Apart from excessive temperature, dust and water are probably the biggest threat to reliable operation of electrical and electronics equipment. While different measures are in use for temperature control the measures against entry of solids (dust and smoke mostly) and water in liquid or vapor form are specified in different ingress protection standards. Special enclosures are designed for electrical and electronic equipment to provide them protection against such damaging elements at different levels of safety.
Why Ingress Protection Standards?
Different national and international bodies lay down standards for ingress protection of electrical equipment against these elements. These are necessary to protect a user against vague promotional descriptions, eg, “water-proof”, or “water resistant”. What is exactly meant by “water-proof”? Will it prevent entry of water when exposed to a casual shower, or will it be safe when immersed 200 feet underwater for 48 hours? The standards are an effort to prevent this ambiguity.
For example, an enclosure rated at IP68 in addition to being "dust resistant" can also remain "immersed in 1.5 meters of freshwater for up to 30 minutes". As another example of clearer specifications, a socket rated to IP22 is safe to an insertion of fingers. It will also not be damaged or become unsafe when exposed to “vertically or nearly vertically dripping water” under specified test conditions.
IP Standards in Vogue
International Electrotechnical Commission (IEC) has laid down a set of standards called the IEC 60529. Europe has an equivalent standard with name EN 60529. Britain, which is now out of the European Union had already adopted the same standards with the code name BS EN 60529.
In North America and much of the world follow the IP standards published by the National Electrical Manufacturers Association (NEMA) which defines NEMA enclosure types via NEMA standard 250. While The IEC, EU, and BS standards with number 60529 are essentially the same, NEMA ratings are not directly translatable. NEMA ratings include additional feature specifications and tests which may include tests such as working under icy conditions. Specification for enclosures to be used in hazardous conditions, knock-outs occurrence for cable connections and some other specifications are also included in the NEMA standard 250.
Vehicle Enclosures Standards
The German national standard DIN 40050-9 added to the IEC 60529 system with an IP69K for wash-down applications at high-pressure, high-temperature. The addition was primarily prepared for road vehicles like trucks and concrete mixers which need intensive washing at high pressure with hot water. However, it also finds application in car wash systems and machinery used in food processing. ISO 20653:2013 Road Vehicles-Degrees of protection later superseded the IP69K. ISO 20653:2013 enclosures are not only dust-tight as in IEC IP6X, but must also withstand cleaning with steam under high-pressure.
The IP Code Structure
The IEC 60529, EN 60529 and BS EN 60529 use a four-figure code for example, IP66, which may in cases be followed by additional letters. The letters IP are always present at the start and are followed by two digits. An X in place of a figure means no specification. The additional letters have different predetermined meaning.
The first Digit-Solid Ingress
The first digit following the letters IP indicates the level of protection against ingress of solid particles or objects of various sizes. Levels zero through six are defined with following interpretations.
“0” as the 1st digit means there is no protection against solid particles / objects of any size.
“1” means the enclosure is protected against objects of dimensions larger than 2 inch (50 mm). This includes any large surface of a body, even the back of a hand, but there is no protection against deliberate contact with a body part.
“2” Protection is provided against particles or objects of size larger than 12.5 mm (half inch). This could include fingers, etc.
“3” Digit in the first place means protection against particles of size larger than 2.5 mm. This would prevent insertion of tools and thick wires.
“4” This level protects against solid objects of size 1.5 mm (0.039 in). Slender screws, most wires, and large ants etc. will be prevented.
“5”. Digit 5 in the first place indicates dust may enter but not enough to prevent satisfactory operation of the equipment.
“6” This level of protection means a totally dust-tight enclosure where no dust can even force its way in. testing is done by maintaining a vacuum in the enclosure for up to 8 hours (depending on air flow rate around it.
A letter X after the initial letters IP indicates no test data is available.
Second Digit-Liquid Ingress
The second digit following the “IP” descriptor specifies the level of protection against liquid ingress. Digits 0-9 are defined. A letter “X” in this place indicates no specification, i.e., no test data is available. Meaning of each digit in this place is explained below.
“0” in the second digit means no protection against liquid ingress at all.
“1” indicates that vertically falling drops equal to rain rate of 1mm per minute shall have no harmful effect on the specimen when mounted in an upright position onto a turntable and rotated at 1 RPM” for a test duration of 10 minutes
“2”. A digit 2 in the second place means water drops equivalent to rain fall rate of 3 mm (0.039 in) rainfall per minute should have no effect on the enclosure when each side of it is exposed at a tilt angle of 15 degrees (from normal orientation) for period of 2.5 minutes each. The total test duration will be 10 minutes.
“3”. This level specifies protection against sprayed water. A spray of water at any angle up to 60° from the vertical shall cause no harm. Two test spray methods are specified, ie, an “oscillating spray” or a “nozzle with a counterbalanced shield”. The oscillating spray test should be conducted for 5 minutes and then repeated with the enclosure “rotated horizontally by 90°” for another 5-minute test. The water rate is to 0.07 liter per minute per hole. The test with nozzle counterbalanced shield is conducted for a minimum of 5 minutes with 1 minute per square meter of surface for at least 5 minutes. Water flow rate is to be 10 liters per minute at a pressure: 50–150 kPa or 7.3–21.8 psi.
“4” in the second digit specifies protection against splashing water against the enclosure in any direction. The oscillating tube test is conducted for 10 minutes while the spray tube test should be conducted for a minimum of 5 minutes.
“5”. This level indicates protection against water jets. Water from a nozzle of dia 6.3 mm (0.25 in)) against the enclosure from any direction shall cause no “harmful effects”. The test is to be conducted for 1 minute per square meter of enclosure surface for at least 3 minutes with flow rate of 12.5 liter per minute at a pressure of 30 kPa (4.4 psi) from distance of 3 meters (9.8 ft).
“6”. A digit 6 in the second place indicates the enclosure will withstand powerful jets (12.5 mm (0.49 in) of water from any direction will cause no harmful effects during a test for at least 3 minutes with 1 minute per square meter. Water rate is to be 100 liters per minute at a pressure of100 kPa (15 psi) from distance of 3 meters (9.8 ft).
“6k”. This is not in IEC 60529 but from ISO 20653 (which replaced DIN 40050-9). It guarantees protection against even more powerful jets. 75 liter per minute through a nozzle of quarter inch at 1000 kilo Pascal from any direction at a distance of 3 m will “cause no harmful effects”. Test duration is to be at least three minutes.
“7” A digit seven in the second place means an enclosure tested for immersion up to one meter deep under water for 30 minutes.
“8” A digit seven in the second place means an enclosure tested for immersion more than one meter deep under water. Depth and test duration is negotiable with the manufacturer.
“9k” This specification is from ISO 20653 and included in IEC 60529 as IPX9. Specifies protection against high pressure, high-temperature close-range sprays. Tests are conducted at a distance of 0.15–0.2 meters (5.9 in–7.9 in).
Some standards may use additional letters for more specific information. Here is a list.
C stands for protection against access with a tool
D Protection against intrusion of a wire
F Means oil resistance
H Means a high voltage device
M Device moving during water test
S Device standing still during water test
W Weather conditions
The letter K is specified in DIN 40050-9 (which was superseded by ISO 20653), and not in IEC 60529.
National Electrical Manufacturers Association of the US defines NEMA enclosure types as NEMA standard 250. Ratings are not directly convertible. NEMA specs also specify more detailed tests. The table below lists some correspondence between NEMA codes and IEC 60529 IP code.