There is probably not a fleet mechanic or fleet manager who has not heard something about grounds for trucks. But for all the talk about grounding trucks, including rules and commentary, there is very little consideration for how grounding connections are made to a vehicle. Unlike most every other procedure in the utility industry, there are no OSHA guidelines, consensus standards or best practices for connecting the truck to the truck ground. There are rules requiring grounding of trucks, but there are no best practices, procedures or methodologies for connecting grounds or ground attachments to trucks to allow grounding. So, that’s what we’re going to discuss in this installation of “Focus on Fleet Safety.”
For fleet managers to effectively facilitate the grounding of trucks, we need to understand the purpose of grounding and why it fails to do the job expected. Actually, the job expected often is the bigger issue because it may not be what you think. Grounding a truck does not directly protect workers from electrical shock, nor does it eliminate a shock hazard. Grounding trucks has one purpose: to cause immediate operation of a protective device. The protective device is the circuit breaker through which voltage and current are delivered to the electrical system. A truck is not an electrical conductor – it is a mechanical device, meaning that to ensure that current flow across the truck is sufficient to cause operation of the circuit protective device, an electrical connection must be employed to bypass the vehicle’s nonelectrical isolation from ground. Nonelectrical isolation refers to mechanical interfaces of bolted parts, the rubber tires and the outriggers on earth. Current has to pass these mechanical barriers to initiate circuit-breaker operation. In an electrical contact with a truck, the circuit breaker feeding the system in contact with the truck may not trip. As often happens, the circuit will continue to feed current into the vehicle, resulting in fire as well as a continuing electrical shock hazard to any person near the truck. So, the purpose of grounding is to create a good path for electrical current to flow. That good path causes a higher current to flow, resulting in fast tripping of the breaker feeding the electrical circuit. Fast tripping minimizes the damage to the electrical system and the truck.