February – March 2024 Q&A

Q: We were driving ground rods with a hammer drill for a switch pad on a construction site when OSHA inspected the site. OSHA was there to see the general contractor, but they cited our crew for not using a ground fault circuit interrupter (GFCI) where we were plugged into the site’s construction temporary. That brought up these questions: Why GFCI? What does GFCI do and how does it work?

A: The GFCI or GFI (ground fault interrupter) was invented by University of California at Berkeley Professor Charles Dalziel. A GFCI does not limit voltage; you can still be shocked, but you won’t be killed if the GFCI is successful.

In a tool or appliance circuit, the GFCI operates at the speed of light when it senses a current imbalance between the hot side of the circuit and the circuit’s neutral side. Let’s get basic and use the example of a drill motor. First, most drill motors today are double insulated with no external conductive parts that can become electrified. Those drills have two-wire plugs and are marked as double insulated. Plugs with the third pin are called grounded plugs and used when the external case of an electrical appliance could become energized if there is a fault in the appliance. The ground wire in the electrical cord is internally connected to the metal housing of the drill. Under normal operation, the drill motor draws a finite amount of current through the motor. If the electrical circuit in the drill shorts out or becomes defective, that condition can electrically charge the conductive housing of the drill. Grounding of the drill-motor housing creates a fairly resistance-free pathway back to the circuit source.

The resistance-free pathway causes a high current on the circuit, tripping the circuit breaker and removing the continued exposure risk caused by an energized drill housing. Ground wires don’t route current away from the person holding the drill. If you are holding it when it short-circuits, you can still be electrocuted even if the circuit breaker trips very quickly. That is where the benefit of the GFCI comes in.

GFCIs are designed to trip before a short circuit can deliver enough current into the circuit to electrocute the worker holding the drill. Normally, the power current going to the drill is the same level of current as the neutral current returning to the source through the circuit breaker. The GFCI has a balancing coil in both the hot wire and the neutral wire. As long as the currents are equal, the coils hold a magnetically held spring-loaded switch closed and the circuit breaker stays operating. If current leaves the path through the motor, a net change occurs in the hot circuit and the neutral circuit, releasing the magnetic hold into the spring. If that change is greater than 3 to 5 milliamps, a spring-loaded switch is tripped, opening the circuit. The intent is that the GFCI opens before the current leaking into the drill housing or appliance can become great enough to injure the user.

Q: Our sales rep told us blast blankets are required in energized manhole work. Is that accurate?

A: Blast blankets are not required by any particular rule and certainly not by OSHA. The employer may choose to use blast blankets as a method of protecting employees from the electrical arc blast that could occur in a cable failure, but that depends on the hazard analysis and the choices the employer has to protect employees. Distance from a blast source, likelihood of a blast, condition of cables, work being conducted, and types of cable or bus in the manhole all have a role in the hazard analysis. A blast blanket does not necessarily solve the hazard of an arc blast. Poorly installed blast blankets have been reported to be the mechanism of injury when a blanket blew away from a fault, striking and injuring a manhole occupant. Another reported incident occurred due to the concentrated blast energy that was directed outside of the open end of a wrapped blanket. We don’t have a simple solution; it’s certainly not throwing in a blast blanket because it’s a hot manhole. You should study the application, uses and limitations of blast blankets and perhaps use them as part of a system of protection for workers.

Q: If we have double circuits, one at 34.5 kV and one at 13.8 kV, can workers have both Class 2 and Class 3 gloves, or do they have to use the gloves rated for the highest voltage? Can they change them for the voltage they are working?

A: Because somewhere a reader is going to say that “cradle to cradle” means one pair of gloves unless you cradle and then change, let’s clear that up right away. Cradle to cradle is a legitimate working policy that has value but is not required by OSHA. Cradle to cradle, ground to ground and lock to lock are all methods of increasing the safety buffer in hot work. These policies have existed sporadically in some form across the industry, but they became more popular with employers when they were adopted and published as best practices by the OSHA Electrical Transmission & Distribution Partnership.

Obviously, Class 2 gloves tested for use at 18 kV would not meet the phase-to-ground 19.9 kV of a 34-kV circuit. Gloves must meet the voltage exposure. If you enter the minimum approach distance of an uncovered bus, you are exposed and required to don gloves for the exposure voltage. If a crew has 34 kV and 13.8 kV on the same structure, there is no reason two classes of gloves could not be issued in the same bucket and changed as needed. When you back out of the MAD for the 34 kV, it would be legal to remove the Class 3 gloves and don the Class 2 gloves before you enter the MAD for the 13.8 kV.

Some readers may protest this line of thinking, but we are simply stating the requirements of insulate or isolate under OSHA rules and industry standards and practices. Whatever method the employer chooses, they must be able to defend it as compliant with the minimum standards required by OSHA. We suggest that your training and policy documents require that, when changing gloves, the workers in the air call out the glove change and the workers on the ground reply, acknowledging that a glove change is occurring.

Q: What would you suggest as appropriate PPE for hydro-vacuuming around hot cable? We are aware of companies that require arc-rated clothing, and insulating personal protective equipment (e.g., gloves and dielectric footwear) seems common. We have also seen EPZ requirements for this work. Do any organizations require arc-rated face shields?

A: PPE requirements are always based on an assessment of the hazards involved with the work. The whole idea of hydro-vac is to avoid damaging underground facilities. Good practices typically require a good cable location and depth determination, followed by routing the vac operation from outside toward an undermining cable to prevent any contact with the cable. Still, there are obvious risks involved that require protection of the operator.

If a worker has their hands on a vacuum chute in the ground, they might have an exposure if the vacuum contacts energized cables. In that case, voltage-rated rubber gloves would certainly be required. Footwear protection would also be a consideration since a circuit would be made from vacuum chute to worker to ground. It is also reasonable to assume an arc flash could occur below the worker, resulting in a heat rise out of the vacuum hole, so an arc-rated shirt and arc-rated pants might be required. As to EPZ, grounding the vac truck might be in order. If the vacuum blows up a cable, grounding the truck will help to speed the clearing of the circuit’s protective devices. Grounding the truck will not protect a worker who is not on an equipotential mat bonded to the truck.

Q: When does OSHA require that we place a circuit on non-reclose? We have been operating under the assumption that non-reclose is not required if we are working behind fuses.

A: It is probably a mistake to assume a lateral fuse negates the need for a one-shot on the feeder, and this is not true. All you need to do is look at your breaker relay curves and lateral fuse curves to see that a breaker will trip and reclose on instantaneous before many lateral fuses will clear. An instantaneous is about the speed of light, but even a speed-of-light reclose is a lifetime at 30,000 degrees. Non-reclose limits the duration and thus the exposure.

The other mistake is to assume customer convenience is more important than lineworker safety. Many utilities are concerned that a non-reclose might cause an outage if some other part of the circuit has a tree branch strike a lockout feeder, so they want to limit non-reclose use. We must be very careful to judge the relative difficulty and hazards associated with live-line work in comparison to the needs of the users on the circuit.

OSHA is not too wordy when it comes to when to use non-reclose, except on two occasions. One is found at 29 CFR 1910.269(q)(2) regarding stringing in an energized environment, and the other is found at 1910.269(q)(3) regarding barehand live-line maintenance. You will see much discussion on non-reclose as a way to prevent transient overvoltage (TOV) during live work. That typically applies to transmission. TOV is not an issue below 72 kV. Following is a reference from the National Electrical Safety Code that the nature of the work typically determines when non-reclose is used.

Non-reclose is used most often on distribution when:

• Pulling conductors near or over/under live circuits.
• Transferring dead-ends or moving conductors.
• Gloving distribution.
• Replacing insulators.
• Climbing above distribution.
• Maching out jumpers and removing or installing jumpers.
• Setting poles in conductor.
• Climbing and working on distribution.