The Role of the Electric Meter
It is 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 and two hot wire connection points for the incoming (line) and outgoing (load) wires. There is also a connection point for the grounding wire. These wire connection terminals are usually not visible unless the meter mechanism itself is removed from the box.
The incoming overhead feeder wires descending from the weather head arrive into the meter through a metal mast, then connect to the top two hot connection points (the line connections) via terminal lug connections. In a typical 100-amp service connection, these wires will likely be #2 THHN. The center post is for connecting the incoming neutral/ground wire.
The outgoing connection points are the load connection points. This is the portion of the meter that feeds the main service panel or the electrical disconnect. As with the line connection, the load connection has the two hot feeds as well as a center neutral connection. There is also a #6-gauge ground wire that links the neutral/ground connection on the meter to the grounding rod.
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 over-sized mason jar. Inside, the glass 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 line 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.
Connecting the Feed Hot Wires
When the utility company connects the meter, the technician will bring the service wires down from overhead, 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), then attach them into their designated terminals. He 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.
Wiring the Load Side of the Meter
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. Again, the technician will tighten the screws and tug on the wires to make sure the connections are secure.
Connecting the Ground Wire
Along with the hot and neutral wires, the system includes a separate grounding wire that leads from the meter box to the earth. 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.
The ground wire is connected to the ground terminal in the center of the meter, located next to the neutral terminal. The other end of the ground wire attaches to a grounding rod via a fitting known as a grounding lug.
In residential installations, the neutral and ground use a single common connection called a neutral/ground connection.
Connecting the Neutral Wires
The final step is connecting the neutral line and load wires, which are typically marked with white tape. The technician strips and attaches these neutral wires to the top and bottom neutral terminals 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, then turns on the power to the service wires and checks to make sure the meter runs correctly.