FIRE PUMP 208 FED BY 240V.

V

VENgineer

Member
Location
Miramar Fl
Occupation
Electrical Engineer
I have the following situation.

A client contacts me because they have a fire pump (125hp) connected to their 240V system and the pump is designed to operate at 208V. During the test, the control system triggers a high voltage alarm.

Based on my research in the NEC and NFPA, I have two options.

  1. Install a step-down transformer (240 delta to 208Y) 150KVA. (The issue with this approach is that the transformer, according to NEC, must be protected on the primary side. Since it feeds the fire pump, it should be sized at least 6x FLA, requiring an OCPD of at least 2000A and finding space to place it (there is not much space in the electrical room).
  2. Replace the pump. (more expensive)
My question is, I want to make sure that I am correct and that there is no exception for the transformer to be connected without OCPD because it feeds the fire pump.

Please, I await your opinions. Thank you very much
 
I also found that a Buck-Boost transformer from 240V to 208V could help, but it needs to be larger than 150 KVA, and it's not easy to find. This type of transformer also has to comply with NEC 450.3(B) and 695.5(B), so I would still need a 2000A disconnect.

Please correct me if I'm wrong.
 
I think the autotransformer would be a lot smaller than 150 kVA. It only has to provide the difference in voltage. Having said that, the correct solution is to replace the motor and probably get the control system re-configured for 240 V. A fire pump system should be as simple and reliable as possible.

(I assume the supplier has been asked if the motor could run at 230 V. Many motors are "triple-rated" for 460, 230 and 208. The high voltage alarm could be re-calibrated if that is the only issue. They would have to get something in writing from the supplier if they go that route, IMO).
 
David Castor said:
I think the autotransformer would be a lot smaller than 150 kVA. It only has to provide the difference in voltage. Having said that, the correct solution is to replace the motor and probably get the control system re-configured for 240 V. A fire pump system should be as simple and reliable as possible.

(I assume the supplier has been asked if the motor could run at 230 V. Many motors are "triple-rated" for 460, 230 and 208. The high voltage alarm could be re-calibrated if that is the only issue. They would have to get something in writing from the supplier if they go that route, IMO).
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Costumer answer: ("Neither the inspector nor I were the ones who rejected this. The equipment manufacturer was the one who requested it because when the equipment was turned on, the OVER CHARGE alarm went off. That's when he said he wouldn't turn on the pump. He gave me the option to either change the pump, which is impossible, or reduce the voltage, which is done with a transformer. In a separate email, I'll send you the information about the transformer that the electrician asked for so that you can certify it.")

I explained to the client that if a transformer is connected to the fire pump, a Disconnect needs to be added to the primary side of the transformer, which, according to NEC 450.3(B) and 695.5(B), would be approximately 2000A. This is not economically feasible.

Both pump motors (main and jockey) can operate at 240V. The nameplate indicates 208-230/460V.
The only thing needed is to speak with the manufacturer to calibrate the controller to that voltage level or change the controller if necessary.

Am I correct??

Why doesn't the manufacturer provide this solution?
 
AlaskaElectric said:
Costumer answer: ("Neither the inspector nor I were the ones who rejected this. The equipment manufacturer was the one who requested it because when the equipment was turned on, the OVER CHARGE alarm went off. That's when he said he wouldn't turn on the pump. He gave me the option to either change the pump, which is impossible, or reduce the voltage, which is done with a transformer. In a separate email, I'll send you the information about the transformer that the electrician asked for so that you can certify it.")

I explained to the client that if a transformer is connected to the fire pump, a Disconnect needs to be added to the primary side of the transformer, which, according to NEC 450.3(B) and 695.5(B), would be approximately 2000A. This is not economically feasible.

Both pump motors (main and jockey) can operate at 240V. The nameplate indicates 208-230/460V.
The only thing needed is to speak with the manufacturer to calibrate the controller to that voltage level or change the controller if necessary.

Am I correct??

Why doesn't the manufacturer provide this solution?
Click to expand...
If motor is already rated 208-230 volt changing it won't make the alarm go away. As you mentioned calibration of controller is needed, and maybe verifying anything else that is connected can operate at 240. Control transformer, if there is any, very likely can have tap changed so reset or replace voltage monitor for the higher volts, the manufacturer rep should be well aware of this if they are any good.

What probably happened is nobody confirmed the system is 240 volts when ordering, but sounds like is fairly easily changeable in the field. This tech needs to come down from his pedestal IMO.
 
AlaskaElectric said:
Why doesn't the manufacturer provide this solution?
Click to expand...
That’s the real question here. I was in the Fire Pump Controller business for a few years, one clear message I got from that is that everything having to do with fire pumps is VERY regulated and controlled. This sounds like a fustercluck from the outset. I mean, how does someone order a Fire Pump with the wrong voltage?

Or was the FP bought used or surplus? That might explain it, in which case the owner has to accept the costs of doing it correctly.
 
Jraef said:
That’s the real question here. I was in the Fire Pump Controller business for a few years, one clear message I got from that is that everything having to do with fire pumps is VERY regulated and controlled. This sounds like a fustercluck from the outset. I mean, how does someone order a Fire Pump with the wrong voltage?

Or was the FP bought used or surplus? That might explain it, in which case the owner has to accept the costs of doing it correctly.
Click to expand...
If bought used or surplus why is a manufacturer rep even involved in startup?
 
David Castor said:
I think the autotransformer would be a lot smaller than 150 kVA. It only has to provide the difference in voltage. Having said that, the correct solution is to replace the motor and probably get the control system re-configured for 240 V. A fire pump system should be as simple and reliable as possible.

(I assume the supplier has been asked if the motor could run at 230 V. Many motors are "triple-rated" for 460, 230 and 208. The high voltage alarm could be re-calibrated if that is the only issue. They would have to get something in writing from the supplier if they go that route, IMO).
Click to expand...
Agree. FLA of a 125 HP/ 208V motor is 342A. That would be about a 123kVA power draw. Pauto= 123 kVA X (16/(16+120)) = 14.5kVA. The nearest three-phase autotransformer is 15 kVA (3 X 5 kVA, 120/240V: 16/32V will do).
 
topgone said:
Agree. FLA of a 125 HP/ 208V motor is 342A. That would be about a 123kVA power draw. Pauto= 123 kVA X (16/(16+120)) = 14.5kVA. The nearest three-phase autotransformer is 15 kVA (3 X 5 kVA, 120/240V: 16/32V will do).
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Something doesn't seem right about the above calculation.

A 5 kVa transformer with 16V secondary has an output current rating of 312.5A. The calculation suggests a wye connection, so the 342A motor FLA will flow through this secondary.

The calculation does show the huge benefit of using an autotransformer setup.

Jon
 
winnie said:
Something doesn't seem right about the above calculation.

A 5 kVa transformer with 16V secondary has an output current rating of 312.5A. The calculation suggests a wye connection, so the 342A motor FLA will flow through this secondary.

The calculation does show the huge benefit of using an autotransformer setup.

Jon
Click to expand...
Good catch! I screwed that up. That should have been 12/24, 120/240V. The series winding current rating is 417A. Sorry.
 
The OP must have the unicorn of motors. A nominal 200 volt motor. I would want to verify that fact prior to moving forward. After that I agree that I would require a solution from the manufacturer. But can you post a picture of the motor nameplate?
 
Strathead said:
The OP must have the unicorn of motors. A nominal 200 volt motor. I would want to verify that fact prior to moving forward. After that I agree that I would require a solution from the manufacturer. But can you post a picture of the motor nameplate?
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Post 4 he says the nameplate on the motor says 208-230/460.

should be rated for 208 or 240 volt supply, or even 480.
 
Birken Vogt said:
[sidetrack] from a job I was on this summer. Are they super rare? I was not there for the fire pump but it was already there.

View attachment 2569525View attachment 2569526
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I think it might be more common to see 208-230/460 rated motors for about 60 HP and under than it is for over 60 HP. Not just fire pump motors but any motor. start getting larger and they are single volt rated motors as a general rule. Multiple leads are usually there for part winding/delta-wye starting instead of for dual voltage application reasons.
 
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