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Grounding Motors

Grounding MotorsArticle 430, Part VIII is titled, “Grounding—All Voltages.” Is it really talking about grounding?

When we ground something, we connect it to the earth [Article 100]. On the load side, this serves no electrical purpose. It won’t create an equipotential plane and it won’t provide a low impedance path back to the source (for undesired current). Over the past few code cycles, the NEC has made headway on language consistency. But this is a case where work still needs to be done.

Some confusion arises because the motor bonding system connects to the equipment grounding conductor (EGC). But this is very different from driving a ground rod next to the motor and considering the installation electrically safe once a connection’s made from the motor pedestal to that rod. The earth has a far higher impedance than a conductor, meaning some undesired current will flow through that ground rod but much will flow through other paths such as motor bearings and people.

The EGC, being a conductor, offers a low-impedance path back to the source. Simply bonding the motor to nearby metallic objects won’t create this path. That’s why the Code Making Panel 11 (responsible for Article 430) hasn’t simply changed “grounding” to “bonding” and called it a day. You need to bond to the EGC.

Keep these distinctions in mind when “grounding” motors.

Source: Mark Lamendola | Mindconnection