EQUIPMENT
by Gary Weidner
A
This stationary pressure washer uses a
NEMA 4X electrical enclosure (circled).
42 • September 2007 • CleanerTimes
n electrical enclosure
seems like a pretty
mundane thing—a
box that houses various electrical components. But like so much else in
life, the matter is more complex when
you get into the details.
The functions of an electrical
enclosure can include:
• Provide support for internal
components;
• Prevent people from coming
in contact with dangerous
components;
• Allow access for servicing;
provide protection against
water, dust, or solids;
• Resist corrosion;
• Resist certain weather conditions such as rain, snow, sleet,
and ice;
• Provide ventilation for internal
components;
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CleanerTimes • September 2007 • 43
• Allow operation in an explosive
atmosphere;
• Provide a barrier against electromagnetic interference.
This article highlights two widely
used systems for designating an electrical enclosure in terms of what sort
of barrier it provides between the
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For information circle 64
outside world and its internals. One system, widely
used in the U.S., is that of
the National Electrical
Manufacturers Association standard NEMA 250,
Enclosures for Electrical
Equipment (1000 Volts
maximum). The other system, widely used internationally, is that of the
standard IEC 60529, Degrees
of protection provided by
enclosures (IP code).
NEMA Enclosure
Designations
The NEMA 250 standard pertains to all electrical enclosures except
motors. Underwriters Laboratories standard UL
50, Enclosures for Electrical Equipment, is similar to NEMA 250 and
uses the same numbering system to
designate enclosures.
NEMA 250 divides enclosures into
two groups, those for use in hazardous areas and those for use in nonhazardous areas. Within those two
groups, numbered designations indicate specific application environments.
Table 1 summarizes nonhazardous
designations.
IEC Enclosure Designations
The IEC 60529 standard takes a
different approach to designating
enclosures. It simply focuses on two
parameters: protection against entrance
of objects (from parts of people down
to dust-size), and protection against
entrance of water.
Enclosures (including motor enclosures) are designated by an “IP Code,”
which consists of “IP” followed by two
numbers called characteristic numerals (and a couple of optional extra
characters). The first characteristic
numeral specifies the degree of solid
object protection, and the second
numeral specifies the degree of water
protection. Tables 2 and 3 summarize the characteristic numerals.
Motor Enclosures
The term “enclosure” here means
the same as “frame” or “housing.”
Internationally, the IP
designation is used for
motor enclosures as well
as other enclosures.
As already mentioned, the NEMA enclosure designation system
described in Table 1 does
not apply to motors.
NEMA presently offers
two choices for designating motor enclosures:
• Traditional (ODP,
TEFC, etc. as
defined in NEMA
standard MG-1);
• The IEC IP system.
Comparing the Two
Enclosure Systems
Is one system better
than the other? That can’t
be answered with a yes
or no, because although
there is some overlap,
the two systems are
based on different approaches to
defining enclosure characteristics.
In general, some NEMA-type enclosures meet the requirements for
certain IP ratings. On the other hand,
an IP-rated enclosure does not meet
requirements for NEMA-type ratings. That’s because the NEMA
requirements address additional
issues not covered by the IEC standard,
such as:
• Construction requirements;
• Door and cover securing;
• Corrosion resistance;
• Effects of icing;
• Gasket aging and oil resistance.
If you specify or purchase electrical enclosures, it’s important to
understand the designation systems
so that your enclosures will do what
is required of them. CT
More Info
An excellent resource for
understanding the two enclosure
designation systems is “A Brief
Comparison of NEMA 250—
Enclosures for Electrical Equipment
(1000 Volts Maximum) and IEC
60529—Degrees of Protection
Provided by Enclosures (IP Code).”
The document can be downloaded as a pdf file at no cost
from www.nema.org/stds/
briefcomparison.cfm.
For information circle 208
CleanerTimes • September 2007 • 45