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melted disconnect--cause?


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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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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 . . .

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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!

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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.

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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.)

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