Yes, bonding bushings are likely required on both ends of the RMC conduit run. Here's the reasoning

NEC Requirement - 250.92(B) (Effectively)

While not directly stated, NEC 250.92(B) requires that metal raceways that contain service conductors be bonded. This ensures a low impedance path for fault current back to the source. While there are exceptions, they don't generally apply in this common service configuration.

Why Bonding Bushings are Needed



To Ensure Continuity

While RMC threads provide some contact, they aren't considered a reliable bonding connection on services, especially at this amperage. Bonding bushings, properly installed, create a solid electrical connection between the conduit and the enclosure (meter can and panel).

To Meet Listing and Labeling Requirements

Meter cans and panels are often listed and labeled for use with specific bonding methods. Using bonding bushings that comply with those requirements ensures the installation is compliant.

Specific Considerations



At the Meter Can

A bonding bushing and jumper (properly sized) are required at the point where the RMC enters the meter can. The bonding jumper connects the bonding bushing to the meter can's grounding bus or designated grounding point.

At the LB/Panel

A bonding bushing and jumper are required where the RMC enters the panel. Again, the bonding jumper connects the bushing to the panel's grounding bus.

Grounding Electrode Conductor (GEC)

Make sure the grounding electrode conductor (GEC) is properly connected to the neutral at the service disconnect (usually in the panel) AND to a grounding electrode (ground rod, water pipe, etc.) This is a separate, but critical part of the grounding system.

Key Takeaways



Err on the Side of Caution

When in doubt, install bonding bushings. It's a small cost for a significant safety benefit and helps ensure compliance.

Local AHJ

Always check with your local Authority Having Jurisdiction (AHJ). They may have specific interpretations or requirements.

Proper Installation

Make sure the bonding bushings are properly torqued and the bonding jumpers are sized correctly per NEC Table 250.102(C)(1).

In summary, for a 400A 120/208V service with RMC containing service conductors, bonding bushings with jumpers are almost certainly required at both the meter can and the panel. Consulting with your local inspector is highly recommended to confirm specific requirements in your area. Flag for review