Has anyone found a workable solution to installing a ground fault breaker on a constant velocity VFD drive for a submersible pump installed in a lake? I need to satisfy the CEC rules and the OEM pump manufacturers have said their pumps will not work with a GF breaker. I have a cable of 240' from the drive to the pump. Cable installation has passed inspection but I am struggling to find a solution that will actually meet the code and not trip the breaker. I have seen anecdotal discussion of a combination of certain drives and breakers that will work. My concern with trying this solution is that it will only work for a short period and then start tripping - at which point the homeowner will replace the GF breaker with regular 2 pole breaker.
VFD on submersible pump in a body of water
- Thread starter SLE
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mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
ptonsparky
Tom
- Occupation
- EC - retired
You can't hardwire it?
- Location
- Illinois
- Occupation
- retired electrician
What is the circuit voltage and horsepower of the motor?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Anecdotally Pentair VFD driven pumps are supposedly working with Siemens GFCI breakers. No idea why, but Pentair now brand labels the Siemens breaker as their own, then tells you that you must use their breaker or you void the warranty. So I’ve heard.
As a general issue, the problem stems from the VFD inherently creating common mode current as a byproduct of how they function. It’s not a lot, but it’s enough that GFCIs pick it up and assume it is a ground fault. I’ve heard people talk about possible solutions, but I’ve not had occasion to try any have not heard back from anyone who has. So if you find something, please share it.
As a general issue, the problem stems from the VFD inherently creating common mode current as a byproduct of how they function. It’s not a lot, but it’s enough that GFCIs pick it up and assume it is a ground fault. I’ve heard people talk about possible solutions, but I’ve not had occasion to try any have not heard back from anyone who has. So if you find something, please share it.
It will be a 240V 1HP single phase pump motor. And a Pentair one at that. I have read about the Pentair/Siemens solution as being a possible solution. However, Pentair technical support is quite clear in their directive not to run their drives on a GF breaker. Any other drive OEM that I have contacted is also stating not to run their drives on a GF breaker. I was hoping that removing the front end filtering would eliminate the common mode current but have not seen any evidence that this would actually be successful.
As Jraef stated above, if you have a solution please share.
As Jraef stated above, if you have a solution please share.
- Location
- Illinois
- Occupation
- retired electrician
682.15(A) specifies GFCI protection for all outlets associated with a natural or artificial body of water.
kwired
Electron manager
- Location
- NE Nebraska
Greater risk of shock/electrocution from the EGC that is sitting there at a potential above true ground of any electrical equipment that may be on that dock (like boat hoist, shore power outlets, etc. even if GFCI protection is used) than from something under 150 volts and at least 10 plus feet away from what swimmers can touch. Voltage drop on the service neutral and/or POCO MGN is the cause of this and a GFCI will not detect it.
kwired
Electron manager
- Location
- NE Nebraska
The problem is when you have a VFD and the high frequency losses that will make the GFCI trip. This is becoming an issue with some household appliances with variable speed motors on them as well whenever they run into needing GFCI protection which the incidents have gone up especially since areas began adopting 2020 or 2023 NEC
CEC code rule 26-956 1) d) is applicable in Canada. And it partly reads: "ground fault protection shall be provided to de-energize all normally ungrounded conductors supplying the submersible pump, with a ground fault trip setting adjust to function as low as practicable to permit normal operations of the pump, but in no case shall the gf current setting be >10ma for an operating time period exceeding 2.7s;"
ptonsparky
Tom
- Occupation
- EC - retired
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Weren't the VFD driven pumps that worked with Siemens GFCI breakers pool pumps?
A VFD feeding a submersible pump through a 240 foot cable would be driving significantly more capacitance to ground than the VFD of a pool pump. Therefore there would be additional common-mode current drawn by the capacitance of that long cable for a given level of common-mode voltage. That could make it even more likely to have GFCI tripping problems.
A common-mode choke could be tried, however, on at least the input to the VFD. And if that is not sufficient to prevent tripping, an addtioinal common-mode choke could be placed on the VFD output as well.
A VFD feeding a submersible pump through a 240 foot cable would be driving significantly more capacitance to ground than the VFD of a pool pump. Therefore there would be additional common-mode current drawn by the capacitance of that long cable for a given level of common-mode voltage. That could make it even more likely to have GFCI tripping problems.
A common-mode choke could be tried, however, on at least the input to the VFD. And if that is not sufficient to prevent tripping, an addtioinal common-mode choke could be placed on the VFD output as well.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
What's the likelihood of finding a workaround of not having to install a GFCI to a submersible pump in a lake, and someone getting electrocuted, when explained to a jury of a possible multimillion dollar lawsuit ?
ptonsparky
Tom
- Occupation
- EC - retired
Post 11 indicates different protection than from our 5ma GFCI standard.
Has it been adjusted to the limits? Is it user adjustable?
Has it been adjusted to the limits? Is it user adjustable?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
ptonsparky
Tom
- Occupation
- EC - retired
What is constant velocity?
eta: Pressure transducer feedback?
eta: Pressure transducer feedback?
Mystic Pools
Senior Member
- Location
- Park Ridge, NJ
- Occupation
- Swimming Pool Contractor
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
Pentair support will not always give a code appropriate reply. Likely also a desire to not take any liability for it not working, as it is only partially successful in stopping the nuisance tripping.
Also mfg. design and code compatibility seems to be increasingly at odds. GFCI or AFCI being required and MFG. making products sometimes related to energy code that are not compatible with GFCI or AFCI.
Nuisance tripping is not being considered as a concern for the NEC, (although in some cases it should be as it definitely leads to non-compliance.) And that is the issue with these VFD motors, as well as other products.
Water and Electric together is definitely a safety concern and shortcuts can kill.
kwired
Electron manager
- Location
- NE Nebraska
There are definite purpose VFD's for submersible pumps, Franklin and Pentair are couple of the most popular ones. They can be configured to run a three phase pump motor or a three wire single phase pump that was originally intended to have remote start/run capacitors and a potential relay to switch out the starting capacitor. New installs typically I am typically seeing them drop a three phase motor in, but they can be configured to run an existing single phase motor.
The constant velocity pump is also known as a constant pressure pump and is using a pressure xducer for feedback. The pump motor that was installed is a single phase and the controller will be for a 3 wire single phase motor which is configured for residential pump control. The motor and drive are seperate devices on this system.
My mistake on this installation was assuming that the ground fault detection on the drive was sufficient to meet rule 26-956 but in discussions with Pentair there is no defined specification at which the ground fault detection occurs - could be 1A or more. Of course this is not acceptable.
At this point I will most likely install system with a GF breaker feeding the standard start/run winding relay and motor. There is a large market for this VFD application if there was a safe and accepted solution.
My mistake on this installation was assuming that the ground fault detection on the drive was sufficient to meet rule 26-956 but in discussions with Pentair there is no defined specification at which the ground fault detection occurs - could be 1A or more. Of course this is not acceptable.
At this point I will most likely install system with a GF breaker feeding the standard start/run winding relay and motor. There is a large market for this VFD application if there was a safe and accepted solution.