electrical engineering knowledgebase

Some useful articles for the electrical industry.

Earth Leakage detectors

Most of the newer earth leakage monitors for 24v DC are solid state reference type, the older two lamps in series with a resistor down to the hull are known to impress a small current on the hull and can in some circumstances actually promote corrosion. The modern unit functions by measuring the current flow to earth through a potential divider and comparing it to a fixed reference using two amplifiers. If the current signal voltage falls below or rises above the reference voltage, one of two amplifiers switches from high to low, which triggers a RC timer. Once the timing period (pre-set) has elapsed, the normally energised PCB mounted relay de-energises and the voltfree contacts connected to the eleven pin socket change state. Reverse polarity protection is provided using a number of high voltage diodes. These leakage detectors are vital on the 24 - 36 volt DC circuits on a vessel as DC is much more corrosive than AC.


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