It is very rare for a homeowner to work on the electric meter that monitors current usage in the home. This device, which provides the connection point where electrical power enters the home, is officially owned by the power company, not the homeowner. Therefore, any wiring connections should be handled by a professional electrician or by a technician from the power company. In fact, homeowners may be forbidden to work at the electric meter in any way. But it can still be useful to understand the functioning of the electric meter and the particulars of how it is wired.
Anatomy of an Electric Meter
Inside a standard household electric meter box, there is a center neutral bus bar with wire connection lugs at each and two hot bus bars, each with wire connections lugs at each end. There is also a connection lug for the grounding wire, which is bonded to the center neutral bus bar. None of these wire connection lugs is visible unless the meter mechanism itself is removed from the box.
The actual wire connections are quite easy to understand. Three large-gauge stranded wires (two hot wires and one neutral) enter the meter box from a weather head on a metal mast (or from underground service) and are attached to the corresponding line terminals on the hot and neutral bus bars in the meter box. These feeder wires are known as the line wires. The load wires running to the indoor circuit breaker panel are connected to the remaining load terminals on the bus bars. And the grounding wire running to the grounding rod is connected to the grounding lug inside the meter box.
Connecting an electric meter, then, involves making a total of seven simple wire connections: three line connections, three load connections, and a grounding connection.
How the Electric Meter Is Connected
Equipment / Tools
- Wire strippers
Connect the Line Hot Wires
When the utility company connects the meter, the technician will bring the service wires down from an overhead mast or into the meter box through an underground feed. With the meter box open and the service wires shut off, the technician will strip the two hot wires (or attach collars that allow the wires to be bolted on) and then attach them into their designated terminals on the hot bus bars. They will then tighten down the screws and tug on the wires to ensure the connections are tight.
In some systems, the hot feed wires are two black wires, while in other systems there will be a black and a red wire.
Connect the Load Hot Wires
The load side of the electric meter, which carries power to the main service panel, can be wired either directly to the panel or to an interim disconnect. To do this, the ends of the two hot load wires are stripped and connected to the bottom two load terminals on the meter's hot bus bars. Again, the technician will tighten the screws and tug on the wires to make sure the connections are secure.
Connect the Ground Wire
Along with the hot and neutral wires, the system includes a separate grounding wire that leads from the meter box to a grounding rod buried in the earth. The ground wire is connected to the ground terminal in the center of the meter, which is bonded to the neutral bus bar. The other end of the ground wire attaches to a grounding rod via a fitting known as a grounding lug.
To effectively protect this ground wire, the technician may run the grounding wire through a hollow metal conduit to the grounding rod buried in the earth. Without this protection, the ground wire can be damaged by a lawnmower or weed trimmer.
Connect the Neutral Wires
The final step is connecting the neutral line and load wires, which are typically marked with white tape to identify them as neutral. The technician strips and attaches these neutral wires to the top and bottom terminals on the neutral bus bar in the center of the meter box. After tightening the screws firmly with a screwdriver, the technician tugs on the wires to make sure they are secure.
The technician now attaches the meter mechanism, closes and locks the meter, and then turns on the power to the service wires and checks to make sure the meter runs correctly.
How the Electric Meter Monitors Power Usage
The electric meter exists so that the power company can monitor current usage and bill you accordingly. The electric meter is usually a clear, glass-encased metering device resembling an oversize mason jar. The glass dome houses the measuring devices that include dials and wheels on the older model meters. The meter not only measures power but also provides a way that the utility company can disconnect power from your home.
Usually, there are five dials that measure kilowatts and a large rotating wheel that sits below them. This type of meter can be read by the owner of the property who reports the results. Or, the utility company will read it for you, sometimes for a charge. Newer electric meters are digital and are actually read from the utility company's office. A signal identifying your particular meter is sent down the service wires from the electric meter to the utility company.
Electric meters read power usage in kilowatt-hours. In simple terms, 1-kilowatt-hour = 1,000-watt-hours. The meter reads the entire power usage (in watts) of all appliances, light fixtures, and plug-in appliances within the home.
Reading the Meter
If your utility system requires it, once each month you will "read the meter." How you do this will depend on whether you have an older analog meter or a newer digital meter.
On an analog meter, you will note the readings on five dials, from left to right, and copy these readings on the report to the power company. Generally, the pointers on the dial will be between numbers, and you will report the lower of the two numbers. If a dial's pointer is exactly on a number, check the dial immediately to the right. If it has not yet passed 0, you will read use a lower number for the reading of the previous dial. (Your utility company will have precise instructions for how to read your meter; in some cases, it may require you to simply copy the visual appearance of the dials, like drawing clock faces.)
With a digital meter, reading the meter a simple matter of writing down the numerical value shown on the digital readout.