Enclosures and Enclosure Heaters
An enclosure is a container such as a metal cabinet or a plastic case that is intended to hold and protect equipment and protect people and animals outside of the enclosure from the equipment. An enclosure may contain electrical, mechanical, pneumatic, hydraulic and other devices. Enclosures that require temperature and moisture control are usually protecting electronics and we call them Electrical Enclosures. Enclosures that strictly house mechanical equipment are generally referred to as Mechanical Casings. When we talk about enclosures we're usually talking about electrical.
Moisture and dust are the primary enemies of electronics. A relative humidity above 65% will shorten the life of your electrical circuits and components. Prevention can happen when an enclosure’s temperature is raised by 5 Celsius. A controlled heat source is the most common solution. There are many factors that go into choosing suitable thermal and moisture regulating devices. In this article I’ll start by discussing the different types of enclosures. We'll look at temperature/moisture regulating and show four popular products that we manufacture as examples. I'll close by offering some considerations and tools to help you to make informed product choices.
Electrical enclosures are everywhere. They can be part of medical devices, ATMs and traffic lights. They can be tiny housings for wearables and they can be the size of shipping containers. One constant is that they all need some sort of protective outer body to keep out the elements. They also need a way to access the inside of the container. After that, everything is an option. Access to the inside could be a door with a latch and two hinges. It could be a flanged cover fastened with screws. There could even be multiple access points to get inside the product. An enclosure may contain shelves, internal walls, internal supports, din rails, tracks, racks, anchoring hardware, busses, special compartments for batteries and more.
There are so many product variations it is difficult to provide comprehensive coverage in a single article. One popular online electronics vendor makes their enclosures searchable and filterable by way of 78 product names and 452 enclosure types as provided by 56 different manufacturers. It gets even more confusing when products and enclosure types commonly share similar names. ‘Junction Boxes’ are both products and types. There are also categorizations such as boxes, cases and cabinets. They are all categories of enclosures but are sometimes called out separately denoting enclosures as something uniquely different.
To cut through the clutter were going to look at two useful ways to differentiate and understand enclosures, namely, Standards and Special Properties.
Standards are often the primary consideration when choosing an enclosure. If your electronics need to be protected from high pressure hose blasts multiple times a day in a chicken processing plant then you're going to need an enclosure that meets those higher standards.
NEMA and IEC Standards
NEMA (National Electrical Manufacturers Association) and IEC (International Electrotechnical Commission) have standards that address how enclosures stand up to environmental conditions. They primarily address the protection of personnel from equipment as well as the protection of equipment against ingress. (Ingress is the unwanted entrance of water, dust, dirt and any other solid or liquid substances.) For example, a NEMA Type 2 enclosure is for indoor use and among other things protects against dripping and light splashing. An enclosure that meets NEMA Type 4 is built for indoor and outdoor use and protects against rain, sleet, snow and hose directed water.
NEMA enclosure standards primarily pertain to North America. Definitions are segmented into Types numbered 1 - 13 and occasionally followed by a letter. There are currently 16 different enclosure types. Top level NEMA distinctions are based on some combination of indoor/outdoor and hazardous/nonhazardous. For example, NEMA has ratings for enclosures intended for indoor use away from hazardous materials. They also have ratings for outdoor enclosures used near hazardous material.
IEC uses something called IP (International Protection) Codes to define an ingress rating. The letters IP are always followed by two numbers (eg. IP 68). The first number addresses solids protection. In the IP68 example it is the ‘6’. The second number addresses liquids protection. Solids protection ranges from 0 (no protection) to 6 (dust tight). Liquid protection ranges from 0 (no protection) to 8 (continuous immersion in water beyond 1 meter). There is also a liquid level 9 that is particular and addresses protection from steam-jet cleaning.
While protections generally increase as rating numbers increase, progression from a low ingress number to a higher one requires some context and does not necessarily mean that the rules are more strict. For example, NEMA4X addresses ‘Corrosive Agents’ while NEMA 5,6,12,12K&13 do not. Another example is NEMA6, which is the only NEMA type that addresses Ingress of water for occasional prolonged submersion.
While there is no direct equivalence between NEMA Types and IEC IP Codes, NEMA does provide a useful table that attempts to make correlations between the two.
You will see various manufacturers say something like, “We offer traditional JIC sizes as standard or modular products.” The Joint Industrial Council (JIC), was formed in 1963 to encourage the safe and reliable application of controls to machines and equipment used in industrial applications. The JIC is no longer a standards holding body and is handled by the National Fire Protection Association (NFPA). You can still view the JIC Electrical Standards here.
Some vendors specialize in enclosures with niche characteristics such as extreme environmental corrosion resistance. Others sell large collections boasting thousands of standard products sold with a dizzying array of options and accessories. Apart from an enclosure’s dimensions and cost, you may desire a special material property, a unique specification, an innovative feature or compatible accessories.The following is a list of properties that may find importance in your next electrical enclosure project.
- UV resistant
- High ingress rating
- Protects against harmful substances
- Hydraulic oil
- Made from non-conductive materials
- Condensation limiting
- Meets a particular standard
- Blocks / doesn’t block radio waves
- High impact resistance
- Easy to machine
- Versatility in mounting
- Easy to install
- Plug n’ play
- Light weight
- Mounting hardware
- Multiple access points
- Clear lid or window
- Heat resistant
- Interior segmented for different purposes
- Theft / damage / vandalism protections
- Accessories offered
The primary purpose of an enclosure heater is to protect equipment from low temperatures, condensation and corrosion. You can view all Tutco-Farnam Enclosure Heater options on the Enclosure Heaters page.
The following is a detailed breakdown of the various ways an electrical enclosure heater protects electrical components.
- Prevent condensation
- water vapor on components
- even well-sealed environments
- Prevent corrosion
- moisture, gases ,dust speeds up corrosion
- corrosion low if relative air humidity below 60%
- above 65% increases moisture and corrosion
- Prevent circuit failure
- integrated circuit boards
- Maintain minimum temperature
- prevent a low temperature
- protect components from temperature below tolerances
- maintain temperature after shutting down for the night
Enclosure heaters are all around you. The following are just a handful of applications where they are used.
- ATM (Automatic Teller Machines)
- Switchgear Cabinets
- Fast Food Sign
- Deal Drawer or Transaction Drawer
- Pneumatic Tube Transport
- Security Cameras
- Highway Traffic Signs
- Traffic Signal Control Boxes
- Car Wash Controls / Kiosk (customer interface)
- Car Tire Filling / Vacuum Stations
- Outdoor Control Panels
- Outdoor Electrical Power
- Control Valve Housings
- Switchgear Enclosures
- Indicator Panels
- Control Systems
- Alarm Systems
- Pump House
- Load Bank Control Panel
- Gym/School Lockers
There are a few cautions worth noting. It is advisable not to mount heaters on wooden structures. You should be careful not to mount your heater near heat-sensitive components. And finally, you should use a product with appropriate ratings and protections.
Types of Enclosure Heaters
The characteristics of an enclosure and it's enclosed items will have different thermal management criteria. Your product may require a high level of temperature control or perhaps a solution that fits a limited space. Tutco-Farnam designs, manufactures and sells four types made to order as standard or custom products. Configurations and customization provide unlimited possibilities.
Low Mass Surface Enclosure Heaters
- Silicone Rubber heaters are made from fiberglass reinforced silicone rubber. They can take on a wide variety of shapes and can bend with curved surfaces.
- Mica enclosure heaters have heating element that are sandwiched in mica and then pressed between metal. Mounting is easy with peel-and-stick adhesive.
Two different types of surface enclosure heaters manufactured and sold by Tutco-Farnam.
Open Coil Enclosure Air Heaters
- Axial Fan Heaters mount to square axial fan housings. Heaters range from 15W - 1000W with optional fan, thermostats and fuses.
- Crossflow Blower Heaters mount to the exhaust of a crossflow blower. Our standard heaters range from 250W-4500W with integrated thermal fuses and thermostats available.
Two different open coil enclosure heaters manufactured and sold by Tutco-Farnam.
The heating elements used in Axial Fan and Crossflow Blower heaters can be bought independently of the fan units. Be sure to speak with a rep about proper sizing.
A silicone rubber enclosure heater will satisfy many applications with greater thermal control, a high level of versatility and lower cost. This product does require higher volume purchases (eg. 500 unit minimum). The classic durable Mica Enclosure Heater can be purchased in quantities both large and small.
Some applications have small enclosures and don’t require circulating air to get the heat from one place to another. Other units may already have some moving air from vents or fans attached to existing electronics. A larger enclosure however may need some help moving air. Axial Fans are a popular choice. Something the size of an ATM could go either way using Silicone Rubber or an Axial Fan Heater.
If an Axial Fan doesn’t cut it and you really need to throw some hot air a Crossflow Blower will get the job done. Farnam manufactures Axial Fan Heaters and Crossflow Blower Heaters for those applications.
Large enclosures like telecom shacks may have their own Climate Control for heating and cooling, which look like mini HVAC systems attached to the outside of the enclosure. These Climate Control units use open coil heaters that are commonly referred to as strip heaters in the HVAC industry, not to be confused with 'mica' strip heaters. Climate Control units are a good route to go if your enclosure is big enough to contain people. It doesn’t make as much sense to use a Crossflow Blower when the enclosure is that big. Parking lot trailers used for office space overflow or school classrooms will usually have one of these Climate Control units attached to one end of the trailer.
Mounting surface heaters can be accomplished with a preinstalled adhesive such as a PSA (pressure sensitive adhesive) or some sort of bracket. Other options you see for mounting include hardware designed for DIN rails, frames and panels. Some designs use standoffs for airflow and to help minimize side surface temperature. Power connections are commonly terminal blocks, push connectors or SJT.
Enclosure heaters are typically named after the material, size, shape, mounting style and/or some added feature. Here are a few examples:
- Silicone Rubber
- PTC (Positive Temperature Coefficient)
- Polyimide / Kapton
- Axial Fan Heater
- Fan Heater with Thermostat
- Crossflow blower heater
- Space Saving
- Small profile
- Low Profile
- Finned Strip
- Foot Mounted
- DIN Rail
- High Wattage Fan Heater
- Explosion proof
- Energy Saving
Here are some common considerations to take into account when choosing an enclosure heater.
- Space limitations
- Forced air requirement
- Transformer requirement
- Mounting options
- Voltage range
- Energy saving
- Environmental conditions (seasonal temperatures and wind)
- Fan noise
- Various Approvals: UL, cUL, CE, VDE, RoHS
- Is your heater powerful enough to do the job?
Calculate Enclosure Heater Wattage
After you pick the right type and size of heater for the job there are options to consider. Depending upon the product, some of those may include the following:
- Built in Thermostat
- Built in Humidistat
- Built in Hygrostat
- Transformer for Fan
- Fan auto/on switch
- Heater on indicator lamp
- Temperature limiter
- Fan included
- Energy saving features
- Temperature safety protections
- Failsafe thermostat
- Touch safe components
For highly sensitive components you might require heating and cooling within the same enclosure. First check to see if a low mass heater like Silicone Rubber will do the trick. Multiple smaller Silicone Rubber heaters wired in parallel may provide the control you desire.