Locating intermittant opens

[mdshunk]

Which box # and what was the stopwatch reading?

I found them all anyhow. Didn't want to miss one, in case there was more than one offender. I think about 6 hours each for 2 men. Hired a cleaning company to send a couple girls out for an hour early in the morning to clean up all that crap necessarily involved with removing 30-billion ceiling tiles.

 

[cowboyjwc]

Glad you found it. Where I was actually headed was could it have been something wrong with the generator?

Guess it a mute point now:smile:

 

[mdshunk]

Glad you found it. Where I was actually headed was could it have been something wrong with the generator?

Naw.. there's actually 4 circuits in the generator panel. The other 3 go underground to 3 other buildings. Weird thing is, these other three buildings have their own services, each served by their own transformer. They could well have a power outage in one of the other buildings and the generator wouldn't know to start. Pretty messed up affair for otherwise really nice office buildings.

 

[electricalperson]

 

[quogueelectric]

A-m-p-r-o-b-e-2-0-0-5-!-!-!

 

[iwire]

Marc ......... I would change the breaker. :wink: :grin:

 

[JohnJ0906]

I did manage to find the open yesterday evening. I went in after almost everyone left, since the circuit weaved all over the building. Just started tracing things out. The offending connection was in a junction box in one of the suites over top of an x-ray developing machine (naturally ). Had to use my circus acrobat skills to work on that junction box. Seems like the wirenut was simply "pushed" onto the conductors. Seems like I find that from time to time. I wonder what goes on in a guy's head that he completely forgets to twist up a wire nut? The wire was heated up pretty good pretty far back, so I ended up pulling a couple new peices from the the junction box before and after the offending one to get some good wire to work with.

Good job!

It must be some kind of law that the problem is always located in the junction, fixture, etc., that is the hardest to access.

 

[peter]

Well, where was it? Inquiring minds want to know.
Was it a splice that wasn't pretwisted? A WAGO?
I've spent three days thinking about your problem [remote viewing which I'm not good at] and I still couldn't find it. Was it over the broom closet?
~Peter

 

[iwire]

Well, where was it? Inquiring minds want to know.

The offending connection was in a junction box in one of the suites over top of an x-ray developing machine (naturally ). Had to use my circus acrobat skills to work on that junction box. Seems like the wirenut was simply "pushed" onto the conductors.

......................................................................................

 

[ramsy]

I did manage to find the open yesterday evening. I went in after almost everyone left, since the circuit weaved all over the building.

That's what makes maintenance guys so superior to the rest of us. They sneak around in the middle of the night, shut things down, watch how emergency power works, and isolate any circuit they want. Then they visit the production shift, day workers, and tell our boss they fixed it in five minutes.

 

[brother]

Ive read the posts here and im curious as would not an ohm reading (resistance) test on this helped some?? wouldnt it show a higher resistance reading on that intermediate opening than on the the good connections??

 

[ohm]

I got a service call from a public library saying all their receptacles were dead. I spent several hours trying to determine why so many breakers were thrown until I talked to a clerk who said they had a roll around coffee maker & toaster. Seems they kept rolling it around until they had tripped every breaker in sight!

Same story in an office building I worked in. A secretary plugged in a heater under her desk and tripped out twelve computers, many times, until she owned up to it.

 

[mdshunk]

Same story in an office building I worked in. A secretary plugged in a heater under her desk and tripped out twelve computers, many times, until she owned up to it.

That happens a lot. Particularly since some installers favor combining all the circuits of an office cube pigtail into one big circuit.

 

[ohm]

Marc, ever tried assigning an arbitrary number to each of the 50 loads? Then, load down a DVM with a 100 W bulb and record the voltage at each of the 50 users. The lowest of the voltages is the farthest from the panel. The ones with the same voltage are probably on the same "spider" and the one(s) with the really low readings(s) are probably downstream from the bad connection.

By doing so you have "mapped" the circuit and you could backfeed the circuit (from the same breaker) to create an ultra reliable emergency power loop, much like your local power company might do. Any single "downed line" won't affect most users. Nothing (to my knowledge) in the NEC prohibits doing this.

 

[iwire]

Nothing (to my knowledge) in the NEC prohibits doing this.

310.4 prohibits ring or loop circuits.

 

[ohm]

Good call Bob, my bad. I have a hard time with the parallel conductor rule in the NEC after using them for so long aboard ships & industrial distribution systems. In the UK & far East (and I believe theater lighting) ring circuits are used to save on copper. Aboard ships and power distribution systems they're used to re-establish power as fast as possible.

I believe the purpose of 310.4 is to prevent overloading unbalanced conductors but if either side of a ring are fed with conductors large enough to supply the entire ring it might be a good reason to discuss it for inclusion in the 2011 Code, for critical circuits.