of an enclosure that can make a difference to the lP rating
The IP rating of an enclosure is dictated not only by the enclosure
but also by it's fixing method, lid sealing and cable entries.
After the 'IP'
(Ingress Protection) part of an enclosures protection rating,
number equates to the protection offered by the box as regards
objects from screwdrivers and fingers through to fine particulate
Most plastic and metal enclosures offer a 4, 5 or 6 rating (objects
1mm diameter), a 4 is suitable for a basic wiring junction protected
a wall, ceiling, cabinet or similar in a dry environment, but
a 5 or 6 is
the preferred option should the enclosure be exposed in any way
this covers most industrial applications where the box can be
is accessible as part of routine operation or maintenance.
IP Ratings Table
against ingress of solids
against ingress of liquids
against mechanical impact damage
against solid objects over 50mm e.g. hands, large tools
against vertically falling drops of water
against 0.225 joule impact (150g @ 15cm)
against solid objects over 12mm e.g. hands, large tools
against direct sprays of water up to 15 deg. from vertical
against 0.375 joule impact (250g @ 15cm)
against solid objects over 2.5mm e.g. wire, small tools
against direct sprays of water up to 60 deg. from vertical
against 0.5 joule impact (250g @ 20cm)
against solid objects over 1mm e.g. wires
against water sprayed from any direction. Limited ingress permitted.
protection against dust ingress (no harmful deposit)
against low pressure water jets from any direction. Limited ingress
against 2.0 joule impact (500g @ 40cm)
protected against dust ingress.
against high pressure water jets from any direction. Limited
against immersion between 15cm and 1M.
against 6.0 joule impact (1.5Kg @ 40cm)
against long periods of immersion under pressure.
against 20 joule impact (5Kg @ 40cm)
Pressed metal enclosures offer the poorest protection and are
a 4, cast and most polystyrene and virtually all polycarbonate
fall into the 5 or 6 categories. There is a third number that
refers to impact
protection, but is not often quoted; the second number is where
has to be made and where several variables come in to play:
When mounting an enclosure inside a cabinet, fixing to a machine
building wall or a post, the method of attachment can either
instantly downgrade the IP rating of the enclosure assembly.
in an industrial environment that may include water sprays, wash
or atmospheric moisture, a screw fixed '1P65' enclosure with
glands can be rendered '1P64' or lower simply by not employing
between the screw or bolt heads and the enclosure wall when fixing
enclosure in place.
Fixing to posts or uneven surfaces is more problematic and an
fixing of some sort such as cable-tie brackets can be very useful.
or gun applied sealant is also an option.
offering IP67 protection.
The lid sealing of an enclosure is the next major element to
sealing, basic 'click' fit lids are generally IP54 or lower.
enclosures are the worst, allowing either dust or moisture in
easily, whereas plastic 'click' fit enclosures generally offer
provides limited protection from both dust ingress and liquids.
enclosures or industrial plastics such as moulded polystyrene
polycarbonate generally offer much higher levels of protection.
of IP54 and above generally requires an additional compressible
achieve higher protection. Machine applied polymer seals are
more reliable than gasket types as they are not prone to movement
during fixing and a seal that runs inside the lid fixing screws
required for IP65 and above.
Cable entries are present in virtually all sealed enclosures
significant IP rating; they vary from basic cable clamps through
independently rated waterproof cable glands. Basic cable clamps
open holes offer some protection, but where moisture is present
any degree the cable entry must offer a complete seal around
cable sheath. Recent developments in push-fit seals have seen
the grommet type and the moulded-in version offering high ratings
to IP65 in some instances, providing protection from drips to
water sprays and suitable for general above ground outdoor applications.
Underground use, temporary immersion, wash downs in the food
processing industries or exposure to the sea requires IP65 and
this generally requires cable glands fixed to the enclosure wall
quality compression seals. An IP65 rated box is not IP65 when
entries do not offer the same protection.
The harmful effects of both dust and moisture to sensitive equipment,
circuitry and switchgear can cause electrical shorting, component
corrosion and greatly reduced reliability hence proper sealing
Other considerations such as ambient atmospheric moisture combined
with large temperature fluctuations can also cause condensation
In situations where this is likely, it always pays to fit breather
(or grommets) to allow the enclosure humidity and pressure to
without compromising the intended IP rating.
Article by Graham Fox of Spelsberg UK - Tel: 01952-200716
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