Degree of protection IP

Degree of protection IP

The Degree of Protection of rotating electric machines is defined as protection against the penetration of mechanical particles, dust and water. The Degree of Protection is defined in thefollowing standard: IEC 34-5 (NEN-EN 60034-5).


The Degree of Protection is indicated by the ‘IP’ followed by two numbers, the first indicating the protection against mechanical particles and the second indication the protection against water. An example of the Degree of Protection definition: IP-55; the higher the digits, the greater the protection level (see the tables below).

All rotor nl® three-phase electric motors are supplied in IP55 as standard, enabling an outdoor installation. The higher level of protection may, however, cause a few issues:

  1. Tight shaft seals cause additional “sliding friction” which generates heat and contributes to the friction losses, which are more significant at fast running motors.
  2. The condensation drain holes used for draining off the condensation water and the equalisation of the atmospheric pressure (“breathing option”), must be partially enclosed at IP55 and completely enclosed at IP56 protection.

A suitable solution can be implemented to overcome the first problem by fitting an alternative shaft seal in the endshield/flange or the bearing cap, but not on the bearing, as it would cause excessive heat development. The second problem is less easy to resolve. The probability of condensation water accumulating inside the motor is higher at higher protection levels. A moisture-proof insulation system (tropical insulation is standard in all rotor nl® motors) is usually sufficient for IP55 protection. At the protection class IP56 the problem is more difficult to overcome, especially for frame size greater than 100 frame as the air volume in large electric motors is larger and this increases the potential for condensation when changes in temperature occur. To minimise condensation accumulation a stable internal temperature must be maintained (5°C above the ambient temperature). This applies for motors when stationary, as the internal temperature always rises significantly during the operation. The solution is the installation of anti-condensation (or “standstill”) heaters.

The protection class selection is intended to reduce the probability of electric motor failures due to ingress of mechanical particles and water. This, however, is not a guarantee of trouble free operation. Higher protection class should be implemented where necessary and for specific applications as it sometimes can achieve the opposite effect with regard to the reliability of operation. The IP rating displayed on the motor nameplate must be observed during the electric motor installation.

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