I have what must be a very simple problem. I own a rental unit. I wired it myself. Everything has worked fine for 7 years. I lived in it for 4 of the 7 years. Three young women live in it now. They run a lot of electricl stuff, not the least of which are multiple hairdryers. They also have space heaters which I have recently told them not to use. I have no idea if they are responsible for the problem, but its background info nonetheless.

Anyway, last week I get a call from them that the electricity on one circuit is out. I check the breaker - it seems OK - that is to say, no red showing and it was not tripped.

I go to the first J box in the run. It is a ceiling box. I open it up. I undo all the nuts and use my small probe tester on the black wires. Sure enough one of them is hot. I test that same black wire with a light fixture and I get nothing. I even use one of those smal rubber coated bulb holders with two wires hanging out of it and it does not work.

Why or how in the world can the tester work, but not the fixture??

Did you measure 120 volts across the black and white or black to ground?

If you do not get 120 volts across the black and white, but do get it across black and ground, then the neutral white is broken, or opened, and the fixture does not have a return, and will not work.

Where do you get voltage?