Generally speaking, electricity and water are a bad mix. Precision electric motors should be keep clean and dry. But that's not practical in some applications, especially if the application is outdoors, like a cell phone tower, or involves processing fluids that can, on occasion escape, like in a brewery. Such applications are best suited for IP rated step motors. Since this is also an engineering blog, we strive for quantitative analysis. As luck would have it, there's a standard for everything, including ingress protection. Per IEC standard 60529, products claiming protect must be marked with a "IP" followed by two numbers and in some cases, additional letters like "K". The first number reflects the device's level of protection against particles like dust:
|Level||Object size protected against||Effective against|
|0||—||No protection against contact and ingress of objects|
|1||>50 mm||Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part|
|2||>12.5 mm||Fingers or similar objects|
|3||>2.5 mm||Tools, thick wires, etc.|
|4||>1 mm||Most wires, screws, etc.|
|5||Dust protected||Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact (dust proof)|
|6||Dust tight||No ingress of dust; complete protection against contact (dust tight)|
If a motor lists no special protection, it is usually IP40. The "4" means that particles larger than 1 mm in diameter will not fall in and cause damage, while the "0" indicates no protection against water or other liquids. Which brings us to the definition of the second numeral:
|Level||Protected against||Testing for||Details|
|1||Dripping water||Dripping water (vertically falling drops) shall have no harmful effect.||Test duration: 10 minutes.|
Water equivalent to 1 mm rainfall per minute.
|2||Dripping water when tilted up to 15°||Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.||Test duration: 10 minutes.|
Water equivalent to 3 mm rainfall per minute.
|3||Spraying water||Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.||Test duration: 5 minutes.|
Water volume: 0.7 litres per minute.
Pressure: 80–100 kPa.
|4||Splashing of water||Water splashing against the enclosure from any direction shall have no harmful effect.||Test duration: 5 minutes.|
Water volume: 10 litres per minute.
Pressure: 80–100 kPa.
|5||Water jets||Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.||Test duration: at least 3 minutes.|
Water volume: 12.5 litres per minute.
Pressure: 30 kPa at distance of 3 m.
|6||Powerful water jets||Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.||Test duration: at least 3 minutes.|
Water volume: 100 litres per minute.
Pressure: 100 kPa at distance of 3 m.
|6K||Powerful water jets with increased pressure||Water projected in powerful jets (6.3 mm nozzle) against the enclosure from any direction, under elevated pressure, shall have no harmful effects.||Test duration: at least 3 minutes.|
Water volume: 75 litres per minute.
Pressure: 1000 kPa at distance of 3 m.
|7||Immersion up to 1 m||Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).||Test duration: 30 minutes.|
The lowest point of enclosures with a height less than 850 mm is located 1000 mm below the surface of the water, the highest point of enclosures with a height equal to or greater than 850 mm is located 150 mm below the surface of the water.
|8||Immersion beyond 1 m||The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.||Test duration: continuous immersion in water.|
Depth specified by manufacturer, generally up to 3 m.
|9K||Powerful high temperature water jets||Protected against close-range high pressure, high temperature spray downs.||—|
IP65 step motors are dust tight and are unaffected by a light water spray. When done properly, the protection is accomplished by placing water and dust tight gaskets between the stator stack and the end bells and by routing the electrical cable through a sealed cable gland. The front end bell contains a shaft seal. Although the gap between stator laminations is too small for water to penetrate due to its surface tension, if a hot, wet motor is cooled after use, the internal air pressure drops and creates a vacuum that can draw water between the lams. Special, proprietary coating processes are used by the best manufacturers to prevent such damage.
Many modern step motor applications require continuous feedback of the shaft speed and angle. Optical encoders are a popular choice for such applications, but they, too, must be protected from the ingress of liquids and dust. One manufacturer's solution is shown below:
Some applications require motor operation under water, which requires an IP rating higher than 65. This, too, can be done with careful engineering and precision manufacturing. We close with this amusing video of an IP67 BLDC motor operating in a goldfish tank.