Enclosures are the first line of defence

By their very nature, all enclosures provide protection, to a greater or lesser extent, against contact with the housed equipment and against the ingress of solid objects and water.

The relevant international standard is EN 60529, which defines ratings written as IPxx, where the first digit defines the protection against solid objects and the second the protection against water ingress.

The standard sets out the following criteria.

Protection classes for protection against contact and solid bodies

First figure	Scope of protection
0	No protection.
1	Protection against contact by the hand with active or internal moving parts. Protection against penetration of solid bodies with a diameter greater than 50 mm.
2	Protection against contact by the fingers with active or internal moving parts. Protection against penetration of solid objects with a diameter greater than 12 mm.
3	Protection against contact with active or internal moving parts with tools, wires, etc of a thickness greater than 2.5 mm. Protection against penetration of solid objects with a diameter greater than 2.5 mm.
4	Protection against contact with active or internal moving parts with tools, and wires greater than 1 mm.
5	Complete protection against contact with live or internal moving parts and protection against harmful dust accumulation. The penetration of dust is not completely prevented, but it may not penetrate in such quantities that the operation of the equipment is affected.
6	Complete protection against contract with live or internal moving parts. Total protection against the ingress of dust.

Protection classes for water protection

Second figure	Scope of protection
0	No protection.
1	Protected against vertically falling drops of water.
2	Protected against direct sprays of water from up to 15 degrees from the vertical.
3	Protected against direct sprays of water from up to 60 degrees from the vertical.
4	Protected against water sprayed from all directions: limited ingress that does not affect the equipment operation is permitted.
5	Protected against low-pressure jets of water from all directions: limited ingress that does not affect the equipment operation is permitted.
6	Protected against strong jets of water from all directions: limited ingress that does not affect the equipment operation is permitted.
7	Protected against immersion between 150 mm and 1 m for up to 30 minutes: limited ingress that does not affect the equipment operation is permitted.
8	Protected against long periods of immersion under pressure: limited ingress that does not affect the equipment operation is permitted.

A typical enclosure for general-purpose use might be rated IP54; one for use in hostile environments at IP65; and for use in extreme applications, IP66 may be required.

An IP54 enclosure could be used as a handheld controller for shop floor equipment; an IP65 one for equipment outside; and for housing electronics in areas such as food production, where it will be regularly hosed down, IP66 will be needed.

In general, enclosure manufacturers will use two main techniques to achieve the designed protection level. Satisfactory IP54 sealing is readily achieved by using a tongue and groove construction to the joint between the body of the enclosure and a removable panel or lid.

No gaskets are used. The seal is achieved through the combination of a recess in the base section that mates to the corresponding mirror profile in the lid when the lid is screwed down.

To achieve higher levels of sealing, a gasket between the two mating halves will be required. Typically, gaskets will be one of two types. Either a silicone gasket will be injected as a liquid into a groove in one of the mating surfaces as part of the manufacturing process; when it self-cures it is permanently affixed to the enclosure.

Alternatively, a separate, preformed moulded neoprene gasket is inserted between the two mating surfaces.

The separate gasket approach has a number of advantages: a metal enclosure can be painted if required without having to mask the gasket area; the gasket can be easily replaced if it is damaged and, again in a metal enclosure, a conductive gasket can be used to give both environmental and electrical screening.

To eliminate potential weak spots in the seal, it is standard practice to ensure that the fixings are positioned outside the sealed area so that the integrity of the seal is not compromised by screws passing through or inside it.

The majority of enclosure manufacturers will quote the IP rating of their products as part of the specification, enabling the project engineer to select the most appropriate packaging for the intended application - to inadvertently end up with an ideal enclosure that also happens to be rated at IP67 for equipment that will only ever be used in the office environment could be somewhat over the top.

As always, the best advice is to talk to the specialist enclosure supplier as early in the design cycle as practical; timely advice on the selection of the enclosure frequently saves a lot of development time and money.