Locating intermittant opens

[mdshunk]

Anybody got any good ideas on locating intermittant opens on a circuit that weaves its way all around an office building, stopping at lots and lots of junction boxes and devices along the way, some of when may or may not be quite visible at the moment? The application is an emergency lighting circuit, 120V, in a 2-story office building. This single circuit stops at about 40 small lamps installed in troffers, and due to the fact the building has been reworked many times in the last 25 years, there must be 50 junction boxes associated with this circuit. It's not clear where the middle or the end of this circuit even is, to attempt the "divide and conquer" concept or try to use a DLRO. During testing, part of the circuit has intermittantly gone open, but it happens to be fine every time I've checked it. Any troubleshooting ideas come to mind?

[JohnJ0906]

Have you "mapped" the circuit out yet?

You might just have to do this the slow way - Start at the begining, and trace the whole thing, checking every connection, junction, etc.

Are you suspecting a buried J box?

[mdshunk]

Have you "mapped" the circuit out yet?

You might just have to do this the slow way - Start at the begining, and trace the whole thing, checking every connection, junction, etc.I'll do that if I have to, but we're talking about 10,000 square feet of building, in two stories, and lots of tiles to lift. Just seems like there ought to be a gadget or technique. It's been years before I've been put in a position to have to physically trace out every inch of conduit for something.

Are you suspecting a buried J box?No, but there's bound to be a few hidden from immediate view by ductwork, pipes, etc.

[gra electric]

Maybe burn the place down and start over?:grin: Seriously, i think your just going to have to do it the old fashion way and divide and conquer. I have seen this before, and it takes forever.

You mentioned it intermittently opens? Does this place have any security cameras that might give a clue to what lights etc. are going off when it opens? I used this as a last resort one time in an facility that made computer software. Like your situation, tons of rework. We spent many hours chasing our tails. We watched the security cameras, and basically it pin pointed the location where the wiring problem was. I will give props to the apprentice working with us, as it was his suggestion. Talk about thinking outside the box.

I hope that helps, and I will keep brain stormin' for ya!!:grin:

Gerry

[JohnJ0906]

Do you know what exactly is on the circuit?
Is it the same things that go out during the intermittent open?

[mdshunk]

Do you know what exactly is on the circuit?
Is it the same things that go out during the intermittent open?I do know what's on the circuit. I can just start the generator and see what all comes on. Basically a bunch of T-lamp holders in troffers, and R-lamps at the exit discharge areas and stairwells. I get differing reports from the on-site maintenance people about what all doesn't work when part of the circuit goes out. (naturally). No security cameras, but that's an idea I'm going to have to file away. Physically tracing the circuit from beginning to end (actually, every branch of the spider :) ) is my last option, but it might be my only option.

[gra electric]

have you actually seen anything not working when you test the circuit? You what people see and what actually happen are two different things.

Do they just want to repair the circuit, or are they asking you to add on? It might be cheaper to propose running a new circuit with new lighting? Not sure since I haven't seen the facility.
:confused: :confused:

[mdshunk]

have you actually seen anything not working when you test the circuit? You what people see and what actually happen are two different things. I havn't seen it, but they report that it's happened off and on for 10 years. What's not that clear is exactly what part of it stops working. They're just now interested in sorting it out. Nothing new is really going on. If anything new was to go on, the existing circuit is way maxxed out anyhow.

[scwirenut]

maybe you could find the presumed end of the circuit , tie in a recept and induce high current draw through like a hair dryer, this may cause it to go ahead and quit, then its a easy find

[JohnJ0906]

I get differing reports from the on-site maintenance people about what all doesn't work when part of the circuit goes out. (naturally).

Naturally. :roll:

Maybe (since it is maxed out anyway) find a location close to center, split it, and use a 2nd circuit from there. See which one fails next time.

Try to induce an open somehow.

[mdshunk]

maybe you could find the presumed end of the circuit , tie in a recept and induce high current draw through like a hair dryer, this may cause it to go ahead and quit, then its a easy findYou and I must think alike. The circuit, as it stands now, is almost ready to trip a breaker. I'd have to take out a bunch of lamps to put some load on what I think might be the end. Trouble is, the circuit is more or less wired in spider's web fashion, with no "end" per se. Just lots of ends, plural. Not all of it's conduit either. Some NM cable here and there. I might just start taking apart a few junction boxes, starting with a few of the "ugliest" first, to see what I come up with. If that doesn't pan out, then I'll go in some logical order. I just hate like the dickens to take this approach. Just seems like there should be a tool. I have a certain amount of pride in being able to set up a ladder to work on a problem, and not setting up a ladder to work on 50 places where a problem may or may not be.

[peter d]

Are you suspecting a botched splice somewhere that might already be in the melt down phase?

[boboelectric]

Yes,put a boarderline amp draw on its circuitbreaker.Don't trip circuit,just see what quits,Maybe quick wire,stab in the back receptacle.

[mdshunk]

Are you suspecting a botched splice somewhere that might already be in the melt down phase?I have a pretty good idea that's what I'm going to find, if I find it.

[Pierre C Belarge]

In the past, I ran into circuits/situations like this. Sometimes the easiest most cost effective method is to abandon it and run new work.

[mdshunk]

In the past, I ran into circuits/situations like this. Sometimes the easiest most cost effective method is to abandon it and run new work.I'm fighting myself to not run a new MC from the panel to one of the lights everyone agrees goes out. This would essentially "double end feed" the bad section, if I feed it with the same circuit.

[Sparky555]

IMO you aren't going to find one problem, you're going to find a LOT of problems. Dig in & enjoy. It's our chosen career. I just wrapped up a job that had problems in half of what I opened up (approx. 50 J Boxes).

Dave

[JohnJ0906]

I'm fighting myself to not run a new MC from the panel to one of the lights everyone agrees goes out. This would essentially "double end feed" the bad section, if I feed it with the same circuit.

Why not? (assuming you can break to circuit somewhere)

The irony here, is that you usually have a great tool or technique for most troubleshooting situations. I'm not used to hearing you at a loss.

[mdshunk]

Why not? (assuming you can break to circuit somewhere)I'm not even talking about breaking or splitting this existing circuit. I'm just talking about feeding it twice, with the same breaker, at two physically different locations in the run. Two home runs to the same breaker, essentially. The existing one at the beginning, and a proposed new one at the "end". That would provide permanent corrective action, but not address the root cause of the problem, which is why I am fighting myself over that idea.

[JohnJ0906]

I think that you do really need to find the cause. It very well could show itself catastrophically.

[dbuckley]

Putting the wiring under load was my first thought, but from a DC power source, rather than the line, and one wire as a time. Even overloading it some.

The other thought is TDR. Old style TDR with scope display and printout; go looking for differences in discontinuities between hot and cold wires.

Still doesn't solve the route problem though, perhaps a telecomms tone box might save some hard work in that regard...?

[JohnJ0906]

Still doesn't solve the route problem though, perhaps a telecomms tone box might save some hard work in that regard...?

Probably too much distance in this situation. Might help leg-by-leg though.

[Pullnwire]

maybe you could find the presumed end of the circuit , tie in a recept and induce high current draw through like a hair dryer, this may cause it to go ahead and quit, then its a easy find

I think a high draw is the way to go, it might turn your intermittent open into a long term one. I do alot of property management service work, and unfortunatley, I see this stuff too often. open every box, or induce a failure.

[nakulak]

1) find out which tenant screams the loudest to the landlord when they don't have power
2) tell the landlord that because its one of these weird intermittant problems, there are only 2 ways to fix it a) replace ckt, b) trace every junction

3) find out the tenant in #1's busiest day and time of the week
4) give the landlord a reasonable t&m price to trace, and a ridiculous price to replace
5) after he gives you the go ahead to trace, show up on the tenant in #1's busiest day, and shut all the power down, or flick their computers on and off a few times every hour
6) after receiving the emergency "wtf" call from the landlord, agree with him that its better to replace the ckt for the ridiculous price, do it, then send him a bill for the t&m plus the ridiculous price, then take the wife and kids to the beach for the weekend

[mdshunk]

nukulak, I don't know if you were serious or not, but that was hilarious. :grin:

[360Youth]

Just seems like there ought to be a gadget or technique.

If you have to ask I may have my doubts. You always seem to be Mr. Gadget.:)

Normally you just skip every 5 boxes or so and then back track when you finally find it, but it does not sound very normal. Anyway to go in during off hours and teun of all lighting circuits but what you are working on to see just how spread out you are?

[quogueelectric]

I think a high draw is the way to go, it might turn your intermittent open into a long term one. I do alot of property management service work, and unfortunatley, I see this stuff too often. open every box, or induce a failure. I disagree you may very well induce a fire in a compromised circuit. I hate to sound repetitive but amprobe 2005 is coming to mind right now.

[360Youth]

Just change the breaker. :wink:

[electricalperson]

well since i own the ideal suretest with the impedance function i would probably use that since its 120 volts. id start at the first box and hit every 3rd or 4th box. when the impedance is higher than the last box you might of located the loose connection. this would be the method i would probably use. im not sure how difficult the working conditions are in this building are so i dont know if that method would be better than looking in every single box and redoing every splice

[richwaskowitz]

Connect a recording device to monitor the current draw at the source. Come back later, find out what the current dropped to during the outage, calculate the approximate length of the resulting circuit based on the load per light to determine which light was the last to operate during the outage.

[mivey]

Connect a recording device to monitor the current draw at the source. Come back later, find out what the current dropped to during the outage, calculate the approximate length of the resulting circuit based on the load per light to determine which light was the last to operate during the outage.Might work on a straight feed. Unfortunately, he does not know the circuit layout.

[mivey]

If you are in a hurry to get it done, start opening junction boxes.

One option might be to sell them a security system with various cameras. They can get to play big brother and eventually will capture the problem on video.

Another option is to start a employee emergency light Easter egg hunt with a prize for those who identify the section that has been going out (small enough prize that they will not rig up a failure). The employees would have a regular Outlook-type log with notes about the emergency lights working or not working with dates and times. This would be coordinated with the system log.

[cowboyjwc]

I have two questions, 1) why does their emergency power come on so often that they notice a problem? 2) How is the emergency power being fed? UPS? Gen set?

[76nemo]

well since i own the ideal suretest with the impedance function i would probably use that since its 120 volts. id start at the first box and hit every 3rd or 4th box. when the impedance is higher than the last box you might of located the loose connection. this would be the method i would probably use. im not sure how difficult the working conditions are in this building are so i dont know if that method would be better than looking in every single box and redoing every splice

Guess no one heard you Chris. Marc, I know you've shot down the SureTest since day one, but here's where loop impedance testing can be useful. I know you said you only used it to test UPS batteries, but it sure COULD be useful here. You can buy an alligator clip attachment for the SureTest seperately.

[LarryFine]

Any troubleshooting ideas come to mind? I have some, Marc.

1. Ask some specific questions: has anyone actually seen the offending lights go off or on? Do they ever dim or blink like an arcing connection might cause, or simply go on or off at once as if switched?

2. Have you ruled out the possibility of there being a switch that gets operated once in a while, that shouldn't but does cause the intermittent? There may be a misplaced switch or timer in the circuit.

3. If you must physically trace the circuit, you could try (with the circuit(s) de-energized, perhaps) pushing a fishtape in any conduit you're unsure of, and have a helper listen for the other end.

Oh, one more thing: make a box-by-box map as you leapfrog from place to place.

[winnie]

I don't know if this tool exists, but in theory you should be able to gather TDR data from a large number of load locations (say by connecting the TDR where the lamp goes) and then generate a map of the circuit. I know that TDR devices exist, but I don't know if the software exists to combine the TDR data in this fashion.

I'm pretty sure that 'double end feeding' an ordinary circuit would be considered a violation of 310.4.

-Jon

[220/221]

Put it on a 50 amp breaker, plug in a few couple toaster ovens and look for smoke?

[pjg]

If you have an infrared camera you can usually find the loose connection with them. I don't own one but have serviced many installations with the pictures from the cameras. It might get you a bunch of service work with the problems you are sure to find. take the scan pictures to the landlord- a picture is worth a thousand dollars--in mean words

Phil

[mdshunk]

I have two questions, 1) why does their emergency power come on so often that they notice a problem? 2) How is the emergency power being fed? UPS? Gen set?1) It doesn't, but it is tested every month for an hour or so for some reason. 2) It's fed with a generator, but this is a 25 year old installation, so we'll not dwell on that. Yes, they are in the dark for a bit while the generator starts and comes up to speed, in case that was your next question. I tried talking with the owner for a bit about that, but he is content to leave it as-is until someone in authority (the fire chief, in this case) tells him he has to do something about it.

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 :mad:). 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.

[mivey]

Which box # and what was the stopwatch reading?

[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]

http://www.idealindustries.com/media/img/products/test_measurement/product/suretest_circuit_analyzers.jpg
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[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 :mad:). 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.