Ah - is this to do with a difference between a 'main' and a 'service'? If so, can you possibly educate me?
Kind Regards, John
is this TN-S or PME?
- Thread starter THRIPSTER
- Start date
Kind Regards, John
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A main is the cable that generally runs along a street from a substation to which multiple customers are connected.
A service is a cable from a main to an individual customer.
It does exist, that if you ignore the all possible direct N-E shorts you might have consumers installations supplied by the same TNS service cable...
And what would you make of it if the point at which the conductor from the star point of the transfomer is tied down to physical earth and inititally separates into neutral and earth is not within the transformer room but actually in the consumers main panel? TNS or TNCS? the supply authority call it PNB but BS7671 doesn't recognise that...
PNB
Protective Neutral Bonding. This refers to the technique of using the
Supply Neutral Conductor directly from the transformer to provide a
protective earthing facility to a single customer. The neutral is earthed at
one point only normally at or adjacent to the customer’s installation
Protective Neutral Bonding. This refers to the technique of using the
Supply Neutral Conductor directly from the transformer to provide a
protective earthing facility to a single customer. The neutral is earthed at
one point only normally at or adjacent to the customer’s installation
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Thanks. In that case, allow me to repeat my question, translated into that language:
Kind Regards, John
It is certainly not unusual, I hesitate to say common as we have a huge amount of SNE (split neutral earth) cable in use that has no CNE in it
I'm not sure that PNB would qualify as TN-anything, would it? If I understand the terminology correctly, it would probably be something like -T !! The exposed-c-ps of the installation are connected directly to a local earth, and the transformer is not earthed at all, other than through the neutral to the intsallation's 'local' earth. It's almost TN-C-S in reverse, so maybe it's NT-C-SAnd what would you make of it if the point at which the conductor from the star point of the transfomer is tied down to physical earth and inititally separates into neutral and earth is not within the transformer room but actually in the consumers main panel? TNS or TNCS? the supply authority call it PNB but BS7671 doesn't recognise that...
Westie (or anyone), does the I/N/T/C/S terminology cater for PNB?
Kind Regards, John
Ah, but all thats happened is that the star point is extended a few more metres than it would normally be when the connection is made within the transformer room.
So which box would you tick on your cert John as there there isn't a box for PNB
So which box would you tick on your cert John as there there isn't a box for PNB
I doubt it, it is something rather different to the norm. Normally it is treated as TN-S as regards customer wiring
SNE main, CNE service into the building.
It is not a very good picture as there is another joint further back
You tell me! I suppose that, in terms of the current path resulting from an L-E fault within the installation (which is probably the consideration of most importance) it's actually more like TN-C-S, in that the return path to the transformer is entirely along the N conductor. Which would you tick??So which box would you tick on your cert John as there there isn't a box for PNB
[Assuming it were a 'manual' form, I probably wouldn't tick anything - I'd probably just write PNB!]
Kind Regards, John
That's obviously the converse of what we've been talking about. Are you saying that the building concerned receives a TN-C-S supply which is not formally PMEd?
Kind Regards, John
Correct
Yep, totally acceptable and the norm for most new or altered supplies, and gives TN-C-S in the building, all that is done is to bond the NE of the service to Neutral & Earth at the joint.
But it is!!
I seem to be getting some contradictory information here! Westie, if it is 'formally PMEd' where are the multiple earths?
Kind Regards, John
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