Open neutral, or something else?
For the last couple of months or so I have been struggling with what I presumed was an open neutral because the 4 outside lights in front of the house and the two ceiling lights, with 2 bulbs each, in the hallway did not work. It all started, or so it seems, after my ISP installed fibre internet and home phone. One of the installers mentioned that he had been "zapped" by a live cable hanging down beside the breaker panel when they were installing the fibre box on the same plywood board. Living in this house for 35 years and adding circuits, changing breakers, etc. I had never seen this cable before. The zap had kicked out a breaker which I couldn't reset. I found that on the loose cable the black had shorted to the ground, but the black and white had never been stripped, just cut off, like originally the electrician had intended to install a receptacle, but forgot. There is already a receptacle just below the panel anyway. After separating the fused black and neutral and marring them off I was able to reset the breaker. I still don't know the purpose of that cable and will eventually put it in a box to make things safe and to code.
So back to the "missing neutral" mystery. The other day I was trying to resurrect the outside lights by temporarily jumping the neutral to a known good one using a nearby outside receptacle with no luck. Even jumping the neutral to ground at the fixture didn't work. I finally discovered that all 4 outside bulbs were blown, so that solved that mystery. I'd been lazy replacing the outside bulbs because the screws on the fixtures would seize and require a lot of work, so I can see how one or two or three lights could have burned out until the final one did. But I could never anticipate all the hallway lights burning out at once. We would have noticed one or two bulbs burning out first.
Today I was trying to hook up a temporary neutral to the hallway lights before crawling up in the attic to make a permanent connection. But no known good nearby neutral worked. Just out of curiosity I changed one of the hallway ceiling fixture bulbs for a known good one, and VIOLA! I saw the light! All four ceiling light bulbs had been blown at the same time. Mystery solved. It was not an open neutral, just 4 blown bulbs. Now I'm wondering how the bulbs could have been blown. Could the short caused bt the fibre installers have caused a surge that did it? Could it have sent 240 volts through the circuit? Whatever it was, I'm glad the problem is solved.
So the moral of this long story is that you should never always assume the logistical answer. Sometimes the simple one, no matter how preposterous, like 8 bulbs blowing at once, is it.