Test for dirty electricity
Dirty electricity creates electric and magnetic fields whose strength varies much more rapidly than those from the current in the electrical system. Engineers refer to this as high-frequency interference.
Explanations can be found under the question mark at the bottom right.
The dirt can be thought of as electric waves travelling along the wiring in the house and being emitted as radio waves. Before FM radio was introduced, these same radio waves were used to broadcast all radio programmes. Nowadays, they are created by LED lights, computers, television sets, and solar power installations. Because they are similar to radio waves, they can be detected using a radio that can pick up the magnetic and electric fields radiated from the cable. Another method is to take a meter reading of the 'dirt' on the cable. However, these meters do not measure the radiated magnetic or electric fields you hear on the radio.
Using a radio
A radio is the first choice.
Dirty electricity meters
Measures half of the problem.
Using an AM radio
The interference from the domestic wiring is to some extent radiated at the same frequencies that used to be the most common for broadcasting radio programmes. That's why you can listen to them with a radio. But not all radios are the same. Ideally, it should be able to receive radio programmes broadcast on longwave (LW). There will be a button marked 'FM MW LW' or just 'FM LW' or 'FM AM'. On most radios middle wave (MW) is labeled AM, but the function is the same. You can use a radio in AM or MW mode, but in LW mode there is usually more interference to be heard. Long wave (LW) is best. If the radio has both LW and AM or MW, use both modes.
Use the tuning knob to listen to the dirt at different frequencies. Tap the question mark in the bottom right corner to view more technical explanations.
How it works
Electric currents that flow through an electric conductor creates a magnetic field that rotates around it. Dirty electricity does the same thing. Radio waves consist of an electrical part and a magnetic part. A radio tuned to longwave and mediumwave uses the magnetic part to receive radio programmes and therefore works in the same way as a magnetic field meter. The more interference you can hear on the radio, the stronger the magnetic field from dirty electricity. Simpler radios are also sensitive to the electric fields they are tuned to.
A radio is much more sensitive to magnetic fields than any magnetic field meter. It is most sensitive to magnetic fields that go from left to right and least sensitive to magnetic fields that go from back to front. The antenna is only used for FM radio.
The best radio to detect dirty electricity that we have found is the Roberts Sports 925. The radio in the picture is the old version with LW. Sangean SR-35, which looks the same, might exist in an old LW version too. Those can only be found second-hand. A good radio for detecting dirty electricity should not have any noise reduction features when tuning in to radio stations. It's the noise that we want to hear.
Dirty electricity meters
Dirty electricity meters measure the interference on the cable. They do not measure the electromagnetic fields radiated from the cable and to which you are exposed and a radio let you hear. However, they do provide a measurement value. Besides, meters are much more expensive than a radio.
When current is consumed, it flows forward through one conductor and back through the other. The same is true of some high-frequency interference, known as differential mode or symmetrical. Dirty electricity meters measure the voltage of the differential mode interference between the two conductors. However there is another type of interference.
The other type of high-frequency interference does not behave exactly like normal current. It can cause the current to flow in the same direction in both conductors, in which case the interference is known as common-mode or asymmetric. The voltage between the two conductors, caused by common-mode interference, is much smaller than the voltage caused by the symmetrical interference.
Why is this important?
The first picture on top of the page, which shows a rotating magnetic field around a cable, was incomplete. It illustrates what happens when the current only flows through one of the cable's conductors. In reality, it flows in the other direction through the other conductor, creating a magnetic field that rotates in the opposite direction. These two magnetic fields cancel each other out to a great extent, reducing the magnetic field radiated from the cable. The picture on top of the page only showed the resulting magnetic field.
Positive and negative voltage also create opposing electric fields that cancel each other out, but not completely.
The illustrations show that most electromagnetic fields resulting from differential mode interference (symmetrical) cancel each other out, making them less problematic than those resulting from common-mode (asymmetrical) interference. This is because common-mode interference has no 'built-in' opposite pole or mirror image to cancel it out. In simple terms, a radio allows you to hear interference that radiates outwards, whereas a dirty electricity meter only measures differential mode interference. The type of interference that only partially radiates outwards and affects you.
The meters
The purpose of exposure limits for electric and magnetic fields is to restrict the current that these fields create in the human body. Experience shows that this is also the most significant factor. The strength of the current created by the fields depends on how quickly their strength changes, measured per second. A change that is 1,000 times faster results in a current in the human body that can be up to 1,000 times stronger.
Stetzerizer Microsurge Meter
This meter measures the speed at which voltage changes in symmetrical interference in the wall socket. In essence, it measures volts per second, converting this to GS units. One GS unit corresponds to 24 volts per second (V/s). In practice, this means that the meter quickly reaches its maximum value of 2000 GS units in response to rapid changes in voltage, such as those occurring at high frequencies. This is an adaptation to how humans are affected by dirty electricity. Frequency range 4000-150,000 Hz (4-150 kHz).
One step further – the Friman-meter
The Stetzer meter shows how voltage varies between the two conductors in a cord, whereas the Friman meter shows variations in the electric and magnetic fields that affect you. Press the red button to display magnetic fields in microtesla per second (µT/s). Flip down the lever on the left and it measures the current flowing from the metal plate on top of the meter and through your finger, in nanoamperes (nA). This is the closest you can get to a meter that measures the effect on a person. Frequency range 10-200,000 Hz (0.01-200 kHz).
Named after its inventor, the Friman meter was manufactured in small numbers in 2000 and has been revered by Swedish electromagnetic hypersensitives ever since. This meter is not available for sale. Not even as second hand.
Trifield EM100 by Alpha Lab
This description applies to all meters that measure and display the result of differential mode interference in thousandths of a volt. Although thousandths of a volt may not be significant on their own, they may be when combined with the speed of the voltage change, usually expressed as frequency. In some cases, this meter may help to identify the source of the interference. This meter also has a speaker that lets you hear the interference. Frequency range 10,000-10,000,000 Hz (10 kHz-10 MHz).
If you are interested in this kind of meter and want a reading in a value that many are familiar with, you can purchase one once you have bought a radio.
How does differential become common?
Virtually all high-frequency interference begins as differential mode, where the electric and magnetic fields cancel each other out. However, the fields around a cable do not cancel each other out completely due to the distance between the cable's conductors. These remaining fields can then induce interference in another cable. As both conductors in the other cable are affected in the same way by the electric and magnetic fields from the original interference, this new interference becomes common-mode. Common-mode interference never becomes differential-mode.
At some point, the protective earth is connected to the return conductor, which carries the current back to the transformer. Therefore, it is part of the electrical system. Through this connection, one half of a differential mode interference can spread onto the protective earth, far from the mirror image of the interference on the other conductor in the cable. Consequently, anything that is connected to the protective earth will carry common-mode interference. The word 'earth' in 'protective earth' does not refer to Mother Earth.
If you haven't read our page about dirty electricity filters yet, please do so.
