This last method has the advantage of providing an easy solution to the other requirement that is the protection of equipment against certain influences such as:

• The ingress of foreign bodies which could disturb the mechanical or electrical operation. They comprise not only sand and dust but also small animals and flying or creeping insects,
• Water and other liquids which could alter the insulation and generate degradation, mechanical impacts that might deform or break brittle parts,
• Corrosive gas from the environment,
• Radiated electromagnetic fields,
• Various radiations including light.

The IP Code

General
The IP code is described in Publication 529 of the International Electrotechnical Commission.

IP Means: International Protection.

This code allows for the description of the degrees of protection provided by enclosures against access to hazardous parts, ingress of solid foreign bodies and against harmful effects of water, by means of the numerals and letters described hereunder.

This standardised code is intended to be used in product standards. It can also be used to describe an empty enclosure, but then some difficulties can appear as to the application:

• Where to locate harmful parts to keep them at «adequate distance?
• Where may water or dust deposit without disturbing the correct operation of the equipment?

In fact, degrees of protection will only be required when the enclosure is in service with equipment inside.

The assembler is therefore responsible for the final product complying with it's standard. But the manufacturer of the enclosure must state in the documents where equipment has to be installed inside the enclosure to maintain the degrees of protection he has assessed.

Eventually, people in charge of the installation who will connect the equipment (cable pass), fix it and in some cases adapt auxiliaries (pushbuttons, meters) must ensure that the specified degree of protection is maintained.

Letters IP of the code are followed by two independent numerals and sometimes by letters. When the degree of protection corresponding to one of the numerals is not stated (be it unnecessary or unknown) it is, replaced by an X.

First Numeral
As a result of decisions made for previous editions of the standard, decisions, which cannot to be reconsidered, the first numeral indicates simultaneously:

• Protection of persons against access to harmful parts and
• Protection of equipment against ingress of foreign bodies.

To check compliance with the first numeral, two probes must therefore be used (an access-probe and an object probe) with the application forces specified in the standard, or the same probe is used with two acceptance criteria.

The various degrees correspond to the following meanings:

IP 1X		it can be a wire-mesh or an enclosure, the largest opening of which does not allows a ball of 50 mm diameter to ingress. This corresponds approximately to the ingress of a hand (see fig. 3).
IP 2X		the protective wire-mesh has smaller holes and the diameter of the object-probe is 12.5 mm. In addition, the jointed test-finger must stay at adequate distance from harmful parts.
IP 3X		the enclosure must not allow ingress of foreign bodies 2.5 mm of diameter. The test is performed with a steel wire with edges free from burrs, because the use of a 2.5 mm diameter ball would not be convenient.
IP 4X		as for the previous degree but with 1 mm instead of 2.5.
IP 5X     and IP 6X		these two degrees correspond to protection against ingress of dust. IP 5X allows penetration of some dust in places where it is not harmful. IP 6X accepts no ingress of dust at all. The test is performed in a test room where talcum powder is sustained floating by means of an airflow. In addition, the enclosure is de-pressurised internally except if the relevant equipment standard specifies that it be of category 2: that is, the normal operation of the enclosed assembly cannot generate significant internal pressure reduction. Although the test is performed with talcum powder, the effects that might give any other type of dust must be taken into account here.

Second Numeral
The second characteristic numeral of the IP code indicates the degree of protection against harmful effects of water penetration. It is specified that the tests are performed with fresh water (see fig. 4) with no wetting agents.
The interpretation of tests for this numeral may be difficult since water penetration into the enclosure is permitted, provided it does not generate harmful effects.
The various degrees of the second numeral correspond to the following situations:

IP X1		this first degree correspond to the protection against vertical water drops to which indoors equipment can be exposed due to leaks or condensation-drops from the ceiling of the room  or on tubes passing above the enclosure.
IP X2		this degree corresponds also to water drops, but with a larger flow and with an angle up to 15°. It is for instance the case of equipment on ships.
IP X3		this degree corresponds to the protection against rain. The maximum spray angle is 60° from vertical. The base of the enclosure may be open. The test may be performed by means of a oscillating arc-tube equipped with nozzles (over 60° from each side of vertical) or of a mobile spray with a mask limiting the incidence of the jets. In both cases, the water flow is specified.
IP X4		the water flow of each nozzle is the same for this degree as for the previous one but there are nozzles over 180°; in addition, the tube oscillates over ± 180° so that water is sprayed in every direction. This test simulates heavy rain and splashes.
IP X5 and IP X6		the degrees are, tested by water jet hose, simulating water-jets, heavy sea, etc. Test conditions are more severe for degree 6 than for degree 5: a larger diameter of the nozzle and water flow.
IP X7 and IP X8		no longer correspond to water projections but to transient or permanent immersions.

Therefore enclosures complying with these degrees must have double marking if they also comply with a lower degree, for instance IP X5/X7 (a bucket immersed upside down is IP X8, but not IP X4).

Water-tests of the IP code have been recently incorporated into IEC 68-2-18 with the following correspondence

Additional Letter
In some cases, the protection provided by an enclosure against access to harmful parts is better than indicated by the first numeral (which also indicates the protection against ingress of foreign bodies). For instance it is frequently the case of an opening of the enclosure blinded by a staggered joint or a sheet bent.

This protection can be characterised, by an additional letter added after the two numerals. It allows openings useful for thermal dissipation when keeping the degree of protection required for the protection of persons.

It has one of the following meanings:

IP XXA	has no practical application since the test for the letter A is the same as for the first numeral 1 (see fig. 3).
IP XXB	means that foreign bodies of diameter larger than 12.5 mm can ingress into the enclosure, but that the test-finger does not penetrate more than 80 mm, i.e. not beyond its 50 x 20 mm guard and stays at an adequate distance from harmful parts (see fig. 5).
IP XXC	allows penetration of foreign bodies of diameter larger than 2.5 mm, but a straight steel wire of this diameter and 100 mm long stays at an adequate distance from harmful parts.
IP XXD	the situation is similar to the previous degree, but for a diameter of 1 mm. The additional letter is also used when only the protection of persons is aimed at.