Aarea and Instrument Classifications

AArea and Instrument Classifications

An IP number contains two numbers (i.e. IP65) in most instances which relate to the
level of protection provided by an enclosure or housing.
The first number relates to protection from solids as follows:
0: No Special Protection
1: Protected against solid objects up to 50 mm in diameter
2: Protected against solid objects up to 12 mm in diameter
3: Protected against solid objects up to 2.5 mm in diameter
4: Protected against solid objects up to 1 mm in diameter
5: Dust protected
6: Dust tight
The second number relates to protection from liquids as follows:
0: No special protection
1: Protected against dripping water
2: Protected against dripping water when tilted up to 15o from normal position
3: Protected against spraying water
4: Protected against splashing water
5: Protected against water jet spray
6: Protected against heavy jet spray
7: Protected against the effects of immersion
8: Protected against submersion
Example: IP66 = Dust tight and protected against heavy water jet spray

NEMA (National Electrical Manufacturers Association) ratings can be approximately compared to those of the IP system as shown below.
Other factors such as corrosion protection are also involved in the NEMA system, please refer to official documentation for details.
NEMA 1 = IP10
NEMA 2 = IP11
NEMA 3 = IP54
NEMA 4 = IP56
NEMA 4X = IP66
NEMA 6 = IP67
NEMA 12 = IP52
NEMA 13 = IP54

ATEX & Intrinsic Safety Information - Explosive Atmospheres
(helpful information only, detailed reference should be taken from an appropriate agency)

Protection Concepts
ZONE / HAZARD / PROTECTION CONCEPTS
0 / In which an explosive gas/air mixture is continuously present for long periods / Exia or Exs
1 / In which an explosive gas/air mixture is likely to occur in normal operation. / Exd. Exe, Exib, Exp, Exia, Exs
2 / In which an explosive gas/air mixture is not likely to occur in normal operation. / All concepts suitable for
Zone 0 & 1, ExN, ExO and Exq

Standards For Methods Of Protection
METHOD OF PROTECTION / PERMITTED ZONE
OF USE IN UK / CODE LETTER
IEC, EX.., CENELEC, EEX
General requirement / - / -
Oil immersion / 2 / o
Pressurisation / 1 or 2 / p
Powder filling / 2 / q
Flameproof / 1 or 2 / d
Increased safety / 1 or 2 / e
Intrinsic safety / * 0, 1 or 2 / ia or ib
Non-incendive / 2 / n #
Encapsulation / 1 or 2 / m
Special / 1 or 2 / s
* ia: Zone 0,1,2. ib: Zone 1,2. not Zone 0. # n: used locally in UK.

Gas Grouping / Temperature Classification
GAS # GROUP
CENELEC
EN 50 014, IEC / REPRESENTATIVE GAS / T Class / IEC 79-7 / Max. surface temp ° C
I * (mining) / Methane / T1 / 450 ° C
IIA / Propane / T2 / 300 ° C
IIB / Ethylene / T3 / 200 ° C
IIC / Hydrogen / T4 / 135 ° C
T5 / 100 ° C
T6 / 85 ° C
Certification Code
(CENELEC marking information - example [EEx ia] IIC T4)
[ / E / Ex / ia / ] / IIC / T4
Associated apparatus* / Certified to the CENELEC standard / Explosion protected / Protection
concept (IS) / Associated
apparatus* / Apparatus
group
(gas group) / Temperature
classification
(not Gp I)
* (located in safe area and may be connected to hazardous area)

Device Group & Category
DEVICE GROUP / DEVICE CATEGORY /

ZONE

I

/ M = mining / –
Mining / M 1 / –
Pit gas &/or flammable dusts / M 2 / –

II

/ G = gas
Other areas / 1 G / 0, 1, 2
Explosive atmosphere / 2 G / 1, 2
3 G / 2
D is added after G in the certification class number / D = dust
(i.e. GD) if device is dust category approved also / 1 D / 20, 21, 22
2 D / 21, 22
BACK TO TOP / 3 D / 22
Explanation of the categories:
1 - Very high safety = device safety must be guaranteed even in case of rare device failures, e.g. simultaneous failure of two components.
2 - High safety = device safety must be guaranteed if frequent failures can be expected, e.g. failure of one component.
3 – Safe in normal operation = device safety must be guaranteed in normal operation.
Note: A number in brackets before device category designation signifies that the device meets the requirements of an additional category to the main one that is specified.
Example: II (1) 2G signifies that the device meets requirements for both
1 G and 2 G categories

Flashpoint

This is the lowest temperature at which a liquid generates sufficient
vapour to support ignition. This vapour can be ignited in many ways
including temperature or energy (i.e. a spark)

Ignition Temperature

This is the lowest temperature at which the vapour will be ignited.
This defines the temperature class.

Classification of maximum surface temperatures of electrical apparatus (CENELEC)

Temp. Class / Max. Surface Temp.
T1 / <450ºC
T2 / <300ºC
T3 / <200ºC
T4 / <135ºC
T5 / <100ºC
T6 / <85ºC

BACK TO TOP
Apparatus Group (energy ignition)
All surface industry gases/vapours are classed as Group II gases.
Group II is divided into 3 sub groups:
IIA – High energy is required to ignite. Less intense explosion. (Propane)

IIB – Less energy is required to ignite. More intense explosion. (Ethylene)

IIC – Little energy is required to ignite. Most intense explosion. (Hydrogen)

Characteristics of some common flammable materials

Gas/Vapour / Flashpoint / Gas Group / Ignition Temp. / Temp. Class
Acetone / 19ºC / IIA / 535ºC / T1
Butane / -60ºC / IIA / 365ºC / T2
Heptane / -4C / IIA / 215ºC / T3
Ethyl Methyl Ether / 37ºC / IIB / 190ºC / T4

Note: There is no connection between ignition energy and ignition temperature