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Temporary wiring code requirements

Temporary electrical installations are power and lighting systems used during construction, remodeling, maintenance, repair, demolition, emergency operations, testing, experiments, and festive decoration. They are governed by Article 590 of the National Electrical Code (NEC, NFPA 70) and do not supersede the permanent requirements of Chapters 1 through 4, but modify them in specific ways to facilitate assembly and disassembly. All temporary installations must be removed once the need that caused them ceases; in the case of decorative holiday lighting or similar events, the maximum authorized period is 90 days. Circuits for fairs, circuses, and carnivals are covered under Article 525, not Article 590.

Technical Characteristics

Section titled “Technical Characteristics”

Temporary configurations use the same safety principles as permanent ones, but allow simplifications approved by the authority having jurisdiction. Below is a summary of the most relevant electrical and construction parameters.

Wiring Method AWG Size Cross Section Current Capacity (A)
NM Cable (nonmetallic) 14 AWG 2.08 mm² / 0.00323 in² 15 A
NM Cable (nonmetallic) 12 AWG 3.31 mm² / 0.00513 in² 20 A
SE Cable (service entrance) 12 AWG 3.31 mm² / 0.00513 in² 20 A
SE Cable (service entrance) 10 AWG 5.26 mm² / 0.00816 in² 30 A
Flexible Cord (3 conductors) 14 AWG 2.08 mm² / 0.00323 in² 18 A
Flexible Cord (3 conductors) 12 AWG 3.31 mm² / 0.00513 in² 25 A

Overcurrent protection devices are sized per NEC Articles 240.4 and 240.5. In temporary branch circuits, the continuous load must not exceed 80% of the device’s nominal capacity: for a 15 A breaker the maximum continuous load is 12 A, and for a 20 A breaker it is 16 A. Ground-fault circuit interrupters (GFCI) required on construction receptacles must trip at a leakage current of 5 mA.

Types

Section titled “Types”

Temporary installations are classified according to the need that drives them:

  • Construction, remodeling, maintenance, repair, or demolition: supply tools, construction lighting, and auxiliary equipment during work on buildings or structures.
  • Emergency: deployed to restore supply after natural disasters, accidents, or major grid failures.
  • Testing, experiments, and development: allow testing equipment or prototypes without committing to the final installation.
  • Temporary decoration and events: supply power to festive lighting or artistic displays with a maximum duration of 90 days.

Installation Requirements

Section titled “Installation Requirements”

The following points summarize the provisions of Article 590 and Chapters 1 through 4 of the NEC as modified for temporary use.

  • Permitted wiring methods: NM cable (nonmetallic sheathed), SE cable (service entrance), and flexible cords are allowed. SE cable can be installed underground provided it is placed in a suitable conduit. Conductors do not have to be embedded in walls, floors, or ceilings, facilitating subsequent removal.
  • Overcurrent protection: the provisions of 240.4 and 240.5 apply, selecting the conductor size and breaker in accordance with NEC Table 310.16 ampacity.
  • Receptacles: on construction sites, receptacles must not share a circuit with temporary lighting. 15 A and 20 A receptacles in wet locations must be mounted in enclosures that maintain watertightness with the plug inserted; non-locking types must be weather-resistant.
  • Splices and taps: a junction box, conduit body, or enclosure with cover is required, except on construction sites when conductors are flexible cord or nonmetallic multiconductor cable, or metal-clad cable terminated in listed fittings maintaining electrical continuity. A box is also not required for GFCI-protected branch circuits permanently installed in framing walls and ceilings that supply temporary loads.
  • Physical protection: cables and cords must be protected from mechanical damage, sharp corners, and pinch points such as doors. They are secured with staples, cable ties, straps, or other means designed not to damage the insulation, at intervals that ensure their integrity. There is no fixed regulatory distance, but in practice a support every 1.4 m / 4.5 ft is recommended as a good practice reference.
  • Disconnection: each temporary circuit must have switches or plug connectors that disconnect all ungrounded conductors. In multiwire branch circuits, disconnection must be simultaneous, using identified handle ties.
  • Lamp protection: lamps must be guarded against accidental contact by suitable luminaires or lamp holders with guards.
  • Removal: the installation is no longer justified when the work ends, the emergency is overcome, or the test concludes, at which point it must be completely dismantled.

Applicable Regulations

Section titled “Applicable Regulations”
  • NEC (NFPA 70), Article 590 – Temporary Installations.
  • NEC, Articles 230, 240, 250, 310, 334, 338, 400, 406, and 525 for supplementary aspects.
  • Local regulations of the authority having jurisdiction (AHJ), which may impose additional conditions.

Frequently Asked Questions (FAQ)

Section titled “Frequently Asked Questions (FAQ)”

What is the maximum duration for a decorative temporary installation?

Section titled “What is the maximum duration for a decorative temporary installation?”

NEC Article 590.3(B) establishes a maximum period of 90 days for temporary supply of decorative lighting and similar purposes.

What trip current must the GFCI have on construction receptacles?

Section titled “What trip current must the GFCI have on construction receptacles?”

The required ground-fault circuit interrupters must trip at a leakage current of 5 mA, per UL 943 Class A.

What is the maximum ampacity of a temporary circuit with 12 AWG NM cable?

Section titled “What is the maximum ampacity of a temporary circuit with 12 AWG NM cable?”

According to NEC Table 310.16, 12 AWG copper conductor has an ampacity of 20 A under normal conditions.

What minimum size must the grounding conductor have in a 15 A temporary circuit?

Section titled “What minimum size must the grounding conductor have in a 15 A temporary circuit?”

Table 250.122 specifies 14 AWG (2.08 mm² / 0.00323 in²) copper for circuits protected by devices up to 15 A.

What is the maximum continuous load allowed on a 15 A temporary circuit?

Section titled “What is the maximum continuous load allowed on a 15 A temporary circuit?”

The NEC limits continuous load to 80% of the breaker’s nominal rating, i.e., 12 A.

What maximum grounding resistance value is acceptable in a temporary system?

Section titled “What maximum grounding resistance value is acceptable in a temporary system?”

NEC 250.56 recommends a resistance no greater than 25 ohms for the grounding electrode; if that value is exceeded, a supplementary electrode must be installed.

References

Section titled “References”