Ground fault protection,3ph pool pumps and VFD's

[cpblock]

I am working on adding VFD's to 2 20hp 480volt 3ph pumps. The original engineered design had both pumps on normal utility power with GFCI breakers.Before completion of construction one pump was moved to EM power panel without GFCI protection. I have been requested to change across the line starters to VFD's for reasons pertaining to flow and water hammer to plumbing on pump starts.Now the questions, 1. Is GFCI protection required on these pumps? 2.Will the VFD's work with GFCI breakers? Just for info breaker is Eaton/culter hammer HDFE 65k 80 amp frame. installation is all indoors , plumbing is plastic ,and pumps have seperate gnds back to building steel.

 

[Jraef]

I am working on adding VFD's to 2 20hp 480volt 3ph pumps. The original engineered design had both pumps on normal utility power with GFCI breakers.Before completion of construction one pump was moved to EM power panel without GFCI protection. I have been requested to change across the line starters to VFD's for reasons pertaining to flow and water hammer to plumbing on pump starts.Now the questions, 1. Is GFCI protection required on these pumps? 2.Will the VFD's work with GFCI breakers? Just for info breaker is Eaton/culter hammer HDFE 65k 80 amp frame. installation is all indoors , plumbing is plastic ,and pumps have seperate gnds back to building steel.

1) No. VFDs will likely cause a GFCI to trip.

2) But you are confusing GFCI with GFP breaker, they are not the same thing. GFCI is a very specific term meant for personnel protection, and only applies to the Class A GFCI devices you put in bathrooms, kitchens and such, or the 15-20A circuit breakers that will feed circuits that require it. GFP is for equipment protection, not people protection. GFCI is set to trip on 4-6mA of ground current, GFPs will be 30-100ma of ground current, even more on large Service Entrance breakers.

3) In general, protecting a circuit with a true GFCI is only required on circuits with plug-in outlets on it, not hard wired equipment. The only exceptions are swimming pool/spa underwater lighting and some carnival equipment, which is why you can buy a 50A circuit breaker that really is a Class A GFCI breaker.

So even though this is a pool pump, you are likely hard wiring it so you will not be required to have a GFCI on it. That's not to say it wouldn't be a good idea, and starting in 2013 there are new "Classes" of GFCIs that might work now (haven't tested them personally on VFDs). That Eaton breaker you mentioned however is NOT a GFCI breaker, it is a GFP breaker, so it would NOT qualify anyway. But like I said, a true Class A GFCI breaker is almost guaranteed to trip from the common mode leakage current of a VFD.

 

[augie47]

side note to (3) above. In the '08 Code Swimming pool pumps connected to 15 or 20 amp 125 or 240v single phase circuits whether hard wired or cord connected are required to be GFCI protected. In later Codes I think it was expanded to all single phase 120 and 240v pumps.
Not applicable on your 3 phase pumps but just a general clarification for the casual reader

 

[Dennis Alwon]

Gus the 2014 doesn't require gfci on a 3 phase pump. It does require gfci on all single phase 120-240v circuits.

I doubt you will find a 480V 3 phase gfci breaker but I do know they make 3 phase gfp units

 

[Jraef]

Most VFDs provide GFP for the motor down stream of it anyway. It's easy to do if you are already making a VFD, the current measurements already need to be made anyway now for vector control, so implementing residual current detection is just an algorithm in the microprocessor.

Hard wired pool pumps need it now too? Didn't know that. I put one one my hot tub pump, the inspector told me I didn't need it but I wanted it anyway. But that was in 2001, so if it changed later I wouldn't have known, I haven't had occasion to look into it again. Good to know. The one GFCI issue I have had to deal with more recently is GFCIs being required in garages now, with or without laundry facilities. I have a couple of bench tools that I put 3 phase motors and VFDs on. I had to hard wire them to get around the GFCI issue.

 

[cpblock]

1) No. VFDs will likely cause a GFCI to trip.

2) But you are confusing GFCI with GFP breaker, they are not the same thing. GFCI is a very specific term meant for personnel protection, and only applies to the Class A GFCI devices you put in bathrooms, kitchens and such, or the 15-20A circuit breakers that will feed circuits that require it. GFP is for equipment protection, not people protection. GFCI is set to trip on 4-6mA of ground current, GFPs will be 30-100ma of ground current, even more on large Service Entrance breakers.

3) In general, protecting a circuit with a true GFCI is only required on circuits with plug-in outlets on it, not hard wired equipment. The only exceptions are swimming pool/spa underwater lighting and some carnival equipment, which is why you can buy a 50A circuit breaker that really is a Class A GFCI breaker.

So even though this is a pool pump, you are likely hard wiring it so you will not be required to have a GFCI on it. That's not to say it wouldn't be a good idea, and starting in 2013 there are new "Classes" of GFCIs that might work now (haven't tested them personally on VFDs). That Eaton breaker you mentioned however is NOT a GFCI breaker, it is a GFP breaker, so it would NOT qualify anyway. But like I said, a true Class A GFCI breaker is almost guaranteed to trip from the common mode leakage current of a VFD.

OK I understand there is a difference so will this GFP breaker tolerate the drives "noise" put back on line,would be ordering drives with input line reactor ? This aplication situation generates a whole pile of questions

 

[Jraef]

OK I understand there is a difference so will this GFP breaker tolerate the drives "noise" put back on line,would be ordering drives with input line reactor ? This aplication situation generates a whole pile of questions

No way to tell for sure, too many variables. It might under the right circumstances, but the only way to tell for sure is to try it and be prepared. If it does, and you don't want to replace the breaker, a shielded drive isolation transformer will likely take care of it, but that's an expensive way to go. Is there a reason you are going to still do it, as in "I already did it and I don't want to show the customer that I didn't need to!" Perfectly understandable by the way, I'm just curious.

 

[cpblock]

No way to tell for sure, too many variables. It might under the right circumstances, but the only way to tell for sure is to try it and be prepared. If it does, and you don't want to replace the breaker, a shielded drive isolation transformer will likely take care of it, but that's an expensive way to go. Is there a reason you are going to still do it, as in "I already did it and I don't want to show the customer that I didn't need to!" Perfectly understandable by the way, I'm just curious.

I read that an isolation x-fmr may solve issue BUT wouldn't isolation x-fmr just discontinue GFP protection due to NO electric connection from Pri to Sec , I thought this solution was useless as it would add isolation and render GFP breaker inefective , also a transformer will generate I2R heating that will waste energy. I work for a public university that does'nt answer to AHJ ,so sometimes we have to seek our own solutions. I think from this info I will sugjest changing GFP breaker and let VFD monitor situation. I read Code section on pools and saw nothing on this situation, thanks for your opinion, we kinda leaned that way too. WE may try VFD on GFP breaker to see if we can make it fly,that answer may take a while but I'll let you know.