short circuit in furnace. neutral or bad connection?

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Old 08-11-17, 08:19 PM
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short circuit in furnace. neutral or bad connection?

Ac was tripping breaker earlier. Called pro and he turned breaker back on, told me he didn't have any idea why it would have tripped. Blower in furnace was pulling correct power. Came home later, smoke and burning smell in furnace room. Traced the problem to the connection where the wire from the furnace "on switch" met the smaller wires that go down to the blower etc. Both the hot and neutral had melted clean through the old nuts and we're exposed. The neutral had some oxidizing on the exposed wire (little green balls).
The entire dedicated circuit is newer all the way to the switch (on the side of the furnace). From the switch to the burnt spot is all older.
Should replacing the older connections correct the issue? Or may there be an underlying problem in the furnace? As i mentioned, the blower is drawing normally. I ask because with the neutral melted too that would have been hot right? Or could that being hot have been caused by the oxidizing? Or would the oxidizing have been caused that quickly by the short?
I've got a good pic but can't figure out how to post it from my phone.
Thanks guys. I know this is one of those "hard to tell across the internet" questions. Any way to troubleshoot by just looking?
 
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Old 08-11-17, 08:25 PM
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Phone pics can be too large to post. The board limit is 600x600. It will resize a picture of up to 1000x1000 down to 600x600. Anything over that won't be accepted.

http://www.doityourself.com/forum/el...-pictures.html

This will probably get moved to the furnace section after we figure out what's going on.
 
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Old 08-11-17, 08:43 PM
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A short circuit would trip the breaker/fuse right away. You likely had a bad connection. I suggest re-making the connection, start it up and see what happens.
 
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Old 08-11-17, 08:59 PM
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On my phone i don't even see an option to add a pic? I'll post it when i get home. I'm gonna go ahead and reconnect the burnt area but i wanted to see if u guys caught any red flags before i started. Also sorry if this is the wrong section. I assumed this was more electrical than furnace in the big scheme of things lol
 
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Old 08-11-17, 10:39 PM
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Here's the pics. Ok to just redo the connection?

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Old 08-11-17, 10:42 PM
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Oh, and also can you just use Romex or w/e for that small run of wire inside the furnace? Or does it have to be rated something special?
I thought it odd that BOTH wires were melted... hot and neutral... is that run of the mill? No experience with faulty wiring here. (I suppose that's a good thing lol)
 
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Old 08-11-17, 10:44 PM
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Those look like Ideal 73B wirenuts.
Is there a metal insert inside it ?

A wirenut doesn't normally melt like that.

Your wiring looks fine. Cut the wires back. Strip and retwist them and use real wirenuts.
 
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Old 08-11-17, 11:00 PM
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Oh I've never seen anything like it tbh... I would have just cut em back and thrown some new ones on, but it just put me off the way they melted to all hell. Didn't know if this was common in conjuction with other problems or what. THey appear to be old school wire nuts but they do have the little metal piece, it's just melded/fused to the wires.
 
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Old 08-11-17, 11:03 PM
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Also seems strange that both connections would "fail" at the same time... regardless of the wire nuts...?
 
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Old 08-12-17, 12:20 AM
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A loose or corroded connection creates heat. It's extremely rare to see that happen like that and even more rare that both wires did the same thing.

The wirenuts weren't full of water.... were they ?
 
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Old 08-12-17, 12:56 AM
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Not that I know of. They were brittle and dry by the time I found em, but the heat may have evaporated any water. As far as I know that side is dry as a bone.
 
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Old 08-12-17, 06:47 AM
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Definitely a bad connection.

I find it odd that they ran some Romex from the disconnect on the right, all the way to the box on the left, then the furnace wires go all the way back to the right. If it were me, I would just run the furnace wires into the disconnect switch box and connect them there.
 
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Old 08-12-17, 10:07 AM
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I find it odd that they ran some Romex from the disconnect on the right, all the way to the box on the left, then the furnace wires go all the way back to the right. If it were me, I would just run the furnace wires into the disconnect switch box and connect them there.
Agree. It looks to me like the furnace was set up for the power feed and disconnect to be on the left side, but for some reason it was installed on the right side. I also saw what appears to be a plastic tywrap on the MC cable feeding the disconnect switch which is a questionable method of securing the cable.

Strip and retwist them and use real wirenuts.
Real wire nuts? You don't like Ideal wire nuts?
 
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Old 08-12-17, 10:09 AM
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Ideal wirenuts are fine. Those didn't look like they had the metal insert.

I agree Tolyn.... I hadn't noticed the MC feed and the double splices.

Get rid of the Romex and that junction box. Connect the furnace wiring inside the disconnect switch.


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Old 08-12-17, 10:14 AM
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PJmax may be on to something.
  1. Mix warm air with cold and you can get condensation.
  2. If the picture of the wire nuts is properly oriented, the wire nuts would hold water.
Not sure if I'm seeing corrosion in the bottom of that box, or not.
I was strictly low-voltage, but ran into the warm/cold situation often outside and learned to always "point" my connectors up.

Just a possibility.
 
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Old 08-12-17, 01:58 PM
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@Thisoldman - Maybe onto something. That is the way they were oriented. I reconnected with new wire/nuts and oriented upward in case of that situation.

@CasualJoe - Yeah there are zip ties that have the MC secured to the gas piping coming down from the ceiling. It's been like that since I bought the house. While not ideal I don't see another way to secure the MC in the place it's located. Straight from a JB on the joist down to the disconnect. Any suggestions? (when I say "straight" I dont mean literally.. its oriented to where conduit would be a **** show to line up)

@PJMax - I agree, the little run of romex from the disconnect to the blower wires is pretty redundant. I don't see it hurting anything though when done correctly (and not melted).
Whoever installed the whole furnace/AC system was pretty shoddy IMO. The AC coils inside the furnace housing are positioned 90 degrees off what they should be, the outside unit is oversized by at least 1.5 tons (hooray short cycle humidity), and gas line between the wall and the back is touching the damn edge of the furnace itself. It was also previously on a ("newer") circuit that included a bunch of outlets and lights all on a 20A breaker.
I installed the dedicated 15A circuit, and literally the only bit of wire that I didn't do myself is where this occurred. I found similar code violations and just straight-up dangerous things when I re-did the wiring upstairs and through the attic.
There's always something to be said for just doing things yourself (and doing them right), even if you have to learn as you go. I'd never attempt anything I wasn't positive that I could do safely, of course. I do know that a few of the situations I've corrected here (and mostly learned to find/fix from you guys or Youtube) would have been very dangerous for my family. There's no way I could have afforded pro's to do it all, and most likely would never have found a lot of it until it was too late, had I waited until I had the money to pay someone else for the work.

TL;DR: Thanks for the help guys!
 
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Old 08-12-17, 06:47 PM
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I also saw what appears to be a plastic tywrap on the MC cable feeding the disconnect switch which is a questionable method of securing the cable.
You don't think using gas pipe as a means of support for MC cable is a good idea?

Sarcasm alert!
 
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Old 08-13-17, 03:15 AM
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Yeah it's definitely not ideal. It was that way when the inspectors looked the place over. No mention. It would take a perfect storm of horribleness to actually be an issue. I plan on moving the pipe in the near future anyway.
 
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Old 08-14-17, 08:56 AM
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Yeah there are zip ties that have the MC secured to the gas piping coming down from the ceiling. It's been like that since I bought the house. While not ideal I don't see another way to secure the MC in the place it's located.

1/2" EMT secured with a couple minnies would have been a better option than MC cable, but the MC cable is down and dirty and cheap and fast. I am surprised it ever passed inspection, but it's also possible it never was inspected by the AHJ. Years ago I recall seeing in a rural area many furnaces wired with just romex taped to the gas pipe......even cheaper and faster.
 
 

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