Measuring motor current?
Measuring motor current?
(OP)
If I have a motor 150' away from the contactor controlling it and I measure current at the peckerhead and then take a second measurement at the contactor assuming no change in load and regardless of wiring methods should the measurements be identical?
Is it relevant where you measure current in an AC circuit(for example at the breaker versus at the load)?
Thanks
Is it relevant where you measure current in an AC circuit(for example at the breaker versus at the load)?
Thanks





RE: Measuring motor current?
That said they can be different.
Your clamp-on measures the magnetic flux that passes thru its aperture. Unlike a shunt or direct connect meters that measure the actual current thru the shunt a clamp-on measures "what it finds in its aperture". This means its readings can vary by the angle the wire runs thru it. The location the wire runs thru the clamp-on, and whether you have high magnetic fields in the same area, or lots of iron nearby.
Generally the readings would not vary enough for anyone to actually care. The motor loading can shift slightly and it would cause a much larger shift than perhaps any of the aforemented details.
So measure where you will..
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Measuring motor current?
You might Google Kirchhoff's Current Law....
RE: Measuring motor current?
Could I expect the measured current to be lower if wiring to loads was physically seperated?
I have a panel with 13 motor starters in it motor nameplate
FLA-24A but most motors are drawing between 26-27 amps the wiring for the 13 motors is split between 2 raceways for 50' + 100 feet in a wireway with all 13 motor leads.
Thanks
RE: Measuring motor current?
RE: Measuring motor current?
RE: Measuring motor current?
The derating has nothing to do with any violations of Kirchhoff's Current Law.
RE: Measuring motor current?
RE: Measuring motor current?
RE: Measuring motor current?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Measuring motor current?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Measuring motor current?
No, I don't think so. Kirchhoff wouldn't like that and you wouldn't to make Kirchhoff mad now would you?
RE: Measuring motor current?
RE: Measuring motor current?
If you get different flow measurements, that either means that you have a tee fitting in there somewhere that you forgot about, or you have a leak.
Electrically, if you get different current readings, either you have another load tapped into the middle of your feeder run, or you have some leakage current (small leak), or you have a short circuit (big leak).
"Big leak" short circuits are obviously a problem.
"Small leaks" might include insulation breakdown, which can quickly turn into big leaks.... or they could also be capacitive coupling, which is generally not a problem.
RE: Measuring motor current?
RE: Measuring motor current?
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RE: Measuring motor current?
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Measuring motor current?
Jeff gets one for interesting new theory.
Pete gets one for another interesting theory - and very well formulated.
Mark gets one for being on the mark.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Measuring motor current?