Exposures

The smart meters that ESB Networks are currently installing communicate using 2G (or GSM) technology. This operates at narrow bands of frequencies, mainly at 1800 or 900 megahertz (MHz), very similar to many other wireless technologies.

The exposure a person gets to radiofrequencies from a smart meter depends on three factors: the power of the transmission, the distance away from it they are, and the duration of exposure. We consider each of these in the following questions.

Like the mobile phones whose communications technology smart meters borrow, smart meters are designed to transmit with as low a power as possible. The 2G technology used is capped at 2 watts (2 W) the alternative narrow-band 4G that some meters use is even lower.

This is the maximum possible value. In practice, it is usually rather less, because the technology reduces the power level automatically to the lowest level actually needed to maintain communications.

Like any other sort of transmission, the level of exposure reduces with distance away from the smart meter.  Except for very close to the meter, it falls away with what is called an “inverse square” variation, which is really very rapid.  It means that each time you double the distance, the exposure falls by a factor of four.

Mobile phones are designed to be safe (to produce exposures that are below the safety limits) even when used close to the head, just a centimetre or two away.  So smart meters are also safe, even if you managed to get similarly close to them when they were transmitting.  But of course, you would normally not be close to a smart meter.  You would typically be a metre or more away, and at that distance, the exposure levels have fallen many-fold, typically a factor of 20 or more.

Each time the smart meter needs to communicate data to ESB Networks, it does so as a single short package of data, very much like a single text message or a single short email. Each such transmission lasts less than a second and the level of power needed to maintain this link is automatically reduced to a minimum.

The exposure limits specify that the relevant exposure is the exposure averaged over six minutes.  With smart meters, even the instantaneous exposure during a transmission is within the exposure limits.  But when you average over the specified six minutes – which would almost certainly contain just one transmission lasting no more than a second – the averaged exposure drops still further. 

Radiofrequency exposure is measured in two different ways.  When a person is quite close to the source, the Specific Absorption Rate (SAR) is measured, and when they are further away, power density is measured.

If you put your head right against the smart meter, it would probably, as a maximum produce an SAR of around 0.5-1.5 W/kg, depending on the exact orientation. At say 1 metre away, it would probably again as a maximum, produce a power density of around 0.2 W/m2. Both of these values comply with the relevant exposure limits, as explained in more detail below.

As explained above, in the first instance, smart meters are expected to send data (meter readings and status reports) several times a day. In future, that could increase, as electricity supply companies or other businesses take advantage of the technology to offer you new products and services. It will be your choice whether to take up any of these new options that might be offered.

In future, as smart technologies develop, there may be communications within the home.  For instance, you may have an in-home display of your consumption, or smart appliances that can communicate direct with the meter.

These communications would also be wireless.  Because the range required is less – limited to inside the home, rather than having to communicate to base stations outside the home – the power would be less.  It’s quite likely they would use an existing protocol, such as Zigbee.  To take that example, Zigbee is limited to 1/8 W, so a power 16 times lower even than the maximum power the smart meter can use to transmit outside the home. The exposures also would be correspondingly lower.

At this stage the smart meters being installed will not be capable of communicating within the home.

There are numerous sources of radiofrequency exposures in everyday life: mobile phones, Bluetooth, Wi-Fi, DECT phones, baby monitors, etc, plus, of course, all the broadcast TV and radio that has been around for a lot longer.

The highest exposures come from sources that you use close to your body. The most obvious example is using a mobile phone against the head to make a voice call, though even that still complies with the exposure limits.

Other sources produce lower exposures, either because they are lower power (e.g. Wi-Fi, bluetooth) or because you do not use them so close to the body.

Smart meters are to the lower end of the range of radiofrequency exposures in the home, mainly because they are not usually close to the body.

All wireless technologies, including smart meters, work by encoding the data onto what is called a radiofrequency “carrier wave”. They do that by modulating the carrier wave.  It is the carrier wave that carries the signal between the sender and the receiver, and it is the modulation that allows the data to be sent and extracted.

Each wireless technology tends to use a fairly similar carrier frequency, but the details of the modulation vary a lot.  2G then 3G and 4G each developed different and better modulation patterns to be able to send more data, and similarly for other wireless technologies like Wi-Fi. The smart meters currently being installed in Ireland use 2G or a specific type of 4G technologies, and therefore the transmissions have these specific modulations. Smart meters installed in future phases of the rollout could use different technologies with different specific frequencies and modulations.

However, the exposure limits don’t distinguish between different modulation patterns, they simply limit the overall exposure. That is because there is no good scientific evidence that living cells or tissues are able to distinguish the different types of modulation used by different technologies. What matters is simply the overall exposure, and with smart meters, that overall exposure complies with the exposure limits.

Yes, they do, like any other appliance or piece of equipment that uses mains electricity. But smart meters actually produce much smaller mains-frequency magnetic fields than the traditional rotating-disk meters they are replacing do.  Both types of meter produce exposures that are comfortably within the exposure limits, but the smart meter does so by a much larger margin.