Lights and Display Board Circuits

Belgian Earth Fault Detector Schematic Circuit Diagram

Having been affected by earth fault accidents, the author put together this little circuit. It consists of just three elements: the neon with its original resistor — for example, salvaged from the switch on an AC power bar — and a small capacitor (class Y) salvaged from the electronics of a low-consumption lamp. A larger capacitance makes the neon glow brighter. All this for no money at all. The neon lights only when there is an efficient Earth present. This works well at the author’s home, with Live or Neutral either way around. In the Elektor laboratory based in The Netherlands, some concerns were expressed as described in the June 2011 issue [1], as the circuit was sensitive to the relative positions of the Live and Neutral. So the Earth fault detector can also be used as a Phase detector, but probably in Belgium only.

Belgian Earth Fault Detector Schematic Circuit DiagramThe whole thing can easily be incorporated into a power socket; the author used a small transparent cover to protect the neon.

Note. As opposed to the UK and the US, some AC power outlets in Belgium — and all in The Netherlands — are not polarized, i.e. AC power plugs (both earthed and non-earthed) can be inserted either way around. Internet link


Capacitance is the ratio of the amount of electric charge stored on a conductor to a difference in electric potential. Commonly recognized are two closely related notions of capacitance: self-capacitance and mutual capacitance. Any object that can be electrically charged exhibits self-capacitance, for which the electric potential is measured between the object and the ground. Mutual capacitance is measured between two conductors and is particularly important in the operations of the capacitor, a device designed for this purpose as an elementary linear electronic component.

Capacitors provide several different important functions in a circuit. Their ability to store DC charge and offer relatively low impedance to alternating frequency signals make them useful in power supply circuits and bypass applications. We can think of them as functioning as little batteries here.20-Feb-2004

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