Environmental criteria for enclosures

Friday, 20 July, 2007


Electrical equipment can be harmed by environmental factors including water, airborne particles and thermal extremes. The right enclosures minimise the negative impact of the environment - keeping systems safe, preventing failure and contributing to their longevity.

Electricity and the environment are not ideal bedfellows. Electricity can be harmful to people and property. Conversely, electrical equipment can be harmed by people and property, along with rain, dust and all sorts of other climatic conditions. In spite of this conflict, we need electricity and the environment to happily co-exist.

IP ratings

Enclosures are rated for environmental protection using IP ratings, which stands for 'Ingress Protection' as outlined in 'AS60529-2004: Degrees of protection provided by enclosures (IP Code)'. The first of its two-digit code specifies the degree of protection against solids (eg, dust) and the second against liquids, while also indicating the degree of protection to personnel from dangers within the enclosure.

Table 1: IP protection ratings (courtesy Schroff)

AS60529 is the primary specification in Australia for ingress protection. Don't be confused by 'Types' used by North American NEMA, UL and CSA standards; we're not subject to them. Table 2 shows a 'rough' cross-reference between IP and 'Types'.


 

NEMA/UL/CSA Type IP23 IP30 IP32 IP55 IP64 IP65 IP66 IP67
Type 1 X              
Type 2   X            
Type 3         X      
Type 3R     X          
Type 3S         X      
Type 4             X  
Type 4X             X  
Type 6               X
Type 12       X        
Type 13           X    

Table 2: IP versus 'Type' cross-reference chart

Applications

Shane Dwight, Schroff product manager at Soanar advises: "Interior environments might be impacted by sprinklers and/or dust, so IP43-rated enclosures would be suitable for these conditions. The safety requirement to protect personnel is also covered, since foreign bodies couldn't enter the enclosures. IEC suggests IP54 for worst-case indoor conditions and IP55 mostly for outdoors, but in more extreme conditions such jets of water, or immersion in liquids, protection to IP66, IP67, or IP68 is suggested. Remember, any apertures made in the enclosure will affect the IP rating, so sealing devices like cable glands for cable entry should be used to maintain the rating".

Thermal management

Heat build-up in enclosures has the potential to cause component failure, as well as reducing life expectancy. As a rule of thumb, every 10oC of temperature rise above normal room temperature halves the life expectancy of electronic equipment.

Heat build-up in enclosures can sometimes be managed effectively by just correct enclosure sizing. Not only should the width, height and depth of a component be considered, but also the power consumed and heat produced. As these parameters increase, many applications will require active thermal management systems.

Marcel Challita, Rittal product manager, advises: "Climate control of electrical enclosures is not purely an electrical concept. You need to understand the mechanical issues to get it right. It's not as simple as just bolting a fan to a cabinet or rack. You need to consider airflow in enclosures, not just measuring temperature with a thermostat at a localised point. Climate control for electrical enclosures is in some ways like office air conditioning - you don't dump cold air directly on people as this causes discomfort. Likewise, you shouldn't just randomly dump cold air onto active equipment as this can interrupt its normal operation. The path of the cold air through the component must be considered.

"Equipment should be laid out to allow consistent airflow that facilitates temperature continuity throughout the volume of the enclosure. If not laid out properly, hot spots not measured by locally placed thermostats can develop and temperature-related failures can eventually result, even though the thermostats indicate no problems.

"To help contractors work out what climate control they need, a 'heat load calculator' called 'RiTherm' can be downloaded from www.rittal.com.au. Alternatively, they can fill in a form and Rittal will do the calculation for them. In many situations there's no right or wrong answer, so it's worth running it by our experts for some competent advice. We also have a non-product-specific 'how-to' guide that provides instructions on effective enclosure cooling.

"In a dust-free air-conditioned switchroom, a fan can be the best option. Remember, ambient air always needs to be cooler than the desired enclosure temperature. Maintenance, and lack of it, is the biggest issue with fans in dusty environments. Rittal achieves up to IP56 with fans, but this relies on regular maintenance of filters. If they become clogged with dust or deteriorate, dust starts to enter the enclosure.

"When ambient temperature is above what's needed in enclosures, air/water heat exchangers are a good option, although a water source is needed, typically 10 to 30oC depending on how much heat needs to be dissipated. These units are very effective in removing heat, especially in high ambient temperatures up to about 70oC and virtually maintenance-free. Some electricians have reservations about water anywhere near the switchboard, and rightly so. The fact is, they're specifically designed to minimise system failure, being fully sealed and pressure tested; and have alarms and drains to mitigate danger in the very unlikely event of a coil rupture. Containing only coils and a single fan, these units are simple and effective devices that are virtually independent of the environmental conditions.

"Air-conditioners are especially valuable when control cabinets need to be out of the switchroom and near the production line, or if there's no space in the switchroom. They range in price from around $1200 to $5000 depending on capacity. Unlike normal cooling systems, Rittal cooling units never introduce outside air into an enclosure as they run two completely separate air circuits. Cooling only an enclosure means that all necessary infrastructure required for effective switchboard operation is self-contained and independent of external operating conditions."

Challita sums it up well: "Providing equipment with the climate that they're designed to run in through the utilisation of an enclosure cooling offers tangible advantages, but you need to get it right".

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