Circuit breaker not tripping


Old 09-10-05, 07:40 AM
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Circuit breaker not tripping

This is really a basic question, two years ago, after moving into our home (built in 1956, wiring seem to be original {was, much has since been replaced} we were running an older large microwave oven and some other applicances on one circuit. Inside a metal junction box in the basement (which at the time was uncovered) a splice on this line began to glow red hot. My question is, as dumb as it may be, why didnt this over load trip the breaker? This has worried me.
Since then, I have fed three separate lines into the kitchen and changed out that that breaker, oh and i re-spliced that connection. I keep that box open (it is high and out of the way) so i can check it constantly.
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Old 09-10-05, 08:31 AM
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One result of a defective connection is to "insert" electrical resistance , measured in Ohms, in the circuit. When current

is conducted thru a resistance, there is an energy produced in the from of heat. The "power" is calculated by the formula
P = I X I X R, with I = current in amps, and R = resistance in Ohms.

If I = 10 and R = 5 Ohms ( a low-resistance value ), the heat-producing power = 10 X 10 X 5 = 500 watts. The heat from an electric toaster is a 1200 watt power-consumption.

The 10 amp value will not trip the breaker, but will cause a "hot-spot" at the defective connection.
Old 09-11-05, 10:22 PM
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You could also have a trouble some panel, such as an FPE.
Old 09-11-05, 11:42 PM
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I agree with classicsat...Do you have a Federal Pacific panel? Those are notorious for not tripping, and fires have resulted. If you Google Federal Pacific, you will find all sorts of stories.
Another possibility--Do you have aluminum wiring? That's another can of worms...
Old 09-12-05, 05:09 AM
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Although I do agree with all, FPE panels will usually trip on overload, they are notorious for not tripping on a short.
I will have to go with simply a bad connection. I doubt it is AL wire; original 1956.
I have seen this MANY times in commercial settings, even with the commercial standard QO breakers.
Pat's explanation is great. The resistance is shown as heat in the splice, not amperage on the circuit.
Old 09-12-05, 07:34 AM
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This is also a good illustration of one reason why splices must be in approved junction boxes. If that splice had been buried in the wall somewhere, there's a good chance a fire may have occured. The junction box limited the damage to some charred wires, maybe a melted wire nut, and a bad smell.

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