Motors, Part 6

In Article 430, subsections 430.9 through 430.13 present a string of mechanical requirements. There are three mechanical requirements for terminals:

  1. They must be suitably marked or colored to indicate the proper connections.
  2. The conductors must be copper, unless the terminals are identified for use with a different conductor material.
  3. If they are 14AWG or smaller, you must torque them to the specified torque; if no torque is specified, torque to at least 7 in-lb.

Let’s look at these more closely.

When the NEC says something shall be “suitably marked” this means certain conditions must be met. Meeting these conditions is an aspect of good workmanship, and you’ll find them explicitly stated elsewhere in the NEC. They are:

  1. The marking is permanent (e.g., it won’t inadvertently rub off).
  2. The marking is legible.
  3. The meaning of the marking is clear.

When you use dissimilar metals, you get current flow between them; this is the basic idea behind a battery. The default design for terminals is use with copper conductors. For any other kind of conductor, use terminals identified for use with those conductors (and vice-versa).

The NEC assumes you will use a torqueing screwdriver or torque wrench on all motor and controller terminals. The way a bolted connection works is the force applied to assemble it stretches the fastener to its elastic limit, and this gives it its clamping power. Too far either way, and you don’t have a mechanically solid connection.

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