Wednesday: Motor Space Heater Hazards During LOTO
Why locking out the main motor breaker does not always zero-energy the motor peckerhead.
You are preparing to terminate the leads on a massive 4160V medium-voltage motor. You rack out the main feeder breaker, lock it, tag it, and verify the absence of voltage on the primary cables. You pop the cover off the motor peckerhead (terminal box), assuming the entire housing is dead.
You might be touching a live 120V circuit.
Large industrial motors, especially those installed outdoors or in damp environments, are frequently equipped with internal space heaters. These heaters run continuously while the motor is offline to keep the windings warm and prevent destructive condensation from forming on the stator insulation.
The critical danger is that these space heaters are almost always fed from a completely separate, low-voltage power source (typically 120V or 240V from a different panel)—not from the main motor feeder.
Performing a primary Lockout/Tagout (LOTO) on the motor’s main contactor or breaker absolutely does not kill the space heater. Before reaching into a motor terminal box, you must trace, isolate, and verify zero energy on the secondary space heater supply lines. Missing this secondary source is a leading cause of electrical shocks during heavy motor changeouts.