Autotransformer w/ GFCI to pool pump

[brantmacga]

Situation is that I have a 208Y/120 service, and the pool pumps are 230v only. I have verified with Pentair that these IntellifloXF pumps will not work on 208v. The pool contractor needs these specific pumps for this install.

I can't find any mention of autotransformers in article 680. My plan at this point is to install the transformer at each pump location. We have 1" conduits that run from the pool panel under the equipment pad and up into a junction box center of the pad, and from there will branch out to the equipment.

Anyone see a reason this wouldn't be acceptable? In the past the contractor used 208v pumps when necessary but again, this specific 230v model is required.

Pic of area attached for reference ..... the junction box will be just in front of that large gas heater. Conduit will extend from there to each of the 3 pumps. I would set a strut mount next to the pump to mount the buck/boost.

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[GoldDigger]

If you use a 120 to 240 autotransformer, I would expect that you would have to use either a 120V GFCI on the input or a 240V GFCI on the output to be safe. How the code feels about it is less clear.

If you are thinking of using a 208V to 240V boost autotransformer, I would be concerned that the pump might have higher internal leakage to frame and therefore ground when installed with both input leads offset from ground.
In a normal installation both capacitive coupling and resistive leakage to ground from the L1 and L2 side of the motor would balance out to near zero ground current. With L1 and L2 connected to two lines of a delta or wye the leakage will not cancel.
Not necessarily a practical safety problem if the frame is properly grounded and connected to the pool equipotential plane, but it could trip a GFCI.

Did Pentair confirm that connecting to two of three phases of a wye would be acceptable, or were they thinking only of a balanced 240?

 

[brantmacga]

I did not discuss the autotransformer with Pentair; I should call them back tomorrow.

I planned to use a 208-230 buck/boost. If I use a 120-240 transformer, I believe I would have to install GFCI protection on the load side, which would require breaker disconnects at every pump. If I'm going to have to do that, seems it would be easier and probably less costly to install a transformer ahead of the pool panel.

And yes, I will be connecting L1/L2 of a wye service.

Now I have another thought, and that is, how will having the transformer connected to the pump affect the control circuit back to the Intellitouch panel? I usually connect the controls transformer to 240v, but I can also connect it 120v. I need to call Pentair back on this.

I want to say the speed controls located on the pump derive power from the Intellitouch panel, but some of them can operate without an Intellitouch system, so that makes me think they get power from the pump circuit.


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[brantmacga]

Called Pentair, now getting conflicting opinions. One tech support agent says it will only work on 230v, the other says it will run fine on 208 but if it sags any lower, the controls will give an error and shut the pump down. They could not give an answer on using buck/boost.


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[templdl]

Autotransformer are commonly used because they are less costly than an isolation transformer as only enough kva is required to make the voltage change. Going from 208 to 240v is a piece of cake but going from 120-240 there is no cost advantage along with no isolation with the autotransformer in doing so.
If you go the 208-240 autotransformer route you would actually be carrying the EGC through and the autotransformer (boost transformer) actually ends up is series with one of the line conductors in order to boost the L-L voltage. As such a GFCI I would think would work just fine because I you still have the same grounded conductor from the same source. Any L-G leakage would be detected by the GFCI.
Using a 120-240v step up isolation transformer with a 2w secondary you would be simply establishing a new system and grounding the new neutral (I think that neutral would be the wrong term with a 240v2w secondary) and establishing an EGC so GFCI would work and that side too. But you would have to ground one line of the secondary output.
You could use a 120-120/240 step up 3w secondary and you would then have a neutral that you could ground and bring your EGC from supplying your motor with the 240bbv L-L.
The disadvantage of the 2w secondary is that there would be 240v to ground where with a 3w secondary you we would have 120v to ground which is preferable.

 

[brantmacga]

Spoke when a field tech from Pentair for this region..... he said use buck/boost transformers. Said we could expect problems trying to run on 208V.


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[brantmacga]

To add to that conversation;

The controls derive their power from the pump.

It also uses 1-phase AC to D.C. to 3-phase inverter to power the VFD pump.


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[brantmacga]

So they are saying the autotransformer won't cause problems with the communication line


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[chris kennedy]

So they are saying the autotransformer won't cause problems with the communication line

They do know you will have 120V on L1 or 2 and 116 or 108 on the other L right?

 

[kwired]

Sounds to me like the drive is what will have the most problems if it's input voltage is too low.

I realize you already have equipment, but maybe whoever was responsible for providing equipment could have ordered a unit designed for 208 three phase input??

 

[curt swartz]

The communications between the pumps and control panel are optional. It is done through a class 2 cable. I don't think it cares what voltages are used to supply the pumps.

 

[brantmacga]

Sounds to me like the drive is what will have the most problems if it's input voltage is too low.

I realize you already have equipment, but maybe whoever was responsible for providing equipment could have ordered a unit designed for 208 three phase input??

That's right.

We did have a discussion before this started about making sure all equipment was rated for 208v, but I think it got overlooked on the pumps probably because we've never had this issue.

The problem now, from what I understand, is that this setup was designed specifically with this pump in mind, and they don't want to change it. According to the Pentair field service tech, using autotransformers is recommended for this pump. I'm trusting that the guy I spoke to last is more familiar than the people in the call center.


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[Ravenvalor]

Situation is that I have a 208Y/120 service, and the pool pumps are 230v only. I have verified with Pentair that these IntellifloXF pumps will not work on 208v. The pool contractor needs these specific pumps for this install.

I can't find any mention of autotransformers in article 680. My plan at this point is to install the transformer at each pump location. We have 1" conduits that run from the pool panel under the equipment pad and up into a junction box center of the pad, and from there will branch out to the equipment.

Anyone see a reason this wouldn't be acceptable? In the past the contractor used 208v pumps when necessary but again, this specific 230v model is required.

Pic of area attached for reference ..... the junction box will be just in front of that large gas heater. Conduit will extend from there to each of the 3 pumps. I would set a strut mount next to the pump to mount the buck/boost.




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My apologies in advance for the dumb questions.
Can you use some sort of an inverter? Also, can you put the autotransformer, buck/boost transformer or inverter at the source of the feeder circuit?

 

[kwired]

My apologies in advance for the dumb questions.
Can you use some sort of an inverter? Also, can you put the autotransformer, buck/boost transformer or inverter at the source of the feeder circuit?

Inverter, can not increase voltage over the input voltage. The pump controller already has an inverter within it as well.

Had this been a general purpose drive it likely would accept 208 or 240 volt input (probably anywhere between 200 and 255) voltage, you may have to set a parameter to your input for more effective use, and you may be able to drive a little larger motor in some cases on a 240 volt system then you could on a 208 volt system. You can however go the other way with the voltage on a VFD, if OP had a 240 volt supply and needed nominal 208 to the motor being driven the drive could make that kind of conversion without additional transformation, only way this wouldn't work is if for some reason the front end of the drive can't accept 240 volts.

The front end of the drive likely has MOV's connected from each input line to ground. If you use an autotransformer (which is what a buck boost transformer is) one of your drive input lines will be direct connected to autotransformer input lines and still be @ 120 nominal to ground. The other line will be 32 volts higher (on 208-240 boost) and will be 152 volts to ground. Depending on the MOV's used this could be within the clamping voltage full time which is not intended, they are only supposed to clamp surges. This is not real likely to be a problem since this is a 240 volt input drive, but can be a problem on corner ground systems where the line to line volts is much higher then what line to ground would be with a system that has a grounded neutral.

The auto transformer could be in the feeder, but if there are 120 volt circuits supplied from that feeder, one bus is at 120 volts the other is at 152 to neutral. This increases or decreases slightly depending on how much the supply voltage varies from the nominal of 120/208.

 

[kwired]

When it comes to GFCI protection, the pump motors are three phase and are fed from a separately derived source - the load side of the drive.

GFCI on the supply side of the drive will not respond to ground faults on the load side of the drive and is useless IMO other then maybe for some protection of the drive itself. 680.21(C) would not require GFCI protection of the three phase pump motor IMO, but the drive probably is pretty effective at shutting down the output in the event of relatively minor ground faults as well. Maybe not at the 4-6 mA fault range but likely still in the GFPE ranges.

 

[brantmacga]

680.21(C) would not require GFCI protection of the three phase pump motor IMO, but the drive probably is pretty effective at shutting down the output in the event of relatively minor ground faults as well. Maybe not at the 4-6 mA fault range but likely still in the GFPE ranges.

While I agree with you, the input to the pump is 240v 20A 1-phase, so we have to use a GFCI breaker.

You have brought up a very interesting point though; would like to hear some opinions as to whether or not a code change for these VFD pumps is warranted.


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[kwired]

While I agree with you, the input to the pump is 240v 20A 1-phase, so we have to use a GFCI breaker.

You have brought up a very interesting point though; would like to hear some opinions as to whether or not a code change for these VFD pumps is warranted.


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If I understand correctly you are supplying single phase to a VFD controller, and that VFD controller is converting that to three phase output to a three phase motor.

The output side of the drive is it's own system with no direct connection to the input side. A GFCI on the input side will not respond to a ground fault on the output side and is only useful for protection of the input circuit.

682.21(C) requires GFCI protection at the outlet supplying a pool pump that is single phase 120 to 240 volts. Your pump doesn't fit that description and GFCI is not required. As I mentioned though the drive output is probably pretty sensitive to ground faults, but maybe not all the way down to 4-6 mA, but definitely much lower fault level detection then non VFD drive applications typically are.

 

[brantmacga]

You make a good point, but with the pump labeled as 240v single phase, do you think the pump could still be classified as three phase?


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[kwired]

You make a good point, but with the pump labeled as 240v single phase, do you think the pump could still be classified as three phase?


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I am having a hard time understanding why it is labeled single phase if it is three phase.

Maybe it isn't actually three phase? Does this pump have an optional controller with start/run capacitors in it if you don't want to use the variable speed features the drive you are using provides? They do have such things for domestic well pumps, Pentair is one of those companies that makes them.

If that is what you actually have one has to question exactly what the output is. Might not be true single phase or true three phase, but is modified to match the motor needs. A GFCI on the line side of the drive still will not respond to any ground faults on the load side of the drive as it still works in very much the same way as a conventional drive when it comes to rectifying input voltage and then inverting it to what is needed for the output.

 

[brantmacga]

I am having a hard time understanding why it is labeled single phase if it is three phase.
.

The supply is 240v single phase..... there is a DC inverter inside the pump, and then it converts to 3-phase AC to power the VFD.

The pump in question is a Pentair IntellifloXF. http://www.pentairpool.com/products/pumps-inground-intellifloxf-variable-speed-pump-452.htm

Because the supply is 20A 240v single phase, I believe the GFCI rule still applies.


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