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IP54 vs IP65 vs IP68 Busway: What Do the Ratings Mean?

By DHYN Engineering Team  ·  July 27, 2026

Quick answer: IP54 keeps out harmful dust and splashing water, and it is the normal rating for indoor busways. IP65 is fully dust tight and survives water jets, which covers most outdoor runs. IP68 means the busway can stay underwater indefinitely, and in practice that means a resin cast design. Choose from the environment, not from habit, and remember the joint is always the weak point.

Every busway datasheet carries an IP rating, and most buyers nod at it without reading much further. Fair enough, the code looks cryptic. But those two digits decide whether your duct shrugs off a flooded basement or dies in it, so it is worth five minutes to understand what you are actually buying.

What the two digits actually mean

The IP code comes from IEC 60529. The first digit covers solid objects and dust, on a scale from 0 to 6. A 5 means dust can creep in but not enough to cause trouble. A 6 means nothing gets in at all. The second digit covers water, from 0 to 8. A 4 handles splashing from any direction. A 5 handles water jets, tested with a 6.3 mm nozzle pushing 12.5 litres per minute for at least three minutes. An 8 is continuous immersion, and here is the part people miss: the manufacturer declares the depth and duration, because the standard leaves those open. When you buy IP68, ask for those two numbers in writing.

For busbar trunking specifically, IEC 61439-6 requires the declared protection degree to apply to the assembled system. That detail matters more than any single digit, and I will come back to it.

IP54: the indoor workhorse

Dust protected, splash proof. That description covers the huge majority of busway installations: office risers, hotel shafts, shopping malls, hospital corridors, most factory floors. A standard sandwich bus duct reaches IP54 without any special effort, because the bars are packed tight with no open air path. If your run stays indoors and nobody will hose it down, IP54 is the honest answer and anything higher is money spent on nothing.

IP65: the outdoor rating

Dust tight and resistant to water jets. This is what you want for links between buildings, open car parks, humid basements, and washdown zones in food or beverage plants. Getting a sandwich duct to IP65 is mostly about the joint kits: gaskets, sealant, torque on the joint bolts. The straight lengths are easy to seal. The joints are where ratings go to die, which brings me to the next point.

IP68: built to live underwater

In the busway world, IP68 almost always means resin cast. The conductors are cast solid in epoxy resin, so there is no enclosure interior for water to enter, no air gap at all. This is the design for tunnels, pump stations, flood-prone basements, and runs buried in the ground. If flooding at your site is a question of when rather than if, stop looking at sandwich ducts and spec a resin cast busway. Just remember to get the declared immersion depth and time on paper, since IP68 without those numbers is a marketing claim, not a rating.

The joint decides the real rating

We have seen this go wrong on site more than once. A duct rated IP65 in the catalog gets installed with joint kits thrown together in the rain, sealant skipped, bolts half torqued. Six months later there is condensation inside and green copper at the joint. The catalog rating assumed the joint kit went in exactly as the manual says. So when you compare suppliers, ask one question: was the IP test done on a jointed assembly? A serious manufacturer tests the run with joints fitted, per IEC 61439-6, and will send you that report.

One more trap: tap-off boxes. Adding a plug-in box can drop the local protection below the rating of the duct itself. Check the box rating too, especially outdoors.

Which rating for which job

Where the busway runs	Sensible rating	Why
Office or hotel riser, dry shaft	IP54	Dust only, no water expected
Workshop with grinding or welding dust	IP54 to IP55	Fine dust plus occasional hosing
Outdoor link between buildings	IP65	Rain and hose cleaning
Car park, humid basement	IP65	Condensation and splash
Food plant washdown zone	IP65 to IP66	Daily pressure washing
Tunnel, pump room, flood-prone area	IP68 resin cast	Real immersion risk
Buried in the ground	IP68 resin cast	Permanent moisture

Mistakes we see buyers make

The first is over-specifying. IP68 resin cast indoors in a dry tower is a lovely duct and a waste of money. The second is the opposite: saving a few percent with IP54 on an outdoor run, then paying for a replacement two winters later. The third is forgetting condensation. A vertical riser that crosses warm and cold zones can collect moisture inside even at IP65, because the water forms on the inside. In those cases, talk to the manufacturer about drainage or go resin cast for that section.

The short version: match the rating to the environment, demand the joint test report, and get IP68 depth and time in writing. Do those three things and the digits on the datasheet will actually mean something on your site.