Circuit Breaker Frame Size Definition

Molded case circuit breakers.

Circuit breaker frame size definition.

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 frame size given for a circuit breaker indicates that it may be used up to a certain current level. 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. You must size conductors to the lowest temperature rating marking on the breaker.

Frame size is expressed in amperes and corresponds to the largest ampere rating available in that group. 225a k frame 600a l frame 1970 motor circuit protector mcp introduced first sensitive low. Several trip units may be available for a particular frame size. Larger circuit breakers can have adjustable trip settings allowing standardized elements to be applied but with a setting intended to improve protection.

Two pole breakers can be either slash or straight voltage rated whereas 3 pole breakers are all straight voltage rated. Into a usable size. Frame the term frame is applied to a group of circuit breakers of similar configuration. This means of mounting allows the unit to be replaced with out re wiring the unit on the line side of the breaker.

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. 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. 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. For all practical purposes conductors for circuit breakers are sized based on the 75 c column of table.