Measure the insulation resistance between the ground and each speaker line using the megger.
When the measure insulation value is much lower than the specified value, this can be caused by shorts
inside the pipe or joint box, defective taping, incorrect wiring, play of the speaker, or contact of a lead with wall
surface. To ensure effective inspection, divide lines into lots when inspecting them.
If the measured results greatly differ from the calculated impedance, follow the procedure below.
(1) If the measured impedance is much greater than the calculated value, this can be caused by cable
disconnection or incorrect wiring inside the joint box. In this case, supply power to the speaker line using a
small amplifier when inspecting the line.
(2) If the measured impedance is much lower than the calculated value, wiring shorts, attenuator breakage,
wrong connections, or defective insulation may be the cause. In this case, disconnect the wiring at an
appropriate position and inspect the line.
(3) If the total impedance greatly lowers the calculated value whereas both are more or less the same on an
individual line bases, the possible cause is the defective insulation between lines and between the wire
and pipe.