Vfd drive and motor on small machine

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Danny89

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Quick question I've got a simple machine at work. It's a simple vfd circuit.

Incoming to the drive is single phase 120v

The drive output is 3 phase 208v...three hots and a ground feeding a small motor. The machine gets it's power by plug and cord. Standard 20amp industrial 3 wire 120v.

When plugged into GFCI it trips the outlet.
When plugged into regular outlet it doesn't trip the 20 amp single pole breaker...

Any ideas??

Thanks in advance
Danny

Sent from my Moto Z (2) using Tapatalk
 
Danny89 said:
Quick question I've got a simple machine at work. It's a simple vfd circuit.

Incoming to the drive is single phase 120v

The drive output is 3 phase 208v...three hots and a ground feeding a small motor. The machine gets it's power by plug and cord. Standard 20amp industrial 3 wire 120v.

When plugged into GFCI it trips the outlet.
When plugged into regular outlet it doesn't trip the 20 amp single pole breaker...

Any ideas??

Thanks in advance
Danny

Sent from my Moto Z (2) using Tapatalk
Click to expand...
It's a known issue that most VFDs will make a GFCI trip. It's because all VFDs create what's called "common mode noise", meaning electrical noise on the ground plane, something that is inherent in how they work. The problem is, that looks a lot like what a GFCI is looking for.

People have tried various fixes with mixed success. Here are ones I know of and have tried:
1. Put a shielded isolation transformer between the VFD and the GFCI, ground the shield in the transformer. This is the only one I personally have seen work, but not every time.
2. Put in what's called a "common mode choke", which is a ferrite (magnetic ceramic) core (donut) that the wires pass through to dampen the amplitude of the noise current. You see these sort of things on the power supply cord for your PC and you can get them at some electronics supply stores.
3. Evaluate why you are using a GFCI at all and hard wire the machine so that you don't need a GFCI.

Side note; you must use shielded VFD flex cable on the output of the VFD, otherwise you are creating a local FM radio transmitting antenna! On that type of installation, you must ground the shield on BOTH ends of the connections.
 
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