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Circuit Breaker Protection

Most WINCO and WINPOWER generator comes standard with UL approved main line circuit breakers. A circuit breaker is designed to interrupt current when specific types of unsafe conditions occur. It is important to understand how circuit breakers operate so that realistic expectations for protection are maintained. This page will give general information on how circuit breakers work and what their purpose is in a generator system. Nothing in this article substitutes for competent advice from licensed electricians, electrical engineers or other competent professionals.

Purpose of Circuit Breaker

The circuit breaker on a generator system serves two main purposes. The first is to protect the users of the generator from unsafe conditions that are fire or electrocution hazards. The second purpose is to protect the generator from damage that occurs during short circuit or overload conditions.

How Do Circuit Breakers Work

There are several designs of circuit breakers that are designed to protect against dangerous electrical conditions. The mechanism that trips the breaker will determine the speed and accuracy of the over-current protection. The list of tripping mechanisms is not intended to be all inclusive.

Thermal:  Breakers of this design use heat to trigger the power interruption. As current passes through any circuit heat is generated. The more current that passes through the more heat. Thermal breakers are designed to trip at certain temperatures associated with overload. Thermal breakers are reliable for normal use. The main weakness of thermal breakers is that the heat takes time to build up and it can be affected by ambient temperatures. A breaker will take longer to trip on a cold day and it is possible it will trip prematurely in extremely warm condition. A thermal breaker will not trip as quickly as other mechanisms in short-circuit conditions.

Thermal Magnetic: The thermal component of this breaker design works identically to a standard thermal breaker. Heat builds up over time and will cause the breaker to reach the trip point. In order to accelerate the breaker's response in a short-circuit condition a magnetic component is added. All current passing through the breaker passes through a coil that magnetizes. As the current increases the strength of the magnet increases until the breaker trips.  Square D main line circuit breakers can interrupt current at a blazing 1/60th second time with a short circuit. The magnetic component of the breaker will not trip unless under severe overload conditions.

Hydraulic Magnetic: The main weakness of thermal breakers is that they are affected by ambient temperatures and take time to heat up under an overload. Hydraulic breakers are designed to be unaffected by ambient temperatures eliminating the heat up time to trip and the need for the breaker to cool before being reset. The magnetic component of these breakers are designed to handle sever overloads quickly in a similar fashion to the thermal magnetic breaker designs. WINCO uses this design of breaker in all of our two pole GFCI breakers.

Ground Fault Circuit Interrupter (GFCI): GFCI devices are designed to detect ground faults and interrupt the circuit to protect the user from electrocution. The device monitors the difference between the current on the line and neutral side. If the current exceed and acceptable range the device will interrupt the circuit. WINCO uses GFCI devices that are built into both receptacles and circuit breakers depending upon the application. All WINCO GFCI devices interrupt within NEC and OSHA ranges.

What is the difference between an 80% rated and 100% rated breaker?

The percentage rating indicates the amount of the name plate current rating the circuit breaker can handle under a continuous load. A continuous load is described by the NEC to be three or more hours. Most standard circuit breakers are rated at 80%. A standard 100 amp 80% circuit breaker is rated to carry a continues load (greater than three hours) of 80 amps. The breaker is suitable for loads up to 100 amps as long as the load does not remain above 80 amps for periods of more than three hours.

If the desired continuous load for a circuit is 100 amps the following two methods are acceptable alternatives to appropriately size the breaker.

Option 1: If you decide to use an 80% rated breaker for a continuous load it must be oversized. The requirement is 125% or the estimated continuous load. An 80% rated breaker at 125 amps would be required in this application.

Option 2: If you upgrade the breaker to a 100% rated device a 100 amp breaker would be suitable. It is important to note that in order to be rated at 100% the other components in the system with the breaker must be appropriately sized per the NEC. If the whole system is not 100% rated the breaker reverts to 80%. An appropriate professional should be consulted for these applications.

WINCO and WINPOWER by default use 80% rated breakers in our generators which helps keep the thermal overload trip times within acceptable ranges. If your application requires a 100% rated breaker you should notify your sales representative before ordering.