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Case of the Shocking Sealing Machine Sparks Feedback

Jul 1, 2008 12:00 PM

I thought that “The Case of the Shocking Sealing Machine” article, starting on page 16 of the May 2008 issue, was excellent, although a little reading was necessary to follow some of the points. I had to get all the way to the paragraph under “Investigation and Analysis” to understand the conduit was (unintentionally) being used as a “grounding path.” Could you please clarify the following questions?

• Do you happen to recall if the flex conduit was intended to be the only grounding conductor? We are not sure if this is acceptable unless the length is very short, and maybe not even then. Maybe the original installation provided bonding of the control box as compared to the plywood mount shown in the photo?

• Do you know if a grounding conductor was installed in this raceway and was it perhaps broken?

• When the supply wiring was mentioned, it described the disconnect being connected to an internal breaker using conductors installed in EMT, but all this must have been changed from the original. It sounds like it was difficult to determine the wiring method because so much time had passed?

These are all good subjects and are quite typical of the situations encountered in the field — thanks again!
— Bob Dorazio, general building
contractor, Avila Beach, Calif.

Author's reply: I'm glad you enjoyed the article. By describing actual incidents where things went wrong, they remind electrical workers that safety and caution should always be at the forefront during any project.

As with most accident/injury cases, the scene and evidence had been changed multiple times since the original incident. Combine that with unclear and differing statements made years after the accident, and it can take some time to sift through and determine what actually happened. At times, critical facts are unknown or have to be inferred from all the evidence. With that in mind, I will try to address your questions:

1 & 2) I would like to note that as the intent of the article was general in nature, I did not specify all the NEC-related standards applicable in this case. I would point you and other readers to the 2008 NEC, Art. 665: Induction and Dielectric Heating Equipment. Dielectric sealing and RF sealing are analogous terms, so this article is directly applicable to this case. Specifically relating to grounding and bonding, Art. 665.26 states:

“Bonding to the equipment grounding conductor or inter-unit bonding, or both, shall be used wherever required for circuit operation, and for limiting to a safe value radio frequency voltages between all exposed non-current-carrying parts of the equipment and earth ground, between all equipment parts and surrounding objects, and between such objects and earth ground. Such connection to the equipment grounding conductor and bonding shall be installed in accordance with Article 250, Parts II and V.”

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