Toa FS-970 SERIES - Manual (Page 47)

47
13.3.2. Speaker line insulation resistance measurement (Measuring instrument: Megger)
Measure between the ground and the cable for each line. Do not measure between cables, as this can
damage both the speaker and matching transformer. It is recommended that wiring be performed so that the
following resistance values are obtained.
• New line : 10 M
Ω minimum
• Existing line : 5 M Ω minimum
• New line total resistance : 3 M Ω minimum
• Existing line total resistance : 1 M
Ω minimum
Note: Do not measure the insulation resistance with the speaker line connected to the terminal block inside
the main rack.
When the speaker lines are already connected to the terminal block inside the main rack, remove the terminal
block by loosening two screws indicated by the arrow in the figure below, then disconnect the speaker lines
from the main rack.
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.
JP-0410 front panel