ELECTRICITY BASICS
by Mark Bell, ENGsafety.com

Electrical power transmission is based on two factors.
1) Energized wires provide one side of electricity.
2) Earth ground, known as “Ground,” is the other side.

All buildings and sites that receive external utility-generated power also have earth ground. All electrical power depends on an energized conductor and a path to ground. It is purely a path between the two that creates the flow of energy, electricity, through items that use it. It is the power company’s mandate to provide electrical power to its clients, and electrical power is routed in the most efficient means possible. Sometimes shutting down power is not simply a matter of turning off a switch that may be also providing power to hospitals, care facilities, emergency service facilities, traffic control lighting, general lighting, etc. Shutting down power lines may need to be coordinated so the power flow can be re-routed. This procedure takes time.

A power company may choose not to shut down power if shutting down power may create unforeseen additional damage. An electrified TV truck that may catch fire, or has caught fire, may not be a situation that would warrant a large shut down of electricity if that is the only solution, and the truck damage, or personal injury, has occurred.

Some people are aware of the fact that when there is a large grounding of utility power lines, the utility’s circuit breakers will “open” or shut off the circuit, then re-energize automatically after a time period. This period may be 10 seconds, 15 seconds, or may not be automatically controlled. Some power stations are operated manually by an operator who is instructed to turn power back on if there is no planned reason for the outage.

This is what happened at one ENG incident where a person was killed. An operator reenergized the lines, per protocol, while the technician’s body was grounding the truck, the mast of which was contacting an overhead line. Emergency service people on the scene also made a variety of errors, one police officer stating she had just graduated from the police academy, and the electrical safety portion of her training had been cut due to budgetary issues.

At any time, computers that control power may malfunction, or function normally in their own logic, re-energizing or shutting down lines.
Sometimes there are mechanical malfunctions. This sort of malfunction was reportedly responsible for re-energizing power lines at a mass electrocution in Natal Brazil that killed 29, and injured many more, after a truck knocked over a power pole near a rain soaked group of people.

In your van, the generator provides the energized line and ground. The generator chassis, typically in physical and electrical contact with the van chassis, is the ground, making the vehicle chassis “ground,” too. Unless the van is tied to earth ground through grounding rods, earth grounding is not a factor as is typical in utility provided power. The only path of electricity to “ground” is the electrical output of the generator to itself, and the vehicle chassis. This principle has been observed by thousands of TV crews who have performed live shots in the rain while standing on the ground using generator power.

One more item to understand is the phenomenon called “ground gradients.” This is an electrical behavior where a grounded high voltage line produces electrical pulses in the ground. These pulses emanate from the point of contact and dissipate in theoretically concentric rings, or circles. Dangerous? Some firefighters call them “Rings of Death.” They are dangerous, and life threatening.

As the “rings” move away from the point of high voltage wire contact, like the circles in a pond when a rock is thrown into it, the voltage diminishes.
The “gradient” voltage is dangerous if one steps on one gradient, or ring, with one limb, which may be at one voltage, and touches another gradient with another limb, like one’s hand or other foot. The second gradient may be at a significantly different voltage, the difference in voltage conducted through the object connecting them…like one’s hands, or feet and legs.

Gradients are invisible, so they have to be pictured/imagined at any incident. If you are in a gradient field, or suspect it, perceived perhaps by a tingling feeling in your legs, keep both feet together, and hop or shuffle away. 50 yards away is one guideline, or as one firefighter said: “Until you get past the first person laughing at you.”

Gradient fields are the reason you need to keep both feet together, and hop or shuffle away from the point of grounding if you are jumping from an electrified vehicle. Shuffling is defined by moving feet in a shuffling motion with both feet touching, so at no point will the heel on one foot go ahead with the toes on the other foot. Minimal spread of the limbs in the gradient field is the key, so as not to straddle different voltage.
This is also the reason you can’t fall on your hands if you jump out of the truck and are off balance. Your feet and hands will be on different points on the ground and possibly in different areas of the gradient field.