Choosing materials for outdoor cabinets and enclosures
Designing outdoor cabinets and enclosures presents challenges that can impact on profitability. If materials are not chosen well, the weather can damage unprotected equipment enclosures in no time at all, as seen with lightening strikes, or take its time, slowly degrading because of moisture. It’s not only heat, rain, cold and chemicals that present threats, but vandalism and rodents.
Your mission is to create a robust cabinet or enclosure that can stand up to all these potential problems and more. Resistance properties of every component of your enclosure should be considered to prevent a gasket, latch or other part from being a corrosive weak link. The key lies in the materials you choose, but before you can do that, you have to consider some of the challenges you’re up against.
Determining environmental factors
You should first investigate climate and environmental issues where your cabinet or enclosure will be installed. This will tell you if you need a cooling system, the need for more corrosion resistance, water or dust-tight seals, for example. By preparing your cabinet or enclosure for every possibility, you reduce the risk of equipment damage or failure and inefficient operation.
Consider a sealed electrical enclosure that’s been designed to protect against whatever the outside throws at it. The internal temperature can also pose a threat, influenced by the internal heat load, rate of heat dissipation and the ambient temperature of the outside. Exposed to excessive heat, electronic components become less reliable, operate less efficiently and their overall life span reduces.
On the opposite end of the spectrum, ambient temperatures can also drive the internal temperature down. In this case, an air-to-air heat exchange can ventilate the enclosure, keeping operating temperatures within safe levels.
If the ambient temperature of the environment around the enclosure exceeds the internal conditions, you’ll need an air conditioner or another active cooling system.
The cold can actually have more adverse effects on your unit’s performance than heat. If your installation is in a Northern environment, condensation and ice will regularly build up on the outside of component enclosures. You’ll need an additional heating unit to keep internal temperatures where they should be for safe operation.
Wind and rain
The wind itself isn’t a problem for well-designed electrical cabinets and enclosures. Problems occur from what the wind can introduce into the internal environment: particles of dirt, dust, or foreign debris that enter via a substandard or broken seal. The result can create issues with cooling and heat transfer systems, clog ventilation, and limit the lifespan of your unit.
Stainless steel and corrosion-resistant access hardware can help, such as quarter turn spring latches rated IP65. The right sealing gasket used as an additional seal can also prevent these problems. The most effective sealing gaskets for this purpose are made of ethylene propylene diene, better known as EPDM. EPDM is especially robust in standing up to the elements. That includes driving rain, which can get past a weaker material.
Theft and vandalism
To ensure the operational integrity of your outdoor enclosure or cabinet, you’ll need to think about security to limit or prevent access to controls and components. You can implement security systems, alarms, monitoring devices, and remote controllers. The threat of vandalism and theft is less of an issue if you’re designing your enclosure to NEMA-12 and NEMA-4 standards in the U.S., or in Europe, IP56 and IP 52. Due to the air and moisture-tight seals required, your cabinet or enclosure will already have a high level of protection.
What is NEMA?
NEMA stands for the National Electrical Manufacturers Association. They’re the largest trade association of electrical equipment manufacturers in the U.S., where their standards have been adopted. Europe relies on IP ratings (ingress protection) as used by the International Electrotechnical Commission (IEC). You can find a chart with approximate NEMA/IP rating conversions here.
Materials: plastic or metal?
Materials for enclosures fall into two groups: metal and plastic, of which there are subgroups. There are pros and cons to each, so your choice will depend on your enclosure’s function.
Always consider the possibility of electromagnetic interference (EMI). Metal enclosures naturally provide protection and this can be reinforced with EMI gaskets. Plastic enclosures offer no protection against EMI, but you can get around this problem by applying a metallic coating to the interior of a fiberglass or polycarbonate enclosure.
Here’s a quick overview of the advantages and disadvantages of both:
Benefits of plastic
- Generally less expensive than metal
- Lighter in weight
- Electrically insulating, where metals are good conductors. For example, plastic electrical boxes would not require grounding, where a metal electrical box would (taking valuable time to do the job)
- Plastic is often integrated with mounting pillars, making installation generally easy
- Easy-to-clean, smooth surface and aesthetically pleasing
- Easy to modify by cutting holes, which electrical enclosures often need
Disadvantages of plastic
- Limited chemical resistance compared to metal – while compatible with mild acids, plastic should not be used with solvents or alkalis
- Not all polycarbonates are suited for outdoor environments
- Does not stand up to blunt force as well as metal
- Does not protect against EMI unless a metallic coating is applied to the enclosure’s interior, adding to costs
- Unless treated, plastics do not stand up to UV rays well
Benefits of metal
- Fire resistant
- Stronger impact resistance than plastic
- Protects against EMI
Disadvantages of metal
- More expensive than plastic
- Heavier – depending on the size you’re working with, you may need lifting equipment to position your enclosure during installation. This can be a problem if you’re dealing with limited access to your site
- Needs to be painted, which adds costs
- A dent or scratch to the surface can compromise its corrosion resistance
- Can require die work, welding, grinding, and shaping, depending on your design specifications
- Needs to be grounded due to its conductivity
Let's look at plastics in more detail:
Extremely popular alternative to metal, fiberglass is a polyester material reinforced with glass fibers. It’s a rigid, low-cost alternative to metal, resistant to corrosion, making it a suitable choice for outdoor cabinets and enclosures. Fiberglass degrades under direct exposure to sunlight, so you’ll need to formulate this material with UV inhibitors and aluminium trihydrate to provide the UV resistance needed.
Polycarbonate is a high-performance thermoplastic processed by injection moulding or sheet extrusion. It has high impact resistance and performs well in a range of temperatures. The only drawback to polycarbonate is that it does not hold up well in environments where it may come into contact with strong alkalis or organic solvents. In these instances, the polycarbonate will need to be silicone-coated, which will also help with scratch resistance.
Moderately priced, polyester is light, durable and excellent to resisting corrosion and humidity. Blended with polycarbonate, it’s relatively new as an enclosure material, so it can be hard to find. Like polycarbonate, the polyester blend is produced using injection moulding. It has high impact resistance and excellent electrical properties. It also offers outstanding resistance to chemicals and moisture. Polyester holds up better to UV rays than fiberglass, but you should still consider UV absorbers.
Plastic components are outstanding choices for both metal and plastic outdoor enclosures. Domed blanking plugs made of PVC or LDPE snap into place to provide protection from dirt and moisture. Look for PVC edge protectors with a steel spring core. These are highly flexible and easily pressed on by hand. You’ll want your edge protectors to stand up to extreme temperatures of -40°C to +90°C. Cable glands made of tough nylon are another important component for ingress and protecting against stain relief.
A look at metals in more detail:
The different variants of steel have their own specific characteristics. Stainless steels are especially effective at resisting corrosion due to chlorine, sea water, sulfates and bromides, but for an outdoor enclosure containing electrical parts, you have to think about EMI shielding. Not all stainless steels are ferromagnetic, which are materials strongly attracted to a magnet. This redirects EMI from damaging your electrical equipment. You want steel made with nickel, iron or cobalt.
You’ll find raw and anodized aluminium used in front panel and enclosure designs due to its affordability and versatility. Anodized aluminium is more popular because of its durability and aesthetics, but raw aluminium is easy for adding custom branding or colours.
A bonus for aluminium is that it doesn’t conduct electricity in the event of a lightning strike and surge. Yet aluminium also offers ventilation and heat reduction capabilities, which turns your enclosure to a heat resistant enclosure providing protection to your equipment, preventing weakening through ongoing use.
Think about your locks and latches. A quarter-turn slam-shut latch works well if you’re designing a generator with small doors and panels. Look for these made in die-cast-zinc alloy. These are incredibly strong with excellent electrical conductivity and high thermal conductivity. strength and hardness.
Quarter-turn compression locks made of stainless steel are a great option for outdoor cabinets due to their corrosion resistance. Ideally, you want one with special clips for grounding. Also, consider concealed hinges constructed of steel, which prevents tampering from the outside. Ideally, you want a zinc-plated finish to resist corrosion.
For heavy-duty applications when flush mounting is needed, opt for flush cup recessed T handle latches made in Zamak. Zamak is a family of alloys with a base metal of zinc which includes elements of aluminium, magnesium, and copper. Zamak’s copper content makes it useful in your enclosure’s interior environment.
Download free CADs and try before you buy
Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.