ground current?

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NOSSAJ

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I'm doing an predictive maintenance at a facility. While recording variables on a transformer (delta-delta), the installation contractor installed a jumper from the bonding bushing to the case. First, is that jumper necessary? And secondly I amped that jumper (with a true rms meter), and it had 21 amps on it. The jumper was a 1/0 copper. Should there be that many amps on the jumper? Also it was only about one foot long.
 
I'm likely the only one here that is clueless and needs some more information. Is the secondary 240/120D? And the bonding bushing is the centertap for the 120V?

carl
 
NOSSAJ said:
I'm doing an predictive maintenance at a facility. While recording variables on a transformer (delta-delta), the installation contractor installed a jumper from the bonding bushing to the case. First, is that jumper necessary? And secondly I amped that jumper (with a true rms meter), and it had 21 amps on it. The jumper was a 1/0 copper. Should there be that many amps on the jumper? Also it was only about one foot long.
Click to expand...

O.K, FOLLOW ME AS I TRY TO EXPLAIN WHATS HAPPENING. ITS A 480 TO 240 DELTA-DELTA TRANSFORMER. ON THE LINE SIDE THERE ARE 3, 1/0 THHN COPPER WIRES WITH A #6 GROUNDING CONDUCTOR RAN IN AN 2" EMT PIPE. THAT EMT IS CHANGED OVER TO LIQUIDTITE AND CONNECTED TO THE CASE OF THE TRANSFOMER. THE #6 GROUND IS TERMINATED TO A BOND BUSHING. ALSO ON THAT SAME BOND BUSHING A 1/0 THHN COPPER CONDUCTOR IS GOING TO THE CASE, WHICH HAS 21 AMPS ON IT. IS THAT 1/0 JUMPER NECESSARY, AND HAVING 21 AMPS ON IT HAZARDOUS?:confused:
 
coulter said:
... Is the secondary 240/120D? And the bonding bushing is the centertap for the 120V?...
Click to expand...

I still don't know what the bonding bushing is connected to.

Another question: When you say "line side", is that the 480V input to the xfm or the 240 output to a panel?

carl
 
NOSSAJ, please avoid using your Caps Lock button - it makes your post hard to read, and is perceived as shouting.

I am still fuzzy. Where does the #6 go? Does it stop at the bonding bushing or continue on to terminate again somewhere else?

Aside from this recently added 1/0 jumper, is the case bonded to the Equipment Grounding Conductor from the 480V side?
 
NOSSAJ said:
ALSO ON THAT SAME BOND BUSHING A 1/0 THHN COPPER CONDUCTOR IS GOING TO THE CASE, WHICH HAS 21 AMPS ON IT. IS THAT 1/0 JUMPER NECESSARY, AND HAVING 21 AMPS ON IT HAZARDOUS?:confused:
Click to expand...

Are you saying that you have a bond bushing on a 'Liquidtite' fitting? Screwed into this bond bushing is a #6 EGC that comes in with the feeders to the transformer, and a #1/0 that goes from the bond bushing to the enclosure of the transformer?

What is the material of the Liquidtite fitting? Given the conductor sizes, I presume metallic, but it doesn't hurt to ask.

Does this jumper, along with the enclosure, form an electrically closed loop?

-Jon
 
NOSSAJ said:
O.K, FOLLOW ME AS I TRY TO EXPLAIN WHATS HAPPENING. ITS A 480 TO 240 DELTA-DELTA TRANSFORMER. ON THE LINE SIDE THERE ARE 3, 1/0 THHN COPPER WIRES WITH A #6 GROUNDING CONDUCTOR RAN IN AN 2" EMT PIPE. THAT EMT IS CHANGED OVER TO LIQUIDTITE AND CONNECTED TO THE CASE OF THE TRANSFOMER. THE #6 GROUND IS TERMINATED TO A BOND BUSHING. ALSO ON THAT SAME BOND BUSHING A 1/0 THHN COPPER CONDUCTOR IS GOING TO THE CASE, WHICH HAS 21 AMPS ON IT. IS THAT 1/0 JUMPER NECESSARY, AND HAVING 21 AMPS ON IT HAZARDOUS?:confused:
Click to expand...

Remember, typing entirely in capital letters is like shouting.

Is this a 240V 3PH 3W delta ungrounded secondary?

Where is the jumper connected? Between the transformer enclosure/conduitand the core? Between a phase and the enclosure or ground?
 
thank carl for being patient. the bonding bushing is screwed on the threads of the liquidtite connector inside the transformer. on that bond bushing is a lug with the lineside ( the 480 side or primary side) grounding wire and another bonding jumper going to the can.
 
Are there any other grounding/bonding conductors in the transformer with current on them?

It quite possible you set up a short ground loop with the installation of a (SECOND?) bond jumper.

If this is a grounded system and there are no other ground/bonding conductors with current it is possible you have a downstream short.

Try placing an amp clamp on all secondary conductors; does the meter read 21 amps? (Or close to that).

Do the same with the primary.

21 amps is unusually high ground current and the source should be located.
 
Brian's connents are good. Yeah you need it, 21A is way too much.

Tell us about the secondary, Is this 240/120 with the centertap neutral conductor bonded to ground? Or corner grounded delta?

carl
 
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