National Electrical Installation Standards

Standards as High as Your Own

Tuesday, December 4, 2018


We are installing double throw switches upstream of an existing HVAC Unit. The (2) incoming sources are an existing 100A-3P circuit breaker, and a 110A-3P circuit breaker. Can we install 100A-3P double throw switches, or by code do we need to install 200A double throw switches?

Richard Rapp



Hey Richard thanks for your question. You didn't say what type of HVAC equipment they are. If they include air-conditioning equipment with hermetic motors then the disconnect switches must have an ampere rating of at least 115 % of the larger of the nameplate or branch -circuit selection current as stated in 440.12(A)(1). If the disconnecting means is for a standard motor it must also have an a ampere rating of at least 115 % of the motor full load current rating as stated in 430.110(A). If for fixed electric space heating equipment, the disconnecting means must have an ampere rating of at least 125 % of the total heater and motor load as stated in 424.19.

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