Boat Electrics

IP Ratings

by Kurt Küpper*


Often when recommending that customers mount an electrical component in a dry spot we are told: “Why, it’s IP rated! That means it’s waterproof!”

Not so. One could give a colander used in the household kitchen an IP rating, and that is designed to leak water! It seems that many of us don’t really know what these IP ratings mean.

IP ratings define the degree of Ingress Protection an item has. It is a standard developed by the International Standards Organisation. Various national standards organisations have adopted this standard, in some cases with some variations.

The IP Code consists of the letters IP followed by two digits, or one digit and one letter and an optional letter. By definition, the IP Code classifies and rates the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in mechanical casings and electrical enclosures. The purpose of the standard is to accurately define to users the degree of protection, rather than vague descriptions such as dust proof or water resistant.

IP Ratings tableThe first digit indicates the degree of protection from ingress of solid objects such as dust into the enclosure. It also indicates protection from access by human body parts such as hands and fingers.

The second digit indicates the degree of protection from ingress of water into the enclosure.

The larger the value of each digit, the greater the degree of protection from that influence. Where no specification is made about one of these two criteria, the digit is replaced by an X.

The following table summarises the definitions:

Previously the standard allowed for a third letter that defined impact resistance. This has now been removed and is catered for in a separate rating system, known as the IK ratings.

The German DIN standard provides for additional ratings that exceed the above specifications. These are dust protection ratings 5K and 6K and water protection ratings 4K, 6K and 9K. The 9K rating indicates protection from high pressure water jets as are used to clean vehicles and machinery. Such equipment might thus be rated IP6K9K.

The USA NEMA ratings are also based on the ISO standard, but they add additional criteria such as corrosion resistance, gasket durability and other criteria. An IP code can be determined from a NEMA rating, but it is not possible to convert the other way.

For practical purposes, the electrical equipment that we use on boats should have a first IP digit of 5 or 6, and a second digit between 4 and 6. The exact requirement should be determined on a case by case basis, using common sense judgement. Only in very few cases would we require a second digit to have a value higher than 6, such as for underwater lights or submersible handheld radios.

*Kurt Küpper is director of Aquavolt Electric Boat Parts. Tel: 02 9417 8455