In such areas there is a necessity to
eliminate sources of ignition such as sparks, hot surfaces or static electricity
which may ignite these mixtures.
Where electrical equipment has to be used in
these areas it must be so designed and constructed as to not create sources of
ignition capable of igniting these mixtures.
Before electrical equipment can be used in a
potentially explosive atmosphere a representative sample has to be fully tested
and certified by an independent authority such as BASEEFA in the U.K. or UL in
This information is intended as a guide only
and further expert guidance should be sought before placing into service,
maintaining or repairing any item of equipment in a Potentially Explosive
Where comparisons are shown between, for
example, European and North American practice this may be an approximation and
individual standards/codes of practice should be consulted for precise
details.MEDC have spent 25 years
designing and manufacturing electrical equipment suitable for use in potentially
explosive atmospheres. We deal with all the major testing and certification
authorities throughout the world and have a diverse range of internationally
Process plants are divided into Zones
(European and IEC method) or Divisions (North American method) according to the
likelihood of a potentially explosive atmosphere being present.
MEDC advise that all Explosion-proof
electrical equipment is maintained, by suitably trained personnel, in accordance
with the Manufacturers' recommendations.
Any spare parts used should be purchased from
the original Manufacturer and repairs should be carried out by the Manufacturer
or under his supervision, in order that the item remains in conformance with the
All Electrical Equipment, intended for use in
a Potentially Explosive Atmosphere, should be certified as suitable for such
The methods of obtaining certification differ
in detail, see below, between each certifying body or group of bodies (e.g.
CENELEC). Basically this process consists of supplying a representative sample
of the equipment along with a set of drawings to a recognised test/certification
body e.g. BASEEFA who in turn test the equipment against a recognised Standard
e.g. EN50018 and issue a Certificate. The user of the equipment can then refer
to this Certificate to enable him to safely put the item into service in a zone
appropriate to the Certification.
European Practice – after
1st July 2003
After the above date the ATEX
Directive comes into force throughout the EEC. This becomes a mandatory
requirement for all equipment intended for use in a hazardous area. The
fundamental difference between current practice and ATEX certification is that
ATEX addresses the essential safety requirements for hazardous area equipment
and uses Standards as part of the method of conforming to these. Amongst other
documentation required by certifying authorities will be Technical Manuals in
order that the user is informed of installation methods etc.
ALL EQUIPMENT, BOTH ELECTRICAL AND
MECHANICAL, INTENDED TO BE PUT INTO SERVICE WITHIN THE EEC AFTER 1ST July 2003,
WILL HAVE TO HAVE BEEN CERTIFIED IN ACCORDANCE WITH THE ATEX
In practice this means re-certification of
all currently certified electrical equipment.
MEDC have started this process and all
relevant equipment will be covered by the implementation date of 1st July
It should be noted also that
MECHANICAL equipment is covered by the ATEX Directive so for the first
time items such as gearboxes will have to carry ATEX certification.
The equipment coding will be as the current
practice plus an additional code as follows:
Ex – Explosion proof in accordance with
II – Group II surface industries.
|2 – category 2 equipment
.....for use in Zone 1)
Category 1 is
suitable for Zone 0.
||Category 3 is suitable for Zone
G – suitable for atmospheres containing gas (
D is suitable for atmospheres containing dusts).
Equipment will be CE marked when certified to
European Practice – Current – until
30th June 2003
The method is basically as above. In addition
all electrical equipment intended for use in the European Economic Community
(EEC) must comply with Electromagnetic Compatibility regulations (EMC) and
manufacturers must issue, on request, an EC Declaration of Conformity in
accordance with the EMC regulations.
When certified, an item of equipment and its'
certificate, carry a code e.g. EExdIIBT4. This can be broken down as
E – European certificate in accordance with
Ex – Explosion-proof electrical
d – flameproof enclosure type of
II – Group II surface industries
B – gas group B
T4 – temperature class T4 (135 degrees
centigrade surface temperature).
North American Practice
Sample equipment and supporting documentation
are submitted to the appropriate authority e.g. .U.L., F.M., C.S.A.
The equipment is tested in accordance with
relevant standards for explosion protection and also for general electrical
requirements e.g. light fittings.
After successful testing a listing is issued
allowing the manufacturer to place the product on the market.
The product is marked with the certification
details such as the gas groups A,B,C,D the area of use e.g. Class 1 Division
Most countries outside Europe or North
America use the IEC Standards as a basis for their own national
The Russian Federation certifies equipment to
GOST standards, these closely follow CENELEC practice.
There is a scheme in place which will when
fully adopted allow for internationally recognised certification to become a
reality, this is the IEC EX SCHEME. This uses the IEC standards and IEC
recognised test and certification bodies to issue mutually recognised test
reports and certificates. The scheme is in its infancy and its level of success
cannot yet be measured.
2 digits are used to denote the level of
ingress protection that a piece of apparatus enjoys :–
(The first digit
denotes the level of protection against solid objects and the second against
up to 50mm, e.g. hands.
drops of water.
||Protected against solid
up to 12mm, e.g. fingers.
||Protected against water spray
to 15 degrees from vertical.
up to 2.5mm, e.g. tools.
water spray up to|
60 degrees from vertical.
||Protected against solid
over 1mm, e.g. wires.
||Protected against water sprays
(No harmful deposits).
water jets from|
||Protected against strong
from all directions, e.g. Offshore.
15cm and 1m in depth.
||Protected against long