Overheatd AC disconnect

[Ron Bishop]

Attached is a pic of an overheated AC disconnect. What would cause that? Should a breaker have tripped before this overheating occured? Can an AC unit be run if the air handler is off at the breaker?

[John Kogel]

My guess as to the cause would be a short circuit, which allowed a lot of current to flow through the switch. Perhaps the disconnect switch itself developed a partial short, where the contacts were just barely touching.

Assuming there is a breaker correctly installed in a panel ahead of this disconnect, the breaker would not trip until the current exceeded its rating of say 30 - 40 amps. It doesn't take much heat to melt plastic.
Just a guess, given the one pic and no other info. :confused:

[Jerry Peck]

A bad connection at either a terminal or the the pull-out could cause overheating like that.

[Jim Luttrall]

240 volts x 50 amps = 12,000 watts with a properly operating 50 fuse or breaker. Imagine 10 space heaters or blow dryers worth of heat concentrated on that plastic. One loose wire inside that disconnect on a properly operating a/c could easily account for that destroyed disconnect.

[Bob Winchester]

This is caused by a loose connection, the terminals not tightened on the wires that are installed. I use a disconnect like that all the time. It is non fused and a simple pull out. There is a solid copper connection between the line and load terminals on each line of the 240 volts. This is rated at 60 amps and it is probably a 30 amp or less condenser unit. Loose wires get very very hot. I've seen them do worse damage than this. This disconnect must now be replaced. Properly connected wires will let a disconnect such as this operate for many years.

[Robert Sole]

This is caused by a loose connection, the terminals not tightened on the wires that are installed. I use a disconnect like that all the time. It is non fused and a simple pull out. There is a solid copper connection between the line and load terminals on each line of the 240 volts. This is rated at 60 amps and it is probably a 30 amp or less condenser unit. Loose wires get very very hot. I've seen them do worse damage than this. This disconnect must now be replaced. Properly connected wires will let a disconnect such as this operate for many years.

I agree with Bob. I had a new geothermal system installed a couple of months ago and about an hour after the system was started, I was connecting the HRU and started smelling something hot. I looked around and finally noticed the disconnect was very hot. When the installed the new system, they never checked to make sure the old connections were tight. I don't know what would have happened if I had not been nearby.

[Mark Cramer]

Attached is a pic of an overheated AC disconnect. What would cause that? Should a breaker have tripped before this overheating occured? Can an AC unit be run if the air handler is off at the breaker?

Loose connection.

[Bob Winchester]

I just replaced a 50 amp GFCI breaker today because one of the terminals was burned off the disconnect and it was tripped of course. The terminals were loose. I'm surprised the other terminal didn't go up in smoke too. I had to strip back the wire about 6" to get to good wire. It's much cheaper to tighten the terminals than to replace $90 breakers. Heat is an enemy of electrical wiring. Make sure everything is tight. If a terminal is discolored it is probably loose as long as the wire size is correct.

[Don Horn]

Could also be simply a loose or poor connection. The melt down looks like heat over a long period of time -- something a bad connection would produce.

[Bob Winchester]

Why does everybody keep posting that it "might" be a loose connection like it was their idea? That is what the cause was. Case closed.

[bob smit]

Bob W., The case isn't closed.....without the dead front removed, we can only guess. Nobody mentioned a ground fault as of yet, neither has the idea of the disconnect being mis-wired from the start been mentioned. Since this is an outdoor installation, a mass overcurrent such as lightning could have found its way to this unit by various paths.

I have also witnessed all kinds of destruction both as an E-contractor and as an Inspector. One size does not fit all in the destruction zone.
We need a look under the sheets.

[Bob Winchester]

That picture is long term heat, not instantaneous heat. The breaker didn't blow so faulting to ground is not the obvious. The terminals on the left side of the disconnect were loose. It's probably still working too. That is what is sad.

[bob smit]

Ron Bishop, can U get more pics of the disconnect with dead front removed? The assumers' are restless.

[ray jackson]

As an A/C technician I see this all the time. That is a cheap disconnect. Usually the wires aren't tight. They could also be aluminum wire without an anti-oxide compound. Or it could be the "knife blade" connector not making good contact.