Standard Circuit Breaker Sizes Table

Ground wires should be run with all branch circuits.

Standard circuit breaker sizes table. Use page 70 57 9 or tables 4 and 5 if wires are all different size. Ed do not require a fuse rating or circuit breaker setting in excess of 200 percent of full load current. Main circuit breaker 1200 a maximum main circuit breaker 225 a maximum main circuit breaker 600 a maximum main circuit breaker 600 a maximum main fusible switch 1200 a maximum main circuit breaker 1200 a maximum branch circuit breakers 1200 a maximum single two and three pole branch circuit breakers 100 a maximum single two and three pole. A new table was added in article 240.

This is easier to read and just makes sense. In the 2017 nec the paragraph was turned into new table 240 6 a. Mcp breakers for motors 125 or next larger size standard breaker sizes are listed page 70 74 240 6 nec conduit sizing 1. After circuits have been derated to get proper wire size use table 3a if wires are all same size.

Circuit breaker size calculation for continuous non contentious load. With no enclosure where the ambient temperature is held at 40 degrees c approximately 104 degrees f. For a great many code cycles the standard sizes of fuses and fixed trip circuit breakers used throughout the nec were listed in paragraph form in section 240 6 a. In other words the breaker controlling a circuit should be 125 percent of the continuous load maximum current expected to last for three hours or more and 100 percent of the non continuous load.

The original standard in the uk was bs 3871 part 2 1966 which was. As circuit breakers cbs and overcurrent protection devices ocpd are designed for 100 rated current i e. Table 41b2 of the wiring regulations gives the same maximum loop impedances. Of the installation will determine which type of circuit breaker should be used.

Note that the branch circuit extends from the last branch circuit overcurrent device to the load. A 30a circuit breaker can safely carry the exact 30a current but nec suggests 80 as a safe current limit as compared to the rated current of cbs. 80 of breaker max single phase breaker size wire size based on copper thhn wire increase one size when using aluminum conductors at 115 volts at 230 volts 15 amp 14 1 380 2 760 20 amp 12 1 840 3 680 30 amp 10 seldom used on 115 voltage 5 520 40 amp 8 seldom used on 115 voltage 7 360 50 amp 6 seldom used on 115 voltage 9 200 60. The size of a circuit breaker is the maximum current that can pass through the breaker without tripping the circuit and causing a loss of power.

These conditions per ul 489 underwriters laboratories standard for safety for molded case circuit breakers and circuit breaker enclosures include mounting the cb in free air i e.