120v electrical problem
 

Have a problem on a seemingly simple float switch driving a very small potable water pump. 120 volt, 2 wire circuit, so it's not rocket science.

Pump disconnected; float switch closed and I read 127 volts coming out.
float switch open and I read 67 volts on brand A and 79 volts on brand B switch.

Measured the above on two used switches and one brand new switch.

Pump connected and running; I read 125 volts.

All float switches have a 3-4 ohm reading closed and zero ohms reading open.

My question is: Why is it that when I use an ohm meter that there is an obvious open and closed circuit, but as soon as power is applied, there is no totally open circuit. How can there be 67 - 79 volts coming out of a switch that is supposedly off? The pump starts and stops as it should when the float switch is moved.

Stan

I'm no expert ( well maybe I am if you figure that EX = a has been and spurt is a drip under pressure) and I'm sure others will have a better idea.

But I suspect that the float is breaking the ground and not the hot wire.
so when you are measuring power you are not getting a good ground thus the odd voltage.

Ok now one of you sparky's help us both

Thanks for the idea. I thought about that and "reversed polarity" if I can say that about AC. No difference.

I think your meter is just real sensitive, which is a good thing. If there's a million ohms resistance (a little dirt in the lube maybe) across the open switch, and you have a 20,000 ohms/volt (a measure of the sensitivity, and not uncommon) meter on the 200 volt scale, it'll see about 95 volts or so. If you then put a damp finger on the connection and another on something grounded, it'll go down to close to zero, and you won't feel it because the current is so small.

All that has absolutely no effect on normal operations.

j_martin, thanks for the info. You may be on to something. Today I ignored the strange voltage reading, used two new float switches, hooked everything up and lo and behold, it works.

Never mentioned it in the first post, but there are two tanks. A low tank that feeds a high tank, hence the two float switches in series.

I've been around electricity for a little while.......over 50 years.

glad it helped.