Power Outlet Contact Failure

Burnt outlet expander
Burnt outlet expander

Ordinary AC power outlets have fairly robust contacts, designed to last basically forever. I have no idea what the actual design life might be, but it’s rare to have an AC outlet fail.

This one did…

It’s an outlet expander at the end of an extension cord that provides six outlets. I’d installed it at my parent’s house (I was their go-to guy for electrical things, of course) and everything was fine. One visit involved rearranging some appliances and the adapter went nova when I plugged something into it.

Me being their go-to electrical guy, I’m pretty sure this gizmo didn’t experience a whole bunch of mate-unmate cycles in my absence. Most likely it was defective from the factory, so sticking a plug in once or twice was enough to break the contact finger.

Detail of burnt socket

Here’s a contrast-enhanced detail of the outlet in the lower-right of the top picture. The broken finger bridged the brass strips carrying the two sides of the AC line in the left side of the compartment.

Blam: brass smoke!

Oddly, the fuse didn’t blow. It was pretty exciting to have a small sun in the palm of my hand until the contact finger fell to the bottom of the compartment.

The bottom picture shows the offending finger. It’s pretty obvious what happened.

Errant contact finger
Errant contact finger

I’ve read of folks applying silicone lubricant (spray, perhaps) to their AC line plugs to reduce the mating friction in the outlet. While that sounds like a good idea, I think it’s misguided: you don’t want to reduce the metal-to-metal contact area by lubing it up with an insulator. In any event, that sliding friction ensures the contacts have a clean mating surface with low resistance.

Maybe use some Caig DeoxIT, but not an insulating spray!

For what it’s worth, do you know that the durability of an ordinary USB connector is 1500 cycles? That’s far more than PCI backplane connectors at 100 cycles. Some exotic high-GHz RF connectors can survive only a few dozen cycles.

Moral of the story: don’t unplug your stuff all the time. Use switches and stay healthy.

This took place many years ago, so the picture quality isn’t up to contemporary standards.

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