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Sunday, December 20, 2020

Non Contact Hidden Wall Cable Detector By A/C Voltmeter


Alternating Current (A/C) can produce strong radio waves when it is loaded.

And on the contrary, radio wave radiation will cause alternating current, if the wave is caught by an electric conductor or antenna.

A/C voltmeter can detect the presence of alternating current without the need to touch the current source (non contact).

So that the A/C volt tester can be used to trace electrical cables hidden in walls or other enclosed parts.

The method is easy because there is no need for additional electronic circuits, as follows:

Prepare a digital multitester that has an A/C volt tester, with 1 mV (milli Volt) sensitivity.

One probe is pinched with fingers, as earth or ground.

Another probe is connected to an antenna, made of a single electrical wire, about 50 cm long. The longer the antenna, the more sensitive it is.

The antenna wire is coiled, so that it is not too long. If it is straight and long, it will catch radio waves from a large area, making it less accurate to detect the position of hidden electric cables.

The coil diameter is about 1-2 cm. If the diameter too small, it will block the radio waves. Because the inductance will increase.

The following YouTube video shows how this non contact detector works.


On a wall far from the power line, the voltmeter will read as low as 0.010 vac.

If the antenna is held close to a wall which contains hidden power lines. Then the voltmeter will read about 0.020 volts.

If a clothes iron is connected the that hidden electric wire, the meter will read higher to about 0.5 volts. In the photo below you can see the clothes iron cable is connected, and the iron light turns orange.

If the antenna is closer to the cable that is more open. Then the voltage will be even higher, it can be above 1.4 volts.

If there are a lot of metals or electrical conductors around the cable, such as: zinc, aluminum, brass, copper, tin, lead, iron or steel frames, nickle, chrome, silver and gold plating, and so on. The detection will be less accurate.

1 comment:

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