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Old 04-07-2009, 01:39 PM   #1
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Burned wire behind access panel..


Can someone tell me if I can just replace the burned wire seen in the picture or if something (transformer?) needs to be replaced first?
I have 15 years experience in carpentry including basic wiring but I'm not very familiar with HVAC, especially not the wiring.
Just trying to fix this for my grandmother before it dips down into the 20's tonight, gotta keep the lil lady warm.

Thanks!

http://i3.photobucket.com/albums/y89...burnedwire.jpg

http://i3.photobucket.com/albums/y89...irecloseup.jpg


Last edited by woodlake; 04-07-2009 at 01:43 PM. Reason: added closeup picture
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Old 04-07-2009, 01:54 PM   #2
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Burned wire behind access panel..


Well, it got hot for a reason. If it was due to a loose connection, replacement may be an ok fix.

What is the threaded stud it is attached to? Heater element?

If the threaded stud is deteriorated, it may be the source of heat. So, a new wire would get hot too. I would replace the wire, run the item for a short while, SHUT THE POWER OFF, and feel if the wire or connection is hot.

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Old 04-07-2009, 02:08 PM   #3
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Burned wire behind access panel..


I'm not sure what the threaded stud is attached to.
I took those pictures and left her house thinking I would get a friend who does heating and air to come over and fix it but he is out of town.
Had I known he was unavailable I would have gotten a lot more information including the model number etc.. I think it is an "American Underwriters"? unit.
And I know it's at least 30 years old.

Where would I be able to purchase the wire? Lowe's/Home Depot/Ace Hardware?

I will probably be going back over there within the next hour and can get more information about the unit including better pictures. (only had my cellphone for pictures earlier)

Thanks for your reply!
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Old 04-07-2009, 02:36 PM   #4
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Burned wire behind access panel..


Should be able to get wire at any of those places. You will need to match AWG number of the wire (same or larger wire size).

As I said, I would start by replacing the wire and seeing if it continues to get hot.
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Old 04-07-2009, 02:38 PM   #5
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Burned wire behind access panel..


I will go and give it a shot.
I'll let ya know if it worked, thanks!
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Old 04-07-2009, 03:02 PM   #6
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Burned wire behind access panel..


That is not ordinary wire. Should be stranded, high temp stove grade wire. The stud is attached in the back to the element. If not done properly the wiring can overheat and catch on fire, beware!
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Old 04-07-2009, 03:50 PM   #7
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Burned wire behind access panel..


Quote:
Originally Posted by yuri View Post
That is not ordinary wire. Should be stranded, high temp stove grade wire. The stud is attached in the back to the element. If not done properly the wiring can overheat and catch on fire, beware!
Good point. Take a look at what the other wire going to these connections is labeled as. (i.e. THHN/THWN AWG, etc). I was thinking he'd get THHN (should be available at chain stores), but maybe it needs to be higher temp.

Yuri, do you know what type is for high temp? Would local hardware stores have it?

Last edited by Addicted; 04-07-2009 at 03:52 PM.
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Old 04-07-2009, 04:00 PM   #8
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Burned wire behind access panel..


Not sure, I go to my electrical wholesaler and tell him #10 and #12 electric stove grade wire and he knows what it is. Very expensive stuff. Hardware stores won't have it/no demand. Ordinary TEW etc will get brittle and the other stuff stays flexible. I have seen quite a few roasted/burnt electric furnaces in my 30 yrs. Scary stuff. The wire will burn, melt B4 a 100 amp fuse blows.

Last edited by yuri; 04-07-2009 at 04:04 PM.
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Old 04-07-2009, 04:17 PM   #9
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Burned wire behind access panel..


Quote:
Originally Posted by yuri View Post
Not sure, I go to my electrical wholesaler and tell him #10 and #12 electric stove grade wire and he knows what it is. Very expensive stuff. Hardware stores won't have it/no demand. Ordinary TEW etc will get brittle and the other stuff stays flexible. I have seen quite a few roasted/burnt electric furnaces in my 30 yrs. Scary stuff. The wire will burn, melt B4 a 100 amp fuse blows.
Yep.

Get mine at electrical supply house also.

Learn before you burn.

Your families life may depend on it.
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Old 04-07-2009, 04:42 PM   #10
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Burned wire behind access panel..


Quote:
Originally Posted by yuri View Post
The wire will burn, melt B4 a 100 amp fuse blows.
If you wait long enough

"
Practical example> 16 gauge copper wire: Tmelt = 1083, Area = 2581 circ mil, Time = 5 sec,diam = .0524 inches

Using Preece equation:

= 10244*.0524^1.5 = 123 Amps

Using Onderdonk equation:

Ifuse = 2581 * SQRT( LOG((1083-25)/(234-25)+1)/(5*33))

= 2581 * sqrt(log(1058/209+1)/165)
= 2581 * sqrt(.0047)
= 178 Amps
"
If the insulation is only crispy close to the terminal I'd say "loose connection". If it's crispy the whole way upstream, I'd say overcurrent and the fuse failed to melt.

Last edited by Yoyizit; 04-07-2009 at 04:46 PM.
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Old 04-07-2009, 04:45 PM   #11
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Burned wire behind access panel..


Man, you sure are good at looking stuff up/finding info. Howz about that link again? With that amount of current it works like a fusible link. Not sure how they get UL approval as in the old days electric furnaces had cartridge fuses for EACH separate element. Now you get a cascading effect and lots of burnt wire B4 a main fuse or breaker trips.

Last edited by yuri; 04-07-2009 at 04:49 PM.
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Old 04-07-2009, 05:04 PM   #12
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Burned wire behind access panel..


Between work and having a newborn baby in the house, I'm not going to be able to make it back over to her house today.

I did have an idea though..

I see in the picture that there are 3 breaker switches for what I'm assuming is for 3 heating elements? Could I flip the one breaker off that has the burned wire, and just use the 2 remaining heating elements for the night?
Or is that not how it works?

Had to ask!
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Old 04-07-2009, 05:08 PM   #13
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Burned wire behind access panel..


Depends.

That could be the one that also provides power to the blower.
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Old 04-07-2009, 05:20 PM   #14
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Burned wire behind access panel..


looks like that wire is attached to the limit for that element
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Old 04-07-2009, 05:23 PM   #15
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Burned wire behind access panel..


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Originally Posted by beenthere View Post
Depends.

That could be the one that also provides power to the blower.
been there was a thread over at H-Talk concerning connectors ( spade ect)
And wires.

The unit is thirty years old and the stud and nut might have changed metallurgicaly (broken down and the copper composite and is no longer conductive) would that not constitute a need to change the entire conductor?

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