Pool Pump Motors with Built-in VFD are Tripping Breakers

JoeStillman

JoeStillman

Senior Member
Location
West Chester, PA
Occupation
Electrical PE
Three 3HP pool pump motors rated for 208/230V, 12.4/11.2A are fed from a 120/208V, 1Ø, 3W panel, each on a 20/2 GFI breaker. The breakers are tripping after the pumps run a little while. Contractor has tried...
  • Replace breakers with non-GFI. Still trips.
  • Replace 20/2 with 30/2. Still trips.
  • Replace breakers with ones that have same label as pump/drive. Still trips.
  • Put an amprobe on the branch circuit. Pump draws nameplate current.
It's not tripping on startup. Why does a 20A breaker trip on a 12A load?

I'm going out on Monday to take some power quality readings. Wish me luck.
 
MFGs rate there motors funny especially HP ratings on OEM motors. A 3 hp single phase motor the NEC code amps is like 19 amps with no VFD. Your suppose to select the wire, breaker etc off the code amps not the motor name plate but with a VFD that changes.

I am not saying this is your problem but also with a VFD you size the wire and breaker off the VFD input rating. Wire size should be 1.25 x VFD input amps.

Sounds like your having problems with multiple motors. I would recheck wire and breaker size and call the pump mfg if you think everything on the job is correct.

Do these motors have thermal protection or is that built into the drive?
 
Eddie702 said:
MFGs rate there motors funny especially HP ratings on OEM motors. A 3 hp single phase motor the NEC code amps is like 19 amps with no VFD. Your suppose to select the wire, breaker etc off the code amps not the motor name plate but with a VFD that changes.
Click to expand...
I told them they could be using 30A breakers and they tried one. It held.
Eddie702 said:
I am not saying this is your problem but also with a VFD you size the wire and breaker off the VFD input rating. Wire size should be 1.25 x VFD input amps.
Click to expand...
VFD and motor are all one unit. Nameplate amps are in the OP.
Eddie702 said:
Sounds like your having problems with multiple motors. I would recheck wire and breaker size and call the pump mfg if you think everything on the job is correct.
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Bearing in mind that 250% is a maximum, they tried it with a 25A/2P and that has been holding too.
Eddie702 said:
Do these motors have thermal protection or is that built into the drive?
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I don't believe the motors are internally or inherently protected. But the puzzlement to me is that the breakers tripped, and the drives have never gone out on overload.
 
I've been wondering if the problem is because we're using 208V split-phase and the L1-G/L2-G references are not the same vectors as they would be if we were using a 120/240V center tapped transformer source. I've had that problem with a 4WD source feeding a 3Ø VFD before, but these are all 1Ø loads. Plus, the breakers are tripping, not the drives. Are these breakers electronic now, instead of good old-fashioned electromechanical?
 
JoeStillman said:
I've been wondering if the problem is because we're using 208V split-phase and the L1-G/L2-G references are not the same...
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No. Pool pumps with VFDs tripping GFCI breakers is a well known problem. Pentair has their own breakers that supposedly takes care of the problem. I think you said they tried breakers "having the same label as the pump/drive"? Pentair?
JoeStillman said:
But the puzzlement to me is that the breakers tripped, and the drives have never gone out on overload.
Click to expand...
Yeah, that's what happens. The high frequency from the drives messes with the electronics in the breakers. There are some here who say they have had luck with a few turns of each pump supply conductor from the breaker wound through a ferrite doughnut.

-Hal
 
hbiss said:
No. Pool pumps with VFDs tripping GFCI breakers is a well known problem. Pentair has their own breakers that supposedly takes care of the problem. I think you said they tried breakers "having the same label as the pump/drive"? Pentair?

Yeah, that's what happens. The high frequency from the drives messes with the electronics in the breakers. There are some here who say they have had luck with a few turns of each pump supply conductor from the breaker wound through a ferrite doughnut.

-Hal
Click to expand...
Tripping with a non GFCI indicates something else or in addition to what you mention.
 
JoeStillman said:
I'm going out on Monday to take some power quality readings. Wish me luck.
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Verify the equipment grounding is correct and has low ohms and measure the mA of leakage on the EGC form the motors and the feeder itself.
I have seen a pool house panel & pump controller that looked fine on the surface but had weird corrosion on just the lugs, screws and the electronics. It was from pool chemicals being stored in the same shed, which was surprising as they were about 5ft away in a tightly closed bin that had a air vent to outside.
 
I am confused. OP said pumps are rated 11-12 amps says they are drawing 1.6-1.8 amps. Would think the piping is very restricted with the low amps. Also first post said 25A & 30A breaker would still trip now apparently it will run on a 25 or 30.

3hp 1 phase 230 volt motor should draw 12-15 if loaded.
 
My point is/was why doesn't the code, UL and the equipment MFGs (ranges, ACs whatever) figure this crap out before it goes into the field? We are supposed to be electricians who get paid to wire stuff not troubleshoot some ones manufacturing problems. Stop stuffing things in the code that cause people to do work arounds, violate the code or waste time troubleshooting issues that are not ours
 
Eddie702 said:
I am confused. OP said pumps are rated 11-12 amps says they are drawing 1.6-1.8 amps.
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Sounds like they are not running at full speed?

ptonsparky said:
I'd like to see an installation manual for these. Someone have a a Mfg and model #.
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Betcha Pentair. I looked and not much information other than a 15A GFCI breaker is suggested for the 3Hp. I do see though that it's also a controller to control itself as well as lights, heat, chlorinators, etc. and is WiFi enabled. Seems to be a lot going on there if this is what he has.

-Hal
 
hbiss said:
Sounds like they are not running at full speed?
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At the time this was checked. Possible they are running at a high speed at the time the breaker is tripping? If anything need to force it to run at full speed and check draw then?

And keep in mind if this is VFD driven motor even though the supply might be single phase the drive output could be three phase driving a three phase motor. Any current display on that drive might only be the motor current and not input current which will be higher if drive is converting single to three phase.
 
JoeStillman said:
I've been wondering if the problem is because we're using 208V split-phase and the L1-G/L2-G references are not the same vectors as they would be if we were using a 120/240V center tapped transformer source.
Click to expand...
No. All the drive does is rectify to DC. Vectors are irrelevant.

The motors are not single phase. The DRIVES accept and rectify single phase, the recreate 3 phase for the motors. The single phase input current is going to be higher than the 3 phase motor current by the square root of 3, so 1.732. Therefore if the motor current is 12.4A, the current on the single phase side will be over 20A. It will also be high in harmonics, which can skew the thermal trip curve lower.
 
Pentai drive/pump, Siemens GFI breakers, some of which have a Pentair sticker over the Siemens label.

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