IP20 vs IP67 Power Supply: Enclosure Design, Waterproofing and Where Each Belongs

Two letters after “IP” decide whether a power supply lives five years or fries in one. Yet most specifiers pick the higher number by reflex: IP67 must beat IP20. For “power supply enclosure design,” that reflex is wrong often enough to matter. The rating tells you what the box keeps out; it says nothing about what the box keeps cool.

What IP actually codes

Per IEC 60529, IP20 means protected against fingers (12mm) and no solid >12.5mm—no dust seal, no water protection. IP67 means dust-tight and immersion-proof to 1m for 30 minutes. The first digit is solids, the second is water. A “plastic case waterproof switching power supply” at IP67 is sealed; an “indoor power supply” at IP20 is open to air by design.

Why sealed is not always better

Counterintuitive point one: a sealed IP67 unit in a hot location fails faster than an IP20 unit in the same heat. Sealing traps the heat the switcher produces; an IP20 case with passive convection sheds it. At 200W, that gap is 8–12 °C internally, and every 10 °C roughly halves electrolytic-cap life. The waterproof supply you bought for safety can shorten life if it sits in a warm, dry room. Match the seal to the water, not to the fear.

Dust beats rain more often than you think

Counterintuitive point two: in a factory, IP20 versus IP67 is the wrong question. Fine conductive dust + heat kills more supplies than rain does. A vented IP20 with a fan and a dust filter outlasts a sealed can in a welding shop, because the filter is serviced and the heat leaves. If your “indoor power supply” runs in a shop floor, spec airflow and a filter, not a higher IP number.

The gasket is the weak link, not the rating

An IP67 number is measured on a fresh sample. The silicone or EPDM gasket that holds it degrades under UV and thermal cycling—roughly 2–3 years of direct sun cracks it even if the potting stays intact. A “waterproof plastic case switching power supply” facing south at 45° loses its seal on schedule, not on accident. For outdoor fixtures, plan gasket service; the initial rating is a starting point, not a lifetime warranty.

Material and potting choices

• Plastic case (IP67): lightweight, corrosion-proof, cheaper tooling; potting compound (Henkel, 3M) fills voids and transfers heat to the wall.

• Metal case (IP20/IP65): better heat sinking, heavier, needs coating in wet/corrosive air.

• Potting vs conformally coated: full potting costs 0.40–1.20/unit more but lifts IP and shock resistance; worth it for transit and marine.

Matching enclosure to location

• Office / retail ceiling, dry, ventilated: IP20, passive or fan.

• Warehouse, dusty, warm: IP20 + filtered intake, or IP54 if washdown.

• Outdoor signage, light box: IP65–IP67, UV-stable gasket, drain weep.

• Transit tunnel, humid + vibration: IP67 potted, wide temp.

Sizing the enclosure for heat, not just water

For a 250W unit, a sealed IP67 case needs ~30% more internal volume than an IP20 of equal rating just to hold the temperature down—or a derated wattage. Specifiers who ask only “is it waterproof” end up buying a 300W sealed unit to do a 200W job. Read the 60 °C derating curve; if the supplier will not show it, assume the worst.

Closing

Enclosure design is a heat-and-water trade, not a popularity contest of numbers. The page that explains why IP20 can outlive IP67 in a hot room ranks for “power supply enclosure design” because it answers the question engineers actually argue about. Pick the seal for the water, the vent for the heat.