The Electrical Safety Net: Correct grounding and bonding is critical

By Mark C. Ode | Dec 11, 2023
Absolutely the most important part of any electrical system is the electrical safety net, as covered in Article 250 on grounding and bonding. 

Absolutely the most important part of any electrical system is the electrical safety net, as covered in Article 250 on grounding and bonding. Without grounding and bonding, there would be countless tragedies and an unlimited number of fires throughout the industry. I cannot count the number of times that I have encountered accidents just waiting to happen.

A real high-wire act

I have investigated fires, shock hazards and even some electrocutions that could have been prevented if there had been proper grounding and bonding. When I teach grounding and bonding, I usually equate them to the safety net installed for the high-wire acts in a circus. The safety net is installed directly below the wire, with the performers testing the nets during warmup to ensure they are installed properly.

In most cases, our safety nets are not tested after installation to ensure proper functioning. I say “in most cases” since Chapter 18 of NFPA 79, Electrical Standard for Industrial Machinery, does require “verification that conductor insulation can withstand a high-voltage test (commonly called a high potential test or high pot) without breakdown and ensures the continuity of the equipment grounding and protective bonding circuits that are critical for the electrical safety of the machine.”

Sections 250.4(A) and (B) in Article 250 of the National Electrical Code provide performance requirements for grounding and bonding, while the remainder of Article 250 provides the proscriptive requirements or, in other words, the “how to” for proper grounding and bonding. Without proper grounding and bonding, there would be many problems and unnecessary hazards.

Electrocution investigation

About four years ago, the Solano County (Calif.) Sheriff’s Office asked me to help with an investigation into an electrocution of two 17-year-old boys in an irrigation canal. When I arrived, I did an overall review of the electrical system that supplied power to a 20A receptacle for a water pumping station for a grove of fruit trees. The 120/240V three-phase electrical service was mounted on a wooden power pole and supplied by overhead utility company service drop from a three-phase open delta pole-mounted transformer.

The main disconnecting means at the service had been modified by bypassing the main disconnecting means with two din-rail mounted fuse blocks with 20A-rated fuses directly from the utility supply. This effectively bypassed the main disconnect and would have required opening the disconnecting means cover to extract the fuses to disconnect power. 

From the 20A fuses at the service, a 240V circuit with one white conductor and one red one was connected to a PVC LB conduit body and PVC conduit to a metal ½-inch conduit attached to a metal walkway over the irrigation canal. 

On the far side of the metal walkway, the metal conduit was attached to a ½-inch PVC conduit body and PVC conduit supplying a 20A, 240V weatherproof receptacle at a location approximately 50–60 feet from the metal walkway for connection to a portable water pump to supply water to the grove of trees. The ½-inch PVC conduit body and PVC conduit had been damaged so one of the energized (hot) conductors was welded to the inside of the ½-inch rigid metal conduit on the metal walkway, thereby energizing it.

The accident

The day of the electrocution was hot and the boys’ dog went for a swim in the canal. When the wet dog tried to recross the canal on the energized metal walkway, it was shocked and fell into the canal. One boy went into the canal to rescue the dog, reached up to grab the metal walkway while in the water, received an electrical shock and could not let go. The second boy went into the water, reached up to the metal walkway, and also could not let go, but was able to say he was being shocked. A third boy wrapped a t-shirt around his hands and got the dog and the two boys off the energized walkway and onto dry land. Tragically, the two boys did not recover, although the dog did.

Even if someone had been able to turn the main disconnect off, the circuit would still have remained energized. If an equipment grounding conductor had been installed from the service to a metal junction box and connected to the metal conduit on the metal walkway, the point of connection from the hot conductor to the ½-inch rigid medal conduit would have blown a fuse and de-energized the circuit. Poor electrical installations have consequences, and lack of proper grounding and bonding can cause us to pay a heavy price. / DM7 / Alex Koch

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]





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