Enclosures: Metal verses Fiberglass


The sun’s ultraviolet rays will slowly degrade epoxy resin if it is exposed for long periods of time. The ultraviolet light stimulates the epoxy resin to oxidize. This oxidized resin powders and leaves the external fiberglass layers exposed; this is called "fiber bloom".

Durability: Fiberglass gel coats are soft and easily scratched. And worse yet, on dark colored enclosures these scratches stand out dramatically because the fiberglass beneath the gel coat is light colored.

Fiberglass is not durable when exposed to field use. People throw the doors open, throw open the lid, or the wind catches the lid and the hinged component cracks the fiberglass at the hinge points, even though those areas are typically heavily reinforced, and even when continuous type hinges were used.

Security: Because of the durability issues with fiberglass they are much easier than metal enclosures to break into even with padlocks.

Environmental: There is more to the selection of a quality enclosure for solar applications than just the NEMA Type rating. These enclosures must stand up to some very severe conditions in varied parts of the world. Not only does the sun have a greater effect on fiberglass but heat dissipation is critical to the internal components for longevity. Fiberglass is not a good conductor of heat.

Cost: Fiberglass enclosures are typically very competitive in the smaller sizes and with just screw-on covers. For the larger sizes they can be twice as expensive.


Not all metal enclosure are created equal. We have all seen metal enclosures in the field just rusting away. These are usually enclosures that are several years old or have been abused during installation

Durability: Metal enclosures have been the standard in industrial and commercial applications for many years. One of the greatest advantages of using metal enclosures is the ability to withstand the stresses of installing conduit with conduit hubs. When installing conduit hubs in fiberglass enclosures and attaching the conduit the stresses on the enclosure can cause cracking which violates the NEMA Type rating and compromises the ability of the enclosure to keep out water. Over time these small cracks become larger, especially with the aid of the sun.

If you drop a metal enclosure it will only dent and can be repaired easily verses a fiberglass which will crack and possibly shatter.

Security: All enclosures can be violated if someone really wants to get into them. A metal enclosure will provide slightly more protection just for the fact that it is metal and takes more than a hammer to break in to.

Environmental: The biggest advantage of metal over fiberglass is its ability to radiate heat away from the rated components inside. The metal enclosure basically becomes a large heat sink. Metal is a much better conductor of heat than fiberglass. Fiberglass has a thermal conductivity of about 0.04 where carbon steel is about 43.

Metal enclosures can take more punishment from such things as freak hail storms. Metal can withstand larger impacts with no cracking or breaching of the NEMA Type rating.

Cost: Metal enclosures can be very competitive in the smaller sizes depending upon the overall quantities of enclosures purchased by the panel (combiner or monitoring) manufacturer.

Enclosures provided by DST Controls:

After years of providing custom control panels to most of the major vertical markets and after years of testing and evaluating use in the field, DST Controls has selected Rittal metal enclosures for our standard offering. Please keep in mind that if you prefer non-metallic DST can offer this as an option.

For many of the reasons listed above DST is able to offer our clients the benefits of metal at a very competitive price. We are one of the largest users of Rittal enclosures west of the Mississippi. This allows DST to pass on the savings to our clients. Rittal is rated the number one enclosure in the world and gaining more ground here in the US every day.

DST also selected Rittal based on their Surface Treatment specification. This treatment eliminates “undercreep” and provides a textured surface that is far superior to other metal enclosures on the market today. “Undercreep” is when a metal enclosure’s surface is scratched down to the bare metal and then rust migrates under the paint. This is typically a point of failure in most metal enclosures.

Solar systems are getting larger and requiring more strings per combiner. Metal enclosures are much more cost effective in the larger sizes. Fiberglass enclosures in larger sizes can be as much as twice the cost of metal.

For more information or assistance in selections for your application please contact Sales or our Technical Support.