Running multiple VFD/motors on same circuit?

If I understand NEC properly I can run a 50 amp feeder circuit then connect multiple motors to it. I believe I would have to use fused equipment disconnects at each motor. Are there any negatives as far as the VFD's are concerned? Bad feedback, voltage spikes to the others etc?

I am a little lost here are you planning on installing your VFD's at the motors themselves and feeding them from one 50 amp main?

It is entirely fair to connect loads to a branch circuit, up to the capacity of the branch circuit.

Yes, NEC does require a disconnect for each motor or piece of equipment connected to the branch circuit. That can be a plug and cord, or a rated disconnect switch with LOTO capability. It should be nearby and in line of sight to the motor or equipment.

There is no harm in having more than one VFD on a branch circuit, so long as the current capacity is not exceeded.

dana gear said:

I am a little lost here are you planning on installing your VFD's at the motors themselves and feeding them from one 50 amp main?

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Yes... trying to avoid running multiple #8 wiring runs to the same side of the shop (where most of my machines are) because conduit fill limits will dictate that I run 2" conduit to fit all those wires. If I can run them all on the same branch, without exceeding the breaker capacity then I can run it in 3/4" EMT.

JST said:

It is entirely fair to connect loads to a branch circuit, up to the capacity of the branch circuit.

Yes, NEC does require a disconnect for each motor or piece of equipment connected to the branch circuit. That can be a plug and cord, or a rated disconnect switch with LOTO capability. It should be nearby and in line of sight to the motor or equipment.

There is no harm in having more than one VFD on a branch circuit, so long as the current capacity is not exceeded.

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Thanks! Isn't overload protection required on the equipment if the circuit breaker is larger than the equipment? IE, if I have a 2 hp VFD that requires 20 amp circuit protection and I connect it to a 50 amp branch I would have to install fuses right? So at that point I may as well pick up a fusible equipment disconnect (under $20) and use that as my disconnect with circuit protection, regardless of if I use a plug as well or not.

Any run of wire needs "overcurrent protection" (could be fuses) sized to protect it, yes.

If the same size wire runs to a properly rated receptacle, No added fuses need to be there, the equipment attached is responsible for all protection.

If the equipment is hard wired, yes, a fused disconnect is one way of handling that. I don't particularly like fuses in a 3 phase circuit, because usually they do not all blow if there is a fault. But they generally do qualify as "overcurrent protection".

On branch circuits that have multiple VFDs the VFDs should be wired after the disconnect on the end of the branch. From that point outputs from the VFD's should not share the same conduit/flex etc as any other VFD.
You should have a ground that ties the motor to the VFD. Most decent VFDs have a terminal/lug dedicated just for this purpose. Do not rely on metallic conduit or metallic flex to carry this ground it must be hard wired.