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240/120V Single Phase Power

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Split-Phase 240/120V systems are commonly used in North America for residential and light commercial power (up to 144KVA)...

"Most Utility Companies Limit the Maximum
Single Phase 240 Volt Service to 600A"
(240V X 600A = 144kVA or kW @ 1.0PF)
Note that some utilities have a lower limit
of 400 Amps, which is 96kVA

A split-phase (240/120V) power system is a 3-wire, single-phase, mid-point neutral system, which consists of two 120V "voltage sources"; connected out-of-phase by 180 electrical degrees with a neutral connection between them. Note that the lesser known "Two-Phase" system is 90 electrical degrees out of phase and should not be confused with a split phase, (single phase system) or any "Three-Phase" source as these are 120 electrical degrees between coil groups.

The voltage between the two power conductors (L-L) is 240V, therefore the voltage between each live conductor and neutral (L-N) is 120V. Standard 120V lighting and small appliances are connected between a live conductor and the neutral.

Large appliances, such as resistive heating (space heaters), cooking equipment, water pumps, clothes dryers, and window air-conditioners are connected across the two hot conductors (L-L) and operate at 240V, requiring less current and smaller conductors than would be needed if the appliances were designed to operated at 120V. Since the current in each leg of a split-phase system is 180 degrees (out-of-phase), the neutral wire carries only the difference of current between the two lines, or zero current when the load on both legs are equally and or perfectly balanced
(i.e. consuming equal amounts of power).

Example: if 3 ammeters are attached to each power conductor including the neutral conductor and the two meters on the phase conductors read exactly the same amperage... the meter on the neutral will read zero.
If either ammeter attached to the phase conductors read a different value from the other; then the neutral attached ammeter would read the difference between them.

Additional Information

Single phase power systems are generally derived from three phase power systems as in utility power generation where there exists a 3PH generation plant which includes related transmission and distribution system followed by single phase branch circuits with single phase transformers feeding light commercial and residential loads; it is at the single phase pole, pad mount or underground single phase transformer that the split phase system begins.