PME system with earth rod aswell

[davesparks]

It’s a very large installation with its own substation clearly labelled PME. Also the installers who fitted the Distribution board have noted it as PME.

If it has its own dedicated feed from a substation then it can't be PME. For a supply to be PME there needs to be multiple N-E connections along a distributing main, it's not possible to achieve that multi earthing on a dedicated feed.

 

[James]

If it has its own dedicated feed from a substation then it can't be PME. For a supply to be PME there needs to be multiple N-E connections along a distributing main, it's not possible to achieve that multi earthing on a dedicated feed.

Surely you can if you have multiple earth rods connected to the PEN conductor before the main isolator (origin of supply)??

 

[davesparks]

Surely you can if you have multiple earth rods connected to the PEN conductor before the main isolator (origin of supply)??

I don't think so, I'd have to look up the rules and regulations around PME to be sure though.
It just wouldn't make sense for a dedicated feed from a substation.

 

[James]

I don't think so, I'd have to look up the rules and regulations around PME to be sure though.
It just wouldn't make sense for a dedicated feed from a substation.

To be fair, I am not certain myself
but I thought it Simpley meant that the N was referenced to earth at several points before the origin. This becoming a combined N and E when terminated at the origin.

 

[timhoward]

Draw him a diagram showing how the PME earth will have a mini electrode somewhere.
It’s nuts to get rid of a TN system for this reason. As you say it’s even in the regs book now.

If the phases are very unbalanced and the closest PME real earth point isn’t near or has high impedance then there could be a measurable potential difference but it would have to be large to take this action - id prefer to be talking to the DNO about it.

(There’s a formula in the EV section to calculate N current in an unbalanced 3 phase system btw)

Edit - I missed some later posts, sorry