An electric arc flash produces the highest temperatures on earth—up to 35,000 °F (19,426 °C)—causing all materials (metals, liquids, plastic) to vaporize and expand explosively. The blast pressure can throw a person across a room, and spray a person with shrapnel and molten metal droplets. Aside from the primary danger of being burned, intense pressure and sound can cause physical injury and deafness.
The input power requirements for a large motor drive puts it in the high risk category for arc flash. Electrical shock is more commonplace. A slip of the hand and you or your tool connects with a live component. It happens when you’re working too fast or you get distracted while working. Not as destructive as an arc blast, but still deadly. Here are some guidelines for conducting motor troubleshooting safely.
In addition to wearing the proper personal protective equipment (PPE), it’s critical to assess whether your test tools meet safety requirements. Look for the symbol of an independent testing lab such as UL, CSA, TÜV or other nationally recognized testing laboratory (NRTL).
Top six steps for troubleshooting a motor drive
- Prepare safety checklist –Plan the job using NFPA 70E Annex E 2.
- Know the project details –Start with the proper PPE. Determine the risk category for PPE by checking the input power requirements for the drive you’re planning to work on.
- Read the drive fault codes –The drive displays alarm and fault codes to assist in troubleshooting when a problem develops during self-tuning or drive operation.
- Discharge the dc bus capacitors –After disconnecting input power, wait five minutes for the dc bus capacitors to discharge, then check the voltage with a DMM to ensure that the dc bus capacitors are fully discharged.
- Follow the next steps in the drive’s instruction manual to isolate the fault –Disconnect the motor from the drive, check all ac line and dc bus fuses, use a multimeter to check the input diodes and output IGBTs on any open fuses, and reconnect the motor to the drive.
- Look for improper installation as a fault source –Determine whether the drive and motor are grounded as specified in the instruction manual, the control signal wires and power cables are in the same conduit, and unused wires in conduits are grounded at both ends.
Troubleshooting any motor drive is for trained, certified technicians only. NFPA 70E specifies workers must be qualified persons to troubleshoot in this environment.