A GUIDE TO EUROPEAN (EEC) CERTIFICATION FOR
ELECTRICAL EQUIPMENT IN HAZARDOUS AREAS
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INTRODUCTION
Hazardous areas are those in which there exists a risk of explosion
because flammable atmospheres are likely to be present. These
conditions can be man-made as in Petrochemical plants or Refineries, or
occur naturally, as in coal mining. It is therefore necessary to insure that
all electrical equipment and instrumentation installed in a hazardous area
cannot form a spark, or hot surface, which would ignite the flammable
atmospheres.
Before electrical equipment or instrumentation can be used in a
hazardous area, it must b e tested and approved by a recognized testing
authority. Should the equipment pass this examination, then a Certificate
of Conformity is issued which specifies the limits of use of the
apparatus.
ZONES
Hazardous areas are classified into "Zones" according to the degree of
risk.
Zone 0 - where an explosive atmosphere is continuously present for long
periods.
Zone 1 - where an explosive atmosphere is likely to occur in normal
operation.
Zone 2 - where an explosive atmosphere is not likely to occur in normal
operation and if it occurs it is only present for a short period.
Zone 10 - where explosive dusts are present constantly or for long
periods.
Zone 11 - where explosive dusts are present occasionally.
GASES
Gases are grouped together according to their degree of hazard. This is
based on the amount of energy required to light the gas/air mixture.
Gas Group Representative Gas
I (mining)
Methane
IIA
Propane
(Surface)
IIB
Ethylene
(Surface)
IIC
Hydrogen
(Surface)
TEMPERATURE
A gas/air mixture can ignite when it comes into close contact with an
excessively hot surface. The surface temperature at which equipment
operates is therefore of crucial importance. This equipment is temperature
classified as follows:
Temp.
Class
T1
T2
T3
T4
T5
T6
Max. Surface Temp.
450 degrees C
300 degrees C
200 degrees C
135 degrees C
100 degrees C
85 degrees C
TEMPERATURE/GAS CLASSIFICATION
The following chart gives the minimum temperature class of equipment for use in the various gases
most commonly found in hazardous areas.
Gas
Group
T1
I
Methane
IIA
T2
T3
Acetone
Ethane
Ethyl acetate
Ethyl alcohol
I-Amyl acetate
N-hexane
Petrol
Diesel
Aviation fuel
Ammonia
N-butane
Heating oil
Benzol
N-butyl-alcohol
T4
T5
T6
Acetaldehyde
Ethyl-ether
Acetic acid
Carbon
Monoxide
Methanol
Propane
Toluene
IIB
Town gas
IIC
Hydrogen
Ethylene
Hydrogen Disulfide
e.g. T6 rated equipment can be used in any of the above gases but for example, T4 rated equipment can
only be used in T1 - T4 applications
APPARATUS SELECTION WITHIN ZONES
Zone
Suitable
Apparatus
Zone 0
Exi 'a', some Exs
Zone 1
All types except
Exn
Zone 2
All types
APPARATUS MARKING
The following information should appear on "explosion protected"
electrical equipment installed in hazardous locations:
Information
Typical Example
1. The manufacturer's name
MEDC, Zellweger Analytics, Fire
Sentry Corporation
2. The model designation
Manual Call Point Type BG2
3. Code (Cenelec standard)
EEx
4. The type of protection
edm
5. Gas Group
IIC
6. Temperature Classification
T4
7. Serial number
A005
8. Certifying Authority Certificate
BASEEFA No. Ex92C3166
No.
9. Cenelec symbol
10. British standard symbol
11. Electrical rating
Max amps 0.2, Max. volts 254
TYPES OF EXPLOSION PROTECTION
There are various methods used to prevent electrical apparatus from
igniting the surrounding atmosphere when energized.
Flameproof Enclosures - Ex protection type 'd'. (EN50018, BS5501
Part 5).
Equipment that could ignite an explosive atmosphere is housed within a
substantial enclosure. This is capable of containing an internal explosion
without transmitting that explosion to the surrounding explosive
atmosphere.
Increased Safety - Ex protection type 'e'. (EN50019, BS5501 Part 6).
Increased measures are taken to prevent the generation of arcs, sparks
and excessively hot areas in equipment, thus preventing the risk of
explosion inside or outside of the enclosure.
Intrinsic Safety - Ex protection type 'i'. (EN50020, BS5501 Part 7).
Power is limited to this equipment in such a way that a spark or a hot
surface would not be hot enough to ignite the explosive atmosphere.
Pressurized or Purged - Ex protection type 'p'. (EN50016, BS5501
Part. 3).
Here the concept used is to house the equipment in an enclosure, which
is pressurized or purged by inert gas, thus preventing an explosive
atmosphere from reaching the equipment.
Oil Immersion - Ex protection type 'o'. (EN50015, BS5501 Part 2).
All equipment is totally immersed in oil, thus preventing an explosive
atmosphere from reaching the equipment.
Powder Filled - Ex protection type 'q'. (EN50017, BS5501 Part 4).
All equipment is totally immersed in powder, thus preventing an
explosive atmosphere from reaching the equipment.
Non-Sparking and Restricted Breathing - Ex protection type 'n' or 'N'.
(BS4683 Part 3).
This gives a level of protection by housing electrical equipment in
substantial enclosures that inhibit mechanical damage and give some
degree of ingress protection.
Special Protection - Ex protection type 'S'.
This applies to items of equipment not entirely covered by any of the
foregoing concepts but one that can clearly be demonstrated to be
explosion protected.
Moulded/Encapsulated - Ex protection type 'm'. EN50028, BS5501
Part 8).
The apparatus is totally encapsulated by a non-porous compound.
Electrical connection is by flying leads.
CODES AND PRACTICES FOR SELECTION, INSTALLATION
& MAINTENANCE OF EXPLOSION PROTECTED
EQUIPMENT
The correct selection, safe installation and maintenance of explosion
protected equipment is of the utmost importance. Always follow the
relevant standards of the country where electrical equipment is to be
installed, as local requirements vary from country to country.
The selection of the correct type of cable gland is critical. Please refer to
the local codes and standards for the types that may be used. Corrosion
can attack flamepaths and render an enclosure unsafe. Care must be
taken to prevent or reduce corrosion where possible. Spares for, and
repairs to explosion protected equipment should be obtained from the
original equipment manufacturer to ensure compliance with explosion
protection area certification of that equipment.
TESTING AUTHORITIES
Region
Testing Authority
Country
EEC
All
All
BASEEFA
SIRA
UK
UK
PTB
Germany
BVS
SCS
Germany
Cherchar
LCIE
France
France
MS AE
CESI
Italy
AD-PE
INIEX
Belgium
Ex
Denmark
Ex
Spain
-
DEMKO
Laboratorio Oficial
N. America
Marks Used
Underwriters Laboratories
USA
Factory Mutual
CSA
USA
Canada
CENELEC/NORTH AMERICAN STANDARDS COMPARISON
(For general guidance only)
CENELEC
N. America
Zone 0
Class 1, Division 1
Zone 1
Class 1, Division 1
Zone 2
Class 1, Division 2
INGRESS PROTECTION
2 digits are used to denote the level of ingress protection ("IP rating") that a piece of
electrical equipment meets.
Solids
0
No protection.
Liquids
0
No protection.
1
Protected against solid objects up to 50mm, e.g. hands.
1
Protected against vertically falling drops of water.
2
Protected against solid objects up to 12mm, e.g. fingers.
2
Protected against water spray up to 15 degrees from
vertical.
3
Protected against solid objects up to 2.5mm, e.g. tools.
3
Protected against water spray up to 60 degrees from
vertical.
4
Protected against solid objects up to 1mm, e.g. wires.
4
Protected against water sprays from all directions.
5
Protected against dusts. (No harmful deposits).
5
Protected against water jets from all directions.
6
Totally protected against dust.
6
Protected against strong water jets from all
directions, e.g. Offshore.
7
Protected against immersion between 15cm and
1meter in depth.
8
Protected against long immersion under pressure
For example, an IP67 rating would mean that the equipment is "totally protected against
dust" (Solid rating of 6), and is "protected against immersion between 15cm and 1 meter in
depth" (Liquids rating of 7).
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