Mains Electric Cable puzzle.

[macabethiel]

Originally Posted by rayf3262

TNS = DNO separate (S) supplied earth from sub.
TNCS = PME, earth Combined via nuetral
DNO = Supplier eg. Eastern power networks

So if its PME and that's now called TNCS does that point to black being Neutral as it has a lowish voltage reading ?

[rayf3262]

Originally Posted by macabethiel

So if its PME and that's now called TNCS does that point to black being Neutral as it has a lowish voltage reading ?

In all probability the black is neutral, I would suggest checking continuity of this with a known neutral elsewhere in the installation.

On a TN-CS (PME) supply the local installation earth is directly connected to the incoming supply neutral, as such you should normally expect a very small voltage differential between N & E, with a maximum loop impedance of 0.35R

On a TN-S supply, the earth goes all the way back to the sub as a separate conductor, so the N & E voltage differential here is likely to be greater.
This type of supply can often be identified by an lead sheathed incoming cable with the local installation main earth connected to the lead sheath.
The loop max. loop impedance here can be as high as 0.85R.
A reading between N & E of ~50V would suggest this type of supply.

[ian's terrano]

remember the old sparky saying red to red, black to black , blue to bits !!! 300 feet is a long length of cable they might have doubled up on the cable to stop volt drop depending on the size of cable and what load was on it.

ian