Ex 'E': Short on Name - Long on Safety
What does increased safety mean?
It centres on AS 2380.6-1988 covering motors for hazardous situations. Western Electric's Ex ‘e’ range of motors are manufactured to meet these strict requirements which makes them suitable for operation in locations where sparks and hot surfaces could ignite combustible gases.
|EX Explosion Proof Motors
AS 2380.6-1988 defines 'Increased Safety' as: 'The type of protection applied to electrical equipment that does not produce arcs and sparks in normal service in which additional methods are applied so as to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks.'
The increased Safety requirement ensures that motors are suitable for safe operation in hazardous locations where sparks and hot surfaces could ignite combustible gases to cause a disastrous explosion. Additional measures in the design and manufacture of Ex ‘e’ motors make sure that they do not produce arcs, sparks of sufficient heat when operating to cause ignition of gases and vapours.
NAME PLATE DATA
Ex ‘e’ name plates are marked with the approval number and:
- IA/IN - the ratio between the starting current (IA) and the rated full load (IN);
- TE TIME - the time taken for an AC winding - when carrying the initial starting current IA - to heat up to the T rating limiting temperature from temperature reached in rated service; and
- T RATING - the limiting temperature class (which for units from Western Electric is T3 - 200 deg.C.) relating to the maximum surface temperature of any motor component.
- it is the operators responsibility to ensure that the motor is protected against over-heating by the provision of an overload device;
- terminating supply cables to motor terminals must conform with Clause 2.3 of AS 2380.6.
- care must also be taken with the temperature rating of the supply cable and the type of cable gland used (see Clause 3.6 in AS 2380.6).
If Ex ‘e’ motors aren’t suitably protected and terminated then product safety and certification is invalid.
Standard Ex ‘e’ motors aren’t designed or tested for arduous duty. It may be possible, however with careful motor selection and additional thermal protection, to obtain certification for arduous duty - but only after testing.
In addition to extreme testing Ex ‘e’ motors also require:
- special terminals
- defined types of internal cable connections.
- increased clearances between conducting parts
- non hydroscopic insulation with high tracking resistance.
- high quality insulation and varnish
- minimum air gaps
All of the above plus more has to be documented and submitted to the appropriate testing authority for approval.
These additional measures ensure the integrity of the motor, and also account for its increased cost. Where human life and property are concerned the extra safeguards pay their way many times over. Ex ‘e’ is an abbreviated way of saying 'protection and peace of mind'.