fire pump service

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tmkelly1

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A lot of debate around here on this one..
I have a 15hp fire pump with an fla of 46.2 amps and lrc of 257 amps.
my wire size for the motor feeder is 46.2x1.25 or 57.75 amps.
if I use a disconnect or breaker on the service to feed the pump it has to be sized for locked rotor current. So a 400 amp meter section with a 300 amp breaker is in order. But if I tap the power source and install no breaker or disconnect am I still required to use a 400 amp meter section? Or can I use a 200 amp meter? I'll probably be using #6 conductors. Since they are the weakest link in the chain won't the meltdown long before the 200 amp meter?
695.3(a) says that a single source shall be capable of suppling locked rotor current indefinitely.
 
tmkelly1 said:
A lot of debate around here on this one..
I have a 15hp fire pump with an fla of 46.2 amps and lrc of 257 amps.
my wire size for the motor feeder is 46.2x1.25 or 57.75 amps.
if I use a disconnect or breaker on the service to feed the pump it has to be sized for locked rotor current. So a 400 amp meter section with a 300 amp breaker is in order. But if I tap the power source and install no breaker or disconnect am I still required to use a 400 amp meter section? Or can I use a 200 amp meter? I'll probably be using #6 conductors. Since they are the weakest link in the chain won't the meltdown long before the 200 amp meter?
695.3(a) says that a single source shall be capable of suppling locked rotor current indefinitely.
Click to expand...
I'm assuming the voltage is 208 3 phase. If you choose to use a disconnect ahead of the controller it must be sized as per the locked rotor. If you have a 3 phase 208 volt design E motor the locked-rotor is 373 amps. Design B,C,D the locked rotor is 257 amps. Therefore in either case if you choose to use an overcurrent device ahead of the controller you would need a 400 amper rated one. The conductors would be 46.2 x 125%=58 amps which would be #4 copper using the 60 c column, or #6 copper if everything is rated 75 c. I personally doen't put a main ahead of the controller. I put a ct cabinet for the meter only.
 
pismo said:
I'm assuming the voltage is 208 3 phase. If you choose to use a disconnect ahead of the controller it must be sized as per the locked rotor. If you have a 3 phase 208 volt design E motor the locked-rotor is 373 amps. Design B,C,D the locked rotor is 257 amps. Therefore in either case if you choose to use an overcurrent device ahead of the controller you would need a 400 amper rated one. The conductors would be 46.2 x 125%=58 amps which would be #4 copper using the 60 c column, or #6 copper if everything is rated 75 c. I personally doen't put a main ahead of the controller. I put a ct cabinet for the meter only.
Click to expand...

Just a note to add to this. If you only install a CT section the fire pump controller must be listed as suitable for service equipment. I think almost all are be sure to check before you wire everything but this is the same method I do in a large amount of the building I wire.
 
missed the question

missed the question

I have all of that, breaker size, wire size, etc....
let's assume the 257 amps is correct for locked rotor current...
I have an engineer that says the code doesn't require the service to be sized at locked rotor current if we're not using a disconnect or breaker. So by leaving the breaker off he wants to supply this with a 200 amp meter section. My contension is that 695.3(a) says the meter section must be sized to supply the 257 amps indefinitely, which means a 400 amp service.He says the code is a bit ambiguous. It's not specifically spelled out but I do believe that the intent is to have the service larger...
 
tmkelly1 said:
I have all of that, breaker size, wire size, etc....
let's assume the 257 amps is correct for locked rotor current...
I have an engineer that says the code doesn't require the service to be sized at locked rotor current if we're not using a disconnect or breaker. So by leaving the breaker off he wants to supply this with a 200 amp meter section. My contension is that 695.3(a) says the meter section must be sized to supply the 257 amps indefinitely, which means a 400 amp service.He says the code is a bit ambiguous. It's not specifically spelled out but I do believe that the intent is to have the service larger...
Click to expand...
Look in article 695.6(C)(2). Conductors supplying only a fire pump shall have a rating not less than 125% of the fire pump full load current. Therefore, in your case the 200 amp metered section would work. The only time you size it for locked-rotor is like you said if the is overcurrent protection ahead of the fire pump controller.
 
conductor size

conductor size

Well the conductor size for conductors supplying the fire pump motor have to be rated 125% of the fla, ok(695.6(c), but that is feeder size for feeders supplying the motor. 695.3(a) says that this service shall be reliable and capable of supplying locked rotor current indefinitely.What you're suggesting is that a 60 amp service should be enough because the pump feeders only need to be rated for 57.75 amps.
Why should having a disconnect or breaker make any difference in the service size? I contend the service should be sized for locked rotor amps wheather it has a breaker or not, and the service conductors to the service should be sized accordingly.
 
tmkelly1 said:
695.3(a) says that this service shall be reliable and capable of supplying locked rotor current indefinitely.What you're suggesting is that a 60 amp service should be enough because the pump feeders only need to be rated for 57.75 amps.
Click to expand...

tm - 695.3(A) says nothing about a service being capable of supplying locked rotor current indefinitely.

It says, 'a power supply'.....shall be one of the following....
(1) Electric Utility Connection....located ahead of ....the service disconnecting means...

...this service drop/lateral must be large enough to carry the lock rotor current indefinitely....so no, the conductors for a 60A service would not suffice....but certainly the conductors for a 200A service would. IMO
 
dana1028 said:
tm - 695.3(A) says nothing about a service being capable of supplying locked rotor current indefinitely.

It says, 'a power supply'.....shall be one of the following....
(1) Electric Utility Connection....located ahead of ....the service disconnecting means...

...this service drop/lateral must be large enough to carry the lock rotor current indefinitely....so no, the conductors for a 60A service would not suffice....but certainly the conductors for a 200A service would. IMO
Click to expand...

You are wrong! The conductors only need to be sized for the FLA also the only reason you need a service for the fire pump is for the sale of power. If you have only a meter section then you can size this service based the FLA plus 125%. Therfore a 100 amp service would be just fine. As soon as you add any overcurrent then the service will have to be rated to carry the lock-rotor current.
 
695.3(a)

695.3(a)

requires the power supply to be a reliable source capable of supplying locked rotor current indefinitely....now how does that happen (257amps) through a 100amp service?
 
tmkelly1 said:
requires the power supply to be a reliable source capable of supplying locked rotor current indefinitely....now how does that happen (257amps) through a 100amp service?
Click to expand...
The overcurrent protctive device in the controller would provide that. There is nothing in the code that requires an overcurrent device ahead of the controller. If you use the controller as the service disconnect, it must be listed as suitable for service disconnect.
 
pismo said:
The overcurrent protctive device in the controller would provide that. There is nothing in the code that requires an overcurrent device ahead of the controller. If you use the controller as the service disconnect, it must be listed as suitable for service disconnect.
Click to expand...

Thats 100% correct. The fire pump controller has the overcurrent protection as required by that section. Remember that this is a short circuit protection breaker at the controller and not overcurrent protection. So the 100 amp meter section and a controller that is listed to be used as service equipment meet this requirement.
 
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