Answer to Question #12085 Submitted to "Ask the Experts"

Category: Micro/Radio Waves, Radar & Powerlines — Microwaves and Radiofrequency

The following question was answered by an expert in the appropriate field:


My smart meter has a 25 decibel milliwatts (dBm) effective radiated power (ERP). I calculated that this means it has an ERP of 316 milliwatts (mW). This 316 mW is transmitted all through my house and the wiring. The maximum transmission is 400 milliseconds (ms) for each 10 seconds. Is this a safe level of radiofrequency (RF) transmission to constantly be around?


The RF transmissions you describe are typical for smart meters, and the resulting RF exposure will be only a tiny fraction of U.S. and international safety limits.

The effective radiated power (ERP) from an antenna is a measure of the power density ("brightness") of the signal in the main beam of a transmitter. You do not indicate what kind of smart meter you have but most use RF transmitters that are similar to ordinary Wi-Fi devices. The ERP value you mention, 316 mW, is typical of many Wi-Fi transmitters, of the sort that are used in your laptop computer or household Wi-Fi router. Their transmissions consist of series of very short RF pulses with very low duty cycle (low fraction of time actually transmitting), so the average power being transmitted is very low.

Smart meters are typically mounted on the outside of a home so as to direct most of their energy away from the home. Also, they are usually mounted in metal meter boxes that further block transmission into the house. I have measured smart meter signals inside houses, and in all cases the signals were very difficult to detect in the face of much higher background levels of signals from other sources of RF energy in or near the home—Wi-Fi routers and Wi-Fi-equipped devices, cordless phones, cell phones, microwave ovens when they are being used. Other sources of exposure include cellular base stations and broadcast and communications transmitters outside the home.

We are constantly immersed in a sea of RF signals. For ordinary citizens, their RF exposure from smart meters is only a tiny part of their total background exposure. Despite the many sources of exposure, the cumulative RF exposure in ordinary environments is inevitably a tiny fraction of U.S. and international safety limits.

Kenneth R. Foster, PhD
Professor of Bioengineering
University of Pennsylvania

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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