IP stands for Ingress Protection. What is ingress protection, I hear you say.
Ingress protection is the degree to which an electrical device can prevent
itself from being invaded by solids or liquids. That is to say, the degree to
which it can protect itself from ingress.

This can be particularly important as any outside interference from solids or
liquids could have cause an electrical device to malfunction, or worse, could
cause it to be dangerous. Many liquids can act as a conductor of electricity as
can fine dust particles. Solids larger than dust can also pose a threat to the
workings of an electrical device. Obviously, if we picked up a metal object and
managed to poke it into an electrical device, it could give us a nasty shock!
For these reasons, the IP rating is very important.

The IP rating is an internationally recognized standard, and is endorsed by
the International Electrotechnical Commission. Most countries around the
world have adopted this standard. This uniform standard saves companies and
organizations a great deal of time as all they need to do is refer to a device’s
IP rating rather than having to produce a detailed specification each time they
wish to describe how well it is protected from ingress.

Each IP rating comprises two numbers. The first number is a measure of how
well the object can withstand invasion by solids, ranging from no special
protection at all to protection against dust particles. The second number is a
measure of how well it can withstand liquids, ranging from no special protection
at all to watertight under water. Incidentally, this rating is not necessarily a
measure of how watertight a sub-marine vessel may be under water (although it
could be): the test is meant for objects that may be submersed, but only to a
depth specified by the manufacturer, although it could be valid for appliances
being used on a ship, for instance, where heavy seas could cause excessive
splashing.

Taking the first digit, which is for protection against solid objects, the
range is as follows:

0 – No protection against ingress from solid objects

1 – Protects against any object over 50mm

2 – Protects against any object over 12.5mm

3 – Protects against any object over 2.5mm

4 – Protects against any object over 1mm

5 – Protected from most dust ingress, enough to allow normal operation

6 – Complete protection from dust ingress

The second digit concerns protection from liquids:

0 – No protection against ingress from liquids

1 – Protected against vertically falling water drops

2 – Protected against vertically falling water drops when the enclosure is
tilted up to 15 degrees

3 – Protected against spraying water

4 – Protected against splashing water

5 – Protected against water jets

6 – Protected against powerful water jets/heavy seas

7 – Protected against temporary immersion in water

8 – Protected against continuous immersion in water

The above list may require further clarification from the manufacturer of the
specific device, especially for 7 and 8. For instance, the depth of the water
and the duration of continuous would need to be defined. The reason is
that some oceans are so deep that virtually no object could withstand the
pressure, and would collapse. Also, continuous may mean eternally
to some people – and no-one could guarantee anything forever!

To give you an example of how the system works, take the Insectocutor IND65
Fly Killer Machine from Arkay Hygiene. Its IP rating is 65 (hence the name). The
6 means that it is fully protected from dust. The 5 means that it is protected
against water jets, but not as powerful as may be experienced in heavy seas. The
IP65 rating means that the IND65 can be used in facilities where there may be a
lot of dust in the air or where occasional jets of water are experienced. The
IND65 has in fact been recently been re-named as the IP65 as a recognition of
this rating.