The transmitter identifies earth leakage caused by water and/or dust in switches and junction boxes, or damaged cables. Although Ringline can tolerate a single earth on the system, multiple earths can cause partial shorts on the two-wire that can cause the system to fail to safety. This transmitter negates the need to manually check for earths with a meter as part of a regular maintenance program. Partial earths may be identified and cleared during normal maintenance before the problem can cause a shutdown. Internally the transmitter performs a similar function to a moving coil meter with a100k ohm impedance.