Starting Fire Pump in Bypass mode

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cvirgil467

Senior Member
Location
NewYork
Hey There.

The NEC discusses several methods for starting fire pumps. If you use a soft start starter (reduced voltage starter) that has a bypass would you
need to take into account a scenario that the starter electronics would be inoperable and could be in bypass mode when called for? This would
mean you would need to take into account the full voltage starting currents when sizing a generator and therefore not get the benefit of using a
reduced voltage starter or other type of soft start method.

thank
c
 

tom baker

First Chief Moderator
Staff member
I would check with the mfg to see if that starting mode (bypass) would actually occur on electronics failure. I just helped with troubleshooting a 100 hp fire pump on a softstart. It would ramp up in two seconds instead of the desired ten, as the softstart limits voltage to limit current. the pump was lightly loaded and there was not enough current to limit on a start. Owner wanted ten seconds to reduce pressure surges
 

Skokian

Member
Location
Skokie, Illinois
Full Voltage (A-T-L) Starting with a Soft Start Fire Pump Controller.

Full Voltage (A-T-L) Starting with a Soft Start Fire Pump Controller.

Hey There.

The NEC discusses several methods for starting fire pumps. If you use a soft start starter (reduced voltage starter) that has a bypass would you
need to take into account a scenario that the starter electronics would be inoperable and could be in bypass mode when called for? This would
mean you would need to take into account the full voltage starting currents when sizing a generator and therefore not get the benefit of using a
reduced voltage starter or other type of soft start method.

thank
c

The bypass contactor is energized after the accelerate period during every automatic or manual pushbutton start. This is done to reduce the heat build-up which would otherwise occur if the soft starter continued to supply the motor current during running. However, there is also an Emergency Mechanical Manual operator. This always starts the pump in the A-T-L mode. The Fire Pump Standard, NFPA-20, requires that the gen-set must be able to start the pump in this mode without tripping any OCP. However, the 5% and 15% voltage drop requirements are exempted in this mode. I can cite specific code reference clauses if you need me to.

Hope this helps.

BTW, is there a way to be notified by E-Mail when answers to a question are posted?
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
The bypass contactor is energized after the accelerate period during every automatic or manual pushbutton start. This is done to reduce the heat build-up which would otherwise occur if the soft starter continued to supply the motor current during running. However, there is also an Emergency Mechanical Manual operator. This always starts the pump in the A-T-L mode. The Fire Pump Standard, NFPA-20, requires that the gen-set must be able to start the pump in this mode without tripping any OCP. However, the 5% and 15% voltage drop requirements are exempted in this mode. I can cite specific code reference clauses if you need me to.

Hope this helps.

BTW, is there a way to be notified by E-Mail when answers to a question are posted?

Under "Thread Tools" you can "Subscribe to This Thread". You can also do that any time you put in a reply, in "Addtional Options" right below where you type in your response.
 

cvirgil467

Senior Member
Location
NewYork
Thanks for the helpful responses. Found the code reference in NFPA 20.

We are checking the starting kVA of the generator vs starting kVA of the fire pump and also talking with the fire pump controller manufacturer to see what is the largest voltage drop the pump can see before failing to start.

Not sure how to get email notification when somone has responded to a post. Just need to keep checking this site.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Thanks for the helpful responses. Found the code reference in NFPA 20.

We are checking the starting kVA of the generator vs starting kVA of the fire pump and also talking with the fire pump controller manufacturer to see what is the largest voltage drop the pump can see before failing to start.

Not sure how to get email notification when somone has responded to a post. Just need to keep checking this site.

See my post at #4.
 

Skokian

Member
Location
Skokie, Illinois
NFPA-20 Max. Voltage Drops.

NFPA-20 Max. Voltage Drops.

Thanks for the helpful responses. Found the code reference in NFPA 20.

We are checking the starting kVA of the generator vs starting kVA of the fire pump and also talking with the fire pump controller manufacturer to see what is the largest voltage drop the pump can see before failing to start.

Not sure how to get email notification when somone has responded to a post. Just need to keep checking this site.

NFPA-20 (Section 9.4) limits voltage drop during starting to 15% max. of nominal at the controller inlet terminals during normal (electrical) starting, and 5% max. at the motor terminals when the motor is running at 115% of rated motor FLA. Note that voltage drop calculations can be done at 85% P.F. for the running voltage drop (See NEC Chapter 9 Tables); but, should be done at 30% (or 40% max.) for starting voltage drop
 
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