Sometimes a #12 Wire can go on a 40A Breaker

In this episode of the podcast, we talk about condenser wire sizing considerations, ampacity, temperature, conductor sizing, voltage drop, and why a #10 wire doesn't always require a 30-amp breaker.

There's usually nothing wrong with OVERSIZING a wire or conductor. However, you still need to know which wires are safe for operation and comply with the National Electrical Code (NEC) protocols.

Relatively small conductors can carry relatively high voltages. Instead, amperage dictates the size of the wire. Therefore, we use ampacity (amp capacity) to determine the size of a wire. Transformers are a perfect example; wires going into the transformer are small, and wires leading out of the transformer are larger. You also size circuit breakers, fuses, or overcurrent protectors to protect the conductor.

The wire type that goes into a breaker depends on several variables. Some of these variables that affect ampacity include wire material, insulation rating, ambient temperature, and how many other conductors are in the same metal area. Thus, rules of thumb for wire sizing are not reliable. If the ambient temperature exceeds a wire's rating, you can derate a wire by using a multiplier; use the values in Table 310.15(B)2(a).

A major concern for wire sizing is the probability of a short circuit. The term "short circuit" is often misused to describe ANY sort of electrical failure, but that is not the case at all. "Overcurrent" or "ground fault" is a more precise term for excessive amperage. Overload conditions indicate that the load is too large, so high amperage is drawn. Compressors draw the highest amperage out of all HVAC system components.

Overall, size your conductor by minimum circuit ampacity and your breaker based on maximum overcurrent protector

 

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