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One of the most important aspects of choosing a new variable speed drive is ensuring it has a suitable enclosure for the installation environment. Despite this it’s not usually near the top of the list of specifications required when looking for a new drive or a VSD to retrofit in place of an obsolete unit. Often it’s about the quickest solution to solve a breakdown.

Choosing the appropriate enclosure will ensure your AC drive has trouble-free operation for a number of years. Reducing the chance of an unexpected breakdown in the future. So, let’s take a deeper look into the world of Ingress Protection (IP) and UL Type enclosure classifications and equip ourselves with the information to be able to choose exactly which enclosure will maximise the longevity of an AC drive in your application and environment.

What is an IP rating?

IP ratings were created by the International Electrotechnical Commission (IEC) as a collection of enclosure classification designations. Not only are they used on variable speed drives, but you will also see them applied to many consumer electronics, such as mobile phones and tablets. For example, many new mobile phones are now protected against water immersion and their IP ratings reflect this.

The IP rating system is made up of two numbers which directly follow the IP letters. The first number relates to the impact of solids and the second the impact of liquids. The lower the number, the lower the protection offered. In the chart below, you can see exactly what each number represents and protects against.

As you can see from the table, these ratings are tested for both solids and liquids, with different levels depending on what they can withstand. If you were looking for a drive that needed protecting from object 12mm or larger, around the size of a finger, but no water protection, you could go for an IP20 rated enclosure on your drive. If you were in a dusty factory and the drives would be subject to high pressure water washdowns, then an IP66 rating would be suitable.

Sometimes you may see an enclosure that has an ‘X’ in the rating in place of a number for the solid or liquid impact, for example IPX7. This means that whilst it offers a certain degree of protection against liquids, it has not been tested for solids and therefore doesn’t have a rating, rather than using 0 which would mean it has been tested and offers no protection. 

Other rating types

Although IP ratings show you the protection of an enclosure up to a certain level, some variable speed drives for extremely harsh environments will have different ratings. For example, a drive that requires protection in an explosive area or subject to high temperature washdowns wouldn’t be accounted for in the IP ratings. For outdoor and hazardous environments, additional regional and international certification standards are available to supplement the IP rating system.

The differences between IP and UL Type ratings

As we saw with IP ratings, they have two numbers to denote what they can withstand where solids and liquids are concerned. With UL ratings, they are listed as ‘UL Type X’ with just a designation for the class. This means that testing must apply to both solids and liquids. Also, UL Type ratings also cover enclosures where the drive will be used in a hazardous or outdoor environment, whereas IP ratings do not.

North American ratings

In North America, IP ratings are replaced by UL Type ratings which follows a different strategy and requirements. These are based around the NEMA (National Electrical Manufacturers Association) and you might see NEMA and UL TYpe ratings used interchangeably. They are, however, slightly different in the fact that UL Type ratings are independently tested.

UL Type ratings explained

UL Open Type - Usually drives with not much in the way of an enclosure and are closest to IP00

UL Type 1 - Intended for indoor use with minimal protection against surrounding areas. Safe against objects larger than 12mm and falling dirt. Most closely inline with IP21

UL Type 12 - Also intended for indoor use but can be used where there is dust and other non-conductive or non-flammable particulates may be found as well as dripping and light splashing of non-corrosive liquids. Closest to IP54 enclosures.

UL Type 3R - Drives with this rating can be used indoors and outdoors. They have the same protection as Type 12 but with additional protection against rain, sleet, snow and ice forming on the unit.

UL Types 4/4X - Has the same protections as Type 3R with the addition of being completely dust tight and protected against low-pressure washdowns. The difference between 4 and 4X is that Type 4X also provides protection against corrosion. Most similar to IP66.

Next time you specify a drive either as a new project or a replacement, ensure you pick an IP or UL Type rating suitable for your environment to ensure long-lasting, smooth operation.