Amprobe MEGATEST-1000 Megohmmeter - Manual (Page 30)

ALLOWABLE VALUES
The values of test voltage and minimum insulation resistance are reported in the
following table (CEI64-8/6 Tab. 61A):
Rated circuit voltage
(V)
Test voltage
(V)
Insulation resistance
(M###)
SELV and PELV* 250 ###0.250
Up to 500 V included, except for the
above circuits. 500 ###0.500
Over 500 V 1000 ###1.000
* In the new standards the terms SELV and PELV replace the old definitions
"safety low voltage" or "functional".
Table2: Table summarising the test voltage values and relative limit values for
the most common kinds of test.
NOTE:
If the circuit is quite large the conductors running side by side make up a capacity
which is to be charged by the instrument in order to carry out a correct
measurement; in this case it is recommended to keep the GO key pressed (in case
a test is made under manual mode) until the result gets stable.
ATTENTION: When you take measurements among active conductors it is
essential to disconnect all the users (alarm lamps, intercom transformers, boilers
etc) otherwise the instrument will measure their resistance instead of the installation
insulation. Moreover any insulation resistance test among active conductors could
damage them.
The indication "> 1999M
Ω" or “o.r.” (out of range) warns that the insulation resistance
measured by the instrument is higher than the maximum resistance limit (see technical
specifications); this result is obviously far higher than the minimum limits of the above
table therefore if during a test this symbol is displayed the insulation of that point is to be
considered in compliance with standards.
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