PME system with earth rod aswell

[westward10]

How certain are you it is a PME system, TN-C-S is not necessarily PME.

 

[Deleted account]

How certain are you it is a PME system, TN-C-S is not necessarily PME.

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.

I am going to have a chat with the installers as we have a good working relationship with them.

I just wanted to run it past you guys first in case I made a fool of myself.

 

[Risteard]

Let’s open an old thread.

looking fo4 a brief answer. Wishful thinking.

on a pme system having an earth rod as an addition is perfectly ok in my opinion.


im working for and under a new electrician at work.
we have had a distribution board fitted by outside contractors. They have earthed via a 16 mm earth conductor within the 3 phase SWA supplied from a PME system. They have also popped an earth rod in at the new distribution board. We are going to run feeds of this board for various stuff.

the new electrician wants to convert to TT or get rid of the earth rod As he thinks it’s wrong because of “potential differences” I disagree.

Am I wrong? I’m willing to accept this If I am,

but I know earth rods where proposed as additions in PME in the 18th. So I’m sure it’s OK.

An Earth electrode/pit in a TN-C-S installation should be encouraged! In fact many (most?) countries mandate it! A large installation may need a fairly low impedance to be effective though.

But as pointed out TN-C-S could be either PME or PNB.

 

[UNG]

An Earth electrode/pit in a TN-C-S installation should be encouraged!

I would agree with you on a properly maintained, regularly checked system but one or multiple earth rod issues could become dangerous as I have seen in the past

In fact many (most?) countries mandate it!

And they all have different regs and network topology

A large installation may need a fairly low impedance to be effective though.

And that is the difference between an earth rod and a properly installed and tested earth rod

But as pointed out TN-C-S could be either PME or PNB.

With a private substation it could be TNS despite it being labelled PME just because the star point of the transformer is referenced to earth it is only there to keep a stable neutral point and doesn't necessarily make it PME

 

[Deleted account]

I know all the over head cables locally have been switched to PME. However that does not necessarily mean that my installations supply is.

I think most supplies these days have an element of PME as all repairs additions and alterations in the network are going to PME.

having a part of the supply that has been replaced to PME . Does that nessisaritly mean the installation is classed as PME. If it was formally TNS?

I’ve been watching some John ward you tube videos and it has raised more questions than answers.



Anyway forgetting about the merits of PME with or without an earth rod.…

Ive decided the following. I think we should TT it.
the supply we are going to take off the DB in question is going to 3 separate metal containers with an outside enclosure for keeping birds (Parrots). Each container will have a separate small DB for the final circuits.
The nature of the metal containers and its for livestock has convinced me that TT is the better option especially considering the difficulty in identifying earthing arrangements despite labelling. There won’t be any suplimentary bonding issue as there is no other utility supplies. No water or gas contained within.
obviously earthing to the equipot3ntial metal enclosure will happen as it’s in contact with the mass of earth.
Any buried water pipes in the vicinity we know are plastic as we put them in so no issue there.

 

[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