Microshocks from induced voltage

For a proposed design near a high voltage grid line, it might be easier to select EITHER an all metal fence that will be fortuitously earthed by its basic design, OR a wooden fence that cant become live.

If metal wire on insulating posts is required for other reasons, then earthing may be achieved by specifying that say 2% of the posts  should be metallic, with a minimum of two, even if most are wooden.


In view of the minute currents involved, a high resistance connection to earth will be fine, much higher than for earthing any likely electrical installation.

Consider the following worst likely case.

The capacitive charging current is likely to be a lot less than 1ma. Assume 1ma to be generous and assume a very high resistance earth connection of 1000 ohms. That will result in the fence becoming live at one volt.


In practice even wooden posts will usually have a low enough resistance to shunt the voltage to earth, unless newly installed and very dry.

I megaohm might be a reasonable guestimate, or for a medium length fence with 100 posts a total resistance of 10,000 ohms. That will shunt to earth 0.1ma with a voltage rise of one volt.

A longer fence will collect more current, but will have more posts to shunt this current to earth.


I have only once received a shock from a fence under a grid line, and that was while helping to build it. No shock was perceptible by the next week, presumably the insulation resistance had dropped.

For a proposed design near a high voltage grid line, it might be easier to select EITHER an all metal fence that will be fortuitously earthed by its basic design, OR a wooden fence that cant become live.

If metal wire on insulating posts is required for other reasons, then earthing may be achieved by specifying that say 2% of the posts  should be metallic, with a minimum of two, even if most are wooden.


In view of the minute currents involved, a high resistance connection to earth will be fine, much higher than for earthing any likely electrical installation.

Consider the following worst likely case.

The capacitive charging current is likely to be a lot less than 1ma. Assume 1ma to be generous and assume a very high resistance earth connection of 1000 ohms. That will result in the fence becoming live at one volt.


In practice even wooden posts will usually have a low enough resistance to shunt the voltage to earth, unless newly installed and very dry.

I megaohm might be a reasonable guestimate, or for a medium length fence with 100 posts a total resistance of 10,000 ohms. That will shunt to earth 0.1ma with a voltage rise of one volt.

A longer fence will collect more current, but will have more posts to shunt this current to earth.


I have only once received a shock from a fence under a grid line, and that was while helping to build it. No shock was perceptible by the next week, presumably the insulation resistance had dropped.