Fire Pump Ground wire size

[usher]

Hi,

Just wondering what will be the size of ground wire from the Fire pump controller to the Fire pump for a 575/3/60 250HP pump (FLA 242A).

According to Table 250.122 it is sized according to the OCPD, which in this case is 600% X FLA of the fire pump.

it seems quite high to use 3/0-4/0 ground wire for a 242A feed.

Am I on the right track?

 

[gadfly56]

Hi,

Just wondering what will be the size of ground wire from the Fire pump controller to the Fire pump for a 575/3/60 250HP pump (FLA 242A).

According to Table 250.122 it is sized according to the OCPD, which in this case is 600% X FLA of the fire pump.

it seems quite high to use 3/0-4/0 ground wire for a 242A feed.

Am I on the right track?

Not looking at 695 right now, but as I recall you size the conductors for 125% of FLA, including grounds. And the OCPD is sized according to Table 9.5.1.1 in NFPA 20, based on motor horsepower.

 

[usher]

Not looking at 695 right now, but as I recall you size the conductors for 125% of FLA, including grounds. And the OCPD is sized according to Table 9.5.1.1 in NFPA 20, based on motor horsepower.

Gadfly56,

You are correct, according to 695 the conductors are sized 125% of FLA and OCPD is rated according to the Locked Rotor Motor Current.

My questions is how to you size the equipment ground wire? that is ground wire from the controller to the fire pump not the line conductors.

Thanks

 

[david luchini]

Gadfly56,

You are correct, according to 695 the conductors are sized 125% of FLA and OCPD is rated according to the Locked Rotor Motor Current.

My questions is how to you size the equipment ground wire? that is ground wire from the controller to the fire pump not the line conductors.

Thanks

250.122 would apply for the EGC.

 

[gadfly56]

Gadfly56,

You are correct, according to 695 the conductors are sized 125% of FLA and OCPD is rated according to the Locked Rotor Motor Current.

My questions is how to you size the equipment ground wire? that is ground wire from the controller to the fire pump not the line conductors.

Thanks

Same size.

 

[infinity]

Hi,

Just wondering what will be the size of ground wire from the Fire pump controller to the Fire pump for a 575/3/60 250HP pump (FLA 242A).

According to Table 250.122 it is sized according to the OCPD, which in this case is 600% X FLA of the fire pump.

it seems quite high to use 3/0-4/0 ground wire for a 242A feed.

Am I on the right track?

It wouldn't be extraordinary uncommon to use a #4/0 EGC with 350 kcmil circuit conductors.

 

[gadfly56]

Same size.


View attachment 17427

I should have added, "or smaller". The locked rotor current for a 250 HP motor in 9.5.1.1 is 1825 at 460, but you can ratio the voltages, so 460/575*1825=1460. Table 250.122 says 3/0 for 1200 and 4/0 for 1600. So you'll need 4/0, which is less than the 350 kcmil (or so) you need for the ungrounded conductors.

 

[usher]

Thanks for the help guys. it makes sense now

 

[usher]

It wouldn't be extraordinary uncommon to use a #4/0 EGC with 350 kcmil circuit conductors.

I am looking at an easily accessible industrial tray cable or TECK cable with 3/C w/ ground.

The 350MCM 3/C comes with a #3 ground wire, so if use one of these cable I am doing a code violation? since by code I require #4/0 ground ?

 

[kwired]

I am looking at an easily accessible industrial tray cable or TECK cable with 3/C w/ ground.

The 350MCM 3/C comes with a #3 ground wire, so if use one of these cable I am doing a code violation? since by code I require #4/0 ground ?

Any kind of cable can easily get you into trouble when you have special conditions that allow higher then usual overcurrent proetction levels for that particular size of ungrounded conductor or if using the cable as a set of a parallel conductor application. Not that you couldn't special order one with what you need, but most are only stocked with commonly needed EGC size associated with the ungrounded conductors.