Know your degree-of-protection codes

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 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.

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.

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.