Julie.]

I think it's poor wording though, it uses "main protective bonding conductor" to mean both the main protective bonding conductor at the incomer (which is based of the incomer size), and for the remote building.

I think "main protective bonding conductor" should be reserved for the incoming aspect and something like "remote building protective conductor " for the remote building.

Just to distinguish between them or else there will be confusion, 'when I say the main protective bonding conductor, I don't mean the main one, I mean one of the other main ones....'

 

[cliffed]

I have heard of this new Reg but not perused it does it apply to all TN systems.

This is new to me too is the reg present in the latest amendment books

 

[cliffed]

This is what I found & only on non Pme supplies

 

[loz2754]

This is what I found & only on non Pme supplies

See post number 15

 

[Julie.]

This is new to me too is the reg present in the latest amendment books

Yes, it is in the current standard (18th edition amd 2.)

We can only follow the old standard (amd 1) for up to 6 months,

 

[mainline]

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

How far away is the greenhouse
Are you planning on using swa ?

 

[cliffed]

How far away is the greenhouse
Are you planning on using swa ?

There’s a duct into the greenhouse, which comes from a external power point, so maybe rubber cabling