melted disconnect--cause?

[AHI in AR]

This is a photo of the disconnect at an air handler taken recently. I was told it was discovered after the HVAC system failed to work properly. I inspected the home this is in two years ago in January of 2014 and this looked fine. I tested the system in heating mode and it performed properly as a heat pump. My only comment was to recommend changing out the basic thermostat for a heat pump type with an emergency heat setting.

Other than someone removing the disconnect and not getting it back in firmly, I can't come up with a plausible explanation as to why this happened. Any of you guys have a better explanation?

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[Marc]

Looks like a non-fusible type of disconnect. The contacts went bad and caused it to overheat. I'd remove power from it until such time that it can be replaced.

Marc

[Jim Baird]

Outside condenser disco on my house was a simple push-pull with plastic handle. Luckily I was home and smelled burning plastic. HVAC man had no clue, other than to say it obviously became loose enough in its little box to arc and burn. He replaced it with something similar.

[Jim Katen]

Looks like an Eaton/Cutler Hammer disconnect.

I see them overheating and distorting pretty regularly, though never as toasted as the one in your picture. Every time I come across that particular design I look at it very carefully for signs of overheating. Once you get in the habit of looking for the early signs of distortion, it's amazing how often you see it. Don't forget to look at the pullout itself. You'll often find small cracks in the plastic.

I'm surprised that no one accused you of screwing it up . . .

[mjr6550]

Typically loose connections at the screw terminal or the blades of the disconnect will do that.

[Jim Baird]

My question is what kind of force might make those little copper blades lose their tight fit in the device.

Jim, I try to keep a no-throw policy for breakers and don't typically operate disconnects, just like I don't operate plumbing cutoffs.

[AHI in AR]

I do pull the blade and spade type disconnects, and I look for problems with loose connections but don't often see them. With a lot of the discos I see here, that has to be done anyway to get the interior cover off to look at the wiring itself. And while I have seen plenty of cases of single wires overheated, I have never seen a case like this with all 4 of them nuked.

The owners are not accusing me of missing anything or causing this, just trying to figure out how it happened. Some nitwit told them that the entire house was pulling over a 300 amp load through a 200 amp service and that caused this problem!

[Jim Katen]

I do pull the blade and spade type disconnects, and I look for problems with loose connections but don't often see them. With a lot of the discos I see here, that has to be done anyway to get the interior cover off to look at the wiring itself. And while I have seen plenty of cases of single wires overheated, I have never seen a case like this with all 4 of them nuked.

The owners are not accusing me of missing anything or causing this, just trying to figure out how it happened. Some nitwit told them that the entire house was pulling over a 300 amp load through a 200 amp service and that caused this problem!

The initial problems are very subtle - a slight distortion in the plastic housing - and are easy to overlook.

You might tell them that the entire disconnect sold for $6.98 and ohm's law occasionally demands retribution for cheap materials. When they replace it, they should consider spending at least $12 for the replacement part.

[Jim Katen]

My question is what kind of force might make those little copper blades lose their tight fit in the device.

I'm convinced that some of these things are loose right out of the package.

Jim, I try to keep a no-throw policy for breakers and don't typically operate disconnects, just like I don't operate plumbing cutoffs.

Certainly a valid position to take. Everyone has to balance the risks of operating this stuff against the benefit received. Sometimes you pull those disconnect blocks and they come out in several pieces.

(I see this particular disconnect so often that I actually carry a spare disco block for it.)

[Rob Amaral]

It's amazing how vulnerable to failure so many elements of an electrical system installation are to failure.. from the utility down to the lowly light-socket...

[Marc]

Yeah. Electrical has failure modes that out-number just about every other system in a house. That's why the book that tells us how to do it is about 800 pages.

Marc

[Erby]

Ran into this yesterday.

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