Electrical Phase

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The vast majority of residential homes have single-phase electrical service. Many commercial and industrial buildings have triple- phase electrical service (usually in addition to single-phase service).

If you are purchasing a furnace or central air conditioner for your home, you will want to buy a single-phase unit: Installing triple-phase electrical service in your house can be expensive, and since residential furnaces and air conditioners tend to be single-phase, there is little incentive to upgrade.