IP ratings and choosing an enclosure for the environment

Enclosure selection gets delegated more often than almost any other decision in an electrical installation, usually to whoever is placing the order. It looks like a commodity choice. It is not. The enclosure determines whether the equipment inside survives the environment outside, and the two numbers that describe it are routinely misread.

Reading an IP rating correctly

The IP code consists of the letters IP followed by two digits. The first digit describes protection against solid objects, from fingers down to fine dust. The second describes protection against water, from dripping through spraying and jetting to full immersion.

The common mistake is to treat the two digits as a single scale, as though a higher number were always better in every respect. They are independent. An enclosure rated for dust tightness may not be rated for high pressure water jets, and one rated for immersion is not automatically dust tight. A specification should address both axes separately against the actual conditions.

The other frequent error is assuming the water digits are cumulative. Protection against jetting does not necessarily imply protection against immersion, because the mechanisms are different. Where both matter, both have to be specified.

There is also a limitation the code does not express at all. IP testing is performed with clean water at specified temperature and pressure. It says nothing about oils, solvents, cleaning chemicals or steam, all of which behave differently from water and attack seals in ways the test does not reproduce.

What the environment actually does to an enclosure

Dust

Fine dust in cement works, flour mills, woodworking shops and foundries works into every gap, settles on heatsinks and insulates components from their own cooling. Conductive dust from metalworking is worse, because it creates leakage paths across terminals. A ventilated enclosure in a dusty environment is a dust collector with electronics inside.

Water and cleaning regimes

Food processing plants are washed down with hot water and detergent at pressure, which is a far more aggressive test than rainfall. Stainless steel enclosures with smooth surfaces, sloping tops and appropriate gaskets exist specifically for this duty, and a standard painted steel box in that environment will corrode at every seam within a season.

Corrosive atmospheres

Coastal sites bring salt. Water treatment plants bring chlorine and hydrogen sulphide. Plating shops bring acid mist. Material matters more than rating here. Stainless grades differ in their resistance to chloride pitting, and polyester or glass reinforced polyester enclosures are often the better answer in strongly corrosive conditions because they do not corrode at all.

Temperature and solar gain

An enclosure in direct sunlight can run far above ambient, and solar gain on a dark coloured box outdoors is substantial. Sun shields, light colours and orientation all help. In cold climates the opposite problem appears, where condensation forms as equipment cools and anti condensation heaters become necessary.

Vibration and impact

Enclosures on mobile plant, on crushers or near presses face mechanical stress that loosens terminals and cracks mountings. Impact resistance is described by a separate code from the IP rating, and it is specified independently.

The thermal trade off that makes this difficult

Here is the central tension. Raising ingress protection means sealing the enclosure, and sealing it removes the easiest way to get heat out. The components most likely to need a well sealed enclosure, such as drives in a dusty mill, are also the components producing the most heat.

The resolution is to seal the enclosure and move heat without moving air, using air to air heat exchangers or cooling units, which is the subject of our note on heat loss and cooling inside a drive enclosure. What does not work is specifying a high ingress rating and then fitting a ventilation fan into it, which is more common than it should be and defeats the rating entirely.

Details that undo a good specification

An enclosure is only as good as its openings. Every cable gland must carry a rating at least equal to the enclosure, and a cheap gland in an expensive box sets the overall protection. Unused gland holes need blanking plugs of the same rating. Doors with multiple latching points seal more evenly than single point latches on large panels. Gaskets perish and need inspection. And cable entry from below rather than above is a small design choice that keeps water from running along a cable into the enclosure.

Mounting orientation matters too, because a top mounted entry on an outdoor enclosure invites the one failure mode that is hardest to trace.

A practical specification sequence

Describe the environment honestly, including the cleaning regime, because that is frequently more severe than the ambient conditions. Specify the two IP digits separately against solids and liquids. Choose the material on the basis of chemical exposure rather than cost. Check impact and vibration requirements if the location warrants it. Calculate the internal heat load and decide the cooling method before fixing the enclosure size, since cooling equipment needs space. Then specify glands, blanks and gaskets to match, because the weakest opening defines the result.

Where the enclosure houses a motor control assembly, the wider design considerations are set out in our piece on what goes inside a motor control centre panel. General background is summarised in the overview of the IP code.

Frequently asked questions

Is a higher IP number always better?

No. The two digits are independent scales for solids and liquids, and higher sealing makes cooling harder. The right rating is the one matched to the actual environment, not the highest available.

Does an IP rating cover oil and chemicals?

No. IP testing uses clean water. Resistance to oils, solvents, steam and cleaning chemicals depends on material and gasket selection and must be specified separately.

Can I fit a ventilation fan to a sealed enclosure?

Not without losing the rating. Where a high ingress rating and heat removal are both needed, use an air to air heat exchanger or a cooling unit rather than ventilation.

What material suits a corrosive environment?

It depends on the chemistry. Appropriate stainless grades resist many conditions, and glass reinforced polyester is often better in strongly corrosive atmospheres because it does not corrode.

Why does water get into a correctly rated enclosure?

Usually through glands, unblanked holes or perished gaskets rather than through the enclosure itself. Entries must carry the same rating as the box.