Power point in external glasshouse

cliffed · Apr 4, 2022

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

cliffed · Apr 5, 2022

This is what I found & only on non Pme supplies

loz2754 · Apr 5, 2022

cliffed said:
This is what I found & only on non Pme supplies

See post number 15

Julie. · Apr 5, 2022

cliffed said:
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 · Apr 5, 2022

cliffed said:
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 · Apr 5, 2022

mainline said:
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

cliffed · Apr 7, 2022

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

Cheapest option

Except Pme supplies

[ElectriciansForums.net] Power point in external glasshouse

westward10 · Apr 7, 2022

If that is the new book I did wonder if it applied to all TN systems.

cliffed · Apr 7, 2022

westward10 said:
If that is the new book I did wonder if it applied to all TN systems.

It’s in the new book but without looking @ the blue book I’m pretty sure it’s in there too.

cliffed · Apr 7, 2022

I doubt if I would take a Pme supply to the greenhouse anyway.
It just highlights the requirements & the expense, if done correctly the costs of adding a Power point

westward10 · Apr 7, 2022

cliffed said:
It’s in the new book but without looking @ the blue book I’m pretty sure it’s in there too.

It is there but is now amended.

cliffed · Apr 7, 2022

westward10 said:
It is there but is now amended.

Cheers…can’t get to my book yet…having a new bathroom fitted, the house upside down @ the moment

Julie. · Apr 7, 2022

cliffed said:
Except Pme suppliesView attachment 96674

No not except PME, it is except where PME conditions apply.

You should not be applying PME as the CNE will have been split at the header into L, N & E. You should never combine the N & E within the installation.

The note re except where PME conditions apply, was there over several versions of the regs, we would still apply the 50% or min 10mm^2 rule.

In fact there is no sizing for bonding within the (wiring) regulations where PME does apply!

This is usually determined by the utility themselves, and is often 50% or min 16mm^2 for customer service points, and generally 32mm^2 within the network (eg SNE sheath to CNE) even if its to one customer.

cliffed · Apr 7, 2022

Julie. said:
No not except PME, it is except where PME conditions apply.

You should not be applying PME as the CNE will have been split at the header into L, N & E. You should never combine the N & E within the installation.

The note re except where PME conditions apply, was there over several versions of the regs, we would still apply the 50% or min 10mm^2 rule.

In fact there is no sizing for bonding within the (wiring) regulations where PME does apply!

This is usually determined by the utility themselves, and is often 50% or min 16mm^2 for customer service points, and generally 32mm^2 within the network (eg SNE sheath to CNE) even if its to one customer.

I don’t intend to combine N & E..never have…For me it’s gonna be a TT system @ the greenhouse.
Also the 10mm MPBC would apply if using the DNO earth

westward10 · Apr 7, 2022

This has become somewhat confused I asked in #22 if this applied to all TN systems and whilst TN-C-S does not necessarily mean PME I was answered yes it does but it doesn't?

cliffed · Apr 7, 2022

westward10 said:
This has become somewhat confused I asked in #22 if this applied to all TN systems and whilst TN-C-S does not necessarily mean PME I was answered yes it does but it doesn't?

Definitely not apply to TNS

Julie. · Apr 7, 2022

cliffed said:
I don’t intend to combine N & E..never have…For me it’s gonna be a TT system @ the greenhouse.
Also the 10mm MPBC would apply if using the DNO earth

Where do you get the 10mm from?

If that's from table 54.8 or 544.1.1 then as per your wording - those figures are "except where PME conditions apply "

Julie. · Apr 7, 2022

westward10 said:
This has become somewhat confused I asked in #22 if this applied to all TN systems and whilst TN-C-S does not necessarily mean PME I was answered yes it does but it doesn't?

I understood you to mean all tn conditions applicable to electrical installations beyond the utility supply point when I answered yes i.e. the area covered by the wiring regs; but fair enough, within the utility network the content of the wiring regs is not necessarily applicable.

cliffed · Apr 7, 2022

Julie. said:
Where do you get the 10mm from?

If that's from table 54.8 or 544.1.1 then as per your wording - those figures are "except where PME conditions apply "

10mm on a TNCS/ PME supply where the Neutral size is 35mm <

Julie. · Apr 7, 2022

cliffed said:
10mm on a TNCS/ PME supply where the Neutral size is 35mm <

Where do you get this from?

If it's table 54.8 or 544.1.1 then as per your wording - those figures are "except where PME conditions apply "

cliffed · Apr 7, 2022

Earthing systems recognised

cliffed · Apr 7, 2022

Julie. said:
Where do you get this from?

If it's table 54.8 or 544.1.1 then as per your wording - those figures are "except where PME conditions apply "

Yea I know

Julie. · Apr 7, 2022

cliffed said:
Yea I know

So if you believe that the PME note means that in any case where a PME is used to supply a property, the values in 54.8 and 544.1.1 are not correct , just where do you get the correct size from?

Wouldn't this be a glaring omission from the regs? - inability to size bonding if it's supplied via PME.

Or should we understand that "where PME conditions apply" refers to those situations where the Neutral and earth are combined (CNE) forming part of the PME configuration.

In which case, once they have been split at the service head then 54.8 and 544.1.1 apply in terms if bonding size.

cliffed · Apr 7, 2022

Your last sentence is exactly correct

Julie. · Apr 7, 2022

cliffed said:
Your last sentence is exactly correct

Which would mean in accordance with 544.1.1 main bonding in sub-buildings could be sized at 50% of the conductors to that building or 6mm^2 whichever is the greater.

Just running a 1.5 or 2.5 SWA from the cu to this outlet and bonding the metal frame via 6mm^2 from the swa (+cpc if a 3rd core used) would be completely compliant with the minimum expense.

cliffed · Apr 7, 2022

Julie. said:
Which would mean in accordance with 544.1.1 main bonding in sub-buildings could be sized at 50% of the conductors to that building or 6mm^2 whichever is the greater.

Just running a 1.5 or 2.5 SWA from the cu to this outlet and bonding the metal frame via 6mm^2 from the swa (+cpc if a 3rd core used) would be completely compliant with the minimum expense.

I shall be installing a TT System with the appropriate MPBC