Draining a burst water line inside a sealed enclosure

Short answer: cut a 2 in [50 mm] drain in the floor, put a three-plate baffle stack over it, and treat the cabinet as an indoor box from that day on — a floor hole this size takes a Type 4 or Type 12 enclosure down to about Type 1. Size the drain for the flow you cannot stop before a solenoid closes: on a 40 gpm [150 L/min] loop with one supply and return pair on a six-port manifold, that pair carries about 13 gpm [50 L/min], and a severed hose draws more than its share, so design for 20 gpm [75 L/min]. One baffled drain of that size passes about 14 gpm [52 L/min] with 2 in [50 mm] of water standing — enough to hold the flood while a return-line flow switch closes the supply solenoid within 2 s. The interlock does the real work; the drain buys it those seconds.

Size the drain for the flow you cannot stop

Work out the share first. A 40 gpm [150 L/min] pump on a six-port manifold is three supply and return pairs, so the pair feeding the panel carries about 13 gpm [50 L/min] while every branch has similar resistance. A hose that lets go inside the cabinet dumps to atmosphere at near-zero backpressure, so it stops sharing and takes what the pump will give — more than 13 gpm, less than the full 40 gpm while the transformer and heat-exchanger branches keep flowing. Carry the design at 1.5x the share, 20 gpm [75 L/min], and treat that 1.5 as a design assumption you replace with your manifold's real split.

Now the hole. Water leaves a sharp-edged opening at Q = C x A x √(2gh). At 2 in [50 mm] of standing water, √(2 x 9.81 x 0.05) works out to 1.0 m/s, and a hole of the size above carries 1,960 mm² of area. A bare hole at C = 0.62 passes 0.62 x 0.00196 m² x 1.0 m/s = 1.2 L/s [19 gpm]. The baffle stack costs about a quarter of that, so figure C = 0.45, or 0.9 L/s [14 gpm]. That 0.45 is the assumed coefficient for a three-plate stack; prove it at the flood test before you rely on it.

All figures at the same standing head; flow scales with the square root of depth, so four times the head buys only twice the flow.

Left running, 20 gpm against one baffled drain settles where outflow matches inflow: 50 mm x (20/14)² ≈ 100 mm, so 4 in [100 mm] of standing water. Two such drains hold the same 20 gpm at about 1 in [26 mm], and even the pump's full 40 gpm [150 L/min] at about 4 in [100 mm]. Decide from your interlock. With the solenoid closing in 2 s you admit 0.7 gal [2.5 L] — 20 gpm for 2 s — which is 8 mm [1/3 in] of depth on a 24 x 20 in [610 x 510 mm] floor, so one drain with live parts at 6 in [150 mm] covers it. Without the interlock, cut two drains and keep the 6 in [150 mm] line, because one drain at the full 40 gpm settles near 16 in [415 mm], past everything on the backplate.

What the hole does to the type rating

An enclosure holds the type of its weakest opening, and the drain is now that opening — the same weakest-link rule behind what a vent hole does to a sealed rating. Under NEMA 250, Type 4 and 4X enclosures exclude hose-directed water and Type 12 excludes dust and dripping liquids; a floor hole of this size with baffle gaps defeats all three. Call the cabinet what it has become — a general-purpose indoor box, Type 1 for planning — and arrange the room for that: dry cleaning only, no washdown hoses, indoor air.

The code's own drain is a different animal. NEC 314.15 permits drainage openings of 3 mm to 6 mm [1/8 to 1/4 in] in boxes and conduit bodies listed for damp or wet locations, and UL 50E sets a similar weep size for Type 3R; the 3R versus Type 4 drain rules cover that weather-side story. A 6 mm [1/4 in] weep passes about 0.3 gpm [1 L/min] at modest head, which drains rain and condensation. Your burst hose brings 13 to 20 gpm [50 to 75 L/min]. Choose by location: indoors beside the welder, take the Type 1 demotion and cut the big drain; outdoors or in washdown, keep the shell sealed and carry the water in a bagged sleeve, as the last section describes.

The clean split is two boxes — a water-cooled power section that owns the drain, and a sealed electronics box beside it. What Type 4X and IP66 mean and the enclosure selector set up that half by environment and size. A type marking is the manufacturer's own rating against the NEMA 250 tests: ours are rated NEMA 4X / IP66 by the manufacturer and not UL listed, and NEMA itself tests and certifies nothing.

The baffle stack that keeps the hole optically blind

The drain has to pass a flood and still block spray, mist, dust and a directed jet. Mesh alone fails on both counts — you can see through it, and so can the needle jet from a pinholed hose. Build a stack instead: three stainless plates, 4 x 4 in [100 x 100 mm] and 16 gauge [1.5 mm], spaced 1 in [25 mm] apart over the hole, each offset 1 in [25 mm] from the one below so no straight line exists from the room into the cabinet. Bolt or weld them from inside with stainless standoffs, and fit a coarse mesh guard on the outer face to stop swarf and rags reaching the plates. The guard catches solids; the plates do the sealing. That is the whole idea of an optically blind hole: light-tight against a straight path, tight against splash, open to a flood — and the quarter of flow it costs is already in the C = 0.45 figure.

Shut the water off at the return line

Meter the outlet, not the inlet. When a supply hose lets go downstream of an inlet meter, the inlet still reads its normal 13 gpm [50 L/min] — the pump pushes water happily into the broken line — while the return falls to zero. A flow switch in the return, set at about 60% of branch flow (8 gpm [30 L/min] on a 13 gpm branch), sees every in-panel break: severed supply, severed return, split heat exchanger. Wire it to a 24 V DC solenoid on the panel's supply line. A direct-acting solenoid closes in well under a second, so count 2 s for the PLC scan and the relay — that is the 0.7 gal [2.5 L] you sized the drain against.

Add a differential pressure switch across the panel's supply and return as the fast secondary. A burst collapses return pressure while supply holds, and the DP switch slams the same solenoid. Keep both devices: the flow comparison catches a 1 gpm [4 L/min] weep that barely moves pressure, and the DP switch catches a full separation in milliseconds. Fit a check valve in the return as well, so closing the solenoid leaves the loop full instead of draining it back through the pump.

Interlock the water with the power. On a water-cooled SCR, the trip that closes the solenoid must also kill the firing pulses, because a puck that keeps conducting with its cooling gone overheats in seconds. Trip both from one relay contact and test them together.

Keep the jet off the live parts

A pinhole in a 3/8 in [10 mm] hose at a typical 60 psi [4 bar] recirculating pressure throws a needle jet, and it will find the SCR pucks and the bus. Stand 1/8 in [3 mm] polycarbonate deflectors between every water fitting and the live hardware, sloped so the spray runs to the sump corner. Land the hose glands in the lower corner nearest the drain, shroud the terminations, and mount boards and terminal blocks at least 6 in [150 mm] above the floor. Have the base formed with a 1:50 slope to that corner and a 0.5 in [13 mm] sump where the drain sits — in a fabricated stainless base, the slope, the sump and the cutouts happen in one pass.

Building it, step by step

1. Split the panel: water-cooled power and cooling gear in the drained box, sealed controls in their own enclosure beside it.
2. Lay the water out low: gland holes for two supplies and two returns in the lower side wall nearest the drain corner, sized to the measured hose OD — the cutouts and glands guide sets the spacing rules.
3. Form the base with the 1:50 slope and the 0.5 in [13 mm] sump, drain at the low point and at least 1 in [25 mm] from any fold so the baffle plates seat flat.
4. Cut the drain at the low point; in a made-to-order box you place it in the cutout designer before anything is built.
5. Build the stack: three 4 x 4 in [100 x 100 mm] plates, 1 in [25 mm] spacing, 1 in [25 mm] offset per plate, fastened from inside.
6. Run the drain line in pipe to match, at 0.04 ft/ft or steeper — gravity drainage tables put a half-full line of that size at 11.7 gpm [44 L/min] on a 0.0291 ft/ft slope — to a floor drain or the bund tank.
7. Mount the deflectors, the return flow switch at 60% of branch flow, the DP switch, the supply solenoid and the return check valve; wire one trip to the solenoid and the firing board together.
8. Flood-test the panel locked out, before anything is energized.
9. Relabel the cabinet as the indoor box it now is, and mark it on the drawing.

Prove it with a flood test

• Trip test: pull the return hose into a bucket at full pump flow. The flow switch trips, the solenoid closes within 2 s, and the floor holds under 0.5 in [13 mm] of water.
• Drain test: dump 5 gal [19 L] into the floor. A baffled drain at 14 gpm empties it in about 20 s, and the water leaves through the drain, not the door seam.
• Blind test: shine a laser pointer at the stack from outside, from several angles. No dot appears inside.
• Splash test: throw a cup of water at the outer guard. Nothing crosses the plates in a straight line.
• Holding test: close the solenoid and leave the loop overnight; the check valve keeps the return line full.

Mistakes that cost the rating or the SCR

A door that still reads 4X over an open floor drain misleads the next person who washes down that aisle — relabel it and mark the drawing Type 1. An inlet meter reads normal through the whole accident; the return side is where the signal lives. Mesh instead of a baffle stack passes a jet and stays see-through. One drain with no interlock settles at 4 in [100 mm] on a 20 gpm leak and near 16 in [415 mm] at the pump's full 40 gpm [150 L/min], past everything on the backplate. Water that arrives by some other path than the hoses is its own hunt: finding where water got into a sealed enclosure.

Keeping the box sealed: bag the hoses

Where the cabinet must hold Type 4X or 12 — outdoors, washdown, dusty plant air — leave the shell alone and double-skin the water lines instead. Run each hose inside a larger sleeve, sealed to the cabinet wall at the panel end and open into a small bund tank outside carrying a float switch. Any weep, however small, runs down the sleeve into the bund and trips on level, the way chemical dosing lines are guarded. A full burst floods the sleeve too, so keep the return-flow trip and the solenoid from the sections above. Inside, a formed sump with a small pump — 5 gpm [19 L/min] covers a slow leak — moves water out through a glanded pipe, so every penetration stays sealed and the type marking survives.

What to put on the drawing

Specify the material by the room: 304 stainless for an indoor welder panel, 316L where the air carries chlorides or washdown chemicals. Set the base with the 1:50 slope and 0.5 in [13 mm] sump, the 2 in [50 mm] drain, four gland holes to the hose OD, and mounting for the flow switch, the DP switch and the deflectors. Custom enclosures take all of it from one piece — your width, height, depth and every cutout — and arrive delivered in 10 business days, counted from your approval of the drawing. For the sealed half of the split, the enclosure selector picks the box by environment, inside size and DIN module count.

Catalog dimensions to compare

Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.

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