What is an electrical enclosure?
An electrical enclosure is a housing for electrical or electronic equipment. Its purpose is to protect that equipment from the environment (especially in the case of external electrical enclosures) and also to protect people from the equipment (e.g. to prevent electric shock or the propagation of an explosion).
There is a harmonised European standard that specifies the different aspects of an enclosure’s performance and how it should be categorised – at least for low voltage applications. That is EN 62208 Empty Enclosures for Low-Voltage Switchgear and Controlgear Assemblies. General Requirements.
The environmental protection that enclosures typically provide include the following:
Protection against water ingress
Classified by the IEC60529 IP code system – the second digit of the IP code.
The enclosure needs to be reasonably watertight to protect from precipitation. Condensation is also a common problem which can be harder to eradicate since it involves the ingress of water as a vapour. Flooding is an issue in extreme cases and many enclosures (with high IP ratings) are designed to be submerged in water (submarines for example!).
Protection against adverse temperatures (high or low)
Extreme temperatures can damage electronic equipment or stop it working properly. Regulating temperature usually involves adding ventilation (maybe forced, with fans), double skins, insulation layers or even air conditioning units to the enclosure.
When designing the heat management for an enclosure it is necessary to account for typical external temperature fluctuations and solar gain (heating from the sun). However, the electrical or particularly electronic equipment can generate significant heat inside the cabinet too.
Protection from hazards and the cabinet’s strength
The main hazard from electrical enclosures is usually the electrical components inside. The job of the enclosure is to prevent people from coming into contact with these components. If the enclosure is damaged then the electrical equipment and wiring can be exposed and become a shock hazard.
EN 62262 (equivalent to IEC62262) deals with IK ratings for the amount of energy a cabinet can withstand an impact. This gives an indication of how much protection against this aspect of the electrical hazard a cabinet provides.
Plastic cabinets typically having a rating of about IK07, which equates to breaking under a blow from a large hammer. Metal cabinets will withstand much higher impact energies; barely being marked by the maximum impact energy of 20 joules, specified in 62262. In fact, the IK rating system perhaps isn’t really very relevant to metal enclosures as they are so much stronger than the maximum category.
In certain fault conditions, it is possible for live electrical components to touch the body of the enclosure. For plastic enclosures, made from insulating material, this clearly doesn’t raise an immediate hazard, while the cabinet remains closed. Metal enclosures should be earth bonded (sometimes to a local earth spike or mat) to protect against this possible hazard.
Passively Safe Enclosures
The enclosure can also be a hazard in itself – particularly when it is installed by the roadside where it might be crashed into by a vehicle leaving the road.
There is an area of design for street furniture called passive safety in which road-side equipment is designed to shear off or crumple on impact, thereby preventing serious injury to the vehicle occupants.
There are many types of passively safe lighting, sign and signal columns. However, only one passively safe road-side enclosure has been developed – the Ritherdon Passively Safe Cabinet.
