Split phase is a method of delivering electricity to homes using a single transformer that produces two 120-volt lines and one neutral wire. It’s the standard electrical system in North American residences, giving you both 120V for everyday outlets and 240V for large appliances, all from one service connection. The formal name is “single-phase three-wire,” and it works by tapping the middle of a transformer’s output winding to create two equal halves of voltage.
How a Split-Phase System Works
The heart of the system is a transformer, usually the cylindrical one mounted on a utility pole or green box near your home. Power from the utility grid enters the transformer’s primary winding as a single phase of alternating current. The secondary winding, the output side, has a wire connected to its exact center point. This center tap becomes the neutral conductor that runs to your electrical panel.
Because the neutral sits at the midpoint, the voltage from either end of the winding to the center is half the total. Each end delivers 120V relative to the neutral, and the two 120V lines are 180 degrees out of phase with each other. That phase relationship is where the name “split phase” comes from: a single phase of power is effectively split into two mirror-image halves. When you measure from one hot line (L1) to neutral, you get 120V. From the other hot line (L2) to neutral, another 120V. But measure from L1 to L2 and the voltages add up to 240V, because the two waveforms peak in opposite directions at any given moment.
120V and 240V in Your Home
This dual-voltage setup is what makes split phase so practical for residential use. Most of the outlets in your home connect one hot wire to the neutral, providing 120V for lights, computers, coffee makers, toasters, and other everyday devices. Your electrical panel alternates circuits between the two hot legs so that roughly half your 120V loads sit on L1 and the other half on L2.
Large appliances that need more power connect to both hot legs simultaneously, pulling the full 240V. This includes electric dryers, ovens and ranges, central air conditioning systems, water heaters, and EV chargers. These appliances use dedicated circuits with heavier wiring to handle the higher voltage and current.
Why Load Balancing Matters
Inside your electrical panel, two vertical bus bars carry L1 and L2. Circuit breakers snap onto alternating bus bars as you move down the panel, which naturally distributes 120V circuits across both legs. The goal is to keep the power draw roughly equal on each side.
When the loads are balanced, the currents on the two hot legs largely cancel each other out on the neutral wire, resulting in minimal neutral current. If one leg carries significantly more load than the other, the imbalance flows through the neutral instead. A persistently unbalanced panel can cause components to overheat and risks overloading the neutral conductor. Electricians pay attention to this during installation, placing high-draw 120V circuits (like kitchen outlets or bathroom heaters) on opposite legs to keep things even.
Grounding and the Neutral Connection
The transformer’s center tap is connected to a ground rod at the transformer, and the neutral wire carries that ground reference into your home. At your main electrical panel, the neutral bus bar and the ground bus bar are bonded together. This single bonding point is a safety requirement under the National Electrical Code (NEC Article 250). It ensures that if a hot wire ever contacts a metal appliance enclosure or conduit, the fault current has a low-resistance path back to the source, tripping the breaker quickly.
That neutral-to-ground bond only happens at the main panel or the first service disconnect. Everywhere else downstream, neutral and ground wires remain separate. Bonding them in a subpanel or at an outlet would create parallel return paths for current, potentially energizing ground wires and metal enclosures during normal operation.
Split Phase vs. Three-Phase Power
Split phase serves homes well, but it has limits. Because it originates from a single-phase source, the power delivery pulsates: twice per cycle, the instantaneous voltage crosses zero. For a house full of lights and appliances, that’s not a problem. For heavy industrial motors and machinery, those zero-crossings mean uneven torque and less efficient operation.
Three-phase power solves this by using three separate alternating currents, each offset by 120 degrees. The three overlapping waveforms mean power delivery never drops to zero, producing smoother, more constant energy for large motors and industrial equipment. Three-phase also transmits more power using less conductor material for the same amount of copper or aluminum, making it more efficient at scale. The tradeoff is more complex wiring and infrastructure, which is why it’s reserved for commercial and industrial settings rather than homes.
Split-phase systems need only three wires (two hots and a neutral) from the transformer to the panel, keeping residential installation simpler and cheaper. For the vast majority of household loads, from running your refrigerator to charging an electric vehicle, split phase delivers everything you need without the complexity of a three-phase service.
Where Split Phase Is Used
Split-phase 120/240V distribution is the standard residential system across the United States, Canada, and parts of Central America and the Caribbean. Most of the rest of the world uses a different approach: a single 220 to 240V supply with one hot wire and one neutral, at 50 Hz rather than the 60 Hz used in North America. European, Asian, and most African and South American countries deliver their higher voltage directly without needing to split the phase, since their standard outlet voltage is already high enough to run large appliances on a single circuit.
The North American approach of splitting a 240V source into two 120V legs is a historical design choice. Lower voltage at the outlet is generally considered safer for casual contact, while the 240V option remains available for appliances that benefit from it. The result is a flexible system that handles both light-duty and heavy-duty loads from a single, relatively simple transformer connection.