IP ratings and NEMA types, and which one to specify

IP ratings are quoted constantly and understood loosely, which leads to enclosures specified one grade below what the environment does to them.

The two digits

First digit, solids.

• 0 to 4: progressively smaller objects, from a hand down to a wire.
• 5: dust protected. Some dust may enter but not enough to interfere.
• 6: dust tight. No ingress at all.

Second digit, water.

• 1 to 2: dripping, vertically and at an angle.
• 3: spraying, up to 60 degrees from vertical.
• 4: splashing from any direction.
• 5: jets from a 6.3 mm nozzle, 12.5 litres a minute.
• 6: powerful jets from a 12.5 mm nozzle, 100 litres a minute.
• 7: immersion to 1 metre for 30 minutes.
• 8: continuous immersion, to a depth agreed with the manufacturer.
• 9K: high pressure high temperature jets, 80 bar at 80 degrees.

The trap in the numbering

The water digits are not a simple ladder, and this is the detail worth carrying away.

IP67 is tested by immersion and IP66 by powerful jets. They test different things. An enclosure that survives being submerged can fail a pressure washer, because a jet forces water past a seal in a way that static pressure does not.

Where both matter, the specification is IP66/IP67, and manufacturers do rate to both.

Similarly, 9K is not simply a higher 8. It is a distinct test for a distinct environment, and an IP68 enclosure is not automatically IP69K.

NEMA, and why it is not a translation

NEMA types cover similar ground and add requirements that IP does not test at all.

• Type 4 is roughly IP66, and additionally requires resistance to ice formation.
• Type 4X adds corrosion resistance, which IP does not address in any digit.
• Type 12 is roughly IP65 for indoor industrial use, dust and dripping liquid.

So a NEMA type can be mapped to an approximate IP rating, and an IP rating cannot be mapped up to a NEMA type, because the corrosion and ice requirements are simply not in the IP test.

For a coastal or chemical environment, 4X or the equivalent stainless construction is the specification, and an IP66 mild steel enclosure meets the ingress requirement while rusting through.

What to specify, in practice

• Indoors, clean, dry. IP54 is usually plenty, and IP20 with ventilation is common on a plate inside a bigger room.
• Indoors, dusty. IP65 or IP66 and think about cooling, since a sealed enclosure cannot use a filter fan.
• Food and beverage washdown. IP66/IP69K, stainless, sloped tops so water runs off, and no horizontal ledges to hold residue.
• Outdoors. IP66 minimum, plus a sunshade, plus an anti-condensation heater. The rating protects against rain; the heater protects against the water that forms inside.

The rating is only as good as the installation

The point everybody knows and half of installations miss.

An IP66 enclosure with an unused gland hole is IP20. A cable gland not tightened is IP20. A door seal painted over, pinched by a cable, or with the door not correctly latched is IP20.

The rating describes the enclosure as tested, and the installation is where it is either kept or thrown away.