The conductors in MCCs must meet several requirements, such as [430.96]:
- Any conductors in a vertical section must be intended for termination in that section, unless it’s required for interconnection or control wiring. But conductors can travel horizontally through a vertical section if isolated from the busbars by a barrier.
- The phase arrangement on 3-phase horizontal common power and vertical buses is A, B, C from front to back, top to bottom, or left to right (as viewed from the front of the MCC). There’s an exception for rear-mounted units, if they are properly identified.
- Observe the minimum wire-bending space required by 312(D).
- Observe the minimum spacing (between MCC bus terminals and other metal parts) specified in Table 430.97(D).
- Install barriers in all service-entrance MCC to isolate busbars and terminals from the rest of the MCC.
Also, busbars must be protected from physical damage and held firmly in place 430.97(A). The first part of this requirement is a reiteration of 300.4. Because 300.4 is in the first four Chapters of the NEC, the requirement generally applies to all installations. Yet the NEC repeats it in many other places.
To satisfy the second part, ensure you follow the assembly instructions for the busbar and fasteners you’re using. For example, you don’t apply the same torque value to a system that uses a Belleville washer versus one that uses a grade 5 bolt with a split ring washer.