breaker keeps tripping

I have a 40 amp breaker on my main service panel which feeds a pony box in the attic of my house. Two recepticles that are used for a
window air conditioner are tripping the 40 amp breaker at the main panel. Other recepticles in the attic do not trip the breaker. All of the 10 amp breakers in the pony box do not trip. Why is the 40 amp breaker tripping before the 10 amp breaker in the pony box, and why with just two recepticles in the room?
Thanks
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It happens that snipped-for-privacy@sympatico.ca formulated :

There are a few possible causes. 1. Is there another load on the circuit that you may not be aware of? 2.Is the circuit actually protected by the 10 Anp C/B? Is it possible the wiring is incorrect? 3. Is the 10 Amp C/B defective? 4. Is the 40 Amp C/B Defective?
You need to test the continuity from the outlet to the 10amp C/B and measure the load at each C/B.
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I know there is no other load, the circuit is protected and both the 10 and 40 amp c/b do have continuity. The red going to the 40 amp c/b is the culprit. It seems to be showing signs of being hot
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On Jul 13, 1:16 pm, snipped-for-privacy@sympatico.ca wrote:

Is it possible that the problem could be some corrosion or discolouration on the lead edge of the red wire entering the 40 amp breaker?
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formulated :

Is it possible that the problem could be some corrosion or discolouration on the lead edge of the red wire entering the 40 amp breaker?
Seems very likely to me that heating from a poor connection is causing the breaker to trip. Cleaning the wire and breaker connection and proper tightening might be all you need but the breaker may have to be replaced.
Don Young
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snipped-for-privacy@sympatico.ca expressed precisely :

As someone else has posted, yes a high resistance connection on the breaker can cause it to trip. Breakers are cheap and I believe in being safe than sorry...I would replace it. It would be worthwhile to test the insulation resistance for the circuit too. Does the insulation look like it's been hot? I doubt there would be any damage to the cable because the C/B should have protected it. But in the very unlikely event it has been overheated, you will want to consider replacing the cable.
Good Luck! :-)
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