IP54 and IP65 look like neighbouring points on one scale, and buyers often treat the higher number as the safer choice. They are not on the same scale. The first digit measures protection against solid objects and dust; the second measures protection against water. IP54 means dust-protected and splash-resistant; IP65 means dust-tight and jet-resistant. A unit can be excellent at one and ordinary at the other, and the application decides which matters.

What the Two Digits Actually Test

The IP code is defined by IEC 60529 and consists of two numbers plus optional letters. The first number runs from 0 to 6 for solids, the second from 0 to 9 for water. Nothing in the code describes corrosion resistance, chemical resistance, UV stability or mechanical strength.

The step from 5 to 6 on the first digit is a test difference, not a design difference: an IP5X enclosure may let a small amount of dust in provided it does not interfere with operation; an IP6X enclosure must let none in under a partial vacuum test. The step from 4 to 5 on the second digit is the difference between a splash and a directed jet at 12.5 litres per minute.

Why IP65 Is Not Automatically Better

Two practical reasons, both learned the hard way in plants.

Sealing has a cost in heat. A dust-tight enclosure with a jet-resistant seal is closer to a closed box than an IP54 one. Motors and gearboxes shed heat through their surfaces, and a tighter seal reduces the exchange with outside air. On a unit already running warm, moving from IP54 to IP65 can add 5 to 10 K to the winding or oil temperature, which shortens insulation and lubricant life by a measurable margin.

Sealing has a cost in condensation. Every enclosure breathes to some degree as it heats and cools. An IP54 unit with a proper breather exchanges air slowly and keeps its interior dry. A sealed IP65 unit that is not fitted with a membrane breather traps the moisture that entered during assembly or through the cable gland, and that moisture condenses on the coldest surface inside - usually the bearing housing.

The correct specification is therefore not "the highest number available" but "the rating the environment requires, with a breather appropriate to it".

Matching the Rating to the Environment

Note what is missing from the table: chemical resistance. A washdown area with caustic foam will destroy a painted IP66 cast iron housing faster than a plain IP54 unit in a dry hall, because the attack is chemical rather than by ingress.

Where Water Actually Gets In

Seals are not the only path, and on most failed units they are not the path at all.

• Cable glands. An unsealed gland entry is an open door. Every enclosure rating assumes the gland is rated at least as high as the box.
• Breathers. A breather without a membrane lets water in as easily as it lets air out. A breather mounted on the top face of an outdoor unit collects rain.
• Shaft seals. The output seal is a rotating joint and cannot be rated like a static gasket. IP65 on the housing says nothing about the seal lip, which is why washdown units use a labyrinth ahead of the lip.
• Cover joints. Machined faces with an O-ring seal well; stamped covers with a bead of sealant do not, once the fasteners relax.
• Condensation. Water that enters as vapour is not covered by any IP test, and it is the most common cause of water in oil on outdoor units.

The Breather Is the Detail Buyers Skip

An outdoor gearbox that heats by day and cools by night pulls air in and out through whatever path exists. If that path is a sealed enclosure, the pressure differential finds the weakest seal - usually the output lip - and pulls a small amount of water past it on every cooling cycle.

A membrane breather equalises pressure without passing liquid water, and it costs a fraction of the difference between an IP54 and an IP65 build. On any unit that runs intermittently outdoors, the breather matters more than the second digit of the rating.

The same logic applies inside: a unit in a humid indoor plant with a large daily temperature swing needs a breather and an oil that separates water, not a higher IP number.

Motor and Gearbox Ratings Do Not Add Up

A common misunderstanding: the assembly is only as protected as its weakest interface.

A gearmotor with an IP65 motor and an IP54 gearbox is an IP54 machine overall, because the flange joint and the seal between them are not tested as part of either unit. When the specification requires IP65, it must be written for the assembled machine - including the flange, the gland entries, the breather position and the terminal box.

For a shaft-mounted unit, the hollow bore is another interface: the customer's shaft enters an enclosure that was tested without it. That joint needs its own sealing arrangement, usually an end cover with a lip seal and a corrosion-resistant shaft sleeve.

What a Higher Rating Costs and What It Buys

An IP65 gearbox typically costs 5 to 15 percent more than the IP54 equivalent in the same frame, and rather more if it also carries epoxy paint, stainless fasteners and a labyrinth seal. In a dusty plant that extra cost buys years of oil life, because the dominant wear mechanism in dusty service is abrasive dust in the lubricant.

In a clean, dry hall the same money buys nothing, and it takes away thermal margin. The honest question is not "which rating is better" but "what is the actual failure mode here": dust, water, chemical attack, condensation or heat.

A Practical Specification Checklist

1. State the IP rating for the assembled machine, not for the components.
2. State the cleaning regime: hose, foam, high-pressure lance or dry wipe.
3. State the ambient temperature range and whether the unit runs intermittently.
4. Specify the breather type and its mounting position.
5. Specify the paint system and fastener material for the chemical environment.
6. Specify the shaft seal arrangement at the output, and any shaft sleeve.
7. Confirm the cable gland rating with the electrical contractor.

A unit selected this way tends to be simpler and cheaper than a blanket IP66 order, and it lasts longer, because the details that actually admit water have been addressed rather than hidden behind a number. Standard helical and helical-worm units such as the SF87 can be supplied in either build; the choice should follow the environment, not the catalogue page order.

Tell us the duty point and the cleaning regime through the online selection system, and we will quote the protection build that matches it - including the breather and seal arrangement, which is where most of the difference actually sits.

Frequently Asked Questions

Is IP65 waterproof?
No. IP65 resists water jets; it is not rated for immersion. An outdoor unit in driving rain is well served by IP65, but a unit that can sit in standing water needs IP67 or a raised mounting.

Can an IP54 gearbox be used outdoors?
Yes, if it is sheltered and fitted with a breather and a rain shield over the breather and the motor fan cowl. Many outdoor installations have run IP54 units for years; the failures come from breathers facing upward and glands left unsealed.

Does a higher IP rating reduce cooling?
Slightly, yes. A dust-tight enclosure exchanges less heat with the surroundings, and on a thermally loaded unit that can cost a few kelvin. Where the duty is near the thermal limit, the rating decision and the cooling decision have to be made together.

What does IP69K mean and do I need it?
IP69K covers high-pressure, high-temperature jet cleaning at close range, typical of food and pharmaceutical plants. It requires a specific housing design with drain paths, not just tighter seals, and it is only worth buying where that cleaning method is actually used.

Is the motor or the gearbox the weak point?
Whichever has the lower rating, plus the joints between them and the gland entries. Ratings are not additive, and an assembly is judged by its weakest interface.