Objectionable current

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Don D

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On a seperatly derived system where your XO terminal on your transformer is bonded to the grounding conductor, is there ever an inherent current on the bonding wire of the transformer?
 
we seem to only have about .4 amps and it doesnt seem to change. we are using a hand held fluke meter
 
objectionable current

objectionable current

I should have clarified that the current that is on the bonding wire is .4 amps
and that the XO terminal is only bonded at the transformer. Also I have checked the other panel boards and the neutrals & grounds are completely seperated!
 
Welcome to the forum. But I think we need a little more info here. You say this XO terminal is bonded to the transformer, bonded how? What kind of bond are you talking about? If it is bonded to the grounding conductor IMO there shouldn't be any reading at all. Are you using a clamp-on meter reading for amps? I am wondering why the XO terminal would even be bonded to the grounding conductor...
 
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Kdawg67 said:
.....I am wondering why the XO terminal would even be bonded to the grounding conductor...
Click to expand...


Because it can be??

806ecmCQfig1.jpg
 
Don D said:
I should have clarified that the current that is on the bonding wire is .4 amps
and that the XO terminal is only bonded at the transformer. Also I have checked the other panel boards and the neutrals & grounds are completely seperated!
Click to expand...

Take your True RMS Digital Ammeter,turn it on,walk towards your energized
transformer,watch the display,hold the ammeter next to the transformers
ventilation opening (Top or Bottom).The current you will see on the ammeter
is induction. If you clamp around the system bonding jumper and get .4 amps
you will probably get .4 amps just by placing the ammeter on top of the transformer.
 
.4 amps is diddly....Sometimes in a transformer creative electricians set up short ground loops and this will pass current. XO to transformer frame to XO nice copper circle..

A geniune test is take zero sequence measurements.
 
With a large CT or clamp-on meter encompass all phase conductors and the neutral the reading should be ZERO "0". You can do this at every panel to locate the source of the problem I posted the information below previously.

? Perform zero sequence readings on each branch circuit (if possible) use a True RMS amp clamp and measure the phase/phase and grounded/neutral coonductors at the same time the circuits with any amperage are the culprits.
? Measure grounded/neutral conductor voltage at the panel (should be close to ?0? millivolts) circuits with any loads should have an increase in measured voltage (between the grounded/neutral conductor and the Equipment grounding conductor (copper conductor or conduit makes no difference). If the voltage is low, similar to the reading in the PDU, that is a suspect circuit.
? During a schedule outage turn off all the branch circuit breakers, unplug loads if possible and remove the grounded/neutral conductors from the neutral termination bar. Utilizing a low voltage megger 50VDC 0r 100 VDC (I use a low voltage megger to avoid damaging equipment with 500 or 1000 VDC meggers we normally use. The neutrals that megger bad, ?0? megohms, need to be traced out and the ?SHORTED? grounded/neutral conductor will need to be replaced, repaired, lifted depending on the exact nature of the problem.
 
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