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Old 11-05-2008, 11:34 AM   #1
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This wasn't too safe...


When I pulled out the fridge yesterday to replace one of those outlets we were discussing, I unpluged my microwave, and found a suprise.

I guess it was from arching due to the old outlet now grabing the plug well?
Jamie

This wasn't too safe...-img_4444.jpg

This wasn't too safe...-img_4445.jpg

This wasn't too safe...-img_4446.jpg

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Old 11-05-2008, 11:43 AM   #2
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This wasn't too safe...


That stuff happens. I have seen a lot of it over the years.

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Old 11-05-2008, 01:49 PM   #3
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This wasn't too safe...


It looks like the screws are ok, its the outlet. Id get a good Pass & Seymour or Levition receptacle. They seem to hold well.

I had some cheapo receptacles getting hot, they were about 15 years old. Replaced them all, and changed the circuit to a multiwire one because of heavy loads. I already had a red wire present.
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Old 11-05-2008, 01:53 PM   #4
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Originally Posted by rgsgww View Post
It looks like the screws are ok, its the outlet. Id get a good Pass & Seymour or Levition receptacle. They seem to hold well.
.
I like Leviton.

And NEVER use those push in taps in the back. They can arc and cause the same thing you saw in your receptacle. I always use the screws on the side to get more surface area for the electricity to pass.
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Old 11-05-2008, 03:25 PM   #5
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I like Leviton.

And NEVER use those push in taps in the back. They can arc and cause the same thing you saw in your receptacle. I always use the screws on the side to get more surface area for the electricity to pass.
I always use the screws.

Levition has a great variety of receptacles, noise surpression, surge surpression, etc. I couldn't find a 20 amp surge suppressor for my computer, but I found a levition surge surpressing outlet. It has an led for staus and an alarm that will sound when damaged. They make great products.
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Old 11-05-2008, 03:48 PM   #6
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This wasn't too safe...


i LIKE the stab in the back ones, IF they're the screw-lock kind, not 'spring-grip'.

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Old 11-05-2008, 03:59 PM   #7
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This wasn't too safe...


Quote:
Originally Posted by jamiedolan View Post
When I pulled out the fridge yesterday to replace one of those outlets we were discussing, I unpluged my microwave, and found a suprise.

I guess it was from arching due to the old outlet now grabing the plug well?
Jamie

Attachment 5769

Attachment 5770

Attachment 5771
So, the plug was easy to pull out?

The spring contacts lose their force over the years, and this causes high contact resistance, and so some of the current that is supposed to go into the microwave goes into heating the contact interface.
Maybe 10w dissipated in the contacts is enough to do this kind of damage.
And the hotter it gets, the more quickly the contacts lose their force.

Motor loads can be damaged by this high, upstream impedance, because then the more current they demand to meet the load, the less is available.
Low current draw appliances don't pull enough current to heat even bad connections, but microwaves pull quite a bit of amps.

The pass/fail for relay contacts is less than 30 mV voltage drop across the contacts at rated contact current or less, and more than 100 mV at rated contact current or less is definitely bad.
I guess the same standard can be applied to this type of connector.

BTW, a furnace blower relay was just at the 100 mV mark, and the flaky furnace problems cleared up after I replaced the relay, but I don't recall if there was localized melting/charring/scorching around the contacts.

There is also some kind of conductive goop that rejuvenates worn contacts; dunno' who makes it. Car dealers may use it to avoid having to replace worn automotive relays.
Whatever gets you out of their service bay!

A good example of too-high contact impedance is dirty car battery contacts. The resistance is sometimes not so high that the headlights (~6A) don't work but when you try to crank the engine the 250A load is too much and everything goes out. And sometimes you can hear a frying noise and the terminals are hot.

Last edited by Yoyizit; 11-05-2008 at 04:30 PM.
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Old 11-05-2008, 10:32 PM   #8
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This wasn't too safe...


A new outlet won't prevent the problem from happening again IF there is a loose or marginal connection within that molded plug.

Since it is obviously burned to a crisp, I'd suggest replacing the plug on the end of that cord as well, or replace the entire cord assembly.

Otherwise, you may find that new wall outlet burned up in short order.
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Old 11-06-2008, 11:14 AM   #9
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This wasn't too safe...


Yep, You need to replace the cord, plug and receptacle. Make sure all connections are secure. You can get a new plug for the cord. Cutting off the old plug and replacing it will remove the UL listing for the microwave. The pictures you show are a great learning tool for anyone doing electrical work. Your situation was a fire in the making.
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Old 11-06-2008, 12:50 PM   #10
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This wasn't too safe...


Here's how hot
it might have got

http://www.tcforensic.com.au/docs/article10.html

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