Fluke 1550C User Manual page 39

Before and after testing, confirm that the Tester does
not indicate the presence of a hazardous voltage, see
Figure 4. If the Tester beeps continuously and a
hazardous voltage is shown on the display,
disconnect test leads and remove power from the
circuit under test.
3. Push  for 1 second to start the insulation test.
The Tester beeps three times as the test begins, and Xflashes on the
display indicating potentially hazardous voltages may be present on the
test terminals.
The display indicates the measured insulation resistance after the circuit
has stabilized. The bar graph displays this value continuously (in real
time) as a trend, see Figure 10.
Item
Digital main display

Bar Graph

Figure 10. Displayed Measured Insulation Resistance
Any of the following conditions will terminate an insulation test:
User stop (pushing )
Timer limit reached
Interference on the test circuit
Breakdown occurs with ramp test enabled
Battery depleted
XW Warning
1
Description
Insulation Tester
Measurements
2
GHH08.EPS
21