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 B — conduct a bar to bar test of the armature

A bar-to-bar test using a millivoltmeter or specialized growler is the standard diagnostic procedure for identifying open circuits in armature coils. By passing a current through the armature and measuring the voltage drop across adjacent commutator bars, technicians can pinpoint the specific coil with an open circuit that visual inspection missed.