I have a strange one here...
So I go on this service call today, receptacle doesn't work. I find it has an open neutral, and notice a weird rhythmic pulsing of the ohms between ground and neut, from open to something less than open, and frankly forget exactly what the reading was. On about 1.5 second intervals. Ignored it, because, well, it was open.
I find a burned wire nut in the first j-box headed back to the panel. It had a hole burnt through it, thought for sure that was it. Nope.
I check the panel and find a neutral very very loose on the buss. It had about 4 amps on it so advised the customer to shut anything critical down. After they did, measuring zero amps on the neutral in question, I pull it. While I'm re-stripping it and as I'm about to re-land it, someone turns the office lights on which were off, and they started flickering. Rhythmically, on about 1.5 second intervals. WTH? He shut them off, and I carefully re-strip and land the offending neut.
I check the outlet, 118 volts hot to neut, hot to ground. We're good, except in the back of my head that office light thing needs to be addressed. I re-check my ground to neutral resistance, and I'll be damned if it isn't still pulsing, but now from 0 ohms to around 12-18 ohms, again on rhythmic 1.5 second intervals. I start checking around, finding the same weird reading on multiple other circuits. 0 volts, by the way between ground and neut at the outlet.
Back to the panel, ground to neut resistance reading zero to maybe 2-3 ohms, you guessed it, on rhythmic pulses. This is a 208y/120 panel, 200 amps, and there's a 2nd one adjacent to it, both fed from the main service, which is immediately behind these panels in the meter room, to which of course, nobody has a key to. I check neutral to ground resistance in the adjacent panel and it's a rock solid steady zero.
So clearly there's a compromised connection on the first panel's neutral, right?. And I understand a load may be pulling power rhythmically causing the connection to degrade in rhythm with the increased load, although I couldn't find a load doing so.
But what's giving me shingles is that when my receptacle neut was open, this rhythmic pulsing was partially closing the connection between ground and neut. I land the neut and it partially opens it?
Bear in mind no load in this office was malfunctioning, and everything worked except for the one outlet, which worked after the wire in the panel was tightened. There were some fluorescents, a refer, a micro, a few laptops, some phone equipment, and really not much more load that I could see. L1 L2 L3 were all running between 5 - 15 amps. I ran out of time and need to return when they procure a key to the meter room.
But pray tell, Electrical Wizards, what could be causing this anomaly?
So I go on this service call today, receptacle doesn't work. I find it has an open neutral, and notice a weird rhythmic pulsing of the ohms between ground and neut, from open to something less than open, and frankly forget exactly what the reading was. On about 1.5 second intervals. Ignored it, because, well, it was open.
I find a burned wire nut in the first j-box headed back to the panel. It had a hole burnt through it, thought for sure that was it. Nope.
I check the panel and find a neutral very very loose on the buss. It had about 4 amps on it so advised the customer to shut anything critical down. After they did, measuring zero amps on the neutral in question, I pull it. While I'm re-stripping it and as I'm about to re-land it, someone turns the office lights on which were off, and they started flickering. Rhythmically, on about 1.5 second intervals. WTH? He shut them off, and I carefully re-strip and land the offending neut.
I check the outlet, 118 volts hot to neut, hot to ground. We're good, except in the back of my head that office light thing needs to be addressed. I re-check my ground to neutral resistance, and I'll be damned if it isn't still pulsing, but now from 0 ohms to around 12-18 ohms, again on rhythmic 1.5 second intervals. I start checking around, finding the same weird reading on multiple other circuits. 0 volts, by the way between ground and neut at the outlet.
Back to the panel, ground to neut resistance reading zero to maybe 2-3 ohms, you guessed it, on rhythmic pulses. This is a 208y/120 panel, 200 amps, and there's a 2nd one adjacent to it, both fed from the main service, which is immediately behind these panels in the meter room, to which of course, nobody has a key to. I check neutral to ground resistance in the adjacent panel and it's a rock solid steady zero.
So clearly there's a compromised connection on the first panel's neutral, right?. And I understand a load may be pulling power rhythmically causing the connection to degrade in rhythm with the increased load, although I couldn't find a load doing so.
But what's giving me shingles is that when my receptacle neut was open, this rhythmic pulsing was partially closing the connection between ground and neut. I land the neut and it partially opens it?
Bear in mind no load in this office was malfunctioning, and everything worked except for the one outlet, which worked after the wire in the panel was tightened. There were some fluorescents, a refer, a micro, a few laptops, some phone equipment, and really not much more load that I could see. L1 L2 L3 were all running between 5 - 15 amps. I ran out of time and need to return when they procure a key to the meter room.
But pray tell, Electrical Wizards, what could be causing this anomaly?
