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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