From Electrical Installation Guide
If several external influences appear at the same time, they can have independent or mutual effects and the degree of protection must be chosen accordingly
Each condition of external influence is designated by a code comprising a group of two capital letters and a number as follows:
First letter (A, B or C)
The first letter relates to the general category of external influence:
- A = environment
- B = utilisation
- C = construction of buildings
The second letter relates to the nature of the external influence.
The number relates to the class within each external influence.
Additional letter (optional)
Used only if the effective protection of persons is greater than that indicated by the first IP digit.
When only the protection of persons is to be specified, the two digits of the IP code are replaced by the X’s.
Example: IP XXB.
For example the code AC2 signifies:
A = environment
AC = environment-altitude
AC2 = environment-altitude > 2,000 m