Electric Field
Landowners and developers should be aware of the potential for nuisance and startle shocks (caused by induced voltage) that can occur when someone comes in contact with a large conductive object (eg. a vehicle, building or even fencing) located on or off the right-of-way.
These shocks are known as ‘nuisance’ or ‘startle’ since they will not physically hurt someone, but will be noticed by some people and provoke a startle reaction.
These touch currents occur when a grounded individual touches an ungrounded object while standing in an Electric Field (e-field). Conductive objects when placed in an e-field attract a charge, and a person touching that object can experience an annoying or startling shock when a person’s body provides a path to ground for the current to follow.
There are many factors which influence the likelihood of nuisance shocks and the extent that people will notice them. These include:
Line voltage
Conductor to ground clearance
Size of the vehicle or object
Location on or off the right of way
Atmospheric conditions
Personal physiology
Electric fields emanate from any conductor or wire that carries voltage. Higher line voltages produce higher electric field strengths. The closer the conductor is to the ground, the higher the field strength beneath it tends to be, and the increased possibility of shocks.
Larger objects such as a building or a large vehicle have the capability of a larger charge and therefore the shock could be more noticeable. Backyard metallic objects such as swings, portable grills and lawnmowers have been known to deliver similar shocks.
Ungrounded metal wire fences can also receive sufficient charges to cause nuisance shocks. During building construction, workers have also received shocks when installing ungrounded gutters and downspouts on structures built close to the edge of the right-of-way. Homeowners may also experience shocks when cleaning gutters if the gutters are not properly grounded.
People or animals can receive a shock by touching a metal object located near a transmission line.
The shock is similar to that received by touching a television after walking across a carpet. The magnitude and the strength of the charge will be related to the mass of the ungrounded metal object and its orientation to the transmission line.
Induced current can be prevented or corrected by grounding metal objects near the transmission line.
Grounding chains can be installed on tractors. Metal fences can be connected to a simple ground rod with an insulated lead and wire clamp. Electric fences with proper grounding should continue functioning properly even when subject to induced voltage. Refueling vehicles directly under a high-voltage transmission line is not a good practice. A spark from a discharging metal structure with induced voltages to earth could ignite the fuel.
The risk of such ignition is higher with gasoline-powered vehicles than for diesel-powered vehicles.
