HVAC Procedure and Performance Guide

TASK: Determine circuit breaker and wiring sizes

Training for this procedure can be found in these courses:

                         131 – Oil Heat l  and  161 – Boilers l


Circuit breaker and wiring must be sized according to job specifications, manufacturer’s specifications and codes.  Wire size and breaker rating must be adequate to carry connected equipment current load.


    1. Review job specifications, manufacturer’s specifications and codes.
    2. Identify equipment that is connected to each circuit.
    3. Determine manufacturer’s nameplate amperage requirements for each piece of equipment on circuit.
    4. Determine circuit voltage.
    5. Select correct size and type of wire and specified circuit breaker using tables in electrical code or other approved publication.
    6. Repeat Steps 3 through 5 to size wire and circuit breakers for remaining circuits.
    7. Document information on job specifications.