Equipment grounding conductor sizing

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hhsting

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Attached sketch shows incoming electric utility service to enclosed circuit breaker which then feeds fire pump controller ATS combo which feeds fire pump. The ATS controller combo is also fed by generator.

The enclosed circuit breaker is part of listed fire pump assembly service rated and has overcurrent protection in compliance with NEC 2014 Article 695.4(B)(2)(a)(2) and has following:
Short circuit protection only
Magnetic only - non thermal
Instantaneous trip setting (factory set non field adjustable)
No time delay element

Following questions:

1. For equipment grounding conductor sizing for labeled FDR #1 part attached sketch between enclosed breaker and controller ats combo which one of the following 250.122(D)(1) or 250.122(D)(2) be used?

2. For equipment grounding conductor sizing for labeled FDR #2 between fire pump and controll ATS combo part attached sketch which one of the following 250.122(D)(1) or 250.122(D)(2) be used?
a186bc050b1657d7c75ac8976dbe459e.jpg


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hhsting said:
Attached sketch shows incoming electric utility service to enclosed circuit breaker which then feeds fire pump controller ATS combo which feeds fire pump. The ATS controller combo is also fed by generator.

The enclosed circuit breaker is part of listed fire pump assembly service rated and has overcurrent protection in compliance with NEC 2014 Article 695.4(B)(2)(a)(2) and has following:
Short circuit protection only
Magnetic only - non thermal
Instantaneous trip setting (factory set non field adjustable)
No time delay element

Following questions:

1. For equipment grounding conductor sizing for labeled FDR #1 part attached sketch between enclosed breaker and controller ats combo which one of the following 250.122(D)(1) or 250.122(D)(2) be used?

2. For equipment grounding conductor sizing for labeled FDR #2 between fire pump and controll ATS combo part attached sketch which one of the following 250.122(D)(1) or 250.122(D)(2) be used?
a186bc050b1657d7c75ac8976dbe459e.jpg


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Click to expand...

Anyone know which to use 250.122(D)(1) or 250.122(D)(2) to size EGC post #1 questions?

Thank you in advance for your help

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according to my understanding: FDR#1 is not motor circuit, I would just use table 250.122. FDR#2 is motor circuit, 250.122(D) maybe used.

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Well I looked over the code Article 250.122(D)(1) and 250.122(D)(2) both point to 250.122(A). Article 250.122(A) gives you minimum range and maximum range. Minimum is Table 250.122 and maximum is phase conductor size.

So what if I size FDR #1 and FDR #2 post #1 attachment equipment grounding conductor based on maximum size same size as phase conductors would it not be per code 250.122(D)(1) or 250.122(D)(2) based on above reasoning?

Also then one could argue that fire pump needs to be able to run until conductors are burn so its best to go with minimum EGC size instead of maximum EGC size. Not even sure if minimum or maximum size play any role. Would pump run and conductor burns regardless of maximum size EGC? What are all of your opinions regarding all the above? Its all so confusing.
 
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Purpose of EGC is to burn circuit fuses (open breaker) when there is ground fault. Size base on table 250.122. you need to increase the size of conductor if the wiring is very long.

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victor.cherkashi said:
Purpose of EGC is to burn circuit fuses (open breaker) when there is ground fault. Size base on table 250.122. you need to increase the size of conductor if the wiring is very long.

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But D2 gives us an option for motor circuits that may allow use of a smaller EGC.

Then it gets complicated by the fact that fire pumps aren't done the same as other motor circuits, they want the thing to be able to run at locked rotor current indefinitely. Because of this I don't know you can apply D2 to a fire pump since you wouldn't normally use a dual element time delay fuse on a fire pump in the first place. But that is just a guess and not a definite answer.
 
kwired said:
...Then it gets complicated by the fact that fire pumps aren't done the same as other motor circuits, they want the thing to be able to run at locked rotor current indefinitely. ...
Click to expand...

Not to add more confusion or more salt in wound but I am not sure I follow what you said above has to carry indefinitely locked rotor current. You see 695.4(B)(2)(a)(2) says device shall not open within 2 minutes at 600 percent of full load amps.
It also says shall not open within 10 minutes at 300 percent of full load amps.

Sounds to me like that option you can have device open if its run for grater than 2 minutes at locked rotor currents or grater than 10 minutes at 300 percent of full load. Its very confusing one thing says something and another says something else in 695.
 
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the idea, you need certain energy to pass through breakers/fuse in order to open ground fault. make sure your EGC will be big enough otherwise the EGC evaporates before OCPD will act. you can do by doing coordination, put damage curve of EGC and curve of OCPD

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hhsting said:
Not to add more confusion or more salt in wound but I am not sure I follow what you said above has to carry indefinitely locked rotor current. You see 695.4(B)(2)(a)(2) says device shall not open within 2 minutes at 600 percent of full load amps.
It also says shall not open within 10 minutes at 300 percent of full load amps.

Sounds to me like that option you can have device open if its run for grater than 2 minutes at locked rotor currents or grater than 10 minutes at 300 percent of full load. Its very confusing one thing says something and another says something else in 695.
Click to expand...
I see there was a change, I haven't done a fire pump in a while so that doesn't help with keeping up with changes in this section. (a)(2) was new in 2014.

Commentary for this new portion in my 2014 E book says: New provision permitting the overcurrent protection of a fire pump feeder circuit to be provided by an assembly listed for fire pump service.

(a)(1) still requires overcurrent protection to carry locked rotor current indefinitely if not a controller that complies with requirements of (a)(2).
 
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