3 Phase 230v VFD nuisance trips 120v GFI
- Thread starter V02maxed
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
In the places I ran up against this, connecting to a circuit with a standard Q0 in the same load center had no problem, only the GFCI version.
Drives always must have a "pre-charge" circuit behind the rectifier to avoid the current surge of the capacitors charging, usually by placing a current limiting resistor in series with the DC bus for a second or two and taking it out after doing its job. It wasn't that.
So just for clarity and the edumacation of future readers as well, "GFCI" is a specific defined term meaning ONLY a Class A "personnel protection" ground fault device that trips at 4-6mA of current. The higher level (30mA to a % of load) "Equipment Ground Fault" breakers are referred to as proving "GFP" (Ground Fault Protection) or "GFPE / EGFP" (E = Equipment). Different animals, different uses. More recently people have been taking that concept into 20mA GFCI devices (not breakers) that they then refer to as being a Class B , C or D "GFCI", but those only apply to voltages OVER 300V under specific conditions.ghorwood said:
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
All electrical equipment is imbued with the ability to sense the emotional state of the electrician, technician or user. The more frustrated it perceives you are, the less likely it is to work correctly and the more worried you are about it breaking, the more likely it is to fail. Surely you know that by now.... :slaphead:
Brandon_K
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- Pittsburgh / Cleveland
Not to doubt you, but are you sure it's a transformer? Inverter VFD's by their very nature do not need transformers, they do it internally (which is exactly why you can feed one 120v 1ph and get 240v 3ph out of it).
With any VFD, there should be line reactors on the input, which can look very much like a step up transformer. But, if you look closely, there is no primary and secondary windings (IE, H1, X1), there is typically only A1, A2, B1, B2, etc. It's not an isolation transformer, it's straight through. It's role in life is to reduce harmonics that cause some very serious issues with VFD driven motors (like MASSIVE current spikes).
ptonsparky
Tom
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- EC - retired
Pretty sure. We use line/load reactors frequently.
V02maxed
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- Plymouth, WI
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- Industrial Journeyman Electrician
According to the 2017 code, a GFCI has a definition and includes being class A - 6mA or higher trip current. That tells me when the code refers to a GFCI, that is the definition being used. I don't know how you could use an "equipment rated" GFCI by the code if it has a higher trip current than Class A 6mA. Can you explain?
I'm specifically looking at 2017 Code, Article 210:8(B)6. This to me says Class A 6mA GFCI for our 120v outlets in our production areas.
Thanks
V02maxed
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- Location
- Plymouth, WI
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- Industrial Journeyman Electrician
Yes because Article 210.8(B)6 states indoor wet locations for all 50amp or less 3Phase or 100amp single phase. That is most industrial settings with wet locations.
Electric-Light
Senior Member
The output from VSD do not look like what you'd get from an alternator driven by a motor through a CVT.
It uses transistors (at least, a variety of, suc has MOSFET, LGBT ) that are digitally switched at high rates (carrier frequency) to form a secondary frequency. (analogously, the frequency that forms the piercing beep of a smoke alarm is the carrier frequency, while the repetition of beeps you hear maybe 5 Hz or so)
VFDs are usually not isolated and the high frequency component in the carrier frequency can leak through capacitive coupling in a way low frequency signal without high frequency components woudln't
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kwired
Electron manager
- Location
- NE Nebraska
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- EC
Most of the problems you mentioned is on output side of the drive isn't it? In OP they are tripping a GFCI on the input side.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Hey now, be careful. Let's be inclusive here... there's nothing wrong with LGBT power devices.
Electric-Light
Senior Member
Well the two sides aren't isolated so the leakage on the output side could cause a common mode current which the GFCI looks for. The carrier frequency influences the amount of leakage current.
DC is pulsed at a high frequency and the duty cycle modulated to emulate sine wave but the high frequency artifacts pass through.
So when you supply clean 400Hz to a tweeter through a high pass capacitor, you wouldn't have much go through. If you send in 20,000 Hz carrier signal that's modulated at 400 Hz, it can get past that capacitor much better. It's difficult to insulate against high frequency. One of the leads from an electronic ballast in contact with the lamp wall can make it glow through a 1,000v rated THHN and this is due to high frequency capacitive coupling.
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- Location
- Massachusetts
Just a bit of not picking
GFCIs are always for personal protection
GFP is for equipment protection
The breakers you use for heat trace are GFP breakers not GFCI.
Electric-Light
Senior Member
I will use RCD to remove any semantic argument over the device that detects common mode current flow.
The thread starter is using a 120v single phase input,three phase output VFD through a standard RCD protected receptacle.
I am not so comfortable with recommending a equipment rated RCD with a trip current higher than a personnel protection level. It would leave those receptacles unprotected for the purpose of safety and can expose the employer to a liability. If the equipment is semi portable and it gets setup incorrectly, it presents a shock hazard from equipment frame to another grounded object.
The thread starter is using a 120v single phase input,three phase output VFD through a standard RCD protected receptacle.
I am not so comfortable with recommending a equipment rated RCD with a trip current higher than a personnel protection level. It would leave those receptacles unprotected for the purpose of safety and can expose the employer to a liability. If the equipment is semi portable and it gets setup incorrectly, it presents a shock hazard from equipment frame to another grounded object.
V02maxed
Member
- Location
- Plymouth, WI
- Occupation
- Industrial Journeyman Electrician
Thanks for the replies. Our production area is washdown, and commonly wet after setup from that, also at some point most of our conduit and boxes end up full of water that needs to get let out at some point from over zealous sanitation with power washers :rant:.
Most of our mobile machinery is cord and plug connected so it can be removed for washing. The use of GFIs in our plant will only be for personnel equipment. What information we are getting from Allen Bradley is that we will probably never be able to get a VFD to run off a Class A GFI no matter what conditioners, choking, or other methods we try to reduce leakage and GFI tripping. The characteristics of a VFD will trip a Class A, maybe not a Class B, but we cannot use class B.
The next route would be to find, per code, how we can get around the 120v receptacle GFIs so we can continue to run our equipment. One engineer said we can use twist loc recepts. and plugs so that only machinery can be plugged in, not a normal cord per say. I still say that will not meet code for wet location receptacle GFIs despite being twist loc.
For machinery, is there anywhere in the code where our situation could be deemed not necessary or not required by code to use GFI? I have not found anything that gets us by but maybe someone else does.
Thanks
Most of our mobile machinery is cord and plug connected so it can be removed for washing. The use of GFIs in our plant will only be for personnel equipment. What information we are getting from Allen Bradley is that we will probably never be able to get a VFD to run off a Class A GFI no matter what conditioners, choking, or other methods we try to reduce leakage and GFI tripping. The characteristics of a VFD will trip a Class A, maybe not a Class B, but we cannot use class B.
The next route would be to find, per code, how we can get around the 120v receptacle GFIs so we can continue to run our equipment. One engineer said we can use twist loc recepts. and plugs so that only machinery can be plugged in, not a normal cord per say. I still say that will not meet code for wet location receptacle GFIs despite being twist loc.
For machinery, is there anywhere in the code where our situation could be deemed not necessary or not required by code to use GFI? I have not found anything that gets us by but maybe someone else does.
Thanks
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Only way around it is to not have a 15/20 amp 120 volt receptacle. Then comes 2017 NEC - don't know exactly what the changes are yet but I know they have added more GFCI requirements that are for more then just 15/20 amp 120 volt receptacles.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
You could invest in a small isolation transformer and test it out, you might be surprised. I've had it work on a PowerFlex 40 and now the new PowerFlex 525 that were plugged into 120V GFCIs operating fountains (in Vegas). The one I used was an Eaton, S12N12E03N, single phase encapsulated, shielded isolation transformer, 120 in, 120 out. The smallest they make is 3kVA, mine were 1HP drives so it's overkill but that was the smallest I could find. Mind you, this freaking transformer cost more than the VFD and motor combined! The next time, I had the fountain company just change their design to not have the pump plugged in, they hard wire it now. But in those two cases there was no choice after the fact.
V02maxed
Member
- Location
- Plymouth, WI
- Occupation
- Industrial Journeyman Electrician
Yes, 2017 is 3phase <50A and single phase 120v <100A receptacles, so we are up the creek.
Thanks, this is probably the route we will have to look at with our equipment despite the cost.
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