Apparatus for determining the relative positions of power outlets within an electrical circuit

An apparatus for determining relative positions of power outlets within a multi-outlet electrical circuit in which earth and neutral wires are interconnected, the apparatus comprising:

• means for generating a periodic current pulse, probe means for injecting the current pulse into a wiring loop which extends between neutral and earth contact terminals of each of the outlets and for sensing voltage across the contact terminals, means for detecting within the period of the current pulse a voltage drop which occurs along the wiring loop as a consequence of current flow through the loop, means for generating a signal which is representative of the voltage drop along the wiring loop, and an indicator device to which the signal representative of the voltage drop is applied for generating an output display which is representative of level of the signal and of length of wiring between each outlet and a junction of the neutral and earth wiring in the electrical circuit, wherein:
• the means for generating the current pulse includes a ramping circuit for causing the pulse to ramp up and ramp down at leading and trailing ends respectively of the pulse, said apparatus further comprising means for generating an enabling signal for application to the indicator device to inhibit said output display during ramping of said current pulse, and the enabling signal comprises a timing pulse which has a duration shorter than that of the current pulse by an amount at least equal to duration of ramping of the current pulse.