Equipment ground on fire pump

[wyboy]

NEC 695.4 requires fire pump overcurrent protection to be sized to carry motor locked-rotor current indefinitely. How is the equipment grounding conductor sized in this instance? If it is sized off of the overcurrent protection, it would need to be as large as the feeder conductors.

 

[charlie]

Everything for the fire pump installation is sized normally just like any other motor installation until you get to the overcurrent protection. If the fire pump controller is SUSE rated, you don't worry about overcurrent protection at all. If you are installing overcurrent protection, it does have to permit locked rotor current for as long as it takes for the controller to open the circuit.

If you keep this concept in mind, the rest of Article 695 makes sense and is easy to follow. :smile:

 

[don_resqcapt19]

Charlie,
What part of Article 695 modifies the rules in 250.122?

 

[tom baker]

AHJs used to require the fire conductors from controller to FP be sized to carry LRC, which was not the intent of art 695. the 02 or 05 NEC clarifed they are not required to be sized to carry LRC.

 

[charlie]

. . . What part of Article 695 modifies the rules in 250.122?

Don, I don't understand your question. If you are following the requirements of 695 and need to up-size the phase conductors for voltage drop, 250.122(B) has to also be followed. I believe that was the OP's original question that I addressed in an oblique manner. Have I addressed yours? :smile:

 

[infinity]

What if you had a 200 amp conductors and a 1200 amp OCPD would you size the EGC according to 250.122 and 1200 amps?

 

[RUWired]

I think we need to verify if an equipment ground or a grounded conductor is needed. If this is service equipment, a grounded conductor sized by 250.24(C)1 is required.
rick

 

[charlie]

What if you had a 200 amp conductors and a 1200 amp OCPD would you size the EGC according to 250.122 and 1200 amps?

Now I understand what Don and the OP were saying, duh. Since 250.122 is based on the overcurrent protection, the difference would be huge.

If the run is in a metallic conduit system, the conduit would be the grounding conductor so the question would be moot. It the run is considered to be service conductors, the neutral that is required to be installed to the service equipment would be used for grounding so the question would be moot. I would think it would be a rare installation where Table 250.122 would be used.

 

[wyboy]

In this instance the conductors feeding the pump controller are circuit conductors not service conductors and a grounding conductor needs to be installed. I think I need to install a EGC sized off of overcurrent from table 250.122. it will have to be the same size as the ungrounded conductors.

 

[infinity]

Even if there were service conductors involved wouldn't there still be a need for a EGC on the load size of the OCPD feeding the fire pump motor? I'm envisioning a flexible raceway between the fire pump and it's controller which would likely require an EGC. How would you size that EGC using the 200 amp conductors, 1200 OCPD example I mentioned previously?

 

[wyboy]

You are right as far as I can tell. 250.122 (A) states that the EGC need not be larger than the circuit conductors. My motor needs 1/0 conductors and my EGC off of 250.122 needs to be 1/0 as well.

 

[wyboy]

A 1200 amp OCPD requires a 3/0 EGC. However not all pump controllers have OCP for fire pumps. 695.4 allows a direct connection or a connection with overcurrent protection. How would you size the EGC if there is no overcurrent protection as allowed by 695.4?