What is PME and TNCS??

[Guest112]

Hi guys just wondering if someone can explain the difference between the two, was doing a pir today and whilst checking the supply i noticed a western power sticker on their cut out saying the earthing arrangement is either PME or TNCS. But on the reports my company uses the only options to tick regarding the supply are
1. TNCS Pme
2. TNCS protective neutral bond

I know about supplys and im aware that tncs is tera neutral combined seperate being that the neutral and earth is combined to the cutout and separate to the installation via a separate earth off the neutral and so on so can someone explain the PME for me please and how/if its different in the installation?? And a PEN also??? Cheers guys

 

[IQ Electrical]

Hi Peter, firstly, PME and PNB are both classed as TN-C-S supplies which as you rightly state, consist of a PEN conductor which is separated at the point of use into neutral and earth conductors.

The difference is in the M of PME, meaning 'multiple'. The PEN conductor on PME is tied down to earth at Multiple points along it's route.

On PNB, there is a PEN conductor but this is only connected to earth at 1 point and is normally limited to situations where a distribution transformer supplies only 1 consumer.

 

[SW1970]

Hi IQ, is there any way of determining that a transformer is only serving 1 customer? I guess if it's a pole transformer and the overheads don't go on any further and this "last pole" is at a farm in the middle of nowhere that's a good clue, but is there a more scientific way? Thanks, SW

 

[johnboy6083]

PME is protective mutiple earthing, where the protective conductor, PEN conductor) will be earted along its route, usually with rods attached at underground joints, or from overhead lines. As far as im aware, a protecive neutral bond, is where the neutral bar and earth bar within larger electrical distribution opanels are linked together, rather than linking the star point to earth at the supply transformer.

 

[johnboy6083]

Iq beat me too it. PNB is usually used with larger industrial or commercial premises.

 

[IQ Electrical]

Hi IQ, is there any way of determining that a transformer is only serving 1 customer? I guess if it's a pole transformer and the overheads don't go on any further and this "last pole" is at a farm in the middle of nowhere that's a good clue, but is there a more scientific way? Thanks, SW

Hi SW, unless you've got information from the supplier (rare) then you can only go on what you can see.

 

[Engineer54]

Hi Peter, firstly, PME and PNB are both classed as TN-C-S supplies which as you rightly state, consist of a PEN conductor which is separated at the point of use into neutral and earth conductors.

The difference is in the M of PME, meaning 'multiple'. The PEN conductor on PME is tied down to earth at Multiple points along it's route.

On PNB, there is a PEN conductor but this is only connected to earth at 1 point and is normally limited to situations where a distribution transformer supplies only 1 consumer.

TNC-S can also be a DNO supply cable that is in the process of PME, but hasn't yet reached the max Ze level of 0.35 ohms or doesn't yet comply with PME designated requirements. If the truth be known, there are many such situations around the country from what i can make of it. A true PME supply should have the neutral roded at every joint in the supply cable string. This has nothing to do with the supplying transformer, it's the cable that is providing the earth system....

 

[Guest112]

Hi Peter, firstly, PME and PNB are both classed as TN-C-S supplies which as you rightly state, consist of a PEN conductor which is separated at the point of use into neutral and earth conductors.

The difference is in the M of PME, meaning 'multiple'. The PEN conductor on PME is tied down to earth at Multiple points along it's route.

On PNB, there is a PEN conductor but this is only connected to earth at 1 point and is normally limited to situations where a distribution transformer supplies only 1 consumer.

so is a tncs always earthed at points along the route (PME) and if so is PME just another term for the arrangement?
And the PEN conductor on a tncs is the name of the neutral earth conductor what does it stand for lol
And a PNB protective neutral bond is an individual supply from a transformer is that correct? much apreciated btw

 

[Engineer54]

so is a tncs always earthed at points along the route (PME) and if so is PME just another term for the arrangement?
And the PEN conductor on a tncs is the name of the neutral earth conductor what does it stand for lol
And a PNB protective neutral bond is an individual supply from a transformer is that correct? much apreciated btw

Think of PME as a high integrity TNC-S system. PEN stands for ...Protective Earthed Neutral.

 

[GLENNSPARK]

I bet that bloke at the "joint box house" we were at the other week STILL hasn`t been on to the DNO about getting that old cast iron cutout replaced and a TN-C-S earthing arrangement n all.....still on a TT that one...................

 

[johnboy6083]

so is a tncs always earthed at points along the route (PME) and if so is PME just another term for the arrangement?
And the PEN conductor on a tncs is the name of the neutral earth conductor what does it stand for lol
And a PNB protective neutral bond is an individual supply from a transformer is that correct? much apreciated btw

A PNB isnt always a supply from a dedicated transformer. A protective neutral bond is the link between the star point of the transformer, and the earth grid of the transformer. This joint could be made at the transformer itsself, or could be made at the consumers main distribution panel. The latter option is only taken (in my experience) in larger installations.

 

[Knobhead]

If the transformer supplies more than one consumer the DNO will fit a service pillar near the transformer and install the N-E link there. They will not fit the link at a consumer’s switchboard unless it’s a sole supply.

 

[chronyx]

This is what I like about this forum - it even answers the questions I hadn't thought to ask!

This is interesting, thanks all.

 

[Knobhead]

What was the question?