Details

This is an old method mainly used with switchgear. Any spark generated by the operation of the switchgear is formed under oil and the venting is controlled.

There are two protection methods. One maintains a positive static pressure inside the equipment. The other involves a continuous flow of air or inert gas to neutralise or carry away any flammable mixture entering or being formed within the enclosure. Essential to both methods are monitoring systems and purging schedules.

This method involves the mounting of potentially incendive components in an enclosure filled with an inert powder. The enclosure is also vented. The method is primarily of use where the incendive action is the abnormal release of electrical energy by the rupture of fuses or failure of components such as capacitors. The method is commonly used for components inside Ex ‘e’ or Ex ‘N’ apparatus and for heavy-duty traction batteries.

In this method the potential incendive components are contained within an enclosure. Although the flammable atmosphere can enter the enclosure, any resulting explosion is contained and its transmission outside the enclosure prevented.

In this method any components that produce sparks as part of their normal operation are excluded from the equipment. Components are designed to reduce substantially the likelihood of the occurrence of fault conditions that could cause ignition. This is done by reducing and controlling working temperatures, ensuring the electrical connections are reliable, increasing insulation effectiveness, and reducing the probability of contamination by dirt and moisture ingress.

In this method the circuit parameters are reliably controlled to reduce potential spark energy to below that which will ignite the ambient gas-air mixture. This includes the occurrence faults in one 'ib' or two of the 'ia' of the components in the equipment.

The coding ‘ia’ denotes that the unit will not cause ignition of explosive atmosphere under normal operation and with two faults present in the circuitry. The coding ‘ib’ denotes that the unit will not cause ignition of explosive atmosphere under normal operation and with one fault present in the circuitry. You should note that this method does not protect entirely against the local over-heating of damaged connections or conductors and these should be kept sound and suitably protected against damage.

In this method the potentially incendive components are encapsulated so that the flammable atmosphere is excluded. The method also involves the control of the surface temperature under normal and fault conditions

This method, being special, has no exact specification. It is any method which is shown to be safe in use. The ‘s’ coding is used when equipment has been evaluated against one of the individual parts of the CENELEC series but does not comply exactly with it. Because the ‘s’ method does not have a set of rules it is not part of the harmonised series of standards.

BS 4683 Part 3 (Control Gear) has now been superseded by BS 6941.

In this method normally sparking components are excluded.

Precautions are taken with connections and wiring to increase reliability, though not to as high a degree as for EEx‘e’. Where internal surfaces are hotter than the desired T rating they can be tightly enclosed to prevent the ready access of a flammable atmosphere into the internal parts. This is the "restricted breathing enclosure" method. The use of this method also means that high ingress protection ratings of IP65 and above are built into the design.