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Safety Information
Measurement category III (CAT III)
Applicable to test and measuring circuits connected to the
distribution part of the building’s low-voltage mains installation.
EXAMPLE: Measurements on distribution boards (including
secondary meters), photovoltaic panels, circuit breakers,
wiring, including cables, bus-bars, junction boxes,
switches, socket-outlets in the xed installation, and
equipment for industrial use and some other equipment
such as stationary motors with permanent connection to
the xed installation.
Measurement category IV (CAT IV)
Applicable to test and measuring circuits connected at the source of
the building’s low-voltage mains installation.
EXAMPLE: Measurements on devices installed before the main
fuse or circuit breaker in the building installation.
T
Outlet
CAT II
Internal Wiring
Distribution
Panel
Service Entrance
Service Drop
CAT IV
Power Meter
CAT III
Fixed Installation
See: “2.3 Use of Test Leads” (p. 35)
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