Steel framed units multiple PME supplies

Bengaz · Feb 27, 2024

Multiple commercial units within the same steel frame cant each have a PME supply (from the same transformer), we have to install an earth electrode to each unit. Did anyone know that? The NICEIC tech help didnt today...

Even though NPG supply a MET cant be used.

A break in the neutral supplying any unit and the current would flow through the frame and back to the transformer via the PME link in an adjacent unit. You may never know there was an external fault.

westward10 · Feb 27, 2024

Yes this is a problem with multiple supplies in this type of structure the supplier is correct, NICEIC well say no more.

davesparks · Feb 27, 2024

Bengaz said:
Multiple commercial units within the same steel frame cant each have a PME supply (from the same transformer), we have to install an earth electrode to each unit. Did anyone know that?

Yes, this is standard practice with all DNO's, I think may even be derived from ESQCR or something like that.

Bengaz said:
The NICEIC tech help didnt today..

Say no more.

Bengaz said:
.A break in the neutral supplying any unit and the current would flow through the frame and back to the transformer via the PME link in an adjacent unit. You may never know there was an external fault.

It's worse than that, the normal neutral currents of each installation will be diverted via the steel structure of the building via the bonding and back through the other supplies
This means you'll have current constantly flowing through the steel structure which can lead to all sorts of issues, possibly including accelerated corrosion of the steelwork

EricMark · Feb 29, 2024

Thank you, I had not considered the higher current in the good PEN, I must look as the building I work in has 3 or 4 supplies, there were separate units, but now are all combined and the cost of having supplies removed exceeds the cost of the standing change by a huge amount, so they were left in, although lightly used.

I was told it was PME and that the EV charge point has it's own earth rod, but never really looked as had no need to.