Know your degree-of-protection codes
plantservices.com/articles/2019/know-your-degree-of-protection-codes/
Jan 15, 2019
The International Electrotechnical Commission (IEC) standard 60529, “Degrees of
protection provided by enclosures (IP code),” addresses the degrees of protection for
electrical machines (motors and generators). The “IP” acronym means “international
protection” but is sometimes referred to as “ingress protection.” The IP code is
commonly displayed on the nameplates of metric machines that are manufactured to
IEC standards.
The NEMA MG1 Motors and Generators standards have adopted the IEC standards for
IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of
the IP marking is becoming more common. In light of this, let’s consider IP code
designations and examples of the IP codes for common electrical machine enclosures.
IP characteristic letters
The IEC designation for degrees of protection consists of the letters “I” and “P” followed
by two numerals. The “IP” designation may be followed by one of these letters: M, S, or
W. The letters M and S are used for special applications such as open-enclosure
ventilated machines on the deck of a ship, where the machine air entry and air discharge
openings are closed when the machine is stationary.
In such applications, the code letter is specified after the number that indicates whether
protection was proven against damaging water entry with the machine stationary (S) or
with the machine running (M). If the additional letters are omitted from the IP code,
then the degree of protection is maintained in both operating conditions (i.e., when the
machine is running and when it is at a standstill).
The letter W is used for weather-protected machines. Per IEC 60529, it applies to
machines that are used under specific ambient weather conditions and with additional
protective measures or equipment.
Note: In the shipboard example, the degree of protection must be specified for both
machine operating states; thus, the degree of protection would be designated as
IP55S/IP23M.
IP characteristic numerals
The first numeral after “IP” (see Table 1) indicates the enclosure’s level of protection
against incidental contact with internal components by solid materials or by persons.
The second numeral (see Table 2) defines the amount of water ingress against which the
1/3
enclosure must protect. Clause 5.5 of MG1 includes this statement: “When all parts of a
machine do not have the same degree of protection, at least the designation of the
lowest degree shall be shown, followed, if necessary, by the higher designation with
clear reference to the part to which it applies.” In most cases, there will be only one IP
designation on the machine, indicating the minimum level of protection provided.
Note: The dimensions associated with the IP codes in this article are in metric units to
conform with IEC 60529; the conversions to inch values are rounded to two significant
digits.
Typical IP codes
Typical IP codes for some common machine enclosures are given below, along with
descriptive information about them.
About the author: Tom Bishop
Tom Bishop, P.E., is a senior technical support specialist with the
Electrical Apparatus Service Association and has more than 30 years of hands-on and
engineering experience at electrical machinery manufacturing and apparatus service
firms. Bishop has authored dozens of technical articles and papers and presented
numerous seminars on electric motor application, maintenance, and repair. In addition,
he is chairman of EASA’s Technical Services Committee and a principal member of the
National Fire Protection Association Electrical Equipment Maintenance Committee
(NFPA 70B). Contact him at tbishop@easa.com
Drip-proof (IP12) - The first characteristic numeral 1 indicates that the machine
is protected against solid objects greater than 50mm (2.0 inches) in diameter. The
second characteristic numeral 2 indicates that a drip-proof machine has vent
openings constructed such that successful operation is not interfered with when
drops of liquid or solid particles strike or enter the machine enclosure at any angle
from 0 to 15 degrees downward from the vertical.
Totally enclosed (IP54, IP55) - The first characteristic numeral 5 indicates
that the machine is protected against dust deposits. The second characteristic
numeral 4 indicates that the enclosure protects against water splashed from any
direction; the second characteristic numeral 5 indicates that the enclosure protects
against water projected from a nozzle at any direction.
2/3
Weather-protected WPI (IPW23) - A weather-protected Type I (WPI)
machine is a guarded machine with its ventilating passages constructed so as to
minimize the entrance of rain, snow, and airborne particles into the electrical
parts (e.g., windings) of the machine.
Weather-protected WPII (IPW24) - In addition to the enclosure features of
the Type I machine, a weather-protected Type II (WPII) machine has its
ventilating passages at both intake and discharge arranged such that high-velocity
air and airborne particles blown into the machine by storms or high winds can be
discharged without entering the internal ventilating passages that lead directly to
the machine’s electric parts. The normal path of the ventilating air that enters the
electric parts of the machine is arranged by baffling or separate housings so as to
provide at least three abrupt changes in direction, none of which is less than 90
degrees. An area of low-velocity air not exceeding 600 feet per minute (3.0 meters
per second) is also provided in the intake air path to minimize the possibility of
moisture or dirt being carried into the machine’s electric parts. Removable or
otherwise easy-to-clean filters may be provided instead of the area of low-velocity
air.
3/3
