Abstract: Multiple electrical path assembly as in a telephone grid, is rapidly and accurately checked by grounding one end of all but one of the path conductors, applying a test signal to that one end, detecting the presence or absence of signal on both ends of all conductors, and repeating the procedure for all the conductors, as with a computer containing a microprocessor. Where the conductors are individually switched, they can all be switched on beforehand. Detectors can also be connected to the conductors during the testing, to detect unusually high voltages, and testing can be interrupted when such voltages are detected. Switch actuation can be separately tested by detecting the passage of current that is used to actuate them.