An IP rating is not a score. It is two separate classifications printed next to each other, and the second digit is not a ladder that a higher number climbs. A motor rated IP67 has passed a different test from one rated IP65, not a harder version of it, and buying the larger number does not necessarily buy the protection the machine needs. Most of the arguments about which motor is more waterproof come from reading the code as a ranking rather than as a set of test conditions.

Two Digits, Two Independent Questions

The first digit covers solids and contact, the second covers water. Nothing in the second digit says anything about dust, and nothing in the first says anything about water.

The first digit runs from 0 to 6. The distinction that matters in practice is between 5 and 6. A 5 enclosure is dust protected: some dust may enter, but not enough to interfere with operation. A 6 enclosure is dust tight: no dust enters under the test. For a workshop with flour or cement dust, 5 is adequate. For carbon dust, metal powder or anything conductive or abrasive, 5 is not, because the dust that gets in is the dust that does the damage.

The Second Digit Is Not a Ladder

The water tests differ in apparatus, not only in severity. IPX4 is splashing water from any direction at 10 litres per minute and 50 to 150 kPa for ten minutes. IPX5 is a 6.3 mm nozzle at 12.5 litres per minute and 30 kPa for three minutes. IPX6 is a 12.5 mm nozzle at 100 litres per minute and 100 kPa for three minutes. IPX7 is immersion with the enclosure 15 cm to 1 m below the surface for thirty minutes.

Put those pressures in a unit people can picture. One metre of water is about 10 kPa. So IPX6’s jet, at 100 kPa, is a blast equivalent to the pressure at the bottom of ten metres, while IPX7’s immersion test is a tenth of that pressure applied for ten times as long.

That asymmetry is the reason the ratings cannot be substituted. A jet attacks the seal dynamically, driving water at a lip or a gland that may seal well in one direction and poorly in the other. Immersion applies a steady head with no impact, so it finds a different weakness: a seal that holds against a blast can still pass water steadily if its lip faces the wrong way, and a unit that survives a hose can fill through a cable gland given thirty quiet minutes.

This is why IP67 does not include IP65, and why a machine that is both hosed down and occasionally flooded needs both claims tested rather than the higher number assumed.

What the Code Says Nothing About

Condensation is the largest cause of water inside a sealed motor, and no part of IEC 60529 tests for it. A sealed enclosure is not a sealed box. Every temperature cycle expands the air inside and then contracts it, and each contraction draws a little moist air past the seals and glands. Over a season the moisture accumulates with no way out. This is why sealed motors are often fitted with a breathable membrane vent, and why a motor can meet its IP rating and still be wet inside when it is opened.

The same gap covers steam, chemical cleaning agents, salt, UV and ice. Only IPX9K in the extended automotive specification tests a steam jet, and it is a different test from anything in the standard series. A dairy or food plant that cleans with hot water and caustic is not served by an IP65 claim, whatever the number suggests.

“Waterproof” is not a defined term in IEC 60529 at all. It is a marketing word, and it should be treated as one.

Where a Gear Motor Actually Leaks

Four places, in order of how often they are the cause.

The output shaft seal is the only moving seal on the unit, and lip seals are directional. They are designed to keep lubricant in, which is not always the same geometry that keeps water out.

The gearbox joint is a static seal between two parts, often of different materials, and it moves as the unit warms. An O-ring that seals cold can lose its squeeze warm.

The cable entry is the most common of all. A gland that was not tightened to its torque, a cable without a drip loop, or a terminal box facing upward will take water in regardless of the enclosure rating, because the water never has to cross the seal. Running the cable downward and leaving a loop below the entry costs nothing and prevents most of these failures.

And the rating belongs to the assembly as it was tested. A customer who replaces the connector, drills the terminal cover, or mounts the unit shaft upward has changed the thing that was rated.

Sealing Is Paid for in Cooling

A sealed motor cannot use open ventilation, so heat leaves through the frame alone. The same frame is therefore rated lower at IP65 than at IP54, because the winding reaches its limit sooner. This is the part of the decision that rarely reaches the comparison sheet: over-specifying the enclosure is not free, it is paid twice, once in unit cost and again in a smaller continuous torque for the same size.

The sensible target is the lowest rating that survives the actual exposure. A dry indoor machine gains nothing from IP65 except a derating.

What to Send

Four items decide it. The fluid and its temperature, since splash, steam and chemical wash are three different problems. The cleaning method and how often, because a hose and a bucket are not the same test. The mounting orientation and where the cable leaves the unit, since both can defeat a sound enclosure. And whether the unit will sit in a condensing environment, which is a ventilation question rather than a sealing one.