Yes, you can build a control cabinet for a Class I Division 2 area with no purge: the cabinet is a sealed 316L stainless box rated NEMA 4X / IP66 by the manufacturer (not UL listed), and the Division 2 suitability lives in the devices — Class I Division 2, Group D, T3 (200 °C) marks or hermetically sealed contacts on relays, pushbuttons, controllers, and the burner management per its instructions. Keep the cabinet unpierced: glands where cables land, no breather drain, because a 3-6 mm hole is how the outside atmosphere gets in. This page walks the component list, the temperature codes, the heat budget for a sealed box, and the exact lines to put on the order.
Can a Class I Division 2 cabinet run without purge?
Yes — when every device inside qualifies for Division 2 on its own: a Class I Division 2, Group D, T3 (200 °C) mark, sealed hermetic contacts, or simply no arcing contacts, the cabinet stays an ordinary sealed box.
Division 2 assumes gas escapes only when something fails: a gasket lifts, a seal weeps, a line ruptures. Most hours the air around your cabinet is clean. NEC Article 501, the Class I hazardous-location article, lets the cabinet itself stay ordinary when each device inside is marked for Division 2 or carries no ignition source. A junction box in a Division 2 area needs no special construction, and the NEMA 4X junction box in a Class I Division 2 area covers the small version of that logic. Purge and pressurization per NFPA 496 is the fallback for a device that cannot qualify; the purged and pressurized enclosure route walks that path.
What does Division 2 demand of the devices inside?
Every device needs one of three qualifications: a Class I Division 2 mark with group and T code, sealed contacts (hermetically sealed relays carry Groups A through D), or no arcing contacts at all.
Work down your bill of materials and give every line one of those qualifications before you size the box. The burner management unit and its flame detector deserve the extra look: flame detectors usually carry their own Class I Division 2 mark with a group and T code, and you wire them exactly as the maker's instructions show, because those instructions are part of the equipment approval. Your 24 V DC supply keeps contact energy low and suits nonincendive circuits, yet each device still earns its place through its own mark. For how sealed contacts carry a Type 4X build, see page on NEMA 4X cabinets with hermetically sealed contacts in Class 1 Div 2.
| Device in your cabinet | What qualifies it in Division 2 |
|---|---|
| Relay | Hermetically sealed; plates marked Class I Div 2, Groups A-D |
| Pushbutton or pilot light | Contact block with sealed contacts, or a Division 2 mark |
| Controller or PLC | Factory mark: Class I Division 2, group and T code |
| 24 V DC power supply | A Division 2-marked model |
| Terminal blocks, duct, wiring | Ordinary items: no arcing contacts, nothing hot above the T code |
| Burner management and flame detector | Its own Division 2 mark, wired per the maker's instructions |
Which temperature code and gas group do you specify?
Specify T3 for hydrocarbon gas: the T3 mark caps any surface at 200 °C [392 °F], below the roughly 365-540 °C auto-ignition spread of Group D gases, and cooler T codes clear it by more.
The shared NEC and IEC 60079 temperature-code scales set the surface limits:
| T code | Maximum surface temperature |
|---|---|
| T1 | 450 °C [842 °F] |
| T2 | 300 °C [572 °F] |
| T3 | 200 °C [392 °F] |
| T4 | 135 °C [275 °F] |
| T5 | 100 °C [212 °F] |
| T6 | 85 °C [185 °F] |
Group D collects the propane, butane and natural-gas families that dominate platform process areas; its closest IEC group is IIA. Read the group off the area classification drawing and order devices marked for it, or marked Groups A through D where the plate says so. Methane ignites near 537 °C and butane near 365 °C, so a T3 device at 200 °C carries hundreds of degrees of margin. Keep the cabinet itself cool, because the T code assumes the device runs at its rating.
Which material and rating survive an offshore platform?
Build it in 316L stainless rated NEMA 4X / IP66 by the manufacturer, not UL listed: salt fog rules out coated steel, Type 4X adds corrosion resistance over Type 4, and hazardous-location Types 7 and 9 play no part in Division 2.
316L's molybdenum carries the pitting resistance that salt air demands, while 304 pits in the same fog. Coated carbon steel loses its coating at every cutout and gland thread you make. Keep the cabinet skin below about 60 °C [140 °F] near hot process lines: above that temperature, chloride stress corrosion attacks 304 and 316L alike. Type 4X means hose-directed water plus corrosion resistance, and the guide to NEMA enclosure types sets out what each type covers. Catalog stainless lines run 6 x 4 x 4 in to 60 x 36 x 16 in (H x W x D); the size finder filters them, and custom sizes come from one piece.
What size and heat budget does the cabinet need?
A 40 x 32 x 12 in [1020 x 810 x 300 mm] cabinet holds the controller and 20 sealed relays, and its sealed walls shed about 102 W for a 10 K rise (3.7 W/m²K over 2.77 m², 30 °C ambient, 40 °C inside).
Work the example. Convert the box to 1.016 × 0.813 × 0.305 m. Exposed wall area A = 2 × (1.016 × 0.813 + 1.016 × 0.305 + 0.813 × 0.305) = 2.77 m². Stainless steel transfers heat at 3.7 W/m²K, so the box sheds 3.7 × 2.77 × (40 − 30) = 102 W at a 30 °C module room. Now the load: a 24 V DC supply feeding 60 W at 85% efficiency loses 10.6 W, the controller draws 15 W, and 20 sealed relay coils at 0.5 W each add 10 W. Total 35.6 W, which lifts the inside air only 35.6 / (3.7 × 2.77) = 3.5 K. When the deck room reaches 35 °C, the budget halves to 51 W. The same load then lands near 38.5 °C inside, under the 40 °C ambient most electronics carry. Past about 100 W of load, add an air-to-air heat exchanger with a sealed frame rated IP66 on its cabinet side; internal fans only stir a sealed box. A rated internal temperature sensor lets you watch the number without breaching the seal.
How do you seal a cabinet that must stay closed?
Keep the box unpierced: every penetration takes an IP66-rated gland on a round cutout, and the cabinet carries no breather drain — a 3-6 mm [1/8-1/4 in] hole is the path the outside atmosphere uses to get in.
Every fitting you add must match IP66, because the weakest part sets the assembly rating; plug spare cutouts with matching stoppers. The door gasket does the daily sealing work, so keep it clean and swap it when it takes a permanent set. NEC 314.15 permits drainage openings of 3 mm (1/8 in) to 6 mm (1/4 in) in boxes listed for damp or wet locations. That provision suits a rain-exposed Type 3R box; here the hole is how the Division 2 atmosphere migrates into your cabinet. A sealed box holds no fuel and admits none, and that property is what makes the no-purge build work. The sealed-box-versus-vent comparison explains why a closed box also stays drier outdoors.
What goes on the order?
Put six lines on the order: 316L stainless, manufacturer-rated NEMA 4X / IP66 (not UL listed), gland-sized cutouts only, no drain and no vent, a marked component list, and delivery in 10 business days from drawing approval.
The enclosure lines and the component lines ride the same order:
| Order line | Specification |
|---|---|
| Material | 316L stainless, #4 brushed finish; salt fog, brine and washdown |
| Rating | Manufacturer-rated NEMA 4X / IP66; not UL listed |
| Size | Your layout from one piece; catalog lines run 6 x 4 x 4 in to 60 x 36 x 16 in (H x W x D) |
| Cutouts | Round and gland-sized, only where a cable lands; none for vents or drains |
| Door and panel | Hinged gasketed door, removable mounting panel, wall-mount feet |
| Components | Each device marked Class I Division 2, Group D, T3 (200 °C) or lower, or hermetically sealed |
| Delivery | Delivered in 10 business days, counted from drawing approval |
Three cases decide the component list:
- Every device marked or sealed: order the sealed 316L cabinet with no purge and no drain.
- One device cannot qualify, such as an unmarked burner management unit: purge it per NFPA 496 or move it to an unclassified room.
- The area is Division 1, or the specification demands certified hazardous-location equipment: explosion-proof construction or a listed purged assembly — we do not build hazardous-location enclosures.
A finished cabinet with two or more power or control components is an industrial control panel under NEC 409.2. NEC 409.110 calls for an enclosure type number marked on the panel. Shops that list assemblies to UL 508A cover the equipment approval OSHA 29 CFR 1910.303(a) asks of US workplaces. Run your size through the enclosure selector for a catalog shortlist, or send the layout to custom 316L enclosures and it comes back built to your cutouts in 10 business days from drawing approval. Land conductors with the feeder locked out and confirmed dead.
Questions
Does 24 V DC control wiring make a device Division 2?
Only partly. 24 V DC keeps contact energy low and suits nonincendive field wiring, but the device mark does the work: Class I Division 2, Group D, T3 (200 °C) or lower on the label, or contacts sealed inside a hermetic header. An unmarked 24 V relay with bare contacts stays out of the cabinet.
Can a breather drain or vent be fitted to a Division 2 cabinet?
Keep it unpierced: NEC 314.15 permits 3 mm (1/8 in) to 6 mm (1/4 in) drainage openings in damp-location boxes, but a hole that size is the path a Division 2 atmosphere takes into a sealed cabinet, and it drops the assembly below Type 4. Seal every unused cutout with a matching plug.
What does the burner management unit and its flame detector need?
Read the flame detector's label first: most carry their own Class I Division 2, Group D mark with a T code, and the wiring method follows the burner management instructions. A unit without a Division 2 mark needs a purge per NFPA 496, a spot in an unclassified room, or a replacement model; the cabinet rating cannot supply what the device lacks.
How much heat can a sealed stainless cabinet shed before it needs a cooler?
For a 40 x 32 x 12 in [1020 x 810 x 300 mm] 316L cabinet, walls at 3.7 W/m²K over 2.77 m² move 102 W for a 10 K rise (30 °C ambient, 40 °C inside) and 51 W when ambient hits 35 °C. A 36 W load of supply, controller and relay coils rises only 3.5 K above ambient. Past that, fit a sealed air-to-air heat exchanger.
Does the cabinet itself need explosion-proof construction in Division 2?
Division 1 asks for explosion-proof housings; Division 2 puts the ignition control inside the devices, so a plain sealed cabinet is the standard offshore build. We build Type 4X stainless cabinets rated by the manufacturer (not UL listed) and do not build explosion-proof, purged or Types 7/9 enclosures.
