Lighting and Receptacle Circuit Wiring Requirements

This article defines the requirements for lighting and receptacle circuit wiring.


American Petroleum Institute (API)

RP 540 Electrical Installations in Petroleum Processing Plants

National Electrical Manufacturer’s Association (NEMA)

PB 1 Panelboards

National Fire Protection Association (NFPA)

70 National Electrical Code

Distribution Equipment for Lighting and Receptacle Circuit Wiring


  • Lighting transformers shall be dry type, completely enclosed, non-ventilated type, and approved for the area classification where they are installed.
  • In general, lighting transformers shall be rated 480 V to 208/120 V for 3 phase four wire distribution. 277 V lighting shall be approved for specific applications.
  • 480 V delta to 277/480 V transformers shall be required to provide 4 wire 3 phase distribution at the 480 V level.
  • Transformer sizes shall be standardized as 15, 30, 45 and 75 kVA, depending upon the lighting load in the area.
  • Transformers shall be provided with 4 – 21/2 percent full capacity taps with 2 below and 2 above rated primary voltage.
  • Individual lighting transformers shall be provided for each panelboard. The initial panelboard load shall not exceed 70 percent of the transformer rating.
  • Transformers shall be located in close proximity to the panelboard. In general, the transformer and panelboard should be located in the process area; however, where feasible, the transformers and panelboards for area lighting and eceptacles shall be located inside the unit substations and electrical rooms of buildings.


  • Panelboards shall be easily accessible and convenient to personnel. Panelboard locations shall be selected to minimize the length of branch circuits, to reduce voltage drop and permit the use of smaller conductors.
  • Panelboards for 120 V lighting shall be 120/208 V, 3 phase, 4 wire with main breakers. Panelboards for 480 V lighting shall be 480 V, 3 phase, 3 wire. Panelboards shall comply with NEMA PB 1.
  • Branch circuit loads of lighting panelboards shall ultimately not exceed 80 percent of the circuit breaker rating. The initial load shall not exceed 70 percent of the breaker rating.
  • Panelboards shall be provided for outdoor lighting, indoor lighting, receptacles and instrument power. Panelboards shall have approximately 20 percent spare branch circuits.
  • Panelboards in hazardous areas shall be approved for the location. Panelboards in non-hazardous outdoor areas shall be NEMA 4 or NEMA 4x for corrosive areas. Panelboards installed outdoors shall be provided with breathers and drains.
  • Panelboards shall be provided with a directory, indicating circuit numbers and services.

Receptacle Circuit Wiring

120V Convenience Outlets

  • For 120 V convenience outlets, transformers and panelboards as described in Above section shall be strategically located in the process areas and plant buildings. Power for convenience outlets shall not be supplied from instrumentation panelboards.
  • Branch circuits for convenience outlets shall be 20 A, 120 V single phase. Initial loading of branch circuits shall be limited to approximately 70 percent. Convenience receptacles (without dedicated loads) installed indoors and outdoors shall be limited to 8 per branch circuit. Circuit loading shall be based on 180 W per receptacle, unless the receptacle has a dedicated load. The minimum size for branch circuit conductors shall be 4 mm2 (# 12 AWG).
  • Ground fault circuit interruption receptacles for protection of personnel shall be provided in all outdoor locations and all wet locations. In addition, ground fault interruption receptacles shall be installed in indoor locations where required by NFPA 70.
  • In non-hazardous areas, receptacles shall be 20 A, duplex, two-pole, three wire, grounding type, 120 V grade. Outdoor receptacles shall have a weather resistant enclosure.
  • Explosion proof receptacles shall be used in hazardous areas. Explosion proof receptacles shall be certified and listed for use in the hazardous area in which they are installed. The receptacle certification shall meet or exceed the specific ‘Area Class’ or ‘Zone’, ‘Division’ and ‘Group’ for the area in which they are applied. General purpose receptacles shall not be used.
  • In office buildings, receptacles shall be installed no more than 4 m apart along all walls. Each office shall have a minimum of 2 receptacles.
  • Substations, rack rooms and similar rooms or buildings shall be provided with at least 2 receptacles. Larger rooms or buildings shall have receptacles to allow any point to be reached with a 7.5 m extension cord.
  • Convenience outlets shall be installed in process and utility areas in a way that any point can be reached with a 15 m extension cord. Receptacles shall be installed at all manways on tower and vessel platforms.

Welding Receptacles

  • Welding receptacles shall be supplied by thermal magnetic breakers installed in the 480 V Motor Control Centers (MCC’s).
  • Not more than 3 welding outlets shall be installed on a branch circuit. Branch circuits shall be sized for the following loads:

a. One outlet – 40 kVA

b. Two outlets – 70 kVA

c. Three outlets – 90 kVA

  • The minimum sized for branch circuit conductors shall be 70 mm2 (2/0 AWG).
  • Welding receptacles shall be rated 100 A, 480 V. They shall be 3 phase, 4 wire with drain and breather.
  • Welding receptacles shall be installed in the process and operating areas in a way that major equipment can be reached with a cord of 38 m maximum length. They shall be located at the base of towers, heaters and reactors, and on all major platforms on heaters and towers. A welding receptacle shall also be installed at each substation.

Lighting Circuits Wiring Requirements

Power Supply

  • For 120 V lighting, transformers and panelboards as described in above section shall be strategically located in the process areas and plant buildings. Lighting panelboards shall be dedicated exclusively to lighting. No other loads shall be supplied from them.
  • Normal lighting transformers for outdoor areas shall be supplied by lighting contactors in MCC’s in the area substation. Lighting contactors shall be specifically rated for lighting duty. General purpose contactors shall not be used.
  • Essential/standby lighting transformer(s) shall be fed from lighting contactor(s) in the essential/standby MCC’s.
  • Floodlighting shall be served by a 3 phase, 480 V panel, fed from a lighting contactor in one of the MCC’s.

Branch Circuits

  • In general, branch circuits for all lighting (except 480 V floodlighting) should be 20 A, 120 V single phase. Initial loading of branch circuits shall be limited to approximately 70 percent. Minimum wire size shall be 4 mm2 (# 12 AWG).
  • Each 120 V branch circuit shall be provided with a separate neutral conductor. This conductor shall be tagged with the corresponding circuit number.
  • Branch circuits for floodlights shall be 20 A, 480/277 V supplied by 2 pole breakers in 480 V lighting panels. Initial loading of branch circuits shall be limited to approximately 70 percent. Minimum wire size shall be 4 mm2 (# 12 AWG).
  • Adjacent fixtures shall be placed on different branch circuits to minimize the loss of light upon loss of one branch circuit. Circuits for ‘Emergency’ lighting may be installed in the same conduit as normal lighting, as it is actually standby lighting.

Control of Lighting Circuits

  • Local switches shall be provided for control of lighting in individual offices, washrooms, instrument rack rooms, electrical equipment rooms and substation buildings.
  • Control room lighting shall be controlled in sensible groups with flicker free dimmer controllers. Where multiple dimmer controllers are installed in a group, a diagram shall be installed indicating which lights/zones are controlled by which dimmer.
  • Warehouse, workshop and similar locations shall have lighting controlled directly from the branch circuit panelboards.
  • Automatic control shall be provided for process area and floodlighting. A photocell controlled contactor shall control power to lighting transformers and 480 V lighting panels. A manual override switch Hand Off Auto (HOA) shall be Located adjacent to the lighting panel.

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