IP Ratings of enclosures

The areas 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 itself,
but also by it's fixing method, lid sealing and cable entries. After the 'IP'
(Ingress Protection) part of an enclosures protection rating, the first
number equates to the protection offered by the box as regards solid
objects from screwdrivers and fingers through to fine particulate dust.

Most plastic and metal enclosures offer a 4, 5 or 6 rating (objects under
1mm diameter), a 4 is suitable for a basic wiring junction protected by
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 and
this covers most industrial applications where the box can be seen or
is accessible as part of routine operation or maintenance.

 IP Ratings Table

VALUE

FIRST DIGIT

SECOND DIGIT

THIRD DIGIT
 

Protection against ingress of solids

Protection against ingress of liquids

Protection against mechanical impact damage

0
 No protection  No protection  No protection

1
Protected against solid objects over 50mm e.g. hands, large tools Protected against vertically falling drops of water Protected against 0.225 joule impact (150g @ 15cm)

2
Protected against solid objects over 12mm e.g. hands, large tools Protected against direct sprays of water up to 15 deg. from vertical Proteced against 0.375 joule impact (250g @ 15cm)

3
Protected against solid objects over 2.5mm e.g. wire, small tools  Protected against direct sprays of water up to 60 deg. from vertical Protected against 0.5 joule impact (250g @ 20cm)

4
Protected against solid objects over 1mm e.g. wires Protected against water sprayed from any direction. Limited ingress permitted.  

5
Limited protection against dust ingress (no harmful deposit) Protected against low pressure water jets from any direction. Limited ingress permitted.) Protected against 2.0 joule impact (500g @ 40cm)

6
Totally protected against dust ingress. Protected against high pressure water jets from any direction. Limited ingress permitted.  

7
  Protected against immersion between 15cm and 1M. Protected against 6.0 joule impact (1.5Kg @ 40cm)

8
  Protected against long periods of immersion under pressure.  

9
    Protected against 20 joule impact (5Kg @ 40cm)


Pressed metal enclosures offer the poorest protection and are generally
a 4, cast and most polystyrene and virtually all polycarbonate enclosures
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 a decision
has to be made and where several variables come in to play:

When mounting an enclosure inside a cabinet, fixing to a machine wall, a
building wall or a post, the method of attachment can either maintain or
instantly downgrade the IP rating of the enclosure assembly. For example,
in an industrial environment that may include water sprays, wash downs
or atmospheric moisture, a screw fixed '1P65' enclosure with '1P68' cable
glands can be rendered '1P64' or lower simply by not employing grommets
between the screw or bolt heads and the enclosure wall when fixing the
enclosure in place.

Fixing to posts or uneven surfaces is more problematic and an external
fixing of some sort such as cable-tie brackets can be very useful. Gluing
or gun applied sealant is also an option.



Enclosure offering IP67 protection.

The lid sealing of an enclosure is the next major element to affect the
sealing, basic 'click' fit lids are generally IP54 or lower. Pressed metal
enclosures are the worst, allowing either dust or moisture in reasonably
easily, whereas plastic 'click' fit enclosures generally offer IP54, which
provides limited protection from both dust ingress and liquids. Cast metal
enclosures or industrial plastics such as moulded polystyrene and tougher
polycarbonate generally offer much higher levels of protection. Lid fitment
of IP54 and above generally requires an additional compressible seal to
achieve higher protection. Machine applied polymer seals are generally
more reliable than gasket types as they are not prone to movement
during fixing and a seal that runs inside the lid fixing screws is normally
required for IP65 and above.

Cable entries are present in virtually all sealed enclosures offering a
significant IP rating; they vary from basic cable clamps through to
independently rated waterproof cable glands. Basic cable clamps and
open holes offer some protection, but where moisture is present to
any degree the cable entry must offer a complete seal around the
cable sheath. Recent developments in push-fit seals have seen both
the grommet type and the moulded-in version offering high ratings up
to IP65 in some instances, providing protection from drips to low power
water sprays and suitable for general above ground outdoor applications.

Underground use, temporary immersion, wash downs in the food and
processing industries or exposure to the sea requires IP65 and above,
this generally requires cable glands fixed to the enclosure wall and high
quality compression seals. An IP65 rated box is not IP65 when the cable
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 is crucial.
Other considerations such as ambient atmospheric moisture combined
with large temperature fluctuations can also cause condensation problems.
In situations where this is likely, it always pays to fit breather valves
(or grommets) to allow the enclosure humidity and pressure to equalise
without compromising the intended IP rating.

Article by Graham Fox of Spelsberg UK - Tel: 01952-200716



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