GFCI breaker with Hitachi VFD?

[.LMS.]

Searched the forum and didn't see anything so here's the question. I am wiring up my VFD for my shiny new 1236T, and I have to wire in a new 30a circuit into my shop subpanel. Should I use a regular breaker or GFCI? Hitachi manual lists both as possibilities, but as expected says "check your local codes". I know I need to do that, but does anyone have any input on pros and cons of each for this type of application? Sometimes the GFCIs can be fussy and trip too often, seemingly unnecessarily, but I want to do the right thing.

 

[pontiac428]

Sometimes they can be fussy, but code is code. I ran GFCI on every single circuit in my shop, including 220v, and have not had a problem (yet). I was so anticipating trouble that I bought standard breakers to replace all that GFCI once the inspector left. Haven't needed to, it's not an issue.

Current should never be carried on ground. 110v circuits load one hot an one neutral. 220v circuits load two hots. Ground isn't part of the circuit, nor should it be. If ground becomes part of the circuit, either through a short or through your body, the breaker will trip. Bottom line is GFCI is meant to protect your mains breaker, and protect the user from shock when mishandling a receptacle. It should be a transparent part of the circuit. If a VFD is tripping GFCI, then it is somehow using the ground for current in its configuration.

Brace your wallet when buying GFCI breakers. There's no high-tech in them, the manufacturers just know they have you over a barrel because code says you must use them.

 

[.LMS.]

Thanks pontiac. All of the 120 circuits on the panel are GFCI, but the two existing 240 circuits are not and the inspector seemed to be fine with it 15 years ago. Maybe not today? The VFD manual says the VFD and motor should both have an earth ground - would doing that conflict with your statement "ground is not part of the circuit" or is it in line with your statement "it should be a transparent part of the circuit"?

 

[mksj]

GFCI can present an issue for VFD's but typically it is when it involves a neutral, so 120VAC will almost always trip. There may be some mitigation with the use of electrical noise filters, but it depends on the type used. The code can vary, it appears that a 240VAC without a neutral is not required to have a GFCI in the garage. The GFCI requirements seems to apply to receptacles and not hardwired connections. There were a lot of changes in the 2020 NEC guidelines, so almost every receptacle needs some form of GFCI or AFCI, or both. It is worthwhile these days to check with a local electrical requirements.

 

[pontiac428]

Ground is a safety feature to shunt power to earth when something goes wrong. You need to ground the case of the VFD to ensure that a short won't short through you. I have been shocked by equipment in the wild a few times because it wasn't grounded, and that's not fun. Since the current is carried on neutral (110v) and L1-L2 (220v), the ground isn't participating under normal circumstances. By GFCI being transparent, I mean that it should not trip unless power is erroneously shorted to ground. So if everything is working right, it shouldn't trip. Sometimes when plugging stuff in you can get a trip (110v only, 220 doesn't seem to have this problem) depending on the equipment, like when you get a little pop at the outlet when plugging something in. This happens when the ground pin and the hot pin make contact in the receptacle before the neutral. That means it is working like it is supposed to, but if it is persistent, there is something wrong with the appliance.

 

[den-den]

I have had trouble with 120v supply VFDs and GFCI, have not had any experience with 240v supply VFDs and GFCI (because I don't have any 240v GFCIs). I suspect that charging the capacitors in the VFD when powering up, fools the GFCI into tripping.

 

[.LMS.]

Brace your wallet when buying GFCI breakers. There's no high-tech in them, the manufacturers just know they have you over a barrel because code says you must use them.

Yowza! close to $100

 

[rogerl]

If you are going to have the VFD hard wired and not plugged into an outlet why do you need a GFCI in the circuit? My understanding is GFCI's are used anywhere water is present and you can plug something in the wall outlet while you are standing in or on water. Your bathroom, kitchen, and garage outlets all need to have GFCI's for that reason. The power going to the overhead lights and wall switches in bathrooms, kitchens, and garages do not need to be GFCI protected but they need to be properly grounded. If the drive is hard wired with no exposed outlet why would you need a GFCI breaker?

Roger L

 

[.LMS.]

If you are going to have the VFD hard wired and not plugged into an outlet why do you need a GFCI in the circuit? My understanding is GFCI's are used anywhere water is present and you can plug something in the wall outlet while you are standing in or on water. Your bathroom, kitchen, and garage outlets all need to have GFCI's for that reason. The power going to the overhead lights and wall switches in bathrooms, kitchens, and garages do not need to be GFCI protected but they need to be properly grounded. If the drive is hard wired with no exposed outlet why would you need a GFCI breaker?

Roger L

Great question, and I am asking myself the same thing given the expense of the GFCI breaker. I read the attachment that Mark (mksj) attached above, and it says that an auxiliary building (my shop) should be treated like a garage, and the garage requires GFCI protection on the outlets, but doesn't say anything about hardwired stuff. Luckily, the GFCI breaker I have on the way is returnable for free. I am going back and forth on this....

 

[pontiac428]

No, GFCI is not needed if you hard wire an appliance. The lighting circuit I built in my shop does not have a GFCI breaker and passed inspection because of that.