I am having to run 1/0 oflex vfd cable to a 75hp motor 400ft away from Reliance drive. The motor has #2 wire for termination. The pot head is tight to terminate the 1/0 cable. I would like to transition to the #2 in a box 10ft away. Does anyone see a problem with using single pole power distribution blocks for each conductor and grounds and bond the shield as well?
vfd wiring question?
- Thread starter viator_j
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beanland
Senior Member
- Location
- Vancouver, WA
Seems Reasonable
Seems Reasonable
No reason you cannot termiante the larger cable and transition to a smaller cable for the final connection. As always conductor rating must be appropriate and equipment grounding conductor must be up-sized for upsized phase conductors.
I would be concerned about the voltages that can be developed at the motor due to non-sinusoidal voltages/currents being present on such a long line. Check with the VFD maker to see if a reactor is needed at some point.
Seems Reasonable
No reason you cannot termiante the larger cable and transition to a smaller cable for the final connection. As always conductor rating must be appropriate and equipment grounding conductor must be up-sized for upsized phase conductors.
I would be concerned about the voltages that can be developed at the motor due to non-sinusoidal voltages/currents being present on such a long line. Check with the VFD maker to see if a reactor is needed at some point.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
But to beanland's point, that isn't going to help, I think he meant a load reactor.
Has anyone evaluated the viability of using only the VFD rated cables at this distance? Using properly shielded cables helps a lot and some VFDs claim you can do this without added load reactors or filters, but some do not. It should be addressed and acknowledged because the consequence of not doing it right is to lose the motor (and all the associated down time).
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The only problem I ever have with that is the added point of failure. Just be EXTRA meticulous about the connections, should be fine. If you think about it, you are doing the same thing inside the pecker head anyway.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Why would you add a splice box in the middle of a run plus all the labor, splices, material, etc when it's usually just easier to pull the peckerhead off and replace it with a larger j-box?
Get yourself a good gasketed box, pop holes in the back for the mounting bolts, punch out a big hole for the motor leads to come through, add a ground lug and you're on your way.
Get yourself a good gasketed box, pop holes in the back for the mounting bolts, punch out a big hole for the motor leads to come through, add a ground lug and you're on your way.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Standing Wave Voltages
Standing Wave Voltages
The engineer of record should also be aware of possible increased voltage levels (at 400') that could exceed the feeder and motor winding insulation due to pulse width modulated power wave at the output of the drive. The assumption is that your 75hp motor is existing and runs on 3phase 480V and the drive's output signal is pulse width modulated. I realize this does not address the original wiring question but brings to mind a situation we've been through in which we ended up specifying otput filters to mitigate exceeding the 1000V insulation thresholds of the cable and windings.
Standing Wave Voltages
The engineer of record should also be aware of possible increased voltage levels (at 400') that could exceed the feeder and motor winding insulation due to pulse width modulated power wave at the output of the drive. The assumption is that your 75hp motor is existing and runs on 3phase 480V and the drive's output signal is pulse width modulated. I realize this does not address the original wiring question but brings to mind a situation we've been through in which we ended up specifying otput filters to mitigate exceeding the 1000V insulation thresholds of the cable and windings.
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