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Electrical Energy Use of Individual End Uses

Sub-metering at the appliance level may be straightforward or complex, depending on whether the appliance is powered via a dedicated circuit or if it is plugged into a wall outlet that shares the circuit with other appliances. If the appliance is on a dedicated circuit, the electrical energy use can be measured at the breaker. In the other case, where the appliance in question is not on a dedicated circuit, there are several options. If the appliance plugs into a standard 120V socket, there are several power meters that can be plugged in between the appliance and the wall socket. If the appliance is hard-wired (lighting fixtures, for instance, are often hardwired), there are still options, but they usually require a modification to the power cord.

Electrical Energy Use of an Appliance on a Dedicated Circuit

Many major appliances such as water heaters, clothes dryers, and air-conditioners are powered on dedicated circuits so that the electrical energy consumption of a particular appliance may be measured at the main circuit breaker panel. In such cases, the measurement approach is nearly identical to that used to measure whole-house electrical energy consumption using (CTs) at the breaker panel.

Plug Pass-through Watt-Hour Meters

Some major appliances and heating, ventilation, and air conditioning (HVAC) components are powered on dedicated circuits so that their energy use may be monitored directly at the circuit breaker panel. Often, however, we are interested in monitoring individual appliances and electronics that are plugged into receptacles on shared circuits. One way to make these measurements is to create a stubby extension cord that separates the hot, neutral, and ground wires and has two additional wires to tap the voltage, so that you can easily use a current transformer (CT) to measure the supplied current and a watt transducer to calculate the power in a similar way to how these measurements are made at the circuit breaker panel.If you are looking to make a quick measurement or monitor the appliance for a short period of time, and don't require the data to be recorded using the same DAQ as other monitored systems around the house, then a much easier way to measure the electricity use of plug loads is to use portable plug watt-hour meters at the receptacle.