4.3 Reduced Risk (Ex 'n') Flashcards
Define an Ex ‘n’ piece of equipment.
A type of protection applied to electrical equipment such that, in normal operation and in certain specified abnormal conditions, it is not capable of igniting a surrounding explosive atmosphere.
Note 1: additionally, the requirements of IEC 60079-15 are intended to ensure that a fault capable of causing ignition is not likely to occur.
Note 2: An example of specified abnormal condition is a luminaire with failed lamp.
The Ex ‘N’ standard BS 6941 was superseded by BS EN 50021. What was this then superseded by?
IEC 60079-15.
The ‘n’ standard is then subdivided into a number of types:
- Type A: non sparking;
- Type R: restricted breathing enclosure;
- Type L: energy limited equipment (now being replaced by Ex ‘ic’)
- Type Z: enclosure with ‘n’ pressurisation (now being replaced by Ex ‘pz’)
- Type C: sparking where contacts are suitably protected other than by type R, L or Z.
Describe a hermetically sealed device type C.
Where sparking contacts may be safely enclosed within a hermetically sealed enclosure. The seal may be by soldering, brazing, welding or the fusion of glass with metal.
Describe an enclosed break device type C.
A type ‘n’ enclosed break device incorporates electrical contacts. It is able to safely withstand an internal explosion of any flammable gas that may have entered inside.
Describe an encapsulated device type C.
An encapsulated device has similarities with a hermetically sealed device. External connections are normally by flying leads of terminals.
Describe a restricted breathing Type R.
Where an enclosure is designed to restrict, but not totally prevent, the entry of gases. The vast majority of applications are with luminaire. The positioning of restricted breathing enclosures may need to be carefully considered, particularly in open sunlight. Cable entries into a restricted breathing enclosure should be fitted with an IP washer.
Describe an energy limitation Type L.
Where circuit components restrict the maximum available energy in an external circuit to a level incapable of causing gas ignition.
What glands are required for Ex ‘n’ or ‘N’ equipment?
Prior to 2008, cable glanding methods followed conventional practices and did not require certified glands.
However, as from January 2008, all new installations require the use of certified cable glands and adapters. At the time of this publication (2008), no Ex ‘n’ glands are available. Glands therefore have to be Ex ‘d’, Ex ‘e’, or Ex ‘de’.
When should an IP washer be used?
Glands entering unthreaded holes, threaded holes with less than 6mm thread length or where the threads are not square with the surface require an IP seal washer on the outside and a lock nut on the inside.
A start washer may be specified to be fitted on the inside in order to ensure satisfactory earth continuity.
Where should earth tag washers be installed?
Where an external earth tag washer is required, this is to be placed between the gland body metal and the seal washer. It should not be placed between the box and the seal washer.
What markings should be on Ex ‘n’ or ‘N’ equipment?
Ex ‘n’ equipment, conforming to the requirements of the ATEX directives, is marked to indicate conformity with the Directive.
It is also marked with the requirements of the standard (e.g. IEC 60079-15).
Note: Ex ‘N’ equipment does not comply with the requirements of the ATEX directive.
Fore more information, refer to the relevant standards, EEMUA 186 - Practitioners Handbook or the appropriate superior technical authority.
What is Ex n being replaced with?
Ex ic.
