You're correct in your understanding and your argument. There is no NEC requirement to run a neutral conductor to a fire pump controller fed from a separately derived system when it's not needed for the operation of the fire pump or controller.Here's a breakdown of why and relevant NEC references: Fire Pumps and Grounding

Fire pumps are typically supplied by a separately derived system (SDS) or tap ahead of the main disconnect. The grounding and bonding of the SDS are critical for safety and proper operation during a fault.

Separately Derived Systems (SDS) and Grounding (Neutral) Bonding

When a transformer or generator is used as an SDS, the neutral must be grounded. The main bonding jumper is installed at the SDS to connect the neutral to the equipment grounding system.

NEC 695.6 Wiring Methods

This section primarily focuses on the physical protection and fire resistance of the wiring. It doesn't mandate running a neutral if it's not required for the load.

NEC 250 Grounding and Bonding

This article covers the general requirements for grounding and bonding electrical systems. Here's what's relevant:

250.20(B) Systems Required to Be Grounded

This section lists which AC systems must be grounded. A 480V three-phase system is not inherently required to be grounded unless it meets specific conditions. However, if the system is grounded (e.g., a transformer winding is wye-connected and the neutral is grounded), then you follow the grounding rules.

250.30 Grounding Separately Derived AC Systems

This is the key. If your fire pump feed is from an SDS (which it sounds like it is, given it's tapped ahead of the main), you need to establish a grounding electrode system at the source of the SDS. This usually involves grounding the neutral at the transformer. Crucially, this doesn't mean you have to run the neutral to all loads. It means the system must be grounded at its source.

250.24(C) Grounding Electrode Conductor for a Separately Derived System

This section addresses the size and installation of the grounding electrode conductor at the SDS (e.g., the transformer).

Why No Neutral is Needed (Most Likely)

The fire pump motor itself is a three-phase load. It does not use or require a neutral conductor for its operation. The fire pump controller also does not use a neutral for its operation. As long as the SDS is properly grounded at the source (the switchgear enclosure) and the equipment grounding conductors are properly sized and installed to the fire pump controller, there's no need for a neutral.

Bonding

As you mentioned, bonding is crucial. Ensure that the metal conduit or raceway containing the conductors to the fire pump controller is properly bonded back to the service equipment grounding system. This provides a low-impedance fault current path.

To Summarize and Clarify1. Source

You mentioned that the feeder to the fire pump controller is tapped ahead of the main in a separate vertical switchgear enclosure. Thus, this is not a separately derived system.2.

Grounding System

Since it is not an SDS, there is no requirement to ground the neutral.

In conclusion



There is no requirement in the NEC to run a neutral to the fire pump controller if the controller and motor do not require it for their operation and the grounding system is properly installed and bonded in the service switchgear. The grounding and bonding of the system is critical for safety. Make sure all metal raceways and enclosures are properly bonded back to the service equipment grounding system.Always consult with a qualified electrical engineer and the authority having jurisdiction (AHJ) to ensure compliance with all applicable codes and regulations. Provide them with the specific details of your installation, including the source of the power, the grounding system configuration, and the equipment specifications. Flag for review