An open in the armature of a DC motor is suspected, but is not found by visual inspection of the commutator. What would be the next step in troubleshooting this problem?

Correct Answer: Option D — conduct a bar to bar test of the armature

When visual inspection fails to reveal an open armature circuit, a bar-to-bar resistance test using a millivoltmeter and a low-voltage power source must be conducted. Per IEEE 45 standards, this locates high-resistance connections or broken coil leads directly attached to the commutator risers.