Electrical measurements

Dp I'd think so, else the field of one conductor might cancel those of others

As an erstwhile inventor and writer in the field however, at 82 not familiar with that rating, 350 Kcmil x 4 per phase, presuming it's a nominal current value

Dalehileman, why you utter such silly notions, I wonder..

Kcmils express the cross sectional area.

Yes, dpeirish, you can do that, measure one and multiply by the number of conductors of your feeders.

You could also measure each one and add them but the difference would be negligible.

….assuming of course they're all carrying about the same current

Another silly notion..

Obviously they are. It wouldn't come to mind of a professional to install feeders of different cross sections.

For the theory, check here Kirchhoff's circuit laws

Why "obviously" Tim
What if the very reason Irish wishes to take the measurement is a malfunction affecting the respective balance

That and two bucks will get you on the subway.

It could be Tim that I'm misunderstanding you or Dp or both in which case I'd hope to quietly exit via underground railway

I had assumed that Dp wishes to measure the current being carried by a 3-phase (plus ground) cable and is asking whether he should clamp the entire cable whereupon I replied in effect that he must instead free one of the conductors

Somehow the conversation turned to which conductor whereupon you suggested it doesn't matter since they'd presumably all measure the same whereupon I speculated that perhaps the reason Dp wished to measure current owes to a malfunction of some sort that might make them unequal

I'll be first to concede that at my advanced age I'm perhaps not familiar with current terminology (pun intended) so you might enlighten me

Incidentally it's interesting if I recall correctly from my days in Chicago that the subway uses dc at hundreds of volts which I had long speculated vs ac as terribly clumsy method. To save me the morning scanning Google, and for the benefit of other participants why don't we address this--even perhaps splitting off into new thread

Thanks again Tim for your interest

Your assumption is wrong. Read dpeirish carefully.

He has multiple conductors per phase (feeders).

He also has a small clamp on his amp meter.

Look here a typical installation with multiple conductors feeders:


He cannot measure each phase with a clamp like this:


As the conductors have the same cross-section, they will carry the same current.

In order to measure the total current, you either measure one conductor (of each feeder) and multiply by the number of conductors or you measure each one and add them.

Is that clear?


As for the use of DC current on the underground trains, read the DC current section here: Electric power transmission

"Multiple conductor feeders" had me going. I presume then that each phase is carried by four wires all connected in parallel

So I had presumed

Thank you for that Tim\ but yes, I'm familiar with the clamp meter

I had suposed however that he could separate from the bundle the 4 wires carrying each phase, then clamp. Am I still in the dark

Of course, provided there's nothing wrong. I had wondered whether Dp might wish to compare current readings for some reason

Yes Tim I really do understand all that sort of thing, it's just a matter of terminology

As for the use of DC current on the underground trains, read the DC current section here: Electric power transmission

Thanks Tim, I do recall now that dc is sometimes better for long distances because ac loses energy by radiation. as if the conductor were an antenna

See I really do comprehend this sort of stuff. In fact as an erstwhile writer and inventor I have several patents on electrical circuits

I suspect he is only wanting to know the total current and cannot do that at once using his small clamp.

Evidently Tim
Why do you suppose he hasn't responded