Electrical Testing
Tip of the Week: Starting Motors Under Load, or Not

Tip of the Week: Starting Motors Under Load, or Not

Before trying to start a motor under load, you should verify that it can be done.

Some motors can start under load, and some can’t. Where a motor is coupled to the load without an intervening clutch system on the load end, assume the motor cannot start under load unless you verify it can. And that generally means it needs to be a Design D motor, which has “extra high” starting torque.

Photo credit: branex/iStock/Thinkstock

You’ll find Design D motors in punch presses and other forming tools. You’ll also find them in cranes, elevators, and hoists. They typically aren’t used in most other applications.

Pumps are ubiquitous in process plants and other industrial facilities. These are typically powered by Design B motors. The starting torque of Design B motors is considered “medium.”

Something that sometimes happens in plants is an operator tries to start a pump that is “dead headed.” The downstream valve is closed so the pump is (typically) trying to compress a liquid rather than push it through the piping. Because the Design B motor lacks the torque to start under such a load, it will generate considerable heat trying. Then it will blow its overloads. You’ll need to wait a while, maybe a couple of hours, before a restart attempt.

Before starting a Design B motor, ensure it’s not under load. If it runs a pump, ensure the pump isn’t valved out. This doesn’t mean you simply open a closed valve; verify with operations that valve operation is permitted and that flow through the system by operating the pump is also permitted.

Be sure you follow all operating procedures, including any established division of labor rules.

TAGS: Design Motors
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