Safety
The increased occurrence and levels of transient overvoltages in today’s
power systems have given rise to more stringent safety standards for electrical
measurement equipment. Transients that ride on top of power sources (mains,
feeder or branch circuits) can trigger a sequence of events that may lead to
serious injury. Test equipment must be designed to protect people working in
this high-voltage, highcurrent environment.
ake a look at special
nctions built into
imeters. Think about
ou need to do basic
ents, or if you need
dvanced troubleshoot-
s offered by special
to consider:
k environment (voltage
es of equipment, types
rements, applications)
features/functions
nce, frequency, tem-
, non-contact voltage,
dance mode, min-max
ata logging, trending)
n and accuracy
0,000, or 50,000
olution)
sed occurrence and
ansient overvoltages
power systems have
to more stringent
dards for electrical
ent equipment. Tran-
ride on top of power
ains, feeder or branch
n trigger a sequence
hat may lead to serious
t equipment must be
o protect people work-
high-voltage, high-
vironment.
Measurement
category
In brief
Examples
CAT I
Electronic
•
Protected electronic equipment
•
Equipment connected to (source) circuits in which
measures are taken to limit transient overvoltages
to an appropriately low level
•
Any high-voltage, low-energy source derived from
a high-winding resistance transformer, such as the
high-voltage section of a copier
CAT II
Appliances, PCs,
and TVs
•
Appliance, portable tools, and other household and
similar loads
•
Outlet and long branch circuits
•
Outlets at more than 10 m
etres
(30 feet) from
CAT III source
•
Outlets at more that 20
metres
(60 feet) from
CAT IV source
CAT III
MC panels, etc.
•
Equipment in fixed installations, such as switchgear
and polyphase motors
•
Bus and feeder in industrial plants
•
Feeders and short branch circuits, distribution
panel devices
•
Lighting systems in larger buildings
•
Heavy appliance outlets with short connections to
service entrance
CAT IV
Three-phase at utility
connection, any
outdoor conductors
•
Refers to the “origin of installation,” i.e., where
low-voltage connection is made to utility power
•
Electricity meters, primary overcurrent protection
equipment
•
Outside and service entrance, service drop from
pole to building, run between meter and panel
•
Overhead line to detached building, underground
line to well pump
ANSI/ISA S82.02
Service
Entrance
Meter
Meter
Service
Entrance
Meter
Outbuilding
Outbuilding
Transformer
Underground Service
Underground Service
Entrance
CAT I
•
Electronic
equipment
•
Low energy
equipment
with transient
limiting
protection
•
Any high-
voltage,
low-energy
source derived
from a high-
winding
resistance
transformer
CAT II
•
Appliances and
portable tools
•
Outlets and long
branch circuits
– Outlets at
more than
10 m (30 ft.)
from CAT III
source
– Outlets at
more than
20 m (60 ft.)
from CAT IV
source
CAT IV
•
Origin of installation: where
low-voltage connection is made
to utility power
•
Electricity meters, primary
overcurrent protection equipment
•
Outside and service entrance
•
Service drop from pole to building
•
Run between meter and panel
•
Overhead line to detached
building
•
Underground line to well pump
CAT III
•
Equipment in fixed installations:
switchgear and three-phase
motors
•
Bus and feeder in industrial
plants
•
Feeders and short branch
circuits
•
Distribution panel devices
•
Heavy appliance outlets with
short connections to s rvice
entrance
•
Large lighting systems
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