How to design enclosures that protect against water, debris
Protocase sets out to share some of its experience and knowledge of building enclosures that will withstand environmental hazards. This inevitably brings up the issue of NEMA or IP standards, but sometimes there is confusion as to how these work. Protocase offers this information in hopes of providing direction to designers who are tackling this subject. For simplicity’s sake, this article will limit itself to NEMA, but the principles are exactly the same if you use IP, so this should still be relevant to you.
Before starting, I’d like to make the point that designers should clearly consider what they are trying to achieve. Are they just looking to achieve environmental protection? Or are they trying to meet a formal requirement to achieve a NEMA standard (which may have been imposed by a customer or manager)?
I have seen thousands of custom enclosures come through Protocase with environmental resistance requirements, and most of these enclosure orders only need environmental protection. Our customers will often use NEMA standards to explain what they need their enclosure to do, such as offer a certain resistance to dust, dirt or water, but do not need to formally meet NEMA’s standards.
Occasionally, we do see a customer who needs to meet a formal NEMA requirement, which necessitates testing. Although Protocase does not offer testing of enclosures to verify NEMA requirements, some of our customers will send their enclosures to a third-party testing facility in order to receive formal certification that they have met requirements. In this case, the principles I describe below are the same.
Understanding NEMA Classification
The document ‘NEMA Enclosure Types’ is put in place to promote standardized product specifications for electrical devices. Basically, the role of NEMA standards is to specify how an enclosure must perform to meet the classification. Specifically, NEMA standards deal with the following:
1. Protecting personnel from hazardous internal parts
2. Protecting equipment inside the enclosure against environmental hazards
What NEMA does not do is prescribe how to design and manufacture an enclosure to meet performance specifications; I will cover that in the next section of this blog.
The NEMA standard covers a large number of enclosure types. However, our customers generally deal with the following subset of common types:
* NEMA Type 1 – General purpose is for indoor use, provides protection against human contact with live parts and against debris such as dust.
* NEMA Type 2 – Generally used indoors and is drip-proof. This type offers the same protection as Type 1, but adds protection against dripping and light splashing of water.
* NEMA Type 4, 4X – This type is generally used both indoors and outdoors. It is watertight, dust-tight, and sleet-resistant. It offers the same protection as Type 1, 2 and protects against access of falling dirt, rain, sleet, and snow. It also protects against damage due to external ice formation and splashing and hose-directed water. It is rust-resistant (the ‘X’ in 4X indicates corrosion-resistance).
* NEMA Type 5 – Generally used indoors, this enclosure type is dust-tight. It offers the same protection as Type 2, but with added gaskets, it prevents access of settling dust, lint, fibers, and flyings.
* NEMA Type 6, 6P – This type can be used indoors or outdoors and is submersible. It offers the same protection as Type 4, but Type 6 adds protection against occasional temporary submersion while Type 6P adds protection against prolonged submersion at a limited depth.
Note that all of these types will protect personnel against access to hazardous parts.
In the next section, I will discuss different families of enclosures and how they can protect against the environmental hazards addressed by NEMA.
How to meet NEMA requirements
1. Sheet metal enclosures
This type of enclosure is very capable of protecting against dust, debris, and splashing or dripping water. Sheet metal enclosures can be designed to meet the requirements of NEMA Types 1, 2, 4, 4X and 5. However, if your enclosure requires immersion in water, this is not the best choice for you. Here are some guidelines:
* NEMA Type 1: We recommend a simple two-piece enclosure style that is fully covered on the top of the case. (L-shape, U-Shape or Extruded Enclosure would work).
* NEMA Type 2: We recommend overlapping flanges on all open seams of the case, using tack, spot or plug welds to fasten the seams. Depending on the severity of the environment, you may require fully welded seams. A U-Shape enclosure would work best, as there are fewer seams to weld.
* NEMA Type 4,4X: We recommend fully welded seams and the use of gaskets. Gaskets are recommended for anything with water being near or directed at this case. In most applications of this category of enclosure gasket, style foam strips or a full gasket piece will suffice. Fastener sealing is required as soon as you bring water into the equation, so we recommend sealing the fasteners. Fastener sealing can be done in many ways including:
o Strategic placement of fasteners so they do not protrude inside the case.
o Assembling with sealing screws (these are sold off the shelf and have an O-ring embedded under the head of the screw. Your Account Manager can provide you more information).
o Using a latch or lock to fasten the enclosure closed. Hinges are also popular in this style of enclosure.
To achieve Type 4X, choose a corrosion-resistant material such as stainless steel, aluminum or galvanneal, and follow the recommendations above.
* NEMA Type 5: We recommend overlapping flanges on all open seams of the case or fully welded seams, depending on the environment. Again, the U-shape enclosure would work best for this design.
2. Custom CNC machined enclosure
If you’re looking for an enclosure that can be immersed in water, this is it. This type of enclosure can be designed to meet NEMA Types 1, 2, 4(X) and 5. It can also be completely sealed, and with the proper O-rings or gaskets, made waterproof, sufficient to protect against deep liquid immersion and thereby meeting NEMA Type 6(P).
Keep the following in mind when designing this type of enclosure for water immersion:
* The enclosure should be designed in a way to minimize the number of seams to seal, with fewer parts and seams; there is less chance of water entering the enclosure.
* As these are machined, aluminum is by far the best option. It is possible to work with stainless steel, but the machining cost would be much higher. Other options are not sufficiently corrosion resistant.
* If incorporate an O-ring into the design, keep the O-ring toward the inside of the holes used to assemble the enclosure, in order to prevent leakage through fasteners.
* For final assembly, applying even torque to screws to ensure an even O-ring compression is recommended. The screw size for assembling should increase as the enclosure gets larger.
o Note: Consider screw spacing when designing your enclosure. If screws are too far apart, the seal may be affected, thus compromising the effectiveness of your enclosure’s ability to be watertight.
3. Off the Shelf (OTS) cast enclosures with CNC machined customizations
At Protocase, we have recently started offering off the shelf (OTS) cast enclosures. They can be watertight with the proper designing and seals and are very similar to our Custom CNC Machined Enclosures. With minimum customizations or cutouts, along with the proper gaskets or O-rings, this enclosure type could meet NEMA Type 6(P). This type of enclosure will also meet NEMA Types 1, 2, 4(X) and 5 easily.
However, there are two major differences between OTS Cast and custom machined enclosures:
* If you use OTS Cast, we start from a pre-made enclosure, so you are restricted to using a stock size and shape.
* OTS is significantly less expensive (this is because no material is wasted in manufacturing the Cast OTS enclosure, whereas the custom machined enclosure is made from a solid block of material).
Thus, if you can live with the size and shape restrictions, Cast OTS is the economical choice.
With this enclosure, as with custom machined enclosures, if you wish to achieve water tightness, you must ensure that every item that penetrates the enclosure (connectors, switches, etc.) are suitably watertight, and equipped with a gasket or sealed as necessary.
As I mentioned above, Protocase does not perform NEMA/IP testing within our manufacturing facility, but some customers opt to send their enclosures elsewhere for testing. To find out where you can get your enclosure tested, click here.