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In other modules, we have learned that control equipment can be purchased without any enclosure (“open”), or can come within a metal or plastic housing (“enclosed”). Enclosures provide mechanical and electrical protection for the equipment. They also provide protection for the operator of the equipment. Because the control equipment is enclosed, the operator cannot touch live electrical connections and be harmed.
Reasons for Enclosures
The National Electric Code (NEC) and local electric codes determine the proper selection of an enclosure type for a particular application. The National Electrical Manufacturers Association (NEMA) and the International Electro-technical Commission (IEC) have set standards for the protection of devices in various environmental situations. Enclosure types are rated to withstand water, dust, oil, or even to contain sparks that could cause an explosion in a hazardous environment. We will discuss these rating types in the next topic of this module.
Another purpose for enclosing control equipment is to centralize where the devices are located. This centralization can save on the time and expense of running power cables to the devices. It can also make it easier to operate or maintain the devices when they are centrally located, such as with a motor control center.
 In a factory making helicopter parts, an enclosed starter is mounted on a machine that tests the torque on thrust bearings.
Figure 3. Enclosure in a Factory Setting
The enclosed starter has HAND, OFF and AUTO buttons conveniently mounted on its front cover. There is also a reset button in the cover in case the overload relay needs to be reset. Indicating lights tell the operator when the machine is on as it works in the automatic mode. The operator is protected from the mechanical and electrical workings of the starter by its enclosure.
Enclosure Ratings
NEMA assigns Type classifications to enclosures. When an enclosure is rated a particular type, it means it is made of the specified materials and has passed specific tests. IEC also has tests and conforming standards for enclosures. They assign an IP classification.
The most common enclosure types are:
| NEMA Type 1
(Conforms to IP40) –These enclosures are designed for indoor applications. They are suitable for installations where unusual conditions do not exist, but where a measure of protection from accidental contact is required. They are designed to meet tests for Rod Entry and Rust Resistance. For that, the enclosure is made of sheet steel that has been treated to resist corrosion. Depending on the size, knockouts are provided on the top, bottom, and sometimes the sides so that electrical cabling can be easily brought into the enclosure.They are often referred to as general purpose enclosures.
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Figure 4. NEMA 1 Enclosure
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| NEMA Type 3R
(Conforms to IP52) –These enclosures are designed for outdoor use where falling rain, sleet or external ice might form. Like the Type 1, they are sheet steel and designed to resist corrosion. Additionally, they have a gasket on the cover to keep out water. They are designed to pass tests for Rod Entry, Rust Resistance, Rain and External Icing. Depending on the size, a blank cover plate is attached to the top for a conduit hub to be used. Most of them have knockouts on the bottom. They come with removable plugs or device plates to mount cover control.They are often referred to as raintight enclosures.
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Figure 5. NEMA 3R Enclosure
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| NEMA Type 4
(Conforms to IP65) - These enclosures are designed for indoor or outdoor use. They provide protection from splashing water, hose-directed water, and windblown dust or rain. Type 4 enclosures are constructed of sheet steel with gasketed covers. They are designed to meet the NEMA tests for Hosedown, External Icing, and Corrosion Protection. These enclosures have two watertight power hubs installed on the top and bottom of the box, depending on the size of the box. | |
| NEMA Type 4X
(Conforms to IP65) –These are much the same as the Type 4 except that they are made of gasketed, stainless steel. They provide better resistance to corrosion, and must undergo a 200-hour salt spray test.They are often referred to as corrosion-proof enclosures.
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Figure 6. NEMA 4X Enclosure
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| NEMA Type 12
(Conforms to IP62) –These enclosures are designed for indoor use in dirty and dusty applications. They are constructed of sheet metal and provide protection from dripping liquids (non-corrosive), falling dirt and dust. They do not have any Knockouts provided. They come with removable plugs to mount cover control.They are often referred to as dust-tight enclosures.
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Figure 7. NEMA 12 Enclosure
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The chart below shows you how to interpret the IP number to see an enclosure’s protection rating.
1st Digit
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Protection Against:
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2nd Digit
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Protection Against:
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| 0 | No protection | 0 | No protection |
| 1 | Solid objects greater than 50 mm | 1 | Vertically falling drops of water |
| 2 | Solid objects greater than 12 mm | 2 | Dripping water when tilted up |
| 3 | Solid objects greater than 2.5 mm | 3 | Spraying water |
| 4 | Solid objects greater than 1 mm | 4 | Splashing water |
| 5 | Against dust, limited Ingress | 5 | Water jets |
| 6 | Against dust, no ingress (dusttight) | 6 | Heavy seas |
| | 7 | Effects of immersion |
| | 8 | Submersion |
In this cookie factory, the dough is mixed in large tubs. Mechanical arms move the dough around as walnuts and chocolate chips are mixed in.
Figure 8. Enclosures Protect the Food Production Process
An enclosed starter mounted to a support pillar nearby controls the arms.
At the end of the day, the entire production floor and all of the equipment is hosed down with a sanitizing solution.
The NEMA Type 4X enclosure keeps the water spray from entering the starter.
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