In article ,
says...
Hi all,

I've tested out my new VFD and it will operate
like I want it to. So now I ready to permanently
mount it.

Power will come from a local circuit breaker box
which the contains the hot wires, a wire from the
main breaker box which is from the neutral/ground
bus, and the local box is grounded by conduit. The
ground wire in the local box is not tied to
the box (but could be).

The VFD has 1/2" knockouts to cable to. The
physical connection is metal. It is connected to
the place where they also have ground terminals.

So if I run conduit from the local breaker box
to the VFD, then connect the ground wire to
the VFD am I going to run into problems
(ground loops, against code to connect)?

Same issue would apply connecting the lathe.
(grounding by conduit & wire).

I could use insulated connectors to connect
the conduit. But they need to grounded somewhere
for shielding purposes.

I suppose everything (VFD, lathe) could be
grounded only by conduit, but this doesn't
seem right/safe.

Anyone know the correct procedures for this?


I'm not sure I follow everything you've described, but the short answer
is don't worry about ground loops when you're bonding enclosures and
conduit runs. It's likely you can't avoid potential ground loops and
wire to code without going to great lengths anyway, and redundancy is
better than something remaining unbonded. If you want to be conservative
and run shielded cable for the VFD control wiring, ground the shield at
one end of the cable only and try to connect all signal returns to a
single point. The VFD is unlikely to care either way; I've installed
dozens in nasty environments and can't remember ever having a noise
problem other than the noise created by the VFD interfering with other
sensitive devices.

Ned Simmons