VFD for Fire Pump Motors
NFPA 20 requires all the individual pieces of equipment to be "specifically listed" by a national-recognized testing facility, acceptable to the AHJ that has tested all the equipment and maintains records of the test for verification. See NFPA 20, 3.2.3 for a better definition, see 10.1.2.1 for an example on controllers.
NFPA 20 does not specifically require UL or FM. It's just they and a limited few others, depending on the equipment, have actually done the testing and maintain the records. FM jobs pretty much require equipment to be FM. FM approvals use to be an option (adder) on pumps years ago as everyone but them pretty much accepted UL only.
Electric motors were the most recent adders to the pile a few years ago. This was due in part to people putting high-efficiency motors on fire pumps and not paying attention to the locked rotor codes, typically 7 - 8 X FLA. This was not compatible with the 6 X FLA trip established In NFPA 20 for the circuit breaker's locked rotor settings. With the listings you basically you got the same old code G motors that were typically used before only paying more for the listings. This is covered under NFPA 20, 9.5.1.1
Later when Variable frequency drive (VFD) came out, then came the concerns about the various original standard motors' compatibility with VFDs with respect to bearing arcing, and motor winding temperature and voltage ratings, especially VFD drives without any load filtering. Motors for VFDs are also covered under NFPA 20, 9.5.1.4
Originally, non-inverter duty motors with no load filtering in the controller and using the service factor were all accidents waiting to happen. In addition, shaft critical speeds for and "skip" (or jump) frequencies for the VFDs, especially on vertical turbines (due to long shafts) was later also added in NFPA 20, 10.10.12. This has to be coordinated with the pump OEM or you can shake the pump apart. I'm not sure what was done with first generation variable speed engines on pump shaft critical speeds.
My VFD designs were the first ones, and only ones to the best of my knowledge, used with vertical shaft pumps. We did require info on shaft resonant speeds in all cases. Hence, I guess that this aspect is covered. Regarding suitable motors, we always insisted that the motors be Inverter Duty ones and marked accordingly.
In other news, I've learned from official channels that there is now one manufacturer of U.L. Listed Inverter Duty Fire Pump Motors. I have verified this. I suspect that there will soon be some others.
The issue with motors has LRA's above 600% of motor FLA is still an open issue with motors below 5Hp. I'm still working on this issue.
NFPA 20 does not specifically require UL or FM. It's just they and a limited few others, depending on the equipment, have actually done the testing and maintain the records. FM jobs pretty much require equipment to be FM. FM approvals use to be an option (adder) on pumps years ago as everyone but them pretty much accepted UL only.
Electric motors were the most recent adders to the pile a few years ago. This was due in part to people putting high-efficiency motors on fire pumps and not paying attention to the locked rotor codes, typically 7 - 8 X FLA. This was not compatible with the 6 X FLA trip established In NFPA 20 for the circuit breaker's locked rotor settings. With the listings you basically you got the same old code G motors that were typically used before only paying more for the listings. This is covered under NFPA 20, 9.5.1.1
Later when Variable frequency drive (VFD) came out, then came the concerns about the various original standard motors' compatibility with VFDs with respect to bearing arcing, and motor winding temperature and voltage ratings, especially VFD drives without any load filtering. Motors for VFDs are also covered under NFPA 20, 9.5.1.4
Originally, non-inverter duty motors with no load filtering in the controller and using the service factor were all accidents waiting to happen. In addition, shaft critical speeds for and "skip" (or jump) frequencies for the VFDs, especially on vertical turbines (due to long shafts) was later also added in NFPA 20, 10.10.12. This has to be coordinated with the pump OEM or you can shake the pump apart. I'm not sure what was done with first generation variable speed engines on pump shaft critical speeds.
My VFD designs were the first ones, and only ones to the best of my knowledge, used with vertical shaft pumps. We did require info on shaft resonant speeds in all cases. Hence, I guess that this aspect is covered. Regarding suitable motors, we always insisted that the motors be Inverter Duty ones and marked accordingly.
In other news, I've learned from official channels that there is now one manufacturer of U.L. Listed Inverter Duty Fire Pump Motors. I have verified this. I suspect that there will soon be some others.
The issue with motors has LRA's above 600% of motor FLA is still an open issue with motors below 5Hp. I'm still working on this issue.
