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Circuit Breaker FAQs:

How do I pick the right circuit breaker and wire size combination?
The National Electric Code specifies the correct combination based on amperage, wire type, and ambient temperature. A secondary resource for selection of US Breaker brands UL489 breakers may be found at the following link:
What is the difference between C&D curve breakers?
The overcurrent protection of both C and D curve breakers is the same. A C curve will trip the breaker instantaneously between 5X and 10X the current rating. This is closer to the settings of a traditional circuit breaker. A D curve breaker will trip between 10X and 14X the current rating and is typically used on high inrush loads.
What is the difference between a circuit breaker bell alarm and an overcurrent trip accessory?
An overcurrent trip switch, most commonly seen outside of the USA, closes a set of contacts in order to send a signal that a breaker has tripped from an overcurrent condition. A bell alarm accessory will signals for overcurrent, but also for any trip reason (Under voltage release, test, etc).
What is an under voltage release/trip accessory?
An under voltage release/ trip allows a breaker to operate normally as long the voltage it is rated for is applied to it. If that voltage is removed or drops below its designed threshold the breaker will trip.
What is a shunt trip accessory?
A shunt trip allows remote tripping of a breaker when voltage is applied to it. Shunt trips come in various voltages to match the signal being applied.
What is an auxiliary switch for a breaker?
An auxiliary switch is a set of contacts that mimic the position of the breaker contacts (open or closed) under normal operation. This allows for remote signaling of the breakers position or the ability to turn on and off other operations based on the breaker being on or off. A N/O (Normally Open) auxiliary opens and closes the same as the breaker. A N/C (normally closed) auxiliary opens and closes in the opposite position of the breaker).
What is the difference between overload and short circuit?
An overload condition occurs when too much current flows through a circuit breaker for a period of time. An example of this would be a breaker tripping after running two hair dryers for a period of time. This is the “Thermal” reference in a thermal-magnetic breaker. A short circuit happens when current paths are connected directly, like a wrench dropping across two breaker terminals. This is referred to as the magnetic pickup, opening the breaker instantaneously when very high current is reached instantaneously. The overload and short circuit functions of a breaker work together and their combined function may be found on a breakers time-current curve.
What is the difference between UL489 and UL1077?
A UL489 rated breaker is certified to protect cable and devices where applicable. A UL1077 certified breaker is designed to protect a specific component and NOT any other part of the branch circuit.

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