Short answer: onshore turbines get a vented 316L stainless enclosure — a breather plug at the top, a drain at the bottom, and a heater holding the interior 5 K above the dew point, about 15 W in a 20 x 16 x 8 in box. Offshore units get the same shell fully sealed, rated NEMA 4X / IP66 by the manufacturer and not UL listed, with electronics graded for the heat that sealing traps. Tower air in your spec runs -20 to +70 C. Each night a sealed box cools, the air inside contracts about 7%, and the box inhales humid air through its gland seals; over a 10-year unattended life, that water wins. Vent the box wherever the site allows it.
What the tower air does to a box
Inside the tower your box sees humid air, salt near the coast, and a 15-20 K drop every night — rain and sun load stay outside. Take air at 25 C and 60% relative humidity: its dew point sits near 17 C. A box wall that falls to 15 C overnight is 2 K below that dew point, and the condensation starts right there.
The sealing problem is pumping, not steady leakage. Cool a box by 20 K and the air inside shrinks roughly 7% by volume, so the box draws tower air past every gland seal. That air condenses on the next cold cycle, and the water builds one film at a time for years. A sealed unattended box is a slow pump with a ten-year memory. The condensation guide works through the dew-point arithmetic if you want the full method.
Offshore, add chloride to the picture. Salt arrives as salt-laden humid air and, for deck-mounted cabinets, as spray and hose water during vessel maintenance. Chlorides plus wet-dry cycling are exactly what pits stainless steel; corrosion prevention inside an outdoor stainless enclosure covers the coatings and drainage that hold it off.
Sealed or vented: decide by the site
| Site | Enclosure | Breathing | Heater |
|---|---|---|---|
| Onshore, inland | 316L wall-mount, hinged gasketed door (304 suits an inland-only fleet) | Breather at top, drain at bottom | Thermostatic, holds the dew-point margin |
| Onshore, within about 5 km of the sea | 316L wall-mount | Breather at top, drain at bottom | Thermostatic |
| Offshore, spray and washdown | 316L sealed, NEMA 4X / IP66 | Sealed | Thermostatic, conditions the trapped air |
The breather is what makes venting safe: an M8 x 1.0 threaded membrane plug passes air and holds water, so the box stops pumping while staying splash-tight. Fit the drain at the lowest point for anything that does get past a gland. The breather vent vs drain comparison shows the placement that works.
Vented wins onshore because heat leaves with the exchanged air, and the interior rides only a couple of kelvin above tower air. Sealed wins offshore, because a vent fitting in a spray zone is one more part to corrode and every hose-down tests it. Keep the heater in the sealed box too: the trapped air holds a fixed amount of moisture, and holding it 5 K above its dew point drops the relative humidity to roughly 70-75%, so nothing condenses on the walls.
Sizing the sealed box at the top of the tower range
The inputs:
- Tower air: +70 C, the top of the spec range.
- Enclosure: the 316L wall-mount shell named above — 20 x 16 x 8 in (H x W x D) outside, inside 19.88 x 15.88 x 7.88 in (nominal, from the CAD).
- Dissipation: a bare stainless surface in still air sheds about 3 W per m² per kelvin; paint radiates better and reaches 5 W/m²·K, bare stainless stays at 3.
The rule: temperature rise = heat load divided by (surface area times dissipation per kelvin).
The arithmetic, in one pass: the surface is 2 x (20 x 16) + 2 x (20 x 8) + 2 x (16 x 8) = 640 + 320 + 256 = 1216 in², or 0.78 m², and at the bare-stainless rate that path sheds 2.3 W per kelvin. A 10 W node — a fanless acquisition board with its power supply — therefore rises 4.3 K, and the interior peaks near 74 C at the worst hour.
The rise scales straight with the load. A 25 W node climbs 11 K to an 81 C interior; 40 W climbs 17 K to 87 C. Sitting the box inside a steel cabinet shades part of the surface and adds a few kelvin on top of that.
The decision: a sealed interior is always warmer than tower air, so +70 C air fails electronics rated +70 C at any load. For sealed offshore sites, buy the boards in a -40 to +85 C industrial grade, or hold the sealed load under about 35 W where tower air tops out at 55 C — over the same heat path that leaves 15 K of headroom. One size up, the larger 316L box sheds 3.2 W/K and holds the same load ceiling at an 11 K rise. Internal fans even out hot spots, but they move no heat through the wall; where the heat actually goes explains why, and removing heat from a small sealed IP66 enclosure lists what does work.
Holding the vented box above the dew point
Keep the interior 5 K above the dew point; that margin is what decades of outdoor panels have settled on. Sizing the heater is the same heat-loss sum run backwards: against the heat path above, the margin costs about 12 W, so buy a little more heater than that for a cold mounting wall. Switchgear practice runs anti-condensation heaters at half their rated voltage: a 230 V, 60 W element fed 115 V dissipates a quarter of nameplate and runs cool enough to survive a decade of continuous duty. Control it with a simple thermostat set to 10-15 C, mounted low on the backplate, with the electronics above it in the rising warm air.
For smaller boxes, heater selection by size gives the wattages, and when an outdoor enclosure needs a heater tells you which sites need one at all. Save the humidistat for the alarm channel, which the FAQ covers.
304 or 316L for the salt
316L carries about 2% molybdenum, and that addition is what resists chloride pitting; 304 carries none. An inland-only fleet can run 304 and give up nothing. Anything coastal or offshore runs 316L, and buying one material for the whole fleet keeps doors, gaskets and mounting panels interchangeable across every site.
The type itself is tested for this air: the NEMA 250 test for Type 4X adds 200 hours of salt spray against a 304 reference specimen, so the sealed offshore box you buy is graded for exactly the chloride exposure your towers see. NEMA 4 vs 4X vs IP66 compares the types, the 304 vs 316L guide gives the metallurgy, and whether 304 survives coastal air draws the line by distance from the sea. The shells themselves are the 316L wall-mount range.
Size, mounting and the entries
Your 200 channels arrive as network traffic at 10-50 Hz, so the box needs four glands rather than 200 terminals: one power, two Ethernet, one spare. Put all four in the bottom wall with drip loops, and have them cut and sealed at the factory — what NEMA rating a panel keeps after you cut it shows why the factory hole is the one that holds. Every gland you add is a leak candidate on a ten-year clock.
On the backplate, run DIN rail for the node and a small switch, put the power supply beside the gland area, and mount the 128 GB buffer storage above the heater where the warm column rises. A compact node fits the compact 316L enclosure; the storage-heavy version wants the storage-node 316L enclosure. Mount it so the door swings its full 90 degrees: NEC 110.26(A) asks for clear working space and that swing in front of equipment serviced energized. Lock out the feeder before you open the door for service.
What to put on the order
| Line | What to specify | For this fleet |
|---|---|---|
| Body | 316L stainless wall-mount, hinged gasketed door, removable panel | Compact and storage shells as sized above |
| Rating | NEMA 4X / IP66, manufacturer-rated | One rating for onshore and offshore |
| Venting | Onshore: breather (M8 x 1.0) top, drain bottom; offshore: sealed | Factory-cut and factory-sealed |
| Heater | 230 V element run at 115 V, thermostat at 10-15 C | Same part both variants |
| Entries | 4 glands in the bottom wall: power, 2 x Ethernet, spare | Cut from one drawing |
| Backplate | DIN rail plus drilled mounts; storage above the heater | Fleet-standard layout |
Send one cutout drawing covering both configurations and the boxes are delivered in 10 business days from your approval of the drawing, anywhere in the world. Run your layout through the enclosure selector first; it checks inside height, width and DIN count against the shell, then hands the cutout list to a quote. The wall-mount enclosure range holds the sizes between the two named here.
The decision by site, in one line each: inland onshore, vented 316L or 304 with the heater; coastal onshore, vented 316L; offshore, sealed 316L NEMA 4X / IP66 with -40 to +85 C electronics and the sealed load held under the ceiling above, or one size up in box.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 16 × 8 in | 316L stainless | 16 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 316L stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 316L stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How much does the anti-condensation heater warm the vented enclosure?
At full output it lifts this box about 6 K above tower air, and the thermostat holds it there only on cold, humid nights. That is far below any electronics limit. Mount the heater low on the backplate and the storage drives above it, so the warm column reaches the most humidity-sensitive part first.
Can one enclosure part number serve both onshore and offshore turbines?
Keep the shell identical and split by configuration: the same 316L body, one version with factory-fitted breather and drain for onshore sites, one fully sealed for offshore. Cutout drawings, spare doors, gaskets and heaters stay common, which matters across 2000 units. Have the vent holes cut and sealed at the factory rather than drilled on site.
What about lightning-induced surges on the Ethernet lines into the box?
Towers take strikes, and induced surges ride the field cabling, so clamp them at the point of entry. Put surge-protected Ethernet modules on the first DIN-rail position beside the gland plate, ahead of the switch, and bond the cable shields to the backplate there. Fiber on the turbine-to-turbine spans removes the copper surge path entirely.
Will a memory card last 10 years in this enclosure?
Once the heater keeps the dew point off, write cycles are the real limit. Consumer cards give out within a few years at continuous logging rates, so specify industrial flash for the 128 GB buffer and push summaries over the farm network nightly. Budget the card as a 5-year service item, and the enclosure will outlast two of them.
How do I know a heater has failed on a turbine I never visit?
Monitor humidity and alarm near 65% RH on the farm network. A failed heater or a clogged breather shows up as slowly rising relative humidity weeks before any water appears, and one alarm channel covers a fleet of 2000 boxes. Temperature alarms tell you much less, because the box tracks tower air either way.
