Meter Set Up Question

[hbendillo]

One of my clients has an Amprobe DM II Pro meter. This meter will measure the current and voltage of each phase and the reports will show phase voltages and currents; real, reactive and apparent power; and power factor.

The amperage clamps are rated for up to 1000 amps and there is one for all three phases of a three-phase system and one for the neutral. The feeder we're measuring is rated 1200-amps, 208-volt three-phase, four-wire. The feeder has three conductors per phase.

Because of the way the conductors were attached to the lugs at which were taking the measurements my client could not get the amperage clamp around all three conductors of each phase. They only clamped around one conductor of each phase and neutral. The results were interesting. Where I expected to see probably 200 to 300 amps of phase current the report showed 2000 to 3300 amps. This is roughly three time what I would have expected if we would have been able to clamp around all three conductors. Is there a correlation here? What is the effect of only clamping around one conductor of each phase? Can I extrapolate the actual current on each phase from this?

 

[bob]

In a perfect world clamping one conductor should give you 1/3 of the total reading. Sometimes connections may cause the load to divide differently.
Clamp only the phase conductor. Do not clamp the phase conductor and neutral together. Since the meter is only rated for 1000 amps you have
an error some where.

 

[hbendillo]

Yep, one third is what I expected too. I am thinking the magnetic field from the nearby "unclamped" conductors has some effect here. Don't know.

 

[mjolnir]

Meter setup

Meter setup

hbendillo

Looks like CT set up is could be incorrect three choices possible and not plug and play. Yes reading should be about 1/3 unless connections are poor, check for voltage drop across connections if in doubt.

http://www.amprobe.com/manuals/DMIIPRO.pdf

Hope this helps
:smile:

 

[bob]

I am thinking the magnetic field from the nearby "unclamped" conductors has some effect here. Don't know.

No .

 

[brian john]

1. Load will not divide equally, with parallel conductors.
2. There may be a multiplier in the meter some where in set up
3. The CT type may need to be programmed
4. I dislike any amprobe product..if only for the fact their help desk is TOTALLY USELESS.


I had a problem downloading this very meter and could get NO RESPONSE from them, 5 calls. If a manufacturer can not support their product it is not worth purchasing. IMO

 

[LarryFine]

There are amp meters available with a wire loop, rather than jaws, that are ideal for encircling multiple and/or difficult-to-access conductors.

 

[steve66]

Just out of curiosity, what would happen if the clamp weren't quite completely closed? Would the meter read more current than the actual value, or less?

Reminds me of a breaker that kept tripping for no apparent reason. They installed a power monitor with clamp on CT's, and we watched while some maintenance guys started and stopped AHU's and such looking for something that would make the breaker trip.

I nearly freaked when I started seeing 6000-9000 amps on one phase of a 800A breaker. It would spike for a few seconds, then back down to normal. It did that several times.

Finally realized it was one of the guys standing there keying his radio. Boy, did I feel like a... well, you know

Steve

 

[brian john]

if the clamp weren't quite completely closed?

It throws the accuracy of the CT's out of whack, high or low I really do not know as I never check the reading as I am setting up a meter or using my clamp-on.

 

[coulter]

Look for a CT lead. It will be 5A. That big of a feeder, there is likely one close.

Also, as larry said, Rogowski(sp?) coils are available. I've got some 24" and seen pictures of 36" They are flexible and split.

carl

 

[hbendillo]

1. Load will not divide equally, with parallel conductors.
2. There may be a multiplier in the meter some where in set up
3. The CT type may need to be programmed
4. I dislike any amprobe product..if only for the fact their help desk is TOTALLY USELESS.


I had a problem downloading this very meter and could get NO RESPONSE from them, 5 calls. If a manufacturer can not support their product it is not worth purchasing. IMO

Unlike your experience, I was able easily get in touch with Amprobe technical support. I think Amprobe is part of Fluke now. I had one of their technicians tell me that the readings that I am getting are correct and should represent three times the actual current. However, another one of their techs wasn't so sure. We have ordered some some bigger clamps and hope to verify the load in the next couple of weeks.