Smart Meters

The ARRL Smart Meter FAQ Page

By Jerry Ramie, KI6LGY

Q) What is an electric or power meter?

A) In electric-utility parlance, it is the kw-hour meter between your mains and the load center and measures your electric power usage.

Q) What is a smart meter? How does it differ from a conventional electric or power meter?

A) A smart meter is like a conventional power meter in that it also measures your electric power usage, but it has other capabilities, such as the ability to be read remotely without sending a person out to your meter. See Figure 1.

Q) What is the smart grid?

A) The modernization of the electric power grid, often called the "smart grid" by its proponents, is an important goal. Efforts such as the Advanced Metering Infrastructure (AMI), Automated Meter Reading (AMR) and the other phases of intelligent grid management are all part of a smarter grid. Having better control of the power grid will improve its reliability and efficiency and, as applications are developed for end users, point-of-use monitoring and control of power usage and generation will benefit utilities by reducing peak loads and benefit consumers by providing a way to save on their energy costs. See the ARRL Web site for more information at: http://www.arrl.org/electric-utility-communications-applications-and-smart-grid-technologies

Q) Where are smart meters being deployed at the present time?

A) Smart meters are being deployed all over the United States and in many other countries.

Q) In the US, under what part of the FCC rules do smart meters operate?

A) Part 15, just like most other consumer and household electronic devices. On most frequencies, Part 15 permits only very low-power operation -- a few nanowatts in some cases. Under the Part 15 rules, certain bands have provisions for higher-power operation. Because these bands are also used by Industrial, Scientific and Medical devices, these bands are often called the ISM bands. That does not change the status of the smart meters, though; they operate exclusively under Part 15 of the rules, not Part 18 like actual ISM devices. For more information on Part 15 and Part-15 devices, see http://www.arrl.org/part-15-radio-frequency-devices. Other nations have similar rules.

Q) Can Amateurs expect interference from smart meters? Do they have potential RFI generating circuitry, such as digital circuitry?

A) In general, Amateurs should not expect interference from smart meters on most Amateur bands. And yes, smart meters do have digital electronics inside of them that can act and emit RF, much like an ordinary personal computer. There is, however, a greater potential for interference on some cases, particularly when a smart meter system intentionally transmits data on a so-called ISM (Industrial, Scientific and Medical) band that is shared with the Amateur service.

Q) Do you mean smart meters contain an intentional RF transmitter?

A) Sometimes. When a smart meter contains an RF transmitter:

The frequency of operation is typically in the 902 MHz and 2.4 GHz bands.
Power output is typically 1 watt in the 902 MHz band and much less in the 2.4 GHz band.
The intended range of a transmitter in a smart meter is typically very localized. While the utility-side radio needs to reach a neighborhood concentrator, typically mounted on a nearby pole, smart meters can also mesh through other smart meters to communicate with the concentrator. (using five hops or less) See Figure 2.
The smart meter only communicates when it is commanded to do so, typically several times a day.
The smart meter’s transmitter operates under Part 15 of the FCC rules.

Q) I recently upgraded my electric service from 100 to 200 A. My old electric meter had gears and a mechanical readout. The new one however, is all electronic. It has an LCD readout and some sort of radio transmitter in it. I’m happy to report that I’ve had no interference issues with it but wonder… Is it possible I already have a smart meter?

A) Not necessarily. Your new meter may simply have remote reading capability. This means a meter reader can ping your meter for a reading from the street. The meter then transmits the reading by radio. Efficiency is improved since he or she no longer has to enter your property. Smart meter technology, on the other hand, implies two-way communication with the meter. Smart meters also have memory and data processing capability.

Q) Do smart meters use some form of carrier current technology or BPL?

A) First, let’s define “carrier current.” A carrier-current device uses power lines, in-building or utility-controlled to intentionally conduct RF signals. Carrier-current devices are also governed by a carrier-current section in the Part 15 rules.

In some areas, smart meters and/or the smart grid may use carrier-current technology. Each electric utility chooses the architecture they want to deploy, sometimes under the direct or indirect influence of decisions made by state or local regulators. Under Part 15 rules…

If a carrier-current device is used to transmit digital information, and it operates from 1.7 to 80 MHz, it is operating under the BPL rules in Part 15.
If it operates on other spectrum, it operates under the carrier-current rules in Part 15.
If it used exclusively on the high-voltage lines feeding substations, carrier-current devices can operate under the power-line-carrier (PLC) section of Part 15.

So far, in the US, smart-meters have not used BPL. Some of the protocols for home-area-networks that may be associated with smart meters and smart-grid technology may use BPL, but it is likely that the systems will use the HomePlug technology. HomePlug does not use the Amateur bands, so it has little potential to interfere with Amateur Radio. (Other spectrum could experience interference from HomePlug devices.)

For information on BPL, see http://www.arrl.org/broadband-over-powerline-bpl.

If and when a smart meter uses carrier current technology:

The frequency range used by PLC meters use Cenelec Band B @ 63 kHz for the consumer side.
Some smart meters also use BPL for the utility side. It is also possible to have BPL on the home wiring in a home-area-network (HAN) tied to the smart-meter and smart grid.
The intended range of the carrier current communications is typically very localized. Just like a concentrator in the case of radio communications, the receiver is located on a nearby pole.
The smart meter’s transmitter typically operates multiple times per day, but only when the utility “pings” the meter.

Q) How does a smart meter receive commands from the utility, or does it?

A) All smart meters are not the same. Utilities can send commands to a smart meter by both radio and carrier current communications, depending on the type of meter being used. In California, for example, the utilities presently deploying smart meters control the meters using 902-928 MHz FHSS radio. The intended range and frequencies used for sending commands to a smart meter can also vary from utility to utility.

Q) Can Amateur Radio cause interference to a smart meter? What are the rules regarding such interference?

A) Yes, amateur operation nearby can desensitize some meters so they can’t hear commands. The smart meter is operating under Part 15 of the rules, which stipulates that Part 15 devices are not protected from interference from licensed radio services, such as Amateur Radio.

Q) What protection does Amateur Radio have from interference to and from a smart meter?

A) In the US, smart meters in residential areas are required to meet absolute emissions limits for unintentional emitters and/or carrier-current devices and the transmit power limits for intentional emitters as specified in Part 15 rules. Licensed radio services such as Amateur Radio also receive unconditional protection from harmful interference from all Part 15 devices, including smart meters. In addition, Part 15 devices, such as smart meters, receive no protection from interference resulting from licensed radio services.

Note: Although the frequencies typically used by smart meters are also ISM bands, which are covered by Part 18 of the FCC rules, they actually operate under Part 15. This is an important distinction. If a smart meter were operating under Part 18, the Amateur Service would have to accept any harmful interference such a meter might generate. Part 18 devices however, are prohibited from using RF for communications purposes. Since smart meters transmit data, they can’t legally operate as Part 18 devices.

For reference purposes, the following table shows the overlap between the Amateur and ISM bands typically used by smart meters:

Amateur Band

ISM Band*

Notes

902 – 928 MHz

33 cm Amateur Band

2300 – 2310 MHz

2390 – 2450 MHz

2400 – 2483.5 MHz

The Amateur band is broken into two segments. The ISM band extends past the Amateur band at the upper end.

*Note: The higher-power provisions in Part 15 typically use the ISM bands.

Q) What about other types of utilities, such as water and gas? I understand they are also converting to new meters with the capability to communicate by means of RF. Do the same smart meter rules still apply, at least in terms of my concerns about RFI?

A) For the most part – yes. Just like "smart" electricity meters, these water and gas meters often use radio energy to communicate. When they do, they most likely operate in an ISM band under Part 15.

These are extremely low-power devices that spend most of their lives turned off waiting for a contact with the utility radio network. Water & gas meters usually operate on 2.4GHz using a very narrow-bandwidth implementation of the ZigBee Smart Energy Profile.

Since gas and water meters are not connected to a source of electrical energy, they both use "scavenger" (impeller) techniques to generate small amounts of electrical power to keep the on-board battery topped off. This approach provides a battery life expectancy of greater than 10 years.

In many cases, the meter is pinged or timed to contact any nearby "smart" electric meter. The smart electric meter can then store their readings and send them upstream to the utility billing system. Although it's usually communicating with the same customer's smart electric meter, it doesn't have to be. The system is "meshed" and can pass data along as required. The “smart meter” in this case will often have two radios under the glass - one for the consumer side at 2.4GHz and one for the utility side at 902-928MHz.

These two communication "medias" (utility and consumer) are different in each utility jurisdiction. You may be able to learn more about the specific technology being used by your utility from their Web site. For a more thorough discussion of the different utility communications medias and their relative impacts on the amateur service, please see the article on electric utility communications on the ARRL website at: www.arrl.org/electric-utility-communications-applications-and-smart-grid-technologies