How Does An Electric Meter Read Power Usage?

One of the more interesting and noteworthy aspects of modern electrical delivery and monitoring systems is just how un-noteworthy they are. These systems are so reliable that most people don’t need to think about them or the questions arising from their use. For example: How does an electric meter work? What processes are in motion to keep tabs on the amount of electricity that a particular household or business consumes each month?

Perhaps the only time most people think about electric meters is when they’re trimming the hedges and trees around the meters themselves. (Quick note: The electric company will do this for you in order to ease their workers’ access to the site. Don’t plant things you really care about next to your meter!)

Sometimes an electric company will notify homeowners and property owners that a particular meter will be replaced by more modern updated equipment. (Another quick note: Many of these newer smart meters don’t need to be checked manually; they send their data directly to the company. So maybe in that case … plant away!)

Regardless of whether it’s an old-school meter or a smart meter, the question remains: How does an electric meter read power usage?

A Quick Look Inside An Electric Meter

An electric meter measures the amount of electricity in kilowatt-hours (kWh). The utility company measures electrical usage in order to bill customers for the electricity they consume.

The numbers are gathered, either electronically (with smart meters) or by a utility employee (the meter reader). They tally is delivered to consumers in the form of their electricity bill.

When you read your electric bill, you typically note the period of time the bill covers (usually between 28 and 32 days), determine whether the energy usage is within typical amounts for that time of year, and then send your payment.

But do you ever stop to think about the meter itself? How does it do what it does?

Types of Meters

There are several different types of meter. Chances are you have the type of electric meter with the spinny dial inside. This is an electromechanical watt-hour meter. But even if it’s digital, the method of tabulating the electrical charges are the same.

The way your electric company measures your electricity usage and bills you for it is quite ingenious in its simplicity. A current passes through your meter (either mechanical analog — i.e., spinny dial — or digital) at your home’s service entrance. The service entrance is where the electrical wires connect from the power lines (or underground) to your home.

Calculations

Here’s how The Spruce describes the formula used in determining energy usage:

A watt is the product of the voltage and amperage (or current) in an electrical circuit: 1 volt x 1 amp = 1 watt. But this formula represents merely the measure of the electrical potential. To measure actual energy usage, you have to add an element of time. Therefore, electrical usage is a measurement of watts used over a period of time. Your electric meter records electricity usage in kilowatt-hours. In simple terms, 1 kilowatt hour = 1,000 watt-hours. For example, if you turn on a 100-watt light bulb for 10 hours, the energy usage is calculated as 100 watts x 10 = 1,000 watts (or 1 kilowatt hour).

There are lots of little electrical details that are beyond the scope of this blog post. But in the simplest terms, the meter counts the revolutions of the metal disc or dial, which is nonmagnetic but electrically conductive. The speed at which it rotates is proportional to the power that passes through the meter. Thus, the number of revolutions is proportional to energy usage.

When you’re using a lot of electrical devices in your home, you may notice that the dial spins much faster than it does when you’re not using much electricity at all.

Meter Reading

When the meter reader comes by (in the case of a mechanical analog meter), they simply take note of the dial and write down the numbers. Your home’s electrical consumption is calculated by subtracting the previous month’s number reading from the current reading.

By the way, the voltage coil and the current coil each eat up about two watts; only the current coil amount is registered on the dial.

That’s it — the overview of how an electric meter reads power usage.

Let us know if you have any questions.