Oil and Gas MCC Applications: Hazardous Area Considerations

Oil and gas facilities present unique challenges for motor control center design and maintenance. The presence of flammable gases, vapors, and combustible dusts requires careful attention to hazardous area classification, equipment selection, and installation practices. Getting it wrong is not just an equipment issue - it is a safety issue with potentially catastrophic consequences.

Hazardous Area Classifications

NEC Articles 500-506 define hazardous locations where flammable gases, vapors, or dusts may be present. Understanding these classifications is essential for specifying MCC equipment.

Class I - Flammable Gases or Vapors

Most oil and gas facilities contain Class I locations:

Division 1: Areas where flammable concentrations exist under normal operating conditions, frequently, or from equipment failure that also causes electrical failure.

Division 2: Areas where flammable concentrations are handled in closed systems, prevented by ventilation, or adjacent to Division 1 areas.

Group Classifications (Class I)

Group	Representative Gas	Typical Location
Group A	Acetylene	Welding shops, chemical plants
Group B	Hydrogen	Refineries, chemical plants
Group C	Ethylene	Petrochemical plants
Group D	Methane, propane, gasoline	Most oil and gas facilities

Most oil and gas MCCs deal with Group D hazardous locations.

Zone Classification (Alternative)

NEC Article 505 provides a zone-based classification system aligned with IEC standards:

Zone 0: Continuously hazardous (equivalent to the most severe Division 1)
Zone 1: Intermittently hazardous (similar to Division 1)
Zone 2: Abnormal conditions only (similar to Division 2)

MCC Location Strategy

Non-Hazardous Location (Preferred)

The best practice for oil and gas facilities is to locate MCCs in non-hazardous (unclassified) areas:

Enclosed, pressurized MCC rooms: Positive air pressure from a clean source prevents flammable gas ingress. The room is classified as non-hazardous per NEC 500.7(D).
Remote MCC buildings: Located outside the hazardous area boundary, with motor cables run through classified areas.
Control buildings: Combined MCC and control room in a non-hazardous structure.

When MCCs are in non-hazardous locations, standard industrial MCC buckets can be used. This is the most cost-effective and maintenance-friendly approach.

Division 2 Location

When MCCs must be located in Division 2 areas:

Standard MCC enclosures are generally acceptable (NEC 501.10(B))
Components that produce arcs during normal operation (contactors, switches) must be enclosed in approved enclosures
Sealed or non-sparking components are acceptable alternatives
Specific breaker and contactor types must be verified for Division 2 suitability

Division 1 Location

MCCs in Division 1 locations require:

Explosion-proof enclosures for all arc-producing components
Increased safety or explosion-proof construction throughout
Significantly higher cost and maintenance complexity
This is relatively rare and generally avoided through facility design