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# Electrical measurements

Mon 19 Nov, 2012 08:46 am
I have multiple conductor feeders, 350 Kcmil x 4 per phase. I only have a small clamp on meter, do I measure one and multiply by the number of conductors to get the correct amp reading?
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Type: Question • Score: 1 • Views: 1,778 • Replies: 11
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dalehileman

1
Mon 19 Nov, 2012 11:41 am
@dpeirish,
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
timur

1
Mon 19 Nov, 2012 02:37 pm
@dalehileman,
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.
dalehileman

1
Mon 19 Nov, 2012 06:03 pm
@timur,
Quote:
measure one and multiply by the number of conductors of your feeders.
….assuming of course they're all carrying about the same current
timur

1
Tue 20 Nov, 2012 01:23 am
@dalehileman,
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
dalehileman

1
Tue 20 Nov, 2012 02:23 pm
@timur,
Quote:
Obviously they are.
Why "obviously" Tim
What if the very reason Irish wishes to take the measurement is a malfunction affecting the respective balance
timur

1
Tue 20 Nov, 2012 02:42 pm
@dalehileman,
That and two bucks will get you on the subway.

dalehileman

1
Wed 21 Nov, 2012 12:18 pm
@timur,
Quote:
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
timur

1
Wed 21 Nov, 2012 02:22 pm
@dalehileman,

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

dalehileman

1
Wed 21 Nov, 2012 03:13 pm
@timur,
Quote:
Your assumption is wrong. Read dpeirish carefully.He has multiple conductors per phase (feeders).
"Multiple conductor feeders" had me going. I presume then that each phase is carried by four wires all connected in parallel

Quote:
He also has a small clamp on his amp meter.

Code:`Look here a typical installation with multiple conductors feeders: He cannot measure each phase with a clamp like this:`
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

Quote:
As the conductors have the same cross-section, they will carry the same current.
Of course, provided there's nothing wrong. I had wondered whether Dp might wish to compare current readings for some reason

Quote:
…..you either measure one…...and multiply…...or you measure each one and add them. Is that clear?
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
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timur

1
Wed 21 Nov, 2012 03:18 pm
Dalehileman wrote:
I had wondered whether Dp might wish to compare current readings for some reason

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

1
Wed 21 Nov, 2012 07:16 pm
@timur,
Evidently Tim
Why do you suppose he hasn't responded
0 Replies

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