Okay, let's break down this scenario and address the grounding locknut question. Your understanding of the 250.142(B)(2) exception is key here.

Understanding Your System 1000A Service Disconnect

Your service entrance terminates here.

Feeder to Wireway

You're running a feeder (conductors downstream of the service disconnect) from the 1000A disconnect to a wireway.

Ten-Foot Tap Rule

You are using this rule for tapping off the feeder in the wireway to supply individual meter mains.

Bonded Neutral Meter Mains

These meter mains have the neutral bonded to the enclosure.

250.142(B)(2) Exception

You're relying on this exception, which allows the grounded conductor to be used for grounding equipment on the load side of the service disconnect if all conditions are met.

All Metal Raceways

The entire system utilizes metal conduit (e.g., RMC, IMC, EMT).

No Wire-Type EGC

There's no separate equipment grounding conductor (EGC) run within the raceways.

Grounding Locknuts - The Question

The crucial point here is that the 250.142(B)(2) exception only addresses the permissibility of using the grounded conductor (neutral) for equipment grounding on the load side of the service disconnect. It doesn't negate the general requirements for properly grounding the metal raceways themselves.

Relevant NEC Sections and Analysis 250.4(A)(5) and 250.4(B)(4) Electrical System Grounding: These sections mandate that electrical systems that are grounded shall be connected to earth in a manner that limits the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and that all electrical equipment is installed so that there are no differences in potential that would be objectionable. 250.96 Bonding Other Enclosures and Raceways

This section specifically addresses the bonding of metal raceways and enclosures that contain service conductors or feeders. It states: "Metal raceways and enclosures containing service conductors or feeder conductors shall be bonded together so as to provide an effective ground-fault current path..."

250.92 Services

This section deals with the bonding of metal enclosures around service conductors. Even though you are dealing with a feeder here, the principles of maintaining a low-impedance ground-fault current path still apply.

250.97 Grounding bonding of metal raceways to enclosures. Where oversized, concentric, or eccentric knockouts are encountered, the requirements of section 250.97 must be followed.

Therefore, yes, grounding locknuts (or other approved bonding methods) are REQUIRED for your all-metal raceway system, even with the 250.142(B)(2) exception in play. The exception doesn't change the need to ensure the metal raceways themselves are effectively bonded to provide a low-impedance ground-fault current path.

Why Grounding Locknuts (or Equivalent) Are Necessary1. Ground-Fault Current Path

In the event of a ground fault (e.g., a conductor coming into contact with the metal raceway), a low-impedance path is essential to allow sufficient fault current to flow back to the source (the service disconnect) to quickly trip the overcurrent protective device (the breaker or fuse).2.

Safety

Proper bonding minimizes the potential for voltage to develop on the metal raceways during a fault. This prevents shock hazards.3.

Code Compliance

Failing to properly bond the metal raceways would violate the intent and the specific requirements of NEC Article 250.

Acceptable Bonding Methods

Besides grounding locknuts, other acceptable bonding methods for metal raceways include: Bonding Bushings

These provide a more positive bond than standard locknuts, especially for larger conduit sizes.

Threaded Conduit and Fittings

RMC and IMC inherently provide a good bond when properly installed.

Listed Bonding Jumpers

These can be used to bond across sections of raceway where necessary.

Specific Considerations for Your System Wireway Bonding

Pay careful attention to the wireway itself. The wireway must be properly bonded to the metal raceways entering and exiting it. Look for bonding provisions built into the wireway or use appropriate bonding jumpers.

Meter Main Bonding

Ensure the meter mains are also properly bonded to the metal raceways.

Concentric or Eccentric Knockouts

Using reducing washers or cutting larger holes than necessary will increase the impedance of the ground fault current path.

In summary: The 250.142(B)(2) exception allows you to use the grounded conductor for equipment grounding at the meter mains. However, it does not* eliminate the requirement to properly bond the metal raceways, and grounding locknuts (or other approved bonding methods) are necessary to ensure a safe and code-compliant installation. Flag for review