A hard-wired appliance receives its electric supply through a permanent connection integrated into the house wiring. A plug-in appliance is connected to electricity by a flexible insulated power cord terminating with a molded multi-prong plug that fits into a matching receptacle at an electric outlet. It’s possible to convert a plug-in appliance to hard-wired although most conversions go the opposite way by replacing hard-wired connections with plugs.
Converting a plug-in appliance to hard wiring is the reverse of converting a hard-wire appliance to plug-in. You start by removing the existing plug cord, taking note of where the white, black and green wires are connected. Some large appliances also have a red wire. Note where that wire connects. At the wall end, you must replace the plug receptacle with a hard-wire junction box and disconnection switch. In most jurisdictions, this task must be performed by a licensed professional electrician.
The hard-wire connection must be made through flexible electric conduit that contains the wires. At the junction box end, you strip the wire ends and connect the black, white, red (if present) and green wires to the hot, neutral and ground wires from the main service panel. At the appliance end you strip the wire ends and connect each color wire to the appropriate screw terminals.
A hard-wired connection offers about half the electrical resistance of a plug-in connection, but with small appliances the difference in resistance is only detectible with sensitive test instruments and has no effect on function. In addition to reduced resistance, a hard-wired connection for large appliances is more reliable because it doesn’t deteriorate over time. A plug and outlet can corrode, while the contact springs in the outlet can weaken with age and with multiple connections and disconnections. These changes can increase electrical resistance of the plug-in connection, making it hot. This is wasting electricity at best and could create an electrical fire at worst.
Hard wiring is more appropriate for larger appliances with high electric consumption rates like dryers, ranges and water heaters, but may also be required for dishwashers, garbage disposals and central vacuum units whose life span is measured in decades. Once an appliance is hard wired, it is immovable. Converting from plug to hard-wire offers no advantages for small portable appliances, like toasters, food processors and coffee makers that get moved around a lot and that last only a couple of years. Hard wiring of small appliances by their flexible power cords may be in violation of local electrical codes.
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