Fire pump controller service rated grounding question

[hhsting]

I have one utility service going to main service switchboard. The main service switchboard has a tap ahead of main service breaker in one of the compartment which has service conductors going straight to Fire pump controller service rated which then feeds fire pump. See attached riser

The fire pump service rated is in basement opposite corner from main service switchboard 1st floor. See attached floor plan.

See attached below grounding details. The conductor labeled FP GEC bubble in attachment should it go to ground rods as shown or should it go to external ground bus bar GBB? It is not clear what NEC 2017 says. Designer says by placing FP GEC at external GBB creates ground fault current path but i dont see how this is possible. I think their is ground fault current path from the current configuration from switchboard to GBB to steel to rods to FP comtroller. What are your thoughts? Where should FP GEC be?

 

[d0nut]

Either scenario presented would be fine. There are basically an infinite number of possible paths through the bonding in a building, which is why it is essential that each system's neutral is bonded to the ground in only one location. The ground conductors and all bonded stuff should not be carrying current. Only in a fault condition should current flow the ground side of the system.

 

[hhsting]

Either scenario presented would be fine. There are basically an infinite number of possible paths through the bonding in a building, which is why it is essential that each system's neutral is bonded to the ground in only one location. The ground conductors and all bonded stuff should not be carrying current. Only in a fault condition should current flow the ground side of the system.

Either scenario presented would be fine. There are basically an infinite number of possible paths through the bonding in a building, which is why it is essential that each system's neutral is bonded to the ground in only one location. The ground conductors and all bonded stuff should not be carrying current. Only in a fault condition should current flow the ground side of the system.

I was speaking in the fault condition would not under fault the current can flow from main swbd disco to steel to the fire pump controller and return? This would not happen if FP GEC is at GBB. Correct? So how is the scenario
presented under fault be ok in the attached where FP GEC is bonded to the rods?

 

[augie47]

Any time you have multiple service disconnects tied to the GES there will be a current path. Unavoidable & acceptable.
Thr FPC must have be connected to the GES. IMO, rods are not necessary in this situation but if the designer calls for the, no problem.