Suspicious breaker trip on a simple circuit


Old 09-29-01, 12:33 PM
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I had a new 200 amp breaker box installed by professional electricians to make it easier and safer for me to run a couple of additional circuits for a remodeling project. I've ran a 20 amp circuit with only two outlets on it that is devoted solely to provide power to my radial arm saw and other tools as needed. I have a good amount of experience running circuits and checking them, but after using a tool on this circuit the breaker will trip AFTER a period of inactivity the next time I try to start up a tool. It doesn't matter whether it is a small drill or the saw -- so it's not a power draw issue. I can reset the breaker and continue working, but the same thing will happen after a few minutes of inactivity (immediate start-ups do not trip the breaker). The same tools formerly shared a much busier circuit with no such problem. I'm starting to suspect the breaker itself. Ideas? Suggestions?
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Old 09-29-01, 03:20 PM
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Is this a GFI breaker and if so did you connect the white pigtail of the GFI to the neutral bar and the white wire of the circuit to the the grounded lug of the GFI and not the neutral bar then connect your bare to the neutral bar and the hot to the hot lug of the breaker? If you did not wire the grounded leg through the GFI breaker then the GFI will react as you discribe.

Let us know if we hit what you have, we may try another approach.

Old 09-30-01, 07:08 AM
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No, WG, it is not a GFI breaker. Just a standard, square D 20 amp breaker, like several others I've installed for other circuits without any problems.
Old 09-30-01, 11:01 AM
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Heat. I believe your problem is heat at the breaker.

My guess is that the connection to your breaker is not good enough. Perhaps you didn't torque the screw down tightly enough.

Next time the breaker trips, or even before it trips but after using your radial arm saw, feel the breaker with your fingers. Is it warm?
Old 09-30-01, 03:03 PM
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John may be right. Check to make sure that your breaker is plugged in tight and that the spades on the braeker is not abnormally spread allowing a loose connection.

A slight curve to what John said may be the problem. If you have a breaker running hot enough next to that breaker the new breaker may be heated up by an adjascent breker to when the inrush of the motor hits the breaker trips due to already being heated by its neighbor breaker. Worth checking.

The loose connection John is talking of may also be in the circuit between the breaker and the motor load in a j-box or switch etc. also.

Try those ideas and come back in with more info. We will try deeper on the subject.

Old 10-01-01, 07:45 AM
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John, Wg:
We were thinking along the same lines. The breaker WAS slightly askew in the box. I cut power, removed it, checked it for tightness of connections. I've also checked the two outlets of the circuit--they're tight and okay. I don't suspect any switches because the problem occurred with different tools that are in frequent use without difficulty. Then I restored power and ran the saw awhile. I felt the breaker and it didn't feel warm to me. Adjacent breaker is and has remained okay, too. After allowing a 10-minute inactivity period, the same trip occurred when I tried to restart the saw. Visually inspecting the breaker, the contact spades seem okay. I figure I'll replace the breaker with another one and see if the same thing happens. Any other ideas, fellas?
Old 10-01-01, 08:17 AM
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Inrush trip.

Check the label on your radial arm saw. Some few of these are not meant to run on a twenty ampere circuit. A period of operation will warm up the interior of the breaker and alter the operation of the thermal overload portion of the breaker mechanism. The next application of starting current then trips the breaker. The Full Load Ampere rating of the motor should be 16 amperes or less.
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