Selecting the right enclosure for a particular situation requires some thought, as there are several issues to consider. Chris Lloyd of Spelsberg offers this aide memoire to some of the more useful points.
ABS: Acrylonitrile butadiene styrene is a thermoplastic polymer, often used to make enclosures. It is tough, resistant to impact and heat, impervious to most of the common chemical attacks and can bear considerable static loads.
Aesthetics: Enclosures can often be on public or semi-public display, so a well-designed and maintained unit will help instil confidence that it is suitable for the job in hand.
Aluminium: A popular metal for making enclosures, aluminium is light, easily worked and largely immune to corrosion.
Apertures: It is important to consider access to the interior of an enclosure. Sealing, weatherproofing and vermin all need to be considered, as does access to the equipment within.
Backplate: Most enclosure designs include a backplate to which the electrical equipment is fitted and which is used for mounting the enclosure to a wall. This needs to be strong enough for the load and any likely impacts.
Corrosion: Many enclosures will be located in harsh environments, e.g. outdoors or where industrial chemicals are present. Even a benign location is likely to include some rust-inducing moisture.
Cover: Most enclosures are offered with a range of optional covers, e.g. transparent, lockable, hinged, etc.
Customisation: Although there are many standard model enclosures available, custom designs often cost little or no more.
Diecast: A method of manufacture that produces a strong enclosure.
Environmental factors: Humidity, moisture, spray, water, dust, dirt, chemical, impacts etc and their likelihood (constant, frequent or occasional) must be assessed as part of the selection process.
Fireproof: The fundamental job of an enclosure is to protect its contents. A fireproof enclosure is able to withstand extremes of heat and should be used in high-risk applications.
Flame retardant: Flame-retardant materials are suitable in applications where fire is a relatively low risk. Such materials are susceptible to fire damage, but have resistance for a predictable amount of time.
Galvanised: Sheet steel coated with zinc for environmental protection.
GRP: Glass-reinforced plastic enclosures are often as strong as metal ones yet are half the weight and impervious to rust, dents and scratches. Its thermal insulation properties may useful for outdoor usage.
Hinged door: When regular access to the interior of an enclosure is required a hinged door is less likely to be lost or damaged than a loose one.
IEC60529: The international standard relating to the classification of degrees of protection provided by enclosures.
Impact: Enclosures provide constant protection from wind, rain, humidity, etc. However, the likelihood of impacts also needs to be considered, including their force, frequency and consequences.
IP rating: The international standards relating to ingress of dust, dirt, moisture and solid objects.
Material of construction: There are many choices of metal and plastic for the main body of an enclosure, each with attributes that can be matched to the application.
Metal: The first choice of material for an enclosure used always to be metal, but as plastics become more and more advanced they are an increasingly attractive option.
Mounting brackets: There are many forms and sizes of enclosure mounting brackets. As mundane as they sound, poor selection can compromise an installation.
Outdoor: Enclosures destined to be installed outdoors need to be weatherproof at the very least. Other considerations may include vehicular impact, vermin and larger animal attacks, vandal proofing and public safety.
Plastic: Many of today's best enclosures are described as "˜plastic'. This usually refers to a modern high-performance engineering plastic.
Polycarbonate: The most common plastic for enclosures is probably polycarbonate, which is durable, has high impact resistance and a fairly wide temperature resistance.
Polystyrene: Often dismissed as only suitable for disposable cups, polystyrene actually offers medium-strength characteristics and can provide excellent ingress protection.
PVC: Poly vinyl chloride is used as a low-cost option and is suitable for small simple installations where impact and environmental risks are low.
Rust: The oxidisation of ferrous metals can cause structural weakening, seizing of screws and joint and compromise ingress protection.
Stainless: Stainless steel is an option for enclosures used in chemically harsh environments and where hygiene is particularly important.
Temperature Management: Ventilation, heaters to avoid condensation build up.
Ultraviolet degradation: Some plastics will breakdown if exposed to sunlight. It is usually a slow process, but it will limit the working life of enclosures.
To learn more about electrical enclosures, please visit www.spelsberg.co.uk.