There’s hardly any piece of test equipment more fundamental than a volt ohm meter ... are no active devices and this meter is old enough to not use a printed circuit board.

On the other hand, he does mention using ... tested our circuit breakers, this is a relatively safe project. But still, have a read through our nice guide on working with mains voltage if you ...

“Breakers will weaken or fail over time, and when they do, they may not deliver the full 240 volts consistently.” Testing ...