EC&M Tech Talk Video — The Ins and Outs of Insulation Resistance Testing

In this episode of  “EC&M Tech Talk, ” Randy Barnett, an electrical instructor, trainer, inspector, journeyman electrician, and safety expert, walks viewers through the wide world of insulation resistance testing. What exactly is insulation resistance testing, and why do we do it?

Randy begins with a general overview of this important topic and moves into more specific considerations that arise in certain scenarios. Starting off with a reminder of the basic premise behind this test, he explains that the purpose of insulation is to keep electrons in the copper wire — the goal is to keep those electrons from leaking out. If you run a conductor through some raceway like rigid conduit and you nick some insulation off inadvertently, now the current flows from the copper through the missing or cracked insulation into the metal raceway, also known as a ground fault. Under these circumstances, someone could get shocked or even worse. This situation could also cause excessive heat or a fire.

Next, he moves on to a discussion of NEC Article 110 (Requirements for Electrical Installation). Specifically addressing wiring integrity in Sec. 110.7, the way that you verify a completed wiring installation is free of ground faults is to perform an insulation resistance test. In addition to walking viewers through how to perform the actual test, Randy also touches on common mistakes people make when doing so and how to avoid those, specific challenges you may face in certain testing environments, and the proper safety procedures and protocols to follow when performing these tests.

Expanding the discussion to troubleshooting, Randy outlines how and why insulation resistance testing is a critical part of any general maintenance routine and schedule (whether that be for motors, cable, wiring, transformers, etc.). This includes tips for monitoring and predicting when certain pieces of equipment may fail over time. Randy concludes the episode with a discussion on NFPA 70B, Recommended Practice for Electrical Equipment Maintenance — specifically Chapter 11, Table 11.20.1.2, which he notes is going from a recommended way of doing things to the standard for maintaining your electrical equipment.

Note: Insulation resistance tests can only be performed on de-energized equipment and conductors.

Also check out Randy’s latest article, “Use It, or Lose It,” which outlines five practical tips to keep you at the top of the electrical trade. And check back for next month’s edition of “ EC&M Tech Talk” in July.

Barnett is electrical codes and safety program manager for NTT Training in Centennial, Colo.