PME system with earth rod aswell

[Gavin John Hyde]

Been on a job today and debating what to put on the certificate.

The DNO in early 2013 upgraded the supply and installed PME. The previous setup had an earth rod installed. This is still connected to the main earth terminal. Not sure what type the previous set up was as the customer is none the wiser, As the upgrade was done just before she bought the house.all she cared about was that things come on and turn off when required.

I am only filling in a minor works certificate as it only involved extending a radial.

In terms of earthing arrangement would you all agree i have been okay to record it as PME with a supplementary TT rod. making a note in the comments box mentioning there is a rod aswell? Guess it will be 18th edition compliant before its time!

I have so far filled it in as a PME system and am wondering if in addition to recording the Ze of 0.29 ohms i should record Ra aswell? I haven't measured it as of yet as i went with its a PME with supplementary rod.

I have to go back Monday next week to change a light fitting, so can measure Ra if needed.

It does raise the prospect of whether the certificate forms will be updated to reflect 18th edition if supplementary rods are going to be needed.

Thoughts welcome as it is something I haven't dealt with or potentially noticed before as most of my experience is light commercial such as pubs.

 

[Ian1981]

If it's been changed to pme then why bother with the earth rod?
By definition from the DNO having Carried out works it's a TN-CS earthing arrangement

 

[telectrix]

i'd just do as you suggest. record Ze and PME earthing , with a note saying there is a supplementary rod.

 

[Wilko]

Agree TNCS as its the dominant system, with a note.

 

[telectrix]

or diss the rod and say nowt.

 

[Gavin John Hyde]

or diss the rod and say nowt.

Did think of that, but given the way people get slaughtered if something goes wrong this day and age, i figured its best to play it by the rules and not conceal things. ALso given the potential changes regarding supplementary rods in the 18th ed its worth thinking about now.

 

[The Ghost]

I imagine the younger people reading would see @telectrixs' comment "Diss the rod" as
That is a crap rod and looks bad innit, nowadays

 

[telectrix]

I imagine the younger people reading would see @Pete999s' comment "Diss the rod" as
That is a crap rod and looks bad innit, nowadays

i know me and pete are both old coffin dodgers, but surely you can tell us apart. i'm the good looking one.

 

[The Ghost]

Doh! You knew who I meant though
EDIT: Don't know what you mean, maybe new glasses?

 

[Risteard]

It's TN-C-S. The fact it also has an Earth rod is irrelevant (in fact, it is a very good thing). No need to worry about Ra of the rod.

Most of the rest of the world requires Earth electrodes on TN-C-S installations - it's about time JPEL/64 caught up.

 

[Gavin John Hyde]

JPEL/64

JPEL/64 ????
Whats that when its translated in to English?

 

[Ian1981]

JPEL/64 ????
Whats that when its translated in to English?

It's the commitee that decide what regulations we should all now follow ie sticking in an earth electrode on TN systems

 

[westward10]

JPEL/64 ????
Whats that when its translated in to English?

Look in the front of BS7671 you will see the listings for the brains trust.

 

[Ian1981]

Basically they put a list of new regulations into a hat, give it a shuffle and each member picks out a regulation and they have a good chuckle over it!
Let the b*stards (that's us)figure this one out mhaaaaahhhaaa

 

[Gavin John Hyde]

Look in the front of BS7671 you will see the listings for the brains trust.

Ah okay, didnt get that on the find the correct answer test/ wordsearch for grown ups that is the 17th ed.

It sounds like the same method american psychiatrists use when they update the DSM book of mental disorders. basically a shrink proposes a new condition based on what he has seen in patients or hospital. if enough other shrinks agree and put there hands up it ends up the big book and people can be labelled as having the said new condition. absolutely bonkers... and that's just the shrinks.

 

[westward10]

Basically they put a list of new regulations into a hat, give it a shuffle and each member picks out a regulation and they have a good chuckle over it!
Let the b*stards (that's us)figure this one out mhaaaaahhhaaa

Careful now some forum members maybe offended by that

 

[Deleted member 26818]

How old is this thread?
Don't you all know the proposals put forward for next year 's edition of BS7671?

 

[Ian1981]

Na their doing amendment 1 to the 18th now
Out 2020

 

[Wilko]

I'm trying to think of something funny to say about all the new books etc I'll have to buy, but I'm at a loss. Where's @buzzlightyear when we need him ?

 

[buzzlightyear]

QUOTE="Gavin John Hyde, post: 1290550, member: 101583"]JPEL/64 ????
Whats that when its translated in to English?[/QUOTE]
probably a earth planted potato or could be IEE joint chiefs of staffs

 

[buzzlightyear]

I'm trying to think of something funny to say about all the new books etc I'll have to buy

yeah like the beano or dandy !

 

[static zap]

....Most of the rest of the world requires Earth electrodes on TN-C-S installations - it's about time JPEL/64 caught up.

We were a proud nation of Engineers ,
(I'll blame global warming making us all equal)

 

[buzzlightyear]

We were a proud nation of Engineers ,
(I'll blame global warming making us all equal)

is that boiling the kettle at the same time!

 

[Octopus]

Na their doing amendment 1 to the 18th now
Out 2020

Why can't they simply defer the 18th until 2020 ?

Save us all a lot of money....

 

[static zap]

Why can't they simply defer the 18th until 2020 ?

Save us all a lot of money....

Need to keep the printing industry alive , more regulations , Brexit red tape ..!

 

[buzzlightyear]

Need to keep the printing industry alive

yeah ,that's the Chinese has well.
they like coping regs has well .

 

[David M]

i know me and pete are both old coffin dodgers, but surely you can tell us apart. i'm the good looking one.

Sorry I had to disagree, all old people blend into the same look
I often see my old man knocking about, only to find its some other old geezer who looks like him

 

[frank rabbets]

Too many mirrors David.

This reminds me of a house I moved in to in 1975 built in 1936. After a few years I decided to check the earth out as I noticed we had 2 overhead wires + and -. There was no earth system at all so I
Bought an earth rod and wired it to the fuse box accordingly.
Then the MEB came and wired the earth to neutral WTF. If that had never been brought in would they allow that now?
I think they also used to use a 12" square galvanized plate buried in the ground. I've just dug one up here, house built in 1934.

 

[frank rabbets]

Too many mirrors David.

This reminds me of a house I moved in to in 1975 built in 1936. After a few years I decided to check the earth out as I noticed we had 2 overhead wires + and -. There was no earth system at all so I
Bought an earth rod and wired it to the fuse box accordingly.
Then the MEB came and wired the earth to neutral WTF. If that had never been brought in would they allow that now?
I think they also used to use a 12" square galvanized plate buried in the ground. I've just dug one up here, house built in 1934.

 

[frank rabbets]

Too many mirrors David.

This reminds me of a house I moved in to in 1975 built in 1936. After a few years I decided to check the earth out as I noticed we had 2 overhead wires + and -. There was no earth system at all so I
Bought an earth rod and wired it to the fuse box accordingly.
Then the MEB came and wired the earth to neutral WTF. If that had never been brought in would they allow that now?
I think they also used to use a 12" square galvanized plate buried in the ground. I've just dug one up here, house built in 1934.

 

[frank rabbets]

Too many mirrors David.

This reminds me of a house I moved in to in 1975 built in 1936. After a few years I decided to check the earth out as I noticed we had 2 overhead wires + and -. There was no earth system at all so I
Bought an earth rod and wired it to the fuse box accordingly.
Then the MEB came and wired the earth to neutral WTF. If that had never been brought in would they allow that now?
I think they also used to use a 12" square galvanized plate buried in the ground. I've just dug one up here, house built in 1934.

 

[telectrix]

and this week's prize for the most duplicate posts goes to..................................................................................................................................................................................................

the rabbit.

 

[frank rabbets]

Only pressed "post reply" once !!

 

[Toneyz]

Only pressed "post reply" once !!

This seems to be happening a lot.

 

[Midwest]

Only pressed "post reply" once !!

How hard though

 

[DPG]

So was that 4 earth rods?

 

[Deleted account]

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.

 

[DPG]

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.

If the rod is bonded to the distribution board earth then surely there can be no potential difference. Did he mention which two points he was thinking of the difference being across?

I agree with you and really can't see the problem here, but it will be interesting to hear other views.

 

[Deleted account]

If the rod is bonded to the distribution board earth then surely there can be no potential difference. Did he mention which two points he was thinking of the difference being across?

I agree with you and really can't see the problem here, but it will be interesting to hear other views.

Thanks for quick responce. My thoughts exactly. Just had to check in case I had got it wrong.


This new guy has much more experience with these types of systems than me or so he said at interview, coming from industrial and comercail instals, but I’m starting to suspect he’s been relying on others to design his jobs.

 

[DPG]

Thanks for quick responce. My thoughts exactly. Just had to check in case I had got it wrong.


This new guy has much more experience with these types of systems than me or so he said at interview, coming from industrial and comercail instals, but I’m starting to suspect he’s been relying on others to design his jobs.

To be honest I'm no expert either.

Be interesting seeing what else he says.

 

[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