TN-S vs TNC-S (PNB) Earthing System

[Andy-1960]

What are the thoughts of you guys on the differences between a TN-S and a TNC-S (PNB) Earthing System.

My understanding is as follows:

TNC-S (PNB) - the Neutral & Earth Conductor are joined in the main switchboard with the neutral conductor between the transformer and the switchboard then being the earth fault path back to the transformer star point.

TN-S -a separate earth conductor is installed between the transformer and the switchboard and the neutral and earth are joined in the transformer cable box, the earth fault path back to the transformer start point.

So, depending on your thoughts, would you then say the source of supply is the switchboard or the transformer... I know what I think, but I have a customer who disagrees.

 

[telectrix]

the source of the supply is the customer's DNO fuse/s.

 

[Deleted member 26818]

Deleted.

 

[buzzlightyear]

Erection of earthing arrangements (TNC, TN-S, TNC-S and TT) | EEP - https://electrical-engineering-portal.com/erection-procedures-of-earthing-arrangements-tnc-tn-s-tnc-s-and-tt

 

[buzzlightyear]

TNC-S (PEN)

CORRECTED THAT YOU .

 

[westward10]

This has been chewed over many a time. Some argue the neutral from the transformer star point to the customers panel does not have a combined function, it is merely moving the star point to the panel where the earth is taken from so at this point it is TN-S. Others argue the reverse that the neutral does have a combined PEN function and is not shifting the star point from the transformer hence PNB.

 

[buzzlightyear]

PNB is TNS. It cannot be TNC-S as there is no conductor that shares the "earth" and "neutral" functions. It also cannot be "PME" as there is only a single connection to earth. PNB is used where a transformer supplies a single large customer. The earth reference for the transformer star-point is made at the customer's end of the supply cable, as there will not usually be a fuse rack in the DNO's substation.

 

[Deleted member 26818]

In the UK, it’s very rare to find a link between neutral and earth within the customer’s installation.
PNB as Buzz says is more akin to TN-S as it uses separate conductors. However it is treated in the UK as being TN-C-S.

It’s not correct to say there is only one connection to earth.
It will depend on the distance between the transformer and the installation.
Could be just the one electrode and link somewhere between, or there could be two, one close to the transformer and the other close to the installation.

 

[telectrix]

PNB is TNS. It cannot be TNC-S as there is no conductor that shares the "earth" and "neutral" functions. It also cannot be "PME" as there is only a single connection to earth. PNB is used where a transformer supplies a single large customer. The earth reference for the transformer star-point is made at the customer's end of the supply cable, as there will not usually be a fuse rack in the DNO's substation.

christ buzz, you been eating dictionaries?

 

[buzzlightyear]

christ buzz, you been eating dictionaries

yep.

 

[Nigel]

A TN-S will have a single earth conductor from the star point of the DNO transformer.

As in ‘S’ - seperate

A TN-C-S is combined on the DNO side ‘C’ and seperate on the installation side ‘S’.

A PME will be earthed at multiple points along the PEN conductor and then linked out at the termination within the installation.

A PNB will only be linked out at the installation with no other earthing points. As soon as another earthing point is put in along the PEN conductor it ceases to be a PNB.

 

[Nigel]

christ buzz, you been eating dictionaries?

 

[telectrix]

somebody is missing out on his fake sun tan.

 

[buzzlightyear]

Earthing arrangements (Schematics) Page - http://kci.co.ir/en/pages/106-Earthing%20arrangements%20(Schematics).html

 

[buzzlightyear]

somebody is missing out on his fake sun tan.

that sick man.

 

[Deleted member 26818]

A TN-S will have a single earth conductor from the star point of the DNO transformer.

As in ‘S’ - seperate

A TN-C-S is combined on the DNO side ‘C’ and seperate on the installation side ‘S’.

A PME will be earthed at multiple points along the PEN conductor and then linked out at the termination within the installation.

A PNB will only be linked out at the installation with no other earthing points. As soon as another earthing point is put in along the PEN conductor it ceases to be a PNB.

If it has a PEN conductor, then it’s TN-C-S.

 

[buzzlightyear]

PNB is TNS. It cannot be TNC-S as there is no conductor that shares the "earth" and "neutral" functions. It also cannot be "PME" as there is only a single connection to earth. PNB is used where a transformer supplies a single large customer. The earth reference for the transformer star-point is made at the customer's end of the supply cable, as there will not usually be a fuse rack in the DNO's substation.

 

[Deleted member 26818]

Yep.

 

[DPG]

Has Buzz got an alter ego on the IET forum then?

 

[David Prosser]

I may be missing the point, looks to me like the original question was for a HV DNO supply to customer owned switch gear and transformers. But that's just my take on it.