Fire pump Equipment Grounding Conductor

[hhsting]

Please see attached sketch shows service conductor tapped separate enclosure in switchboard ahead of main service disconnects.

The service conductors feed 400A main service fused disco fused at 400A.

Feeder labeled FDR#1 in sketch has 3#2+1#6G load side of the 400A service fused disco that feeds fire pump controller.

Feeder labeled FDR#2 supply from Fire pump Controller to Fire Pump is 3#2+1#6G.

Fire pump is 208V 3 phase, 20HP, Locked Rotor current of 360A

NEC 2017 section 695.6(B)(2) says conductor size ampacity minimum for motor only comply with 430.22 and voltage drop. Note it does Not say those conductors are phase conductors or equipment grounding conductor
There fore it is not clear how to size Equipment grounding conductor

Questions:

1 In attached sketch what code section one can use to size FDR #1 and FDR #2 equipment grounding conductor for Fire Pump?

2. #6 equipment grounding conductor (EGC )ok or its undersized?

 

[don_resqcapt19]

Since there is nothing in Article 695, to address the EGC, then the rules in Article 250 apply. See 90.3

 

[hhsting]

Since there is nothing in Article 695, to address the EGC, then the rules in Article 250 apply. See 90.3

Ok it gets confusing when voltage drop is involved. If phase conductors are increased then so are EGC but what is the intended EGC? What is the intended EGC to work 250.122(b)?

Is the intended EGC based on 400A fuse for Fdr#1 and intended EGC based on overcurrent protection in FP controller for FDR #2 Or some other way?

 

[augie47]

Is the intended EGC based on 400A fuse for Fdr#1 and intended EGC based on overcurrent protection in FP controller for FDR #2 Or some other way?

Yes, so #6 is too small for feeder #1.
The whole scenario is likely to change when you look at voltage drop.

 

[hhsting]

Yes, so #6 is too small for feeder #1.
The whole scenario is likely to change when you look at voltage drop.

For feeder #2 you think #6 is undersized?

 

[augie47]

Most likely.. but you need the controller OCP to make sure.
To CYA you can always size it the same as the phase conductors....can't go wrong then

 

[hhsting]

Most likely.. but you need the controller OCP to make sure.
To CYA you can always size it the same as the phase conductors....can't go wrong then

controller ocp is likely to be trip at 6 to 20 times fla and governed by nfpa 20

 

[augie47]

which is why I said "most likely"

 

[hhsting]

Yes, so #6 is too small for feeder #1.
The whole scenario is likely to change when you look at voltage drop.

If its voltage drop then i have to multiply EGC by ratio to comply 250.122(b). So then what EGC size gets multiplied? The one in 400A fuse?

 

[hhsting]

Can one use NEC 2017 section 250.122(D)(2) to size FDR#1 and FDR#2 EGC? Anyone know? Please

 

[mbrooke]

If unsure the absolute fail safe is to size the EGC half the size of the phase conductors for OCPDs larger than 60 amps providing both short circuit and overload protection. For applications like fire pumps where only short circuit protection is offered sizing the EGC to the phase conductors offers a fail safe withstand.

https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/solution-center/bus-ele-tech-lib-conductor-protection-wire-cable-protection-1.pdf

 

[Greentagger]

Fused at 400A? See table 250.122.? Problem solved.

 

[infinity]

Fused at 400A? See table 250.122.? Problem solved.

The answer is really that simple.

 

[hhsting]

Fused at 400A? See table 250.122.? Problem solved.

What about FDR#2 which is between Fire pump and Fire pump controller?

 

[Greentagger]

What about it? Fuse size hasn’t changed?

 

[hhsting]

What about it? Fuse size hasn’t changed?

Well their is internal breaker in the fire pump controller

 

[Greentagger]

Size?

 

[hhsting]

Size?

Breaker is 80A frame and its tripping setting go from 360A to 1200A.

 

[don_resqcapt19]

Breaker is 80A frame and its tripping setting go from 360A to 1200A.

So still sized based on the upstream 400 amp device.

 

[hhsting]

So still sized based on the upstream 400 amp device.

But if someone places the dial of the motor controller factory installed internal breaker to 1200A (20x full load amps) then sizing based on 400A would be not correct.

Do fire pump motor controller internal breakers have dial or is it factory set so no one can tamper with it? If factory set then what is it the setting set at 6x fla or 20x fla?