Hazardous (Classified) Location Wiring in Colorado
Classified location wiring is governed by the area classification drawing, and the equipment, raceway, and sealing all have to match the division and group.
NEC Article 500 sets the framework. Class I covers flammable gases and vapors, Division 1 means ignitible concentrations can exist under normal operating conditions, and Division 2 means they are present only under abnormal conditions such as a failed seal or a ruptured line. Oilfield gas and petroleum vapors normally fall in Group D. Article 501 then spells out what may be installed in each division, Article 504 covers intrinsically safe systems, and Article 505 covers the zone classification system used on some engineered equipment packages.
In Division 1, wiring is typically threaded rigid metal conduit or Type MI or MC-HL cable, terminating in enclosures listed for the location, with conduit seals placed where Article 501.15 requires them. Division 2 allows a wider set of wiring methods and permits general purpose enclosures for devices that do not arc or run hot. Practical details matter as much as the method: thread engagement on explosionproof fittings, correct damming fiber and sealing compound, drains and breathers where conduit collects water, and listing marks that actually cover the group and temperature code present on site.
What is the difference between Class I Division 1 and Division 2?
Division 1 is where ignitible concentrations of flammable gas or vapor exist under normal operating conditions, or occur frequently because of repair, maintenance, or leakage. Division 2 is where the flammable material is handled or stored in closed systems and escapes only under abnormal conditions such as equipment failure. The practical result is that Division 1 demands explosionproof or intrinsically safe methods throughout, while Division 2 permits a broader set of wiring methods and enclosures.
How far from an enclosure does a conduit seal have to be?
For explosionproof enclosures containing arcing or high temperature parts, NEC Article 501 requires the seal within 18 inches of the enclosure, with nothing between the seal and the enclosure except what the rule allows. Some listed equipment is marked with a shorter distance, and that marking governs. Seals are also required where a raceway crosses from a classified location into an unclassified one.
Does Class I Division 2 equipment have to be explosionproof?
Not always. In Division 2, equipment that does not produce arcs, sparks, or surface temperatures capable of ignition can often use general purpose enclosures, and nonincendive circuits and hermetically sealed devices are recognized options. Switches, contactors, and other arcing devices still need enclosures suitable for the location unless the arcing parts are immersed, hermetically sealed, or otherwise protected. The listing marking on the device is what settles the question.
Based in Golden and on site across the Denver metro, from Lakewood, Wheat Ridge, and Arvada to the foothills.