Circuit Breaker Frame Size Definition

For all practical purposes conductors for circuit breakers are sized based on the 75 c column of table. The frame size given for a circuit breaker indicates that it may be used up to a certain current level. Frame the term frame is applied to a group of circuit breakers of similar configuration.

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This means of mounting allows the unit to be replaced with out re wiring the unit on the line side of the breaker.

Circuit breaker frame size definition.

Molded case circuit breakers. Frame size is expressed in amperes and corresponds to the largest ampere rating available in that group. Larger circuit breakers can have adjustable trip settings allowing standardized elements to be applied but with a setting intended to improve protection. Per nec 240 80 d a circuit breaker which is used as a switch in an hid lighting circuit must be marked as swd or hid.

Two pole breakers can be either slash or straight voltage rated whereas 3 pole breakers are all straight voltage rated. Several trip units may be available for a particular frame size. A removable circuit breaker has two parts a base which is bolted to and wired to the frame and the actual breaker which has insulated parts that electrically mate with the base. Circuit breaker size amps transformer nameplate kva x 1 3 the result of the calculation of part 1 sets the minimum acceptable circuit breaker frame size based on average current considerations.

Into a usable size. You must size conductors to the lowest temperature rating marking on the breaker. 225a k frame 600a l frame 1970 motor circuit protector mcp introduced first sensitive low. A circuit breaker listed as an 800 frame means the manufacturer will use that body to house parts that allow the circuit breaker to be rate for currents say between 250 amps up to 800 amps.

Arc chutes extinguishers and quenchers define the interrupting current capacity of the assembly in conjunction with the insulating and heat. A specific assembled breaker may have a lower continuous current rating than the current designation of the frame manufacturers. For example a circuit breaker with a 400 ampere frame size might have its overcurrent detection set to operate at only 300 amperes to protect a feeder cable. The first compact workable circuit breaker was developed in 1923 when the modified arc extinguisher was coupled.