You've identified a potentially confusing area in the NEC, but there's no direct contradiction once you understand the context. Here's a breakdown

NEC 250.24(D): Grounded Conductor Brought to Service Equipment (AC Systems ≤ 1000V)
Core Concept

This section is a fundamental requirement for grounded AC service systems operating at 1000 volts or less. If the system is grounded at any point (typically at the transformer), the grounded conductor (neutral) must be brought to each service disconnecting means.

Purpose

Provides a low-impedance fault current path back to the source (transformer) for clearing ground faults. Ensures a stable voltage reference for line-to-neutral loads (if present).

Key Phrase

"...if the ac system operating at 1000 volts or less is grounded at ANY point..." This is the condition that triggers the requirement.

Crucially Important

This requirement applies regardless of whether or not there are any line-to-neutral loads. The fact that the system is grounded mandates the presence of the grounded conductor (neutral) at the service.

NEC 250.184(B)(6): Single-Point Grounded Neutral Systems (AC Systems > 1000V) Context

This section deals with high-voltage AC systems (systems operating at over 1000 volts).

Key Concept

It's addressing specifically a single-point grounded neutral system at voltages above 1000V.

"Neutral Conductor Only Required if Phase-to-Neutral Loads Supplied"

This only applies to these high-voltage systems. The idea is to allow for flexibility in system design at these higher voltages where there are no line-to-neutral loads. For example, a purely 3-phase motor load powered directly from the high-voltage system.

Purpose

In high-voltage systems, especially those without line-to-neutral loads, the requirement to run a neutral conductor might add unnecessary cost and complexity. If there are no line-to-neutral loads, there is no need for a neutral conductor. In addition, if the supply transformer is a delta winding, there will not even be a neutral conductor.

Why No Contradiction

The key is voltage level. 250.24(D)

Low-voltage AC systems (≤ 1000V). Grounded conductor (neutral) always required if the system is grounded at the source, regardless of load type.

250.184(B)(6)

High-voltage AC systems (> 1000V) with single-point grounding. Neutral conductor required only if there are phase-to-neutral loads.In essence, 250.184(B)(6) is a specific exception that only applies to high-voltage systems with single-point grounding. It does not override the general requirement of 250.24(D) for low-voltage systems.

Example to Illustrate1. Low-Voltage (480V)

You have a 480V service that's grounded at the supply transformer (wye configuration). Even if all your loads are 3-phase motors (no line-to-neutral 277V lighting, etc.), you must bring the neutral conductor to the service disconnecting means.2.

High-Voltage (4160V)

You have a 4160V service with a single-point grounded neutral system. You only feed 3-phase motors. Because there are no line-to-neutral loads, 250.184(B)(6) allows you to omit the neutral conductor.

In Summary

Always refer to the NEC for your specific application. However, understand that the NEC often provides general rules with specific exceptions based on voltage level, grounding system type, and other factors. 250.24(D) is a general rule for AC systems at 1000V or less, while 250.184(B)(6) is a more specific rule for high-voltage systems (>1000V) with single-point grounding. They don't contradict each other because they apply to different circumstances. Flag for review