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Dedicated 240V for central AC

Mike Lamb

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Interesting question. 

The air conditioner installation instructions that I looked at did not specify dedicated circuits or individual circuits. 

The NEC doesn't specifically say that the AC needs to be on an individual circuit and, in fact, specifically allows the AC and the heating equipment to share a circuit. 422.12 (This assumes that they won't both be operating at the same time.) 

440.34 allows air conditioners to share conductors with "other loads," but it doesn't say how you handle the overcurrent protection. That's the sticking point. If you provide the "maximum" breaker, then there's really no room left for any significant additional load. 

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The NEC doesn't offer any calculations to modify the manufacturer's engineered breaker size/fuse size/conductor size values on his multi-motor equipment so that additional loads can be served by the same circuit.  That should make it obvious that such circuit modifications in the field aren't allowed.

Edited by Marc
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