Purging is used extensively today for ELECTRICAL / instrument enclosures. A purge and pressurized enclosure allows easy maintenance of the internal equipment, and there is no limit to the power that can be supplied. The purge medium, usually COMPRESSED air, is used to keep the enclosure at a higher pressure than the outside of the enclosure, preventing the entry of explosive gas. After CLOSING the enclosure, there must be a purging to dilute any gas that may be present within the enclosure before applying the power, hence the term, “purge and pressurize.”

There are three types of purge: X, Y, and Z:

Type X Purge: Type X reduces the area classification within the purged enclosure from Class I, Division 1, to non-classified where general purpose equipment can be fitted within the enclosure. The enclosure must be purged at least four full volume changes, timed automatically before the electrical interlock supplies power to the general purpose equipment. On loss of pressure the power must be disconnected except under special conditions.

Type Y Purge: Type Y purges reduces the area classification within the purged enclosure from a Class I, Division 1, to Class I, Division 2, where nonincendive (Division 2) equipment can be fitted within the enclosure. The requirements for the operation of the Y Purge are the same as the Z Purge. The difference is the application and contents of the purged enclosure.

Type Z Purge: Type Z purge reduces the area classification within the purged enclosure from Class I, Division 2, to non-classified where general purpose equipment can be fitted within the enclosure. The enclosure must be purged at least four full volume changes before the electrical supply can be APPLIED to the general purpose equipment. This is a manual function completed by the plant operator. On loss of pressure, there is no need to disconnect the electrical supply if the Division 2 area is known to be nonhazardous, but there must be a visual or audible alarm.

Purging is used extensively today for electrical / instrument enclosures. A purge and pressurized enclosure allows easy maintenance of the internal equipment, and there is no limit to the power that can be supplied. The purge medium, usually compressed air, is used to keep the enclosure at a higher pressure than the outside of the enclosure, preventing the entry of explosive gas. After closing the enclosure, there must be a purging to dilute any gas that may be present within the enclosure before applying the power, hence the term, “purge and pressurize.”

There are three types of purge: X, Y, and Z:

Type X Purge: Type X reduces the area classification within the purged enclosure from Class I, Division 1, to non-classified where general purpose equipment can be fitted within the enclosure. The enclosure must be purged at least four full volume changes, timed automatically before the electrical interlock supplies power to the general purpose equipment. On loss of pressure the power must be disconnected except under special conditions.

Type Y Purge: Type Y purges reduces the area classification within the purged enclosure from a Class I, Division 1, to Class I, Division 2, where nonincendive (Division 2) equipment can be fitted within the enclosure. The requirements for the operation of the Y Purge are the same as the Z Purge. The difference is the application and contents of the purged enclosure.

Type Z Purge: Type Z purge reduces the area classification within the purged enclosure from Class I, Division 2, to non-classified where general purpose equipment can be fitted within the enclosure. The enclosure must be purged at least four full volume changes before the electrical supply can be applied to the general purpose equipment. This is a manual function completed by the plant operator. On loss of pressure, there is no need to disconnect the electrical supply if the Division 2 area is known to be nonhazardous, but there must be a visual or audible alarm.