Standard Circuit Breaker Sizes Table

Note that the branch circuit extends from the last branch circuit overcurrent device to the load.

Standard circuit breaker sizes table.

A new table was added in article 240. Ground wires should be run with all branch circuits. 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. After circuits have been derated to get proper wire size use table 3a if wires are all same size.

Of the installation will determine which type of circuit breaker should be used. This is easier to read and just makes sense. 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. In physical size with circuit breakers and capable of being installed in the same.

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. Table 41b2 of the wiring regulations gives the same maximum loop impedances. 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. 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.

Ed do not require a fuse rating or circuit breaker setting in excess of 200 percent of full load current. The original standard in the uk was bs 3871 part 2 1966 which was. With no enclosure where the ambient temperature is held at 40 degrees c approximately 104 degrees f. In the 2017 nec the paragraph was turned into new table 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. Use page 70 57 9 or tables 4 and 5 if wires are all different size. Mar 4 2018 circuit breaker and cable size chart electrical engineering blog. 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.

Mcp breakers for motors 125 or next larger size standard breaker sizes are listed page 70 74 240 6 nec conduit sizing 1.