Tong testing ESR Cabling

[marko333]

Hello!

Where you have ESR cabling "Earth Sheath Return" on a 3phase wye system, am i correct in saying that you cannot tong test each phase and read the correct current flow?(unless the load is balanced..)
This is because the neutral current is travelling back up the sheath?
To get an accurate current reading you need to tong test the cable at a point where the sheath is not present ie- inside a switchboard?
Is there another method testing the current on an ESR cable where the sheath cannot be exposed?

Regards,

Marko

 

[Skogsgurra]

I assume that you are talking about a three-phase system where the phases are in a common cable.

Yes, you are correct in saying that you cannot use a current clamp to measure current in separate phases when they are not accessible (as in a cable) but that holds for cables without a sheet as well and without regard to sheath current or not.

And, yes, you can measure individual phases where they are separated (as in a cabinet). And that is also true regardless of cable type.


If, on the other hand, the three phases are in separate single phase cables, the situation is entirely different since the return current can flow in shath - partly or 100 percent. So a current clamp will not always tell the true current.


Gunnar Englund

http://www.gke.org