NEC: Motors — Part 6

Art. 430, Part VI provides the requirements for motor control circuits, but not for the actual motor controllers (those are covered by Part VII). Most of it has to do with overcurrent protection.

The general requirement for overcurrent protection of these circuits [430.47(A)] consists of a block of text few people can grasp at first glance. Or even a second glance. So, let’s break it down.

It’s really in two parts; the first part applies to a motor control circuit that is tapped from the load side of a motor branch circuit overcurrent protection device (OCPD) and is functioning to control the motor(s) connected to that branch circuit.

This motor control circuit shall:

• Be protected per 430.72.
• Not be considered to be a branch circuit.
• Be permitted to be protected by either a supplementary or branch circuit OPCD.

The second part applies to any motor control circuit that doesn’t meet the two conditions (tapped from and controlling the same branch circuit). Such a motor control circuit must be protected against overcurrent per 725.43 or per the notes to Table 11(A) and (B) in Chapter 9, as applicable.

A simpler way to put it is this: 430.72 applies only when a motor control circuit is tapped from and controlling the same branch circuit. Otherwise, apply 725.43 for a Class 1 circuit or Chapter 9 Table 11(A) or (B) for a Class 2 or 3 circuit.

The conductor protection requirement stated in 430.72(B) is that overcurrent protection be provided per 430.72(B)(1) or (2). This is followed by two exceptions.

The first exception is for when you have something such as a fire pump motor needing to run no matter what. The second one applies when you have a single-phase transformer with a two-wire secondary.

You will need to provide a separate OCPD if the motor OCPD does not provide the protection required by 430.72(B)(2) [430.72(B)(1)]. Let’s look at what that protection is; it depends on whether the conductors extend beyond the motor control equipment enclosure.

• If they do, the OCPD rating cannot exceed the value specified in Column B of Table 430.72(B).
• If they don’t, the OCPD rating cannot exceed the value specified in Column C of Table 430.72(B).

If you have a motor control circuit transformer, you must protect it by one of the five means enumerated in 430.72(C)(1) through (5).

If one conductor of the motor control circuit is grounded, arrange the system so that a ground fault in the control circuit remote (from the motor controller) won’t start the motor or bypass shutdown devices (whether manually operated or automatic safety shutdowns) [430.74].

Part VI concludes with requirements for disconnects. A highlight is you can use two or more separate devices for disconnecting, but they need to be immediately adjacent to each other [430.75].