300F electrical connection in Furnace Air Handler

[gba2331]

Our thermostat started behaving erratically so I got a replacement & installed it but it was providing heat when it should have been cooling. No worries, this t-stat probably has slightly different wiring, so I opened the air-handler to verify the connections there. That's when I saw this:



If you can't tell, the electrical tape on the right is "crispy". I could feel the heat coming off it, so I pulled out the infrared thermometer. The connection on the left was 85F while the right was 300F!

The unit was serviced in the spring and the tech noticed that the electrical tape had melted a bit then, so they rewrapped it but I guess we should have dug deeper. I'm not sure why a mechanical joint develops so much resistance, but we'll find out today when they come to examine it (since they should've caught this earlier, I figured I'd let them take a first crack at it....with "supervision" this time...).

 

[gba2331]

This also seems like a sketchy way to connect (and then protect) the incoming power to the internal wiring, but I don't have any experience here...

 

[mike93lx]

Bolted connections are OK, but what's going on with the sizing there? Is that two #8's to a #2?

 

[gba2331]

Good question, I have no idea. There are no markings on any of the wires but the breaker is 110A and there are fuses inside the handler.

 

[gba2331]

The crispy connection looks even worse on the back side, I guess the corrosion has spread inside the joint.

 

[mike93lx]

No markings at all? That's odd.

I think I'd cut back that heavy gage wire a bit, replace the smaller ones with new and install with Polaris connectors, properly torqued

 

[fitter30]

Use uninsulated crimping lugs and cover with fiberglass sleeve. Sleeve comes in rolls.

 

[gba2331]

Thanks for the advice, I'll talk with the tech about this. IMO, the wrapped free-floating bolt connections seem very sketchy....

 

[gba2331]

No markings at all? That's odd.

I think I'd cut back that heavy gage wire a bit, replace the smaller ones with new and install with Polaris connectors, properly torqued

@mike93lx Sorry, I should have looked at the wire coming into the unit, it says "2 CDRS AWG 1/0-1 CDR AWG 2 AL", so I'm assuming that means 2 gauge Aluminum. Here's a picture:

 

[gba2331]

The tech came & basically said I need a new wiring clamp, but otherwise didn't give me much useful info or reassurance about why it happened, so I think I'll be doing this on my own using the recommendations provided here.

 

[gba2331]

This seems appropriate?

POLARIS Insulated Multitap Connector: Gray, 3 Ports, 10 AWG – 2 AWG Wire Size Range, Plastisol​

https://www.grainger.com/product/POLARIS-Insulated-Multitap-Connector-786F12

 

[whateg01]

It happened because it wasn't tight and oxidation occurred. From there it snowballs, getting hot, causing further oxidation, etc. Depending on the damage to the wire itself the tech might find the wire itself needs to be replaced now.

 

[mike93lx]

This seems appropriate?

POLARIS Insulated Multitap Connector: Gray, 3 Ports, 10 AWG – 2 AWG Wire Size Range, Plastisol​

https://www.grainger.com/product/POLARIS-Insulated-Multitap-Connector-786F12

Yeah, that would work. Cut back to fresh wire on both

 

[gba2331]

Here is the removed wire clamp - it seems hard to believe that a new clamp would corrode this much in 3 years? I haven't unwrapped the other one yet to see what it looks like.

 

[mike93lx]

When you get it back together, I'd throw a clamp meter on both legs and make sure it's not out of balance also check voltage and follow the connections all the way back to the panel

 

[whateg01]

.... Cut back to fresh wire on both

^^^ That's important!

 

[gba2331]

It happened because it wasn't tight and oxidation occurred. From there it snowballs, getting hot, causing further oxidation, etc. Depending on the damage to the wire itself the tech might find the wire itself needs to be replaced now.

Thanks. This seems like something they should be covering since we detected the problem in May (but didn't diagnose properly)...but they're not. At this point, its simpler and more reliable to DIY.

 

[gba2331]

When you get it back together, I'd throw a clamp meter on both legs and make sure it's not out of balance also check voltage and follow the connections all the way back to the panel

I did measure both legs before discovering the issue and both were drawing equally at 80A - which seems high to me, but I don't have any experience here.

 

[BrandonV]

Here is the removed wire clamp - it seems hard to believe that a new clamp would corrode this much in 3 years? I haven't unwrapped the other one yet to see what it looks like.

What is the model number of that clamp? Is it a Penn-Union?

 

[joel63]

Thanks for the advice, I'll talk with the tech about this. IMO, the wrapped free-floating bolt connections seem very sketchy....

No doubt about it, it definitely is.
Why in the hell do people do this kind of work????

 

[whateg01]

No doubt about it, it definitely is.
Why in the hell do people do this kind of work????

In my thread about wiring up a kiln, it appeared that this is perfectly legit when done right. I thought the same thing.

 

[gba2331]

I can't tell, I don't see any markings. My guess is that this is the original clamp from the previous (or previous-previous) system. The tech seemed to indicate that he would get a new replacement & didn't know about the Polaris type of plug, or even check the wire size before he left. Sigh...I thought this company was one of the better ones...

 

[BrandonV]

I can't tell, I don't see any markings. My guess is that this is the original clamp from the previous (or previous-previous) system.

I would suspect it is not rated for an Al conductor. The Al rated clamps use a special copper alloy (or are aluminum) and recommend the use of an oxide inhibiting compound to be applied with aluminum wiring.

Was the Al conductors new when the system was installed (replacing copper wire?).

 

[gba2331]

Was the Al conductors new when the system was installed (replacing copper wire?).

I have no idea, but I doubt it. The routing of the AL conductors doesn't look new to me.

 

[gba2331]

To make things more interesting, the tech was able to pull out one of the four copper wires that runs to the internal fuses and another has scortch marks on it, maybe because the corroded wire clamp was making sporadic contact.

 

[BrandonV]

To make things more interesting, the tech was able to pull out one of the four copper wires that runs to the internal fuses and another has scortch marks on it, maybe because the corroded wire clamp was making sporadic contact.

The fact there are NO markings on the clamp is very odd. Sounds VERY old.

 

[BrandonV]

Thinking about it more... it sounds like the clamp is not rated for the application... no markings... and certainly no oxide inhibiting compound was applied I'm guessing either.

The dissimilar conductors were separated via the spacer right?

Example of what a rated clamp would look like.

https://hubbellcdn.com/specsheet/BURNDY_KSU31_Specsheet.pdf

 

[rmanrman]

That connector is probably not rated for mixed aluminum and copper wires. Also whenever there is aluminum wiring there is a special paste that is applied to all conductors in the splice. Cut back to clean unchared wire and do new splices with approved connector for aluminum/copper wires. Also at 80Amps that must be an electric furnace. Your electrical bill will be very high.

 

[gba2331]

Also at 80Amps that must be an electric furnace. Your electrical bill will be very high.

Its a heat pump but that may have been with the emergency heat kicking in, I dialed it up a good bit to get the system to engage.

Also whenever there is aluminum wiring there is a special paste that is applied to all conductors in the splice.

The tech mentioned Noalox and I bought some with the Polaris connectors, makes sense. I can't tell if there was any applied to the conductor.

 

[mm08822]

@mike93lx Sorry, I should have looked at the wire coming into the unit, it says "2 CDRS AWG 1/0-1 CDR AWG 2 AL", so I'm assuming that means 2 gauge Aluminum. Here's a picture:

That is 1/0, 1/0, and #2 Aluminum conductors.

What is the ambient temperature where the splices are and fuse block?

 

[gba2331]

After some wire brushing, I found the markings.

 

[mm08822]

Here is the removed wire clamp - it seems hard to believe that a new clamp would corrode this much in 3 years? I haven't unwrapped the other one yet to see what it looks like.

Looks overheated for sure. Clean up the area where the index finger is and take a pic of that printing so it is legible.

 

[gba2331]

What is the ambient temperature where the splices are and fuse block?

This is inside the air handler for the HVAC unit (4 ton residential), so room temperature basically.

That is 1/0, 1/0, and #2 Aluminum conductors.

So does this mean that the #2 conductor is the unshielded aluminum in this pic? I'm just surprised that it isn't the same amperage as the other 2 wires.

 

[gba2331]

Looks overheated for sure. Clean up the area where the index finger is and take a pic of that printing so it is legible.

 

[mm08822]

Looks like it is rated for alum......and 90C wiring.

 

[mm08822]

This is inside the air handler for the HVAC unit (4 ton residential), so room temperature basically.


So does this mean that the #2 conductor is the unshielded aluminum in this pic? I'm just surprised that it isn't the same amperage as the other 2 wires.

Yes, the #2 is the manually wound strands. That's a typical cable construction.

 

[gba2331]

Looks like it is rated for alum......

It seems like it is actually made from aluminum...

 

[gba2331]

I don't suppose there is a way to cut 1/0 AL wire with anything other than a $100-200 cable cutter?

 

[mm08822]

It probably was not tight enough when assembled. If so, the entire mass becomes a heat generator. They can get cherry red if bad enough.

Upon repair, I would not splice 3 conductors together. Instead splice onto the end of the 1/0 and into the center of the other conductor used to feed the 2 poles on the fuse block.....it's one less splice and the amount of material to compress in the split bolt connect is less.

 

[mike93lx]

I don't suppose there is a way to cut 1/0 AL wire with anything other than a $100-200 cable cutter?

Sawzall, hacksaw, utility knife and peck away at it with flush cutters