what is the voltage? 180 volt? 220 volt - Myanmar

winayetun · Apr 21, 2021

If I turn off the breaker and measure the voltage across the breaker (upper and lower screws), the voltage is around 180 volt. If I measure the breaker's upper screw and the grounding bar of the breaker box, the voltage is 220.

What is the actual voltage and why is the discrepancy? Thanks.

Marvo · Apr 21, 2021

In normal electrical testing procedures, testing for voltage across a circuit breaker is a meaningless test.

The lower screw of the breaker is connected to the live wire of the circuit wiring. This live wire may or may not have a connection to the neutral via something that's plugged into or connected to that particular circuit. If the circuit has no load connected ie there's nothing plugged into it then that live wire will be 'floating' and you'll get no voltage or a meaningless voltage shown when you test. If there is a load on the circuit you'll see a result on your tester close to the supply voltage but it still won't mean anything.

Testing between the circuit breaker screw and the grounding bar is a far more meaningful test, it will tell you the difference between the voltage at the screw and the voltage at the ground bar which should always be at 0v.

Whenever you test a voltage with a tester it will give you the difference in voltage between the two points you're testing. To get a meaningful result you need one of the points your testing to be at a known voltage like the ground bar or neutral bar which should be at 0 volts or very close to 0v.

winayetun · Apr 22, 2021

Thanks for the reply.

"If the circuit has no load connected ie there's nothing plugged into it then that live wire will be 'floating'"

Is it true even when the breaker is off? I was thinking if the breaker is off, the voltage of the lower screw is zero.

James · Apr 22, 2021

In theory it is zero, however, there are several reasons why this voltage could be there.
type of test meter makes a difference
it would be a guess to start assuming why the voltage is being measured, some reasons are normal , other reasons are down to a fault within the installation.