Table 2-7.--Measuring Circuit Insulation Resistance
components under test contain a large electrical
You need to remember mind that you cannot use a
capacity, the megohmmeter READ button must be
400-volt dc Megger to check insulation resistance on
depressed for a sufficient time to allow its capacitor to
circuits where semiconductor control devices are
charge before a steady reading is obtained. The test
You should use an electron tube
involved.
voltage applied by the megohmmeter to an unknown
megohmmeter to check insulation resistance on circuits
resistance is approximately 50 volts when resistances of
and components where the insulation resistance must be
approximately 10 megohms are measured and slightly
checked at a much lower potential. The megohmmeter
greater than this when higher resistances are measured.
operates on internal batteries. When circuits or
Figure 2-17.--Nomograph for obtaining resistance per foot.
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