Getting Shocked on a Structure?
It’s not static. And there’s a reason that’s important.
Static is defined at www.dictionary.com as a stationary electrical charge built up on insulating material. The Britannica.com website defines static as a phenomenon in which charged particles are transferred from one body to another. For example, if two objects are rubbed together, especially if the objects are insulators and the surrounding air is dry, the objects acquire equal and opposite charges.
So, why are these definitions of “static” important? Because what you are experiencing is not static – it is induction. Why is that important? Because while static won’t kill you, induction can.
If you are getting shocked on a structure, there is likely a transmission circuit nearby, either on the structure you are touching or in the right-of-way. You can get induction from voltages as low as 23 kV, so don’t assume induction hazards only apply to 500 kV.
In many cases, the worker getting shocked by touching the structure is either partly isolated from the structure by work boots or completely isolated by being in an insulating bucket. Either way, the worker’s body is an electrically isolated floating object. If there is an induction source as described above, the worker’s body is being charged by the induction field and discharged when they make contact with the pole or structure.
“OK,” you say, “so now I know it’s not static, but it is induction. Why is that important?” I’m glad you asked! OSHA has a rule that requires the employer to determine whether an induction hazard is a risk to workers. If the employer can’t do that, the workers must assume the risk is hazardous. Under the right conditions, that induction voltage can be high enough to do damage. Every year, lineworkers are knocked unconscious or burned by flashes caused by high induction discharges. In too many cases, they are injured and frequently killed by induction currents they thought they had controlled by grounding.
Grounding will collapse the induction voltage, but it does not eliminate the induction current, and that is where the greater risk is. Induction current is caused by the magnetic field surrounding a high-voltage circuit. There is also a voltage field. The voltage field creates capacitive coupling, producing the voltage that appears on conductors or conductive objects in the induction field. When you ground a capacitive-coupled voltage, the voltage collapses and there is no significant current flowing. With the magnetic field, the coupling is called magnetic or inductive coupling. If there is a complete pathway, the induced current will flow in the pathway.
The pathway is important to understand because a single ground from the circuit to earth is not a complete path. In order for there to be a complete path, there have to be at least two sets of grounds. Two sets of grounds might be bracket grounds or even two crews grounding a bus 20 spans apart. This has gotten some workers in trouble, thinking one set of grounds was all they needed to be safe, and they lifted a second set by hand, putting themselves in a path with high current from an induction circuit.
Ultimately, this induction current and even the circulating current found in the bracketed path are not any more hazardous than any other ground risks. The solution and safety are in the cardinal rules for grounding:
- Always install your ground connection first.
- Always make the second connection to the nearest phase with a hot stick.
- Make all subsequent connections with hot sticks.
- Always remove ground connections with hot sticks in the reverse order that you made them.
- Never handle the disconnected end of a ground cable that is still connected to a phase.
About the Author: After 25 years as a transmission-distribution lineman and foreman, Jim Vaughn, CUSP, has devoted the last 22 years to safety and training. A noted author, trainer and lecturer, he is a senior consultant for the Institute for Safety in Powerline Construction. He can be reached at firstname.lastname@example.org.