[smithjt]

How do I use a small amp probe, clamp on meter, to measure current on multiple feeder conductors? Do I measure one and then multiply by the number of conductors?

[Stratmando]

You can't clamp around a cable, it needs to be clamped around a single conductor, and 10 amps will read 10 amps, If you have a long enough single conductor, wrap 10 turns(coils), then clamp around, it will read 10 time higher.
Handy if measuring a small current.
If you measure with 10 turns, and read 16 amps, the actual draw would be 1.6 amps.

[hfcarson]

If you are attempting to read a three-phase feeder for example...
measure and record the amperage of each hot leg, A phase, B phase and C phase.
For the connected load on each phase multiply your reading x the applied voltage...
i.e. a reading of 10 amps on A phase x 120 volts = 1200 kVA (or watts if you assume power factor is equal to 1 or unity)
a reading of 20 amps on B phase x 120 volts = 2400 kVA
a reading of 30 amps on C phase x 120 volts = 3600 kVA
then add the totals, 1200 + 2400 + 3600 = 7200 kVA
Is this what you were looking for?

[tkrussell]

I will guess that Smithjt has parallel conductors on each phase.

If so, not the best method, but you can measure the current in each conductor and add the sum of each for the total current for each phase.

Will get you close, but not 100% accurate, better off with a meter with a large jaw, or flexible current probes, that can surround all conductors of each phase.

[smithjt]

Yes, thank-you, much appreciated! Multiple 350 Kcmil per phase.

[hfcarson]

Note: if there are for example three conductors per phase, then measurements of each conductor in each set should be relatively equal...
If they are not, it is a good indication that the terminations require tightening...

[tkrussell]

The difference is amps on multiple conductors of one pahse is usually due to minor difference in length of conduotrs.

[hfcarson]

Tk, allow me to qualify my response...
If the readings are "very" different, let's say more that 10% +/- then
As preventative maintenance the terminations should be re-tightened...
We saw this with a transformer and a distribution panel at a soft drink plant.

[shuntripper]

wow 10A x 120V = 1200 kVA?

1,200,000 watts?


priceless

[shuntripper]

The difference is amps on multiple conductors of one pahse is usually due to minor difference in length of conduotrs.

Occasionally, a minor difference in length usually has no effect on measured loads, more often than not the problem lies in how the source transformer is loaded. Unbalanced loads on phases from the source transformer causes voltage to vary as supplied to other or all loads on any phase.
And since perfect balance is nearly impossible to maintain even when a facility is first produced, changes in the balanced loading of the transformer's phases will be further upset as changes are made to the facility over time, like remodeling, additions of new equipment yadda yadda yadda

Variations in available voltage on each phase will translate as unequal currents drawn by a load.