Washdown enclosures for food and beverage plants

What the food rules actually say

None of the food regulations rates an electrical enclosure's protection against water; that is the job of NEMA types and IP codes. What they set is cleanability, and they apply to equipment that never touches food:

• FDA, 21 CFR 117.40 (food facilities): equipment "must be installed so as to facilitate the cleaning and maintenance of the equipment and of adjacent spaces", and equipment in food areas "that does not come into contact with food must be so constructed that it can be kept in a clean and sanitary condition."
• USDA FSIS, 9 CFR 416 (meat and poultry plants): non-food-contact surfaces of facilities and equipment "must be cleaned and sanitized as frequently as necessary to prevent the creation of insanitary conditions and the adulteration of product." Equipment must also not be built or located so that it prevents inspectors from checking that it is sanitary.
• FDA Food Code 2022 (a model code for retail food, adopted by state and local regulators): non-food-contact surfaces exposed to splash, spillage or food soiling, or that need frequent cleaning, shall be corrosion-resistant, nonabsorbent and smooth (4-101.19), and "shall be free of unnecessary ledges, projections, and crevices, and designed and constructed to allow easy cleaning and to facilitate maintenance" (4-202.16).
• 3-A Sanitary Standards: design criteria for processing equipment and systems. The 3-A Symbol identifies equipment that meets them, and 3-A states that independent Third Party Verification inspection applies to all equipment built to its standards.
• EHEDG: the European Hygienic Engineering & Design Group publishes more than 50 guidelines on hygienic design, including Guideline 8, Hygienic Design Principles, and Guideline 13 for equipment in wet-cleaned open processing areas.

Which rules apply depends on your plant and its regulator. For an enclosure, the practical reading is the same: smooth, corrosion-resistant, nothing that traps soil or water, and installed so you can clean around it.

Rating: NEMA 4X, IP66 and where IP69 fits

NEMA Type 4X covers windblown dust, rain, splashing and hose-directed water and adds a corrosion test, which is what washdown with chemicals needs. The NEMA hosedown test uses a large stream at low pressure: NEMA's comparison table gives a 25.4 mm (1 in) nozzle, 240 L/min (65 gal/min) and a nozzle pressure of about 31 kPa (4.5 psi), from 3.0-3.7 m (10-12 ft). The full comparison with IP66 is in NEMA 4 vs 4X vs IP66.

Hot, high-pressure cleaning is a different load. The IPX9 test in IEC 60529 sprays water at 80 °C (±5 °C) from 175 ± 25 mm, from all practical directions, for 1 minute per m² of surface and at least 3 minutes; NEMA's table puts its jet at 15 L/min and about 2,494 kPa (362 psi) at the nozzle, roughly 80 times the Type 4 hose pressure. IP69K is a similar code from the road-vehicle standard ISO 20653. The 2020 edition of NEMA 250 also lists a fan-jet nozzle and a high-pressure, high-temperature water-jet test set-up in its contents, so ask what a product was actually tested to rather than assuming. If your sanitation crew uses high-pressure hot water close to the equipment, ask for that rating, or shield the enclosure and keep the lance away from it.

Hygienic design: no ledges, no crevices, nothing to pool

The Ten Principles of Sanitary Design, developed by the American Meat Institute and republished by Manitoba's agriculture ministry, turn the regulations into design rules. Several apply directly to enclosures:

• Self-draining: "Equipment should be self-draining to ensure liquid does not collect or condense on the equipment." "Horizontal surfaces must be avoided. Surfaces should always slope to one side."
• Enclosures: maintenance enclosures and interfaces such as push buttons, switches and touch screens must be designed so product, water or product liquid does not penetrate or accumulate in or on them, and "physical design of the enclosures should be sloped or pitched to avoid use as storage area."
• Welds: attached items should be continuously welded rather than fixed by drilled and tapped holes; welds should be smooth, continuous and ground smooth, with no tack or spot welds.
• Fasteners and niches: avoid screw threads, rivets and bolts, which trap food; parts should be free of pits, cracks, corrosion, open seams and gaps.

The European stainless steel association's food-industry brochure adds two points. Crevices under bolt heads, at flanges or between equipment and the surface it sits on retain soil and trap cleaning agents, which then cause corrosion. And non-metallic fillers are not a satisfactory substitute for a continuous weld, because they can crack or separate and leave a crevice. It also notes that hygienic design makes equipment non-contaminating and cleanable but cannot guarantee sterility.

For a washdown enclosure, from any maker, that means asking for: a sloped or pitched top where the plant standard calls for it, continuous seam welds, no exposed threads on the outside, hinges and latches you can clean around, and labels kept to a minimum.

Mounting: off the wall or sealed to it

The gap behind a wall-mounted enclosure is where soil and water collect. The FDA Food Code gives three acceptable ways to install fixed equipment (4-402.11): spaced to allow access for cleaning along the sides, behind and above; spaced from adjoining equipment, walls and ceilings by not more than 1 mm (1/32 in); or sealed to adjoining equipment or walls if exposed to spillage or seepage. Floor-mounted equipment that is not easily movable is to be sealed to the floor or raised on legs giving at least 15 cm (6 in) of clearance (4-402.12).

Standoff mounting also suits the enclosure rating. NEMA notes that many type-rated enclosures need a mounting means outside the electrical cavity, such as feet or a bracket, rather than holes drilled through the back. Mount on the external feet with enough space behind the enclosure to clean, and bring cables in from the bottom so water runs off the entries. The mounting guide covers wall, stand and pole mounting.

304 or 316L against cleaners and sanitizers

Both grades are standard in food plants. Chlorides decide between them: brine, salty or acidic product, chlorinated water and chlorine-based sanitizers attack the passive film locally and cause pitting and crevice corrosion, and the molybdenum in 316L improves resistance to exactly that. One food-plant chemical bulletin warns that high chlorides at low pH pit stainless steel, recommends 316 for cheese brines, and calls for a freshwater rinse before acid sanitizer where brine is used. The full comparison is in 304 vs 316L stainless for enclosures.

Surface finish matters for product-contact surfaces. EHEDG Guideline 8, as quoted by the stainless steel association, recommends that large areas of product-contact surface have a finish of 0.8 µm Ra or better. An enclosure is not normally a product-contact surface, but the same logic applies to anything that gets splashed: smoother surfaces hold less soil and clean more easily.

Gaskets, glands and the door

The enclosure walls are rarely where washdown water gets in. The door gasket, the glands and anything mounted in the door are:

• Gaskets: NEMA 250 includes gasket aging, compression and oil-immersion tests. We recommend inspecting gaskets on a schedule, replacing damaged or hardened ones, and never scraping or prying them during cleaning.
• Openings: NEMA's rule is that the installed assembly is only as good as its least-rated component, so every gland, plug, breather and door device must be rated at least to the enclosure type. See cutouts, glands and HMI windows.
• Displays: an HMI or panel PC in the door is sealed by its own front gasket. Our HMI enclosures have an IP65-type front seal with the display installed, so keep jets off the display face; the HMI enclosure guide covers sealing and mounting.
• Cooling: fans and filters exchange plant air with the inside and do not belong in a washdown area unless the unit carries the enclosure's rating. Closed-loop heat exchangers and air conditioners keep the plant air out.

Cleaning practice that protects the rating

Most washdown failures come from how the enclosure is cleaned. Our recommendations:

• Keep the door closed and latched during washdown, and check that it is closed before the hose comes out.
• Use the pressure and distance the rating covers. A NEMA 4X-type enclosure is tested with a hose stream at about 4.5 psi nozzle pressure from 10-12 ft, not a lance held at the gasket.
• Rinse chloride-containing cleaners and sanitizers off with clean water; do not let them dry on the surface. Never use hydrochloric (muriatic) acid on or near stainless steel.
• Avoid cold water on a hot enclosure where you can. IEC 60529 requires a pressure balance when test water is more than 5 K colder than the enclosure, because the sudden cooling pulls air, and water, inside. A vent drain rated to the enclosure type relieves that vacuum; see the condensation guide.
• Inspect for pitting, rust spots and residue under labels and around fittings, and deal with them early.

Frequently asked questions

Sources

1. 21 CFR 117.40, Equipment and utensils (eCFR)
2. 9 CFR Part 416, Sanitation (USDA FSIS; 416.3 equipment, 416.4 sanitary operations) (eCFR)
3. US FDA, Food Code 2022 (4-101.19, 4-202.16, 4-402.11, 4-402.12)
4. 3-A Sanitary Standards, Inc., About 3-A (standards, 3-A Symbol, Third Party Verification)
5. EHEDG, Guidelines (Doc 8 Hygienic Design Principles, Doc 13 wet-cleaned open equipment)
6. Manitoba Agriculture, "Sanitary Design of Equipment" (the Ten Principles of Sanitary Design)
7. Euro Inox, "Stainless Steel in the Food & Beverage Industry" (surface finish, EHEDG Doc 8, crevices, welds, hygienic design)
8. Hydrite, "Chloride Pitting of Stainless Steel" (Dec 2022)
9. IMOA, "Which Stainless Steel Should Be Specified for Exterior Applications?" (chloride cleaners, hydrochloric acid)
10. IEC 60529 Ed. 2.2 (IPX9 test conditions; water temperature and pressure balance)
11. ANSI/NEMA 250-2020, contents and scope (gasket tests, high-pressure water-jet figures)
12. NEMA, "NEMA FAQs: Enclosures" (Q13 hose test, Q15 weakest link, Q16 external mounting)