A battery-powered cellular device going outdoors needs three things from its enclosure: a watertight body, an antenna that still reaches the cell tower, and room for the board and its battery with no ventilation. The answer to all three is a sealed stainless enclosure with the antenna mounted outside on a bulkhead connector. The board and battery sit inside, the radio signal never has to pass through metal, and the heat load is so low that the box stays sealed. Our enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
Why a cellular board changes the enclosure question
A plain junction box only has to keep water off terminals. A cellular device adds radio-frequency energy that has to get out, and a battery that has to live in whatever temperature the box reaches. Both push the design in the same direction: a sealed box with a deliberate antenna path through the wall.
The heat side is easy. A cellular board transmits in short bursts at a watt or two, and a lithium-ion battery charges and discharges at a few watts at most. For a box the size of a 12 x 10 x 6 in enclosure, that heat dissipates through the walls with a temperature rise of only a few degrees Celsius above ambient. If your device is bigger than that, the analysis in the sealed enclosure overheat article walks through the numbers, and calculating internal temperature rise in sealed plastic enclosures covers the method in detail.
So no vents, no fans, no filtered openings. Every hole you skip is a hole that cannot leak. What ventilation holes in a sealed enclosure cost you explains the trade in full.
What the enclosure material does to the signal
Material matters more than wall thickness. A cellular modem transmits somewhere between about 700 MHz and 2.6 GHz depending on the band. At those frequencies:
- Stainless steel and other metals reflect and absorb the signal. A board antenna sealed inside a stainless box loses most of its range. Do not plan on transmitting through the wall.
- Plastic, polycarbonate and fiberglass pass cellular frequencies with only a small loss, typically a few dB or less for thin walls. An internal antenna in a plastic enclosure works.
- Wall thickness matters far less than material. A 0.06 in (1.5 mm) stainless wall blocks the signal about as thoroughly as a thick one. A plastic wall blocks little at any practical thickness.
If you choose stainless for its corrosion resistance outdoors, and outdoors is exactly where you want it, the antenna has to go outside the box. That is a solved problem.
Taking the antenna through the wall
The clean method is a bulkhead connector: an SMA or similar connector mounted in a hole in the enclosure wall, with the antenna attached outside and a short cable to the board inside.
- The connector itself seals the hole, especially with an O-ring under its flange.
- The antenna ends up at least a few inches from the board, which is good practice anyway: circuitry, wiring and the battery close to an antenna detune it and cut the link budget.
- Keep the external antenna clear of large metal surfaces. Mounted on top of the box, or on a short mast bracket, it radiates in all directions.
The hardware details are in the SMA connector article and the antenna feedthrough sealing article. If you would rather run a cable to a remote antenna, the bulkhead gland comparison covers making that entry removable without leaks.
One warning: do not field-drill the connector hole in a finished stainless enclosure unless you can deburr, seal and verify it. Factory cutouts are cleaner, sealed and covered by the manufacturer rating. The custom stainless enclosure page explains how to put the hole on the drawing instead of in your hands.
Placing the board and the battery inside
Inside the box, treat the cellular board like any other DIN-rail or panel-mounted electronics:
- Mount the board on the removable backplate, standoffs or a small subpanel, not loose on the battery.
- Strap or clamp the battery so it cannot shift and load its own connector or the board's. Vibration kills battery leads first.
- Keep the battery away from the antenna feedthrough by a few inches, both for signal quality and so the cable is not strained.
- Leave service clearance so you can open the door, swap the battery and reach the SIM holder without dismantling the panel.
A LiPo battery is happy between roughly 0 C and 45 C during charge. In a sealed stainless box in the sun, the internal temperature can exceed ambient by 20 C or more from solar gain alone, so in hot climates pick a battery chemistry and charger rated for it, or shade the enclosure. For cold climates, the anti-condensation heater article covers the opposite problem, including the small heater that keeps the box dry through freeze-thaw cycles.
Condensation: the reason to seal tight, not just keep rain out
A sealed outdoor enclosure breathes in one direction only: when the box cools at night, the air inside contracts and pulls on every seal. Any leak lets damp air in, and the next temperature drop condenses it on your board and battery terminals.
That is the real argument against casual venting and in favor of good gaskets on every penetration. The antenna connector, any cable glands and the door gasket are the three leak paths. Check the gasket seating and the connector torque at installation. Corrosion prevention inside an outdoor stainless enclosure covers what trapped moisture does over a season.
If your device is solar-fed as well as battery-fed, the solar powered IoT enclosure article covers the panel and charge-controller side.
What to specify
Put the whole question on the drawing once:
| Item | What to specify |
|---|---|
| Material | 304 stainless for general outdoor, 316L near coast, salt or chemicals |
| Size | Inside dimensions that fit the board, battery, mounting and service hand access |
| Antenna hole | Connector type, hole diameter and center position on the wall |
| Cable entries | Gland sizes and positions for any other wiring |
| Backplate | Removable mounting panel, drilled for your standoffs or DIN rail |
| Rating | Manufacturer-rated NEMA 4X / IP66, not UL listed |
The size finder filters wall-mount stainless enclosures by grade and outside size; the smallest boxes around 6 x 4 x 4 in hold a cellular board, a battery and one antenna connector. Custom work is delivered in 10 business days from your approval of the drawing, anywhere in the world.
One last check before you order: if your specification or inspector requires a listed enclosure, a manufacturer rating alone will not satisfy it. See the guide to NEMA enclosure types for what each type covers, and confirm the listing requirement with your authority having jurisdiction.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 6 × 4 × 4 in | 304 stainless | 6 x 4 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 10 × 8 × 6 in | 304 stainless | 10 x 8 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does the antenna have to be outside the enclosure?
Not always, but with a stainless steel enclosure it is the safe choice. Stainless blocks the radio signal almost completely, so a board antenna sealed inside loses most of its range. Plastic and fiberglass pass cellular frequencies well, so an internal antenna can work there. Outside the box, use a bulkhead or SMA connector through the wall and keep the antenna a few inches from any large metal surface.
Will the battery overheat in a sealed box?
No. A lithium-ion battery and a cellular board draw a few watts at most, often far less on a sleep schedule. That heat spreads into the enclosure walls and the mounting surface without a meaningful temperature rise. Ventilation is not needed, and adding vents costs you the seal against water and dust.
How far should the antenna be from the cellular board?
Keep the antenna at least a few inches from the board and its wiring, and away from the battery. The board's own circuitry and cables can detune a nearby antenna and reduce signal strength. An external antenna on the enclosure wall naturally gives you this separation.
Can I get a custom enclosure with the antenna hole already cut?
Yes. Specify the connector hole size and position on the drawing and the enclosure arrives with the cutout made in the factory, with the rating the manufacturer states. Delivered in 10 business days from your approval of the drawing, anywhere in the world.
Is a manufacturer NEMA 4X rating as good as a UL listing?
It is a manufacturer rating of the enclosure type, not a UL listing. Some inspectors and specifications require a listed enclosure, so check the requirement before ordering. We state ours as rated NEMA 4X / IP66 by the manufacturer; not UL listed.
