Application Note

5 Fluke Corporation Who sets the rules for electrical testing and safety?
Transient protection
The real issue for meter circuit
protection is not just the maxi-
mum steady state voltage range,
but a combination of both steady
state and transient overvoltage
withstand capability. Tran-
sient protection is vital. When
transients ride on high energy
circuits, they tend to be more
dangerous because these circuits
can deliver large currents.
If a transient causes an arc-
over, the high current can sustain
the arc, producing a plasma
breakdown or explosion, which
occurs when the surrounding air
becomes ionized and conduc-
tive. The result is an arc blast, a
disastrous event which causes
numerous injuries every year.
•
CAT III covers distribution
level wiring. This includes
480-volt and 600-volt circuits
such as three-phase bus and
feeder circuits, motor control
centers, load centers and
distribution panels. Perma-
nently installed loads are also
classified as CAT III. CAT III
includes large loads that can
generate their own transients.
At this level, the trend to
using higher voltage levels in
modern buildings has changed
the picture and increased the
potential hazards.
•
CAT II covers the receptacle
circuit level and plug-in loads.
•
CAT I refers to protected elec-
tronic circuits.
Some installed equipment may
include multiple categories. A
motor drive panel, for example,
may be CAT III on the 480-volt
power side, and CAT I on the
control side.
A higher CAT number refers
to an electrical environment
with higher power available and
higher-energy transients. This
is a key principle to understand
when it comes to choosing and
using test instruments. A mul-
timeter designed to a CAT III
standard can resist much higher-
energy transients than one
designed to CAT II standards.
Within a category, a higher
voltage rating denotes a higher
transient withstand rating, e.g.,
a CAT III-1000 V meter has
superior protection compared to
a CAT III-600 V rated meter.
Key Point:
•
The hazard category system
detailed by ANSI, CSA and
IEC provides useful informa-
tion for preparing against the
hazards of transient voltage
impulses (voltage spikes) in
the environments where most
industrial electricians work.
The concept of categories
is not new and exotic. It is
simply an extension of the same
common-sense concepts that
people who work with electric-
ity professionally use every day.
It’s another tool you can use to
better understand the hazards
you face on the job, and work
safely.
All of the regulations we have
covered are built in the same
way. They grow from experience,
and they are based on experi-
ence and sound, common sense
principles. No tool, however, can
do the job alone. It’s up to you,
the user, to learn these safety
regulations and standards, and
use them effectively on the job.
After all, it’s your safety at
stake. Read up, and work safely.
Independent testing labs help ensure safety compliance
You want your tools and equipment to help you work safely. But how do you
know that a tool designed to meet a safety standard will actually deliver the
performance you are paying for?
Unfortunately it’s not enough to just look on the box. The IEC develops and
proposes standards, but it is not responsible for enforcing the standards. Word-
ing like “Designed to meet specification ...” may not mean a test tool actually
performs up to spec. Designers’ plans are never a substitute for an actual inde-
pendent test.
That’s why independent testing is so important. To be confident, check the
product for the symbol and listing number of Underwriters Laboratories (UL),
the CSA, TÜV or another recognized testing organization. Those symbols can
only be used if the product successfully completed testing to the agency’s stan-
dard, which is based on national/international standards. That is the closest
you can come to ensuring that the test tool you choose was actually tested for
safety.
What does the CE symbol indicate?
A product is marked CE (Conformité Européenne) to show it conforms to health,
safety, environment and consumer protection requirements established by the
European Commission. Products from outside the European Union cannot be
sold there unless they comply with applicable directives. But manufacturers
are permitted to self-certify that they have met the standards, issue their own
Declaration of Conformity, and mark the product “CE.” The CE mark is not,
therefore, a guarantee of independent testing.
Underwriters
Laboratories (UL)
Canadian Standards
Association (CSA)
TUV and VDE (German stan-
dards organizations) are
approval/listing agencies