Surge Protection for MV fire pump motors

[Parkpower]

Hello everyone,

MV fire pump controllers use vacuum contactors to switching fire pump motors. Surge arrestors are normally required to protect motors from operation overvoltage when motors are stopped by vacuum contactors.

However, NFPA does not require surge arrestors on MV fire controllers. Surge arrestors are requied only on LV fire pump controllers. What is the reason for this regulation?

Practically, shall surge arrestors be installed in the terminal box of MV motors or is it not needed?


Thanks,

Parkpower

 

[jraef]

I think you have a couple of misconceptions here.

1) surge arrestors are not "required" for MV motors controlled by vacuum contactors. It's a good idea, but chop currents from VC switching are a debated phenomenon, some mfrs of VCs claim to have solved the problem in the contactor design. Either way, a Fire Pump is not turning on and off daily, or even monthly. In the absence of a fire, it only gets operated for periodic testing. Even if your VC produced chopping currents, it's unlikely the motor would suffer any significant loss of service life.

2) I have never seen where surge arrestors are required on LV motors. Lightning arrestors are a good idea if there is a high risk of lightning in the area. But that is not everywhere and there are certainly plenty of Fire Pump Controllers out there for LV motors that have no surge arrestors.


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[Parkpower]

Hi jraef,

Thanks for the answers.

Surge arrestors for protection of LV motors are not installed on LV motors, but on LV fire pump controllers. This is required in NFPA 20.

You are right that fire pump motors are not switched on/off so oftern as the other motors. Our client insists on surge protection on all the MV vacuum contactor feeders. On the 6000V feeders we install surge arrestors in the motor controller cubicles. However,the MV fire pump controller manufactured by Firetrol is a certified product without surge arrestors. We can not add the surge arrestors in the controller. So we have to find a good reason to ask the client to waive the requirement or find a solution. When I check NFPA 20, surge protection is only required in LV controller. It is not applicable to MV fire pump controllers. I want to know the mechanism of the regulation. I will contact the supplier whether the problem of switching overvoltage has been solved.


Parkpower