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I have been reading into wiring and circuits and found someone post that they had a circuit breaker tripping because of a loose wire in the circuit. They claimed the hot screw/lug combination increased the resistance in the loop (because it created heat) which is why the breaker was tripping. Now if I understand properly if the resistance is increased, the current is decreased (V=I*R) and this shouldn't trip a breaker.

My understanding of a breaker is that if too much current runs through it, the breaker will trip or blow depending on the type (it will disconnect the circuit either way).

Could someone confirm that what actually happened is this loose connection (somehow) reduced the resistance in the circuit, thus tripping the breaker? If so, does anyone know how it could be reduced at an expected termination point?

He claimed that by tightening the screw it removed the short circuit.

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If the circuit used alternate current, it might happen that a wrong terminal would introduce additional series capacitance or inductance; these could cause the breaker trip if the original load was mostly inductive or capacitive respectively. But it is not probable that the effect of a termination would be sufficient for this.

Instead I conjecture that there was an internal capacitor in the load. After losing its voltage during a short power breakage at the faulty terminal, it would have recharged too fast, causing a transient current surge.

The connection at the wrong terminal could be re-established just from a random mechanical reason, or could even occur due to negative differential resistance of some oxide layer.

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  • $\begingroup$ This is (very often) the cause. Intermittent connections cause inductive and capacitative effects which mean you get horrible current spikes. $\endgroup$ – tfb Dec 22 '16 at 13:50
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I think that your reasoning is correct: A standard circuit breaker should not trip if the resistance of a circuit is increased. However, in recent years there is a new kind of house circuit breaker called an AFCI circuit breaker which may trip if there is a loose or poor connection in a circuit. That may be the type of circuit breaker that they were talking about.

An AFCI circuit breaker is a new, advanced type of circuit breaker which is designed to detect the presence of a dangerous electrical arc in the circuit. Electrical arc faults are a leading cause of electrical wiring fires in houses. An AFCI circuit breaker detects the presence of an electrical arc by using advanced electronics to continuously monitor the current through it and trip itself if it detects a sudden, erratic burst of electrical current, which is a signature of an electrical arc somewhere in the circuit.

If you have a loose screw at a connection point in an electrical circuit and the AFCI breaker is tripping, that essentially means that the AFCI breaker is trying to warn you that connection point is potentially dangerous: The poor connection could result in localized overheating and a fire. Don't know why someone was claiming that tightening the screw "removed the short circuit", though.

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You are correct that as you increase the resistance, current decreases but due to loose contact with the connection, high resistance interrupts the flow of current making it difficult for it to pass through this high resistance so this current find its way to make contact with the connection producing an arcing which we know that arcing produces high heat making the insulation melt and burn. This is due to deterioration of the connection due to vibration or rusting caused by oxidation.

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