Fire Pump Normal Feeder Neutral

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barone

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The situation:

Fire Pump Design
480V-3PH-WYE service lateral to 4000Amp gear lineup
Incoming Utility section, then CT section, then fire pump tap section, then the service main
Fire pump is 100+HP and is 480V-3PH-delta

The inspector has required us to include a neutral conductor with the normal feeder to the fire pump ATS/Controller. The load is a totally balanced 3PH load. The ATS has a solid neutral and the EM generator is not bonded (not a separately derived system). He did not site a code section so I'm left to assume.

I assume he is requiring this because of 230.82(5), which requires the tap for a fire pump from the service supply to be treated as service entrance conductors, thus requiring the neutral. I have no intention of bonding this neutral at the ATS/Controller, but rather landing it on a lug and calling it a day. But in a couple of cases the inspector made the contractor bond the neutral and ground a second time at the ATS/Controller, and provide a ground to the building grounding electrode system.

I have reserves about designing the 3PH delta fire pump tap normal feeder with this neutral conductor re-bonded a second time for fear that it may cause a problem with an objectionable path for current, and it seems a waste of good money and copper. I most certaily have no intention of bonding it again, or providing a second ground. I have been designing this feeder with an EG in lieu of the neutral. They are basically the same thing in this situation as they are all bonded together at the service gear and are sized based on 250.122. I may have been wrong for years and am now second guessing myself.

If the feeder conductors were coming directly off of the utility transformer and not through the service gear I could see the need for the neutral as the system is a wye system and is not bonded at this point. Except of course the secondary XO.

My question:

Has anyone else been required to do this, and what problems if any might it cause? Also is there an issue with not running this neutral and using only the EG?
 
I assume he is requiring this because of 230.82(5),

I don't see where it says you have to have a neutral there.


have been designing this feeder with an EG in lieu of the neutral. They are basically the same thing in this situation as they are all bonded together at the service gear and are sized based on 250.122.


exactly. If you run two wires and connect them together at both ends and they are not current carrying, and they are bonded at both ends, I would call that an eg.
 
250.24(C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(3).

The ATS/Controller for the fire pump is service equipment since the tap is made ahead of the normal service disconnecting means. Repeat after me, the inspector is almost always correct. :smile:
 
charlie said:
250.24(C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(3).

The ATS/Controller for the fire pump is service equipment since the tap is made ahead of the normal service disconnecting means. Repeat after me, the inspector is almost always correct. :smile:
Click to expand...

The same can be said for charlie :D
 
Thanks

Thanks

augie47 said:
The same can be said for charlie :D
Click to expand...
Thanks for the kudos.
icon11.gif
 
Not a Feeder

Not a Feeder

This is not a Multi Campus Complex so the source is not a FEEDER.
The source for the fire pump off the transformer is consider a SRVICE source .
 
Charlie and Gus, I don't want to rain on your parade, but the grounded conductor doesn't need to be larger than table 250.66 since these service conductors are being run to the service disconnect. An EGC is not needed to run with the grounded conductor. I believe the OP was trying to eliminate running a grounded conductor and an EGC together in the same conduit. If he sizes the grounded conductor to table 250.66 and bonds it to the enclosure, he should be good.

Rick
 
barone said:
The situation:


. The ATS has a solid neutral and the EM generator is not bonded (not a separately derived system). He did not site a code section so I'm left to assume.
Click to expand...

Did you run a grounded conductor from the generator to the fire pump transfer switch? If no, and you said the the gen set is not bonded, then if there is a fault while the generator is running, there is not an effective ground fault return path to trip the breaker.With a 3-wire generator feed, it should be treated as a SDS.

Rick
 
RUWired said:
. . . the grounded conductor doesn't need to be larger than table 250.66 since these service conductors are being run to the service disconnect. . .
Click to expand...
Rick, I didn't discuss sizing the grounded conductor. However, you are correct.

RUWired said:
. . . With a 3-wire generator feed, it should be treated as a SDS. . .
Click to expand...
Rick, I have no problem with this as long as the ATS has the neutral taken to it, the neutral is switched, and the ATS is SUSE rated. :smile:
 
charlie said:
Rick, I have no problem with this as long as the ATS has the neutral taken to it, the neutral is switched, and the ATS is SUSE rated. :smile:
Click to expand...

Charlie i think the OP has a problem. I don't believe he ran a grounded conductor from the generator to the transfer switch and he didn't bond the generator xo to ground.

Having a solid neutral transfer switch won't matter with a 3-wire feeder. No parallel conductors.

He did run an EGC or a SBJ to the generator, but that only went to the frame. With the generator running, the fault current will go back to the bonding jumper in the service equipment and transformer but it will dead end at the open point on the utility side and will dead end at the generator without the grounded conductor and without the bonding jumper.

Rick
 
Fire Pump Primary?

Fire Pump Primary?

I have also see in done in a manner where they take the primary switch double lug it, route a set of conductors underground to the F.P. provide a small substation ∆-∆ with a primary fuse and connect the fire pump ATS/Controller to the secondary, the thought is that under a condition where the F.P. is activated a line-grd. Fault would not remove the F.P. from service.
 
I understand the codes but am still not sure

I understand the codes but am still not sure

Charlie,

I am still not sure about this situation here. To me, because we are already grounded at the service enclosure, providing the bond at the generator neutral and to another ground rod, gives an objectionable path to the source through the generator bond and ground and the solid neutrals in each ATS. We have been switching the neutral for years (although this in not the case here) whenever the generator was a separately derived source, and article 250.24(C) is already accomplished at the main service equipment. What I am getting at is that the requirement to provide the neutral to the controller and rebond and reground the system there is cause for alarm. It is no different that doing it at a sub-panel, except the tap is ahead of any mains.

I am not trying to ague away the need for the neutral conductor, just trying to figure out its purpose in this case. There is no over-current device to trip in this case, so what is the purpose of the neutral? If the fire pump service were coming directly from the source, or was an unbalanced load I could argue for the neutral being needed, but in this case it seems that all we are providing is an objectionable path for current. You and I both know the primary fuse could be well oversized by the utility on the service transformer and may never blow, just cook the transformer. To me it seems that if we need the neutral we should not be bonding it over and over again or making a direct connection to another source with it.

All I am saying is that I need to look at this again because I am not sure that the requirement of 250.24(C) takes into account my situation. This situation is popping up all over the place because the contractors see it as a way to save $$ by not having to run the normal feeder all the way back to the source. They are just tapping the service switchgear ahead of the main devices in its own section.

Correct me if I am wrong, but I think we want to provide switched neutrals at each transfer switch, and fire pump controller/ats, and bond the generator as a separate source. Provide the needed neutral conductors to the controller/disconnect from both the normal source and EM source, and then ground at both the main switchgear and the generator. We would need EGC from both the main gear and the generator to the controller. We would not bond the neutral to ground at the fire pump controller/ats, or any other ats, as is being required by the inspector.

I should note that this was not our design, but another engineer's and we were asked to come in and clean things up. The inspector had the contractor ground at the service gear where the normal tap originated, again at the fire pump controller/ats , and a third time at the generator. All of the neutrals in the all the ATS's are solid and un-switched. Does this not cause a problem with objectionable paths for current?

I hope this is not too much and I sure hope I do not come off as being stupid in this regard, but I have been second guessing myself and am loosing confidence in both the inspectors and my own ability to conceptualize grounding systems. I just want to make sure that things are installed in a manner that is safe for the poor guys who have to actually work on this equipment. The day someone gets hurt on my account is the day I stop doing this, and I love doing this!

Thanks for your help, your comments are always appreciated and respected.
 
Each service is required to be connected to the Grounded conductor as indicated in my first post. The fire pump transfer switch is a service. Bonding of the neutral is required for a ground fault current return path to the source (serving electric utility transformer bank). The fire pump controller has overcurrent protection that will not operate properly without this being done complete with grounding and bonding.

I suggest looking at the fire pump system without looking at the generator. The service is now the transfer switch and controller. Will everything work as a stand alone system?

Will the same view work with the generator and fire pump without the electric utility power? By not using the neutral from the generator or taking the neutral from the transfer switch, haven't you set up a separately derived system? All of the metallic parts have been bonded to the grounding system. The neutral from the generator is not brought out or used. If the utility power is being used and a ground fault occurred, the fault current return would take out the ground fault protection in the controller. If the generator power is being used and a ground fault occurred, there would be no fault current and the fire pump system would continue to run.

This is the way I understand the situation. :smile:
 
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