Paralleling VFD Power Cables

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augie47

augie47

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State Electrical Inspector (Retired)
I have an installation where the 400 HP motors are fed using Type TC VFD Power Cables.
These particular cables incorporate (3) grounding conductors and appear to meet the requirements of 250.122(A) as "Sectioned" conductors but those "sectioned" conductors are sized per the one cable and not parallel cables in regard to the OCP ahead of the drives.
Would this be a violation as far as 250.122 sizing or is would the drive have a bearing on sizing the equipment ground ?
 
ON this particular install, the cables are in an over-sized conduit. If they were to install individual equipment grounds as the required conductor would that have a negative effect on the drive (defeat the VFD cable) ?
 
augie47 said:
ON this particular install, the cables are in an over-sized conduit. If they were to install individual equipment grounds as the required conductor would that have a negative effect on the drive (defeat the VFD cable) ?
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I don't see how you can get around the code requirement to have the EGC in the cable.

I personally suspect it would make no difference whatsoever performance wise.

Is it metallic conduit?

The CMP really need to revisit this kind of thing and figure out how to make the code and reality work together.
 
Note for some VFD cables the 3 segmented EGCs add up to an oversized ground that could meet the 250.122 requirements even when paralleled.
 
"Note for some VFD cables the 3 segmented EGCs add up to an oversized ground that could meet the 250.122 requirements even when paralleled."

In other words, the 3 EGC's added together may equal the ampacity of the phase conductors, but 1 of the 3 EGC's may be sized enough by itself to meet the code requirement. Yes?
 
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