The Hidden Hazards of Electrical Maintenance

Common hazards with planned maintenance

It is often believed that planned maintenance tasks are inherently safe because there is time to plan the job and consider potential hazards before the activity begins. It certainly is true that taking time to plan the work does increase the level of safety in executing the task, which is why OSHA and NFPA 70E require every electrical task to be planned. That plan should not only outline the steps to be taken, but also identify some of the potential hazards along the way. One of the biggest risks for planned maintenance is the mindset of “this is all de-energized and safe,” which often causes workers to let their guard down. However, de-energizing the equipment is not enough; it must be placed in an electrically safe work condition per NFPA 70E Art. 120 (see Table).

Only when the equipment is in an electrically safe work condition is it considered electrically safe and free from electrical hazards. However, one often overlooked hazard comes during the process of putting it in and out of that electrically safe work condition. Depending on the equipment and the voltage levels, the act of opening and closing the means of disconnect could pose an electrical hazard.

A risk assessment must be performed to determine what electrical personal protective equipment (PPE) is required to operate the disconnect device. Putting the equipment back into service after maintenance can carry even more risk due to potential human error. Devastating equipment failures have occurred as a result of a protective ground being left on a conductor inside an enclosure.

It is a best practice to give all protective grounds a unique number, and — as part of the maintenance procedure — document which ground is placed at which location. Then, at the end of the task, document each ground as it is removed and compare to the initial list to make sure all grounds that were installed are documented as being removed. In addition, if a ground is placed inside of a closed compartment, put a magnetic sign or flag on that compartment as a visual reminder that a ground is installed inside the compartment.

Another aspect of establishing an electrically safe work condition that involves a potential electrical safety risk is verifying the absence of voltage. Since the equipment is in the process of being placed into an electrically safe work condition (but the process is not complete), the equipment and conductors are still to be treated as energized. During the process of verifying the absence of voltage for any circuit rated 50V or greater, voltage-rated gloves and protectors must be worn as a minimum. Depending on the voltage level and incident energy levels, arc flash PPE may also be needed while performing the live-dead-live method to verify the absence of voltage.

The live-dead-live method is the process of using a properly rated digital voltmeter to check all phases and ground to verify the absence of voltage. Ideally, the meter is used to check the voltage on a known energized source of the same nominal voltage to verify that the meter works. Then, without making any changes to the meter, check all phases and ground for all the circuits involved in the maintenance task to confirm the absence of voltage. Then, go back to the known energized source to confirm that the meter is still working. The live-dead-live method eliminates the risk of a meter failure or operational error by including steps to confirm the functionality of the meter.

Another risk to consider and evaluate is the potential hazards associated with what is in the proximity of where the maintenance task is being performed. Too often, workers get narrowly focused on only the specific equipment that is being worked on and overlook hazards in the surrounding area. Workers must do a risk assessment on the area and consider all hazards to which they may be exposed. They must verify that they will not be working within the limited or restricted approach boundaries of any other exposed energized conductors or take appropriate mitigation steps if they are inside one of those boundaries. A large enclosure may contain two systems: one that is in an electrically safe work condition for maintenance and one that is still operational. Often, there is other electrical equipment adjacent to the work area that remain energized. If there is “look-alike” equipment in the same area, consider using the “tape in” and “tape out” technique to avoid inadvertently opening the wrong equipment. Place warning tape/signs on the equipment that is still energized to keep workers out, and place barriers or tape to help guide workers to the electrically safe equipment.

Thermography or infrared (IR) inspection is a predictive maintenance activity that continues to become widely used by more organizations. Thermography can reveal developing abnormalities well before they trend to failure, allowing the opportunity to plan a downtime to make a repair and avoid the looming unplanned outage due to equipment failure. For thermography to be effective, the equipment must be energized and ideally heavily loaded. In addition, the thermography camera needs to have a direct line of sight on the conductors or parts needed for inspection, which means the conductors or parts are typically exposed.

Opening and closing enclosures of energized equipment can be a hazardous activity, especially while wearing voltage-rated gloves and arc flash PPE. A better alternative would be to de-energize the equipment, remove the necessary covers, barricade the area, and then re-energize the equipment for the inspection. A best practice would be to mark the area on the enclosure where the components that need to be viewed for inspection and install infrared (IR) windows at those locations. Then future inspections would not require opening the enclosures, but simply viewing the equipment through the IR windows.