Fire Pump Locked Rotor Protection
Fire Pump Locked Rotor Protection
(OP)
Hi,
I have read NFPA20 which requires that the thermal overload is not required to protect the motor but the locked rotor protection is required.
I have question about the electric fire pump locked rotor protection. Is it necessary that the protective relay curve needs to lie below motor safe stall time(hot and cold)in order to protect the motor from locked rotor protection ?
Thank you,
I have read NFPA20 which requires that the thermal overload is not required to protect the motor but the locked rotor protection is required.
I have question about the electric fire pump locked rotor protection. Is it necessary that the protective relay curve needs to lie below motor safe stall time(hot and cold)in order to protect the motor from locked rotor protection ?
Thank you,





RE: Fire Pump Locked Rotor Protection
Bill
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Jimmy Carter
RE: Fire Pump Locked Rotor Protection
I commented to fire pump vendor that their setting protection curve is above hot stall time and as such the motor is not really protected from locked rotor condition which will cause damage to motor.
However they said that the fire pump set is approved as UL listed and as such they cannot change the setting of curve even though the protection curve is above locked rotor safe stall time.
I wonder that whether this setting violate NFPA20 or not ?
If this setting condition complies with NFPA20,this means that there is no meaning to protect the motor against locked rotor condition but why the NFPA20 still require and has clause regarding to locked rotor protection ?
RE: Fire Pump Locked Rotor Protection
But to be blunt, if you have to ask this question and you don't know where to get the answer or how to interpret what is being said, you probably have no business taking on this task. Please consider that this is not about general electrical engineering, this is about life and safety. If you were in a fire and the sprinklers failed to come on because the fire pump motor tripped off line because of a protective relay setting being too sensitive, you or your survivors are not going to be happy.
But their lawyers will be.
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RE: Fire Pump Locked Rotor Protection
RE: Fire Pump Locked Rotor Protection
I agree it doesn't sound like standard protection... sounds like a code question. Maybe power engineering or code forum have insights.
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(2B)+(2B)' ?
RE: Fire Pump Locked Rotor Protection
RE: Fire Pump Locked Rotor Protection
The overcurrent protection on the fire pump feeder must sized to carry locked rotor current indefinitely (to motor destruction) without tripping. There is only short circuit protection.
And not only is thermal overload protection not required, it is not ALLOWED.
Fire pump requirements trump motor protection and pretty much everything else.
RE: Fire Pump Locked Rotor Protection
Besides, you don't set the instantaneous trip of the breaker below the locked-rotor current or expected inrush current for any motor. Doing so would cause the breaker to trip when you started the motor.