When designing, selecting, or assembling a linear system, you may have noticed that some components have an IP rating — IP54 or IP65, for example — while others don’t. Here we explain why that is, and what the IP ratings mean.
IP: International Protection (or Ingress Protection)
The “IP” acronym stands for “International Protection,” although it is often mistaken for “Ingress Protection,” because the IP specification defines the level of protection an electrical enclosure provides against the ingress of solids and liquids. The IP rating system and associated testing procedures are defined by the International Electrotechnical Commission in standard IEC 60529.
The IP rating system consists of two numeric digits. The first digit — which ranges from 0 to 6 — identifies the level of protection against solid objects, based on the size of the object. The higher the digit, the smaller the object that is prevented from ingress. In other words, the higher the number, the better the protection. For example, a first digit of “6” indicates a dust-tight enclosure, while a first digit of “3” indicates protection against solid objects larger than 2.5 mm (a screwdriver, for example).
The second digit in the IP rating — which ranges from 0 to 9 — identifies the level of protection against the ingress of liquids. The two primary criteria for determining protection against liquids are the quantity of liquid and the direction of its approach toward the enclosure. However, when applicable, the test also specifies a time-based component and, for water sprays or jets, defines the nozzle size, delivery pressure, and distance between the nozzle and the enclosure.
Note that there is also an IP69K rating, which was originally defined by the German standard DIN 40050-9, to ensure that electrical components on road vehicles could withstand high-temperature, high-pressure water and steam cleaning conditions. The DIN standard has been withdrawn, and the IP69K rating is now defined in ISO 20653. Even though it technically does not exist in the IEC 60529 standard, the IP69K rating is useful for food and beverage, medical, and pharmaceutical applications where hygiene and sanitation are essential.
When IP ratings apply to linear motion components (and when they don’t)
So why do some linear motion components and systems have IP ratings, while others don’t? Per the IEC 60529 standard, IP ratings apply to “enclosures for electrical equipment.” This means that purely mechanical components and systems, such as ball and lead screws, linear guides, couplings, rack and pinions, and so forth, do not qualify for ingress protection ratings. Although there may be internal components (such as the balls inside a ball screw) that need to be protected against dust and liquids, there are no electrical components to be protected, so the IP standard does not apply.
However, if a component or system has integrated electrical equipment and is fully enclosed — an actuator with an integrated motor or integrated motor/drive combination would fall into this category — it will likely be tested for ingress protection and have an IP rating. On the other hand, if an electrical component is merely mounted to a mechanical component — such as a proximity switch on a linear actuator or a linear encoder on a guide rail — with no enclosure covering the entire assembly, the electrical component itself may have an IP rating, but the entire assembly (actuator-plus-sensor or rail-plus-encoder) would not.