I have read several threads to try and get an answer to my dilemma and have not had any success. Most of the threads deal with the obvious issues with providing an alternate source of power for a fire pump and how to make those connections. Here is where I get fuzzy and take issue with the way most installations have been done. Since the fire pump ATS/Controller is service entrance equip. we must provide a neutral conductor on the normal side and provide a main bonding jumper in the fire pump ATS controller. We do not however provide a neutral conductor from the generator, as there is nowhere to land it at the FP ATS or is it required because the load is delta. So what we have is an unbonded generator (not a SDS) and 3-pole transfer switches with solid neutrals, everywhere but at the fire pump ATS/controller. So my question is, how are we providing a low impedance path for fault current to actuate the emergency source overcurrent device (short circuit protection only) mounted on or near the generator? And if the path does exist (if we have an additional ATS with solid neutral anywhere else in the system, or if we are providing our normal source from a tap section in a service switchboard, which we are) then is that path not objectionable?
The way I see it if a phase to ground short occurs in the fire pump supply conductors or the fire pump itself for that matter, when the system is in emergency mode, current will flow through the equipment ground to the bond in the fire pump ATS, then through the normal neutral or the water pipe ground to the service switchgear, then back through the service neutral to the other ATS normal feeder neutral, across the neutral block in any other ATS and back to the generator alternator thorough that ATS's neutral conductor, or every ATS's neutral conductor should we have many, which we do (not to mention any stray currents that may flow in the equipment grounds). Thus being objectionable.
Code does not address this at all. Other than requiring that low impedance paths for fault current must not be objectionable.
Keep in mind that there is not a Fire Pump ATS/Controller manufacturer that will provide a connection for the neutral conductor from the emergency source or will they build a 4-pole transfer switch into them. They come one way only, grounded normal input and ungrounded emergency input. I have yet to see them any other way, and in talking to the manufacturers they just do not make them. With this in mind, providing a neutral conductor from the generator to the fire pump ATS is a waste of wire, as there is nowhere to land it, without violating its UL listing. And if I bond at the generator, they do not make a four pole fire pump ATS, so there is no way to switch the neutral. Again a waste of wire.
Sorry for the long post and lack of code sections, this was hard to describe.
The way I see it if a phase to ground short occurs in the fire pump supply conductors or the fire pump itself for that matter, when the system is in emergency mode, current will flow through the equipment ground to the bond in the fire pump ATS, then through the normal neutral or the water pipe ground to the service switchgear, then back through the service neutral to the other ATS normal feeder neutral, across the neutral block in any other ATS and back to the generator alternator thorough that ATS's neutral conductor, or every ATS's neutral conductor should we have many, which we do (not to mention any stray currents that may flow in the equipment grounds). Thus being objectionable.
Code does not address this at all. Other than requiring that low impedance paths for fault current must not be objectionable.
Keep in mind that there is not a Fire Pump ATS/Controller manufacturer that will provide a connection for the neutral conductor from the emergency source or will they build a 4-pole transfer switch into them. They come one way only, grounded normal input and ungrounded emergency input. I have yet to see them any other way, and in talking to the manufacturers they just do not make them. With this in mind, providing a neutral conductor from the generator to the fire pump ATS is a waste of wire, as there is nowhere to land it, without violating its UL listing. And if I bond at the generator, they do not make a four pole fire pump ATS, so there is no way to switch the neutral. Again a waste of wire.
Sorry for the long post and lack of code sections, this was hard to describe.
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