cafci and vfd nuisance tripping

[mark thomas]

I installed a VFD that trips a CAFCI every time the VFD starts the motor. I've read/heard about problems with VFDs and GFCI, AFCI, CAFCI, but never seen any definitive statements.

Note the VFD is not on the CACFI circuit. The panel with the CAFCI also has a breaker that feeds a subpanel, and that subpanel has a circuit with the VFD on it. The VFD circuit is 220v.

Should I suspect and investigate a wiring problem, or just chalk this up to "issues" with VFDs? Remove the CAFCI? Any other solutions? I am going to try swapping the VFD with another brand/model and see if that makes any difference.

 

[ptonsparky]

Try putting a line reactor and/or the optional RFI filter on your drive.

I have a cheap drive on the well for my house (because I could and wanted to) with neither and it does not trip the AFCIs. AM radio is non existant while the drive is on but I am aware of no other problems.

 

[ELA]

Thats an interesting scenario. AFCI's do detect an Arc signature in part by detecting high frequency currents like those that the VFD puts back onto the power lines. However in this case the VFD is not a direct load on the AFCI.

What brand of AFCI and does it have indicator lights like the Siemens do?
That is helpful in knowing of it thinks it is an ARC of GF.
I favor the idea of temporarily wiring in a brand that has the diagnostic LEDs in cases like this to help determine where to look.

The AFCI uses a current sensing coil to detect the arc signature and so in an ideal world it would only recognise high frequency currents on its load side.

If the cause of the trip is high frequency (or Arc detection) of the AFCI then the previously suggested external EMI filter on the Drive should help.
If it is GF then it will most likely not.

Have you measured the load current on the AFCI? If the load current on that circuit is less than 5 amps then the AFCI should not be reacting to any high frequency currents (either from its load or external to it).

It should always be recognized that some manufaturers AFCIs are more immune than others to false tripping ( if this is the case).

 

[mark thomas]

This is a Cutler Hammer BR style. No LED. Do third parties make compatible breakers with LEDs?

Interesting point about the 5 amp threshhold. I have not measured load, but I am sure it's well under 5 amps when tripping. I will measure it next time however.

I will try RFI filter.

 

[ptonsparky]

I have the BR style breakers. Real PIA but no problems relating to the VFD.

 

[mark thomas]

I tried a different brand VFD, same result. On a few more tests, I found that there's not just one breaker tripping, but any of several CAFCI breakers on the panel will trip. Not all however. Seems semi-random, but somewhat load related. For example, consistent tripping with a circuit load in the ~500 watt neighborhood, but doesn't trip at all when load ~100 watts. (I didn't actually measure the load -- I'm just eyeballing the equipment and lights on.)

On the hunt for an RFI filter to try...

 

[ghostbuster]

A grounded centre tapped drive isolation transformer may work as well and is probably easier to source.

 

[weressl]

I installed a VFD that trips a CAFCI every time the VFD starts the motor. I've read/heard about problems with VFDs and GFCI, AFCI, CAFCI, but never seen any definitive statements.

Note the VFD is not on the CACFI circuit. The panel with the CAFCI also has a breaker that feeds a subpanel, and that subpanel has a circuit with the VFD on it. The VFD circuit is 220v.

Should I suspect and investigate a wiring problem, or just chalk this up to "issues" with VFDs? Remove the CAFCI? Any other solutions? I am going to try swapping the VFD with another brand/model and see if that makes any difference.

Those devices do not like to play on non-sinusodial lines.