Electric Shock - Improper identification of green Bond wire Violation Section 250-118 (04-27-02)
In order to wire air condition units at dwellings, my employee cut three equal lengths to install in the flex to the unit. One day, they identified the equipment ground after the conductors had been sleeved in the flex. BAD IDEA. When the circuit was energized, one wire from the load side of the disconnect was connected to the ground in the unit. The A/C breaker never saw the fault because the grounding path had been broken. The current traveled through the Freon line to the air handler in the attic. The breaker on the air handler tripped but the A/C breaker never did.
At the time, I was in the attic and had one hand on the air handler and the other on a grounded metal box and I got shocked. I had 120 volt to ground on the air handler and I began to check it out. The 14-2 feeding the air handler had melted the entire sheath and most of the insulation off the wires. Where the NM had been pulled across a tray ceiling, there was a sharp bend in the wire; enough to allow the conductor to sever. I think this saved us from an insurance claim and possibly someone's life.
Please take my advice, buy green or bare for your equipment grounds. Do not rely on the ability of your employees to mark them correctly. I stopped every employee I had at the time and made them pack up and drive over to see what had happened. It was a great lesson. Thankfully, not a costly one and no one was injured.
Mike Holt's Comment: The NEC contains the following requirements
250-119. Identification of Equipment Grounding Conductors
Unless required elsewhere in this Code, equipment grounding conductors shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes except as permitted in this section.
(a) Conductors Larger than No. 6. An insulated or covered conductor larger than No. 6 copper or aluminum shall be permitted, at the time of installation, to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor is accessible. Identification shall be accomplished by one of the following:
1. Stripping the insulation or covering from the entire exposed length
2. Coloring the exposed insulation or covering green
3. Marking the exposed insulation or covering with green tape or green adhesive labels
As we can see, it would be best to ID the conductors before they are installed!