Current Imbalance
Current Imbalance
(OP)
What could be the possible cause of the following situation?
Soft Start load (300hp MOTOR) reading as follows:
A phase/Parallel 250MCM #1 - 134A
A phase/Parallel 250MCM #2 - 134A
*B phase/Parallel 250MCM #1 - 124A*
B phase/Parallel 250MCM #2 - 134A
C phase/Parallel 250MCM #1 - 134A
C phase/Parallel 250MCM #2 - 134A
When B phase leads were reversed in the lug configuration on the load side of the Soft Start, the OTHER B phase lead also read 124A.
That rules out that the wire with the first reading was a different length.
Very strange. Could smeone maybe shed som light?
Soft Start load (300hp MOTOR) reading as follows:
A phase/Parallel 250MCM #1 - 134A
A phase/Parallel 250MCM #2 - 134A
*B phase/Parallel 250MCM #1 - 124A*
B phase/Parallel 250MCM #2 - 134A
C phase/Parallel 250MCM #1 - 134A
C phase/Parallel 250MCM #2 - 134A
When B phase leads were reversed in the lug configuration on the load side of the Soft Start, the OTHER B phase lead also read 124A.
That rules out that the wire with the first reading was a different length.
Very strange. Could smeone maybe shed som light?





RE: Current Imbalance
RE: Current Imbalance
For instance, sometimes if the threads of the steel set screw are binding or galling into the aluminum lug body, you are tightening to the specified torque value but not all of that force is translating into compression strength in the cable strands. Try using a little conductive anti-seize compound on the threads such as Loctite Graphite 50 or CRC Nickel Anti Seize compound.
If separate lugs, look also at the connection of the lug to the heat sink. If a little non-conductive grease got on there during assembly it could be affecting the metal-to-metal contact.
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RE: Current Imbalance
RE: Current Imbalance
RE: Current Imbalance
What do you mean about swapping the leads at the softstarter... does the softstarter have two output terminals per phase or one terminal per phase with two lugs landed? If two output terminals, can you see where they're joined or is that internal (if joined all)?
How long is the run of parallel cable?
Small conductors have primarily resistive impedance but large conductors like this have primarily reactive impedance. For a high resistance loose connection to signficantly effect the initially-reactive impedance of a long run of large-diameter cable, you have to have a pretty womping high ressitance.... to the point I would expect you would see discoloration at terminations by simple visual inspections. Far lesser hotspots will be easily visible with thermography, assuming the terminations are accessible for inspection while under load.
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