Circuit Breaker Frame Size Definition

The frame size given for a circuit breaker indicates that it may be used up to a certain current level.

Circuit breaker frame size definition.

For all practical purposes conductors for circuit breakers are sized based on the 75 c column of table. Frame size is expressed in amperes and corresponds to the largest ampere rating available in that group. This means of mounting allows the unit to be replaced with out re wiring the unit on the line side of the breaker. 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. Larger circuit breakers can have adjustable trip settings allowing standardized elements to be applied but with a setting intended to improve protection. You must size conductors to the lowest temperature rating marking on the breaker. Several trip units may be available for a particular frame size.

The first compact workable circuit breaker was developed in 1923 when the modified arc extinguisher was coupled. 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. Molded case circuit breakers. A specific assembled breaker may have a lower continuous current rating than the current designation of the frame manufacturers.

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. Two pole breakers can be either slash or straight voltage rated whereas 3 pole breakers are all straight voltage rated. Frame the term frame is applied to a group of circuit breakers of similar configuration. Into a usable size.