Hvac Circuit Breaker Sizing

The air conditioner specification plate calls for maximum breaker size of 20 amp.

Hvac circuit breaker sizing.

As circuit breakers cbs and overcurrent protection devices ocpd are designed for 100 rated current i e. The over current device fuse or circuit breaker must be sized for the ampacity of the service drop and available fault current. The circuit breaker also needs to be large enough to support the minimum circuit ampacity which for this example would be a circuit breaker rated for at least 34 amps which means we d jump up to. Observed that the circuit breaker for ac unit is over sized 50 amp.

Breaker size based on wattage the size of a breaker is determined by the amp draw. If you see a plug with two diagonal prongs and one straight prong under it assume 240 v of power requirement. Notice that the mca is 28 6 amps and the maximum fuse or circuit breaker is 50 amps. 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 amp 6 seldom used on 115.

Take a look at the lennox air conditioning condensing unit tag on page 19. 210 22 c 220 3 a 220 10 b and 384 16 c all relate to the sizing rules for overcurrent protective devices ocpds. However typically electric furnaces require a draw between 60 and 80 amps. Difference between circuit breaker and isolator disconnector circuit breaker size calculation for continuous non contentious load.

This means it is allowable to install this unit on a circuit breaker rated at 50 amps and a conductor rated at 28 6 amps according to the nec s nfpa 70. The first three all specify the same requirement. An over sized circuit breaker could result in damage to ac unit and or electrical wiring. If you see a normal household plug on it with three straight prongs assume 120 v of power requirement.

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. If you don t see a voltage requirement check the plug on the air conditioner. Ocpd size 100 of noncontinuous load 125 of continuous load. By multiplying the volts by amps you will receive total wattage.

The service drop conductors must be sized from table 310 17.