Direct Ground Voltage - Shock Hazard?
I ran into something that I had seen from one of Mike's videos on youtube. I saw a 220V run cut from an outdoor appliance and the two conductors were directly into the ground about 1 inch. They clearly were charred from the electrical arcing on the conductors as they were very black. If I kneeled down to inspect this line, what type of potential voltage would I be at risk to receive if my knee is 2 feet away from the line?
Is it buried deep enough to matter? Ground is moist but not wet.
Not a whole lot, in this specific case, because:
- There isn't much surface area where the copper is in contact with the soil; it'll be a high-impedance connection, and
- The electric field in the soil will be confined to the zone between the two hot wires.
A significant hazard exists when one hot wire faults to a large metal object that is in contact with the soil and not bonded back to the source. An electric field is then established in the soil, starting at the point where the fault contacts the soil and terminating at the point where the source is grounded to the soil. At any two points between, a voltage exists, (such as the two points where your knees contact the soil) proportional to the distance between the two points, the distance between the fault and the source ground, and the conductivity of the soil.
I pretty much agree with the previous post except one minor correction - not all the electric field stays between the two wires. Most of it will stay between the wires, because that is the lowest resistance. However, some will also flow sideways and even away from the wires, in a big arc and around from one wire to the other. The electric field and flow of current will look something like this:
And also remember, you need two points to measure a potential difference or shock hazard. If you only have one knee and your feet on the ground, and your boots are well insulated, you aren't at as much risk for shock.
On the other hand, if you have both knees on the ground, the shock hazard will depend on how far apart your knees are, and exactly where they are in relation to the wires.
Edit: Also, since its a grounded system, some current could be flowing back to the grounding electrodes. Especially if the two hot wires don't have equal connections into the earth. That could also affect your risk for a shock depending if you are between the wires and electrodes (more risk) or away from the wires and electrodes (less risk).
Last edited by steve66; 04-21-17 at 11:03 AM.
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