Pscc and Pefc

Bsharp · Mar 28, 2021

Can anybody give me the definitive answer to the question of why on TNCS earring arrangement when testing Pefc and Pssc sometimes the values are different? When we are essentially testing down the same path as the earth conductor and neutral are combined? And therefore both share the same parallel paths etc.

Lister1987 · Mar 28, 2021

Bsharp said:
Can anybody give me the definitive answer to the question of why on TNCS earring arrangement when testing Pefc and Pssc sometimes the values are different? When we are essentially testing down the same path as the earth conductor and neutral are combined? And therefore both share the same parallel paths etc.

Think of the supply cable, it shares a characteristic with T&E in so much as the CPC strands of either the PEN/CNE cable can be of a lower CSA than that of the line conductor, same can be said about the tails.

Bsharp · Mar 28, 2021

Lister1987 said:
Think of the supply cable, it shares a characteristic with T&E in so much as the CPC strands of either the PEN/CNE cable can be of a lower CSA than that of the line conductor, same can be said about the tails.

Yes I understand the difference in size of the conductors but if the earth and neutral are combined I.e. connected in the cut out then surely the only difference is the size of the earthing tails conductor which at a length of say max 3m’s should be negligible.
So line to earth (CNE)
Or line to live (CNE)
Share the same path?
this is where I get a little confused.

timhoward · Mar 28, 2021

It's easier to compare the the Ze and the impedance of the return path from phase to neutral (which on my MFT you have to do first anyway) and see whether the csa difference reasonably accounts for it.

Mathematically, a difference of 0.01 ohms between the two makes a much bigger difference to the calculated PEFC and PSCC.
To get the idea do 230/0.05 and 230/0.06 and see the difference 0.01 ohm makes.

Bsharp · Mar 28, 2021

timhoward said:
It's easier to compare the the Ze and the impedance of the return path from phase to neutral (which on my MFT you have to do first anyway) and see whether the csa difference reasonably accounts for it.

Mathematically, a difference of 0.01 ohms between the two makes a much bigger difference to the calculated PEFC and PSCC.
To get the idea do 230/0.05 and 230/0.06 and see the difference 0.01 ohm makes.y

makes sense now thanks for the replies.