Understanding 220 and 230 Volt Wiring
Using 240 volt wiring for residential homes is a necessity, for powering some heating and cooling equipment as well as large appliances. 220 volt circuits are now commonly known as 240 volt circuits. In order to accommodate increasing electric loads, American utilities have increased the nominal voltages in order to reduce the electric current and wire size requirements over the years. This is the same reason 110 volt circuits are now 120 volt circuits. However, people still use the old 110/220 volt terms in conversation, but in reality those have not been used since the 1960's and 1970's in most locations.
The design relies on the principals of electrical phases. Two 120 volt circuits, that are 180 degrees out of phase, are connected together to form one 240 volt circuit. This allows twice the amount of electrical power to provided with the same size wire. There are two main types of 240 volt circuits depending on the appliance you're supplying power to, and each type of circuit has slight variations that cause them to function differently. Understanding these differences will help you determine the correct type of wiring to use when installing an appliance, or new heating and cooling systems.
3-Wire 240 Volt Wiring
Most of today’s common appliances and fixtures operate off 120 volt wiring and circuits. Connections to this equipment is done through three wires. The hot wire (typically blue or black), carries the electrical current to the appliance. The white wire is neutral, which completes the circuit. This wire can be traced back to the electrical panel where it is connected to the neutral busbar. The green wire, or bare copper wire, is the ground, which is there for electrical safety.
240 volt wiring, on the other hand, may not need a neutral white wire. Instead there is an additional hot wire which is usually red or blue in color. The two hot wires complete the circuit. This wiring must be connected to a two-pole breaker at the circuit panel to account for the two leads. In essence, a two-pole breaker is 2 single-pole breakers that have been wired together. This type of 240 volt wiring is most commonly used for providing power to electric water heaters, boilers, or condensing units. These appliances do not require 120 volt power.
4-Wire 240 Volt Wiring
Another type of 240 volt wiring is used to power appliances such as stoves and dryers. These devices require 240 volts to power their main function but use 120 volts to power accessory equipment such as clocks and timers. In addition to the two hot wires, this type also contains a white neutral wire to complete the circuit for the accessories that require a 120 volt circuit. As with any type of electrical wiring, a bare copper wire or green wire is also used as the ground wire. Similar to 3-wire 240 volt wiring, the use of 4-wire 240 volt wiring will require the installation of a two-pole breaker in the circuit panel. Changes to the National Electrical Code (NEC) now require that this type of wiring be used predominantly in residential home construction. That is why most of today’s dryers and oven ranges come equipped with a 4-prong plug.