National Electrical Installation Standards

Standards as High as Your Own

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Tuesday, December 4, 2018

Question:

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

A

Answer:

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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