Locating intermittant opens

[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]

I second that motion

I second that motion

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 ). 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?