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#43414 - 10/12/04 07:43 PM Panel Meter Question
Merlin Offline
Member
Registered: 01/27/04
Posts: 170
Loc: NW Indiana
I recently installed a panel meter on a single phase load of 10 hp, 230 volt, FLA 55. My local supply house sold me a 0-75 amp meter, and 75-5 amp donut transformer. I installed these as I have a few in the past. The running load on my Fluke is 22 amps. However the meter only reads about 5 amps. The only thing I can figure is either a defect. or possibly the donut is to close to another load. Is anyone familar with these things. Thanks.
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#43415 - 10/12/04 11:51 PM Re: Panel Meter Question
e57 Offline
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Registered: 05/27/03
Posts: 2876
Loc: S.F.,CA USA
Emon-demon? Are the donuts and meter a match for eachother and calibrated? Also, the placement of the donut is crucial. If it is sitting on the side at an angle to the conductor you'll get false readings. They should be as centered and squared on the conductor, which can be hard to do in most panels.
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#43416 - 10/13/04 01:18 AM Re: Panel Meter Question
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Also,
Has the Ammeter got the correct shunt attached to it?.
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#43417 - 10/13/04 05:35 AM Re: Panel Meter Question
Merlin Offline
Member
Registered: 01/27/04
Posts: 170
Loc: NW Indiana
e-57,

I don't know if they are matched, this is what my supply house sold me so I assume so. It is sitting pretty square although it is laying on top of other wires in a very crowded box.

Trumpy,

What do you mean by a shunt?

Thanks for the reply
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#43418 - 10/13/04 11:04 AM Re: Panel Meter Question
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Merlin,
Quote:
What do you mean by a shunt?

An ammeter only carries a very minute amount of current, compared to the amount that it may be measuring.
A shunt is a resistance that is lower than the resistance of the meter movement itself, this shunt is placed in Parallel with the meter movement.
In this way, when connected to the circuit, the majority of current is passed, or Shunted, through the Shunt resistance.
Thereby ensuring that the meter only recieves a small proportion of the total circuit current and prevents the movement being damaged.
Hope this helps.
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#43419 - 10/13/04 01:08 PM Re: Panel Meter Question
NJwirenut Offline
Member
Registered: 09/15/01
Posts: 806
Loc: Bergen County, NJ
Quote:
My local supply house sold me a 0-75 amp meter, and 75-5 amp donut transformer.


Check the meter carefully. Did they actually sell you a 0-75A meter, or a 0-5A meter with a 0-75A scale? You need a 5A meter for use with the CT.

Other than that, check the orientation/centering of the conductor in the CT window, and make sure all the secondary CT wiring is OK. Insert another ammeter in the CT loop, and verify how much current is being developed on the 5A side.
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