HT instruments SPEED418 - Manual (Page 75)

400 Series
EN - 74
14.3. CHECK OF THE CIRCUIT SEPARATION
14.3.1. Definitions
A SELV system is a system of category zero or very low safety voltage featured by:
autonomous source (ex. batteries, small generator) or safety (ex. safety transformer)
power supply, protection separation to other electrical systems (double or reinforced
insulation or a metal screen connected to the earth) and no earthed points (insulated from
the earth).
A PELV system is a system of category zero or very low safety voltage featured by:
autonomous source (ex. batteries, small generator) or safety (ex. safety transformer)
power supply, protection separation to other electrical systems (double or reinforced
insulation or a metal screen connected to the earth) and there are earthed points (not
insulated from the earth).
A system with electrical separation is featured by: insulation transformer or autonomous
source with equivalent features (ex. generator) power supply, protection separation to
other electrical systems (insulation not lower than that of the insulation transformer)and
protection separation to the earth (insulation not lower than that of the insulation).
14.3.2. Purpose of the test
The test, to be effected in case the protection is realized through separation (64-8/6 612.4,
SELV or PELV or electrical separation), shall check that the insulation resistance
measured according to the indications below (depending on the separation type) complies
with the limits reported in the table relative to the insulation measurements.
14.3.3. Installation parts to be checked
 SELV system (Safety Extra Low Voltage):
 measure the resistance between the active parts of the circuit under test (separate)
and the active parts of the other circuits
 measure the resistance between the active parts of the circuit under test (separate)
and the earth.
 PELV system (Protective Extra Low Voltage):
 measure the resistance between the active parts of the circuit under test (separate)
and the active parts of the other circuits.
 Electrical separation:
 measure the resistance between the active parts of the circuit under test (separate)
and the active parts of the other circuits
 measure the resistance between the active parts of the circuit under test (separate)
and the earth.
14.3.4. Allowable values
The test result is positive when the insulation resistance indicates values higher or equal to
those indicated in Tab. 4