My question has to do with a piece of equipment in my home, but I thought I would post my question here because I am interested in the behaviour of the electricity rather than anything else.
There is a submersible electric sump pump in my basement. It sits in a pit dug out of soft rock, where water accumulates. The water is fresh water, in the sense that it is rainwater and not seawater, though it is muddy. When the water reaches sufficient depth, a float switch causes the pump to switch on and pump the water out of the house.
Yesterday, I was cleaning sediment out of the pit with my hand. The pit had a substantial amount of water in it. I felt a tingle: Electricity.
I did a quick experiment with my multimeter. I put one probe in the soil and one probe in the water. With the pump plugged in, I measured a small voltage (about 0.5 V AC). When I unplugged the pump, I measured no voltage.
So yes, this is a dangerous situation. The pump is dangerously defective. I have unplugged the pump and am arranging for its replacement. This is not the point of my question here.
My question is what is actually happening with the electricity. I think it’s safe to assume that somewhere in the pump, the 240 VAC mains current is exposed to the water. So:
Why did I feel a small tingle and not the full force of 240 VAC? In the same vein, why do I measure only 0.5 VAC in the water?
Why did I feel anything? Why wouldn’t the exposed wire short directly to the nearest ground point through the water?
Would I have felt a stronger shock if there had been less water in the pit?
What happens in situations like this, in which a whole swimming pool becomes electrified?