Split phase is a method of delivering electricity to homes by taking a single 240-volt power supply and splitting it into two 120-volt lines using a center-tapped transformer. This is the standard residential electrical system throughout North America. It gives you 120 volts for everyday outlets and 240 volts for heavy-duty appliances, all from one service connection.
How Split Phase Works
A transformer on the utility pole (or a pad-mount transformer on the ground) receives high-voltage power from the grid and steps it down. The secondary winding of this transformer has a wire connected to its exact center point, called the center tap. This center tap becomes your neutral wire. The two ends of the winding become your two “hot” wires, commonly labeled L1 and L2.
Because L1 and L2 come from opposite ends of the same winding, their voltages rise and fall in mirror image of each other. When L1 is at its positive peak, L2 is at its negative peak. Electrically, they are 180 degrees out of phase with each other relative to the neutral. This phase relationship is the key to the whole system.
Where the Voltages Come From
Each hot wire measures 120 volts when compared to the neutral. That’s what powers your standard wall outlets, lighting, and small appliances. But because L1 and L2 are opposite in polarity at any given instant, measuring from L1 directly to L2 gives you 240 volts. The two 120-volt halves add together rather than canceling out.
So from a single transformer, your home gets access to two voltage levels. The line-to-neutral voltage is always half the line-to-line voltage. Your breaker panel is wired so that standard 15- and 20-amp circuits tap one hot leg and the neutral for 120 volts, while dedicated 240-volt circuits connect across both hot legs.
What the Neutral Wire Actually Does
The neutral wire serves as the return path for 120-volt circuits. When you plug in a lamp on L1 and a toaster on L2, current from each flows back through the shared neutral. Here’s the clever part: because the two hot legs are 180 degrees out of phase, the currents flowing through the neutral partially cancel each other out. The neutral only carries the difference in current between the two legs.
If both legs are drawing exactly 10 amps, the neutral carries zero amps. If L1 draws 10 amps and L2 draws 6 amps, the neutral carries just 4 amps. This means the neutral wire can be smaller than it would need to be if it had to handle the full load from both legs independently. For 240-volt circuits like an electric dryer, current travels from one hot leg through the appliance and back on the other hot leg. The neutral isn’t involved in carrying that load at all.
Appliances That Use 240 Volts
The 240-volt capability of a split-phase system exists because certain appliances draw too much power to run efficiently at 120 volts. At higher voltage, an appliance can do the same work while drawing less current, which means smaller wires and less heat buildup. The major 240-volt loads in a typical home include:
- Electric dryers: 2,400 to 6,000 watts
- Electric ranges, cooktops, and ovens: 3,000 to 12,000+ watts
- Electric water heaters: 3,000 to 4,500 watts
- Central air conditioning compressors: 2,000 to 6,000+ watts
- Level 2 EV chargers: 3,300 to 11,500 watts
- Hot tubs and pool pumps: 500 to 3,000 watts
- Large workshop tools: table saws, welders, and big air compressors
Each of these gets a dedicated circuit with its own breaker sized to match the load.
Why It’s Called “Single Phase,” Not “Two Phase”
This is a common point of confusion. Split phase delivers what looks like two separate voltages, so many people assume it qualifies as two-phase power. It doesn’t. A true two-phase system, which is now obsolete, used two windings separated by 90 electrical degrees. That 90-degree separation could create a rotating magnetic field capable of starting an induction motor on its own. Split phase, with its 180-degree relationship, cannot do this.
The technical reason comes down to what the system can produce. In a genuine polyphase system (two-phase at 90 degrees or three-phase at 120 degrees), you can combine the phases to create a smoothly rotating electrical field. Split phase can’t. The power waveforms from both legs peak at the same time, dropping to zero twice per cycle, just like any single-phase source. So engineers classify it as a single-phase, three-wire system. The term “split phase” simply describes how that single phase is divided at the transformer to provide two voltage levels.
Why Load Balancing Matters
Your breaker panel alternates connections between L1 and L2 as you go down the rows of breakers. When an electrician installs or modifies your panel, they aim to distribute the electrical load roughly evenly between the two legs. Large consumers like your dryer and oven should ideally land on opposite legs so one side isn’t doing all the heavy lifting while the other sits mostly idle.
When loads are unbalanced, the overburdened leg draws more current, which generates more heat in the wiring and can shorten the lifespan of appliances on that side. The neutral wire also ends up carrying more current than necessary, since it has to handle a larger difference between the two legs. Balanced loads keep neutral current low, reduce wasted energy, and help everything in the panel run cooler. If you notice breakers tripping on one side of the panel while the other side never trips, unbalanced loading could be the issue, and an electrician can redistribute circuits to even things out.
Split Phase Outside North America
Split-phase 120/240V power is primarily a North American standard. Most of Europe and large parts of Asia use a straight 230-volt single-phase supply for residential buildings. There’s no center tap and no split. Homes get one hot wire at 230 volts and a neutral, which is enough to power heavy appliances without needing a second voltage level.
That said, the center-tap concept does appear in other contexts. In the United Kingdom, construction sites use a center-tapped 110-volt supply (55-0-55) for power tools and portable lighting. This keeps the maximum voltage to ground at just 55 volts, significantly reducing the risk of electric shock in wet or hazardous conditions. Large agricultural operations in some countries also receive center-tapped supplies at higher voltages, such as 230-0-230, to handle heavy equipment loads.