Construction Wiring: A Guide for Electrical Installations at Construction Site


Any construction site must have electrical power. Though construction wiring is temporary, it’s essential to operate efficiently. Due to improper weather conditions, rough use, and frequent relocation of sites. So, make sure that maintenance and installation standards are enforced as part of the project safety program.

Table of Contents

SEOOW cable

Image: SEOOW cable

What is Construction wiring?

Construction wiring is an electrical wiring system with flexible cables and cords that give power to construction and demolition sites. It is not a part of the permanent wiring system, and it does not include electrical cords and cables that connect the primary power source to different appliances.

Construction wire: Flexible cords and cables

According to NEC Article 305 — “Temporary Wiring,” all non-metallic sheathed cables work in dry locations and do not use them outdoors or indoors in wet areas. Always run the NM-type electrical cord on the ground or the floor. For outdoor and damp places, use type NMC and install it per article 336.

  • You can use junior hard-service cords as portable cables indoors and outdoors. These include Type SJ, SJO, and SJT. However, you must not use a rugged service cord (Type 5, SO, and SI ) at such locations. Instead, use them for extreme conditions such as vehicle traffic, rocky surfaces, damp areas, and surfaces with frequent moves as they have high abrasion resistance.
  • Avoid using worn or frayed cords. If there are splices, they must have proper insulation, outer sheath, and other characteristics of the original cable. You can also connect the lines with suitable cord connectors and plugs.
  • Try to protect the cords from mechanical damage. Do not use cords as a substitute for permanent wiring. Do not stabilize or secure the cords to walls and ceilings unless designed.
  • Try not to run cords and connecting devices through water, concrete, or mud. Plugs and cord connectors may lead to leakage current when submerged and can trip a GFCI.
SOOW Flexible Cord

Image: SOOW Flexible Cord

Possible hazards with the temporary construction wiring

A temporary electrical system at the construction site may become hazardous.

Construction Wiring: Electrical injuries

The construction site circuit wiring is 120-240 volts, and thus, it can cause severe injuries to workers if they come in contact. How severe the shock is depends on the amount of current flow and the time of contact of the body.

Construction Wiring: Fire hazards

Electric power in construction wiring is a significant cause of fire hazards, and there is no systematic arrangement of construction activities. As a result, the chances of minor errors are higher. These errors can result in short circuits, overloads, overheating, ground faults, and arcing faults, leading to ignition.

Construction Wiring: Power failures

The loss of electric power at construction sites can lead to severe issues, be it partly or wholly. Firstly, there is fear of darkness for workers working at any complex location, and further, prolonged loss of power can lead to shutting down the job.

Construction site

Image: Construction site

How to Ensure a Safe Construction Wiring?

Follow the requirements and methods below to make sure they are safe.

Design requirements

An electrical distribution system at the construction site must have enough capacity to provide the maximum anticipated load. While designing the electrical system, you must keep in mind the growing demand for power in electric lighting, welding, power tools, and other heavy equipment used at construction sites. According to the National Electrical Code and the OSHO special requirements, all electrical systems must follow the standards and codes. It includes:

  • Article 310 “Conductors for General Wiring”—NEC lists the ampacities of aluminum conductors. All circuits must have fuse or circuit breakers of current rating less than conductors. Every temporary course must have disconnecting means.
  • Every motor and motor controller must have a disconnecting means. It must be visible from the controller’s location and must have an option of a “locked off” position.
  • Ensure that you use all the equipment based on its function, location, and types of use. Don’t use indoor equipment outdoors and vice versa. Ensure that all equipment comes from testing laboratories like Factory Mutual System or Underwriters Laboratories Inc., which are nationally recognized.
  • Ensure that all conductors must enter and leave the cabinets and boxes through holes and on conduits only. Use box connectors and bushings for cables entering and leaving the boxes. It prevents cuts or bruises from the sharp edges or holes.
  • All electrical equipment must have proper covers to prevent accidental touch with any energized part. Further, ensure that only authorized personnel remove those covers after de-energizing the equipment.

System grounding

You can do this by connecting the central neutral conductor to the grounded electrode with the help of a grounding electrode conductor. This grounding system will reduce the voltage difference when lightning strikes or in case of any primary or secondary faults.

A grounding electrode system may have a metal water pipe with a rod or pipe electrode. Alternatively, it can have a metal frame of the building, which consists of an electrode encased in about 2 inches of concrete. According to NEC, it is essential to bond all such electrodes to form a system. If electrodes are not there, pipe electrodes will suffice. However, you must verify these “made” electrodes for their resistance. When resistance is greater than 25 ohms, you must add one more such “made” electrode”.

Grounding of equipment

You must ground all electric tools and equipment through an equipment grounding conductor in the cord and grounding terminal in the plug and receptacle. Don’t use a neutral conductor as an equipment grounding conductor. The stranding and mechanical protection of the circuit conductor and the grounding conductor are the same. Ground the metal guards with temporary grounding strings.

If you make portable cords, make sure not to interchange circuits and the grounding conductors. Mark the grounding conductors in mobile cables as green and neutral conductors as gray or white.

Electrical equipment may have metal conduits, electrical panel board enclosures, motor starter boxes, switch boxes, metal fencing, and outlet boxes. Make sure to ground these metal enclosures keeping away the fixed equipment 5 feet horizontally and 8 feet vertically from the ground.

In all tunnels and shafts, ground all the metal enclosures, reflectors, light strands, and frames through an equipment grounding conductor or the conductor that connects to a ground terminal bar in the circuit panel board that supplies power to the equipment. There is no need to ground the frames of portable generators that supply one kW or less power.

Ground fault protection

Single-phase receptacles of 15-20 ampere and 20 volts, which are not part of permanent installation and are used by personnel, require ground fault protection. You can provide this protection through a ground fault circuit interrupter (GFCI) or an efficient equipment grounding conductor program.

The equipment grounding conductor grounds the equipment or conductive metallic parts. Whenever a ground fault occurs, it helps to operate overcurrent protection.

A Ground Fault circuit interrupter detects leaking current from an electrical system. If the leaking current exceeds a predefined level of 5mA, GFCI interrupts the circuit. There are GFCIs that can protect individual receptacles or entire circuits. You can also use a portable GFCI as you need it only when the receptacle is used. Just plug in the receptacle to the portable GFCI and unplug it when done.

There are three types of GFCI.

  • The plugin type that protects one or two protected receptacles
  • The cord-connected type has a molded box with many protected receptacles
  • GFCI attachment plug, which you can install on a cable.

You can also use GFCIs in outlet boxes with no cord connection.

Receptacles, attachment plugs, connectors

When picking receptacles, make sure that they are grounding. Further, use them only for the circuits that list the class, current, and voltage compatible with the receptacles. Receptacles’ configurations are not interchangeable, listed in the ANSI C-73 standard.

Ensure that all conductors end at the correct terminals of the receptacle, connector, and attachment plug. Follow the below-mentioned rules for conductor termination.

  • Terminate equipment grounding conductor at the green-colored plug
  • Neutral wire or white wire at “W” terminal or white/silver colored terminal
  • Ungrounded conductors at “X,” “Y,” and “Z” marked terminals or brass-colored terminals

Remember, improper connection of conductors can lead to personal injury or equipment failure.

For attachment plugs and connectors, follow these precautions.

  • The connectors and attachment plugin construction wiring should be capable of handling rough environments.
  • Further, their grips should hold the conductors properly without damaging them.
  • Separate all the terminal and wire cavities from each other so that there are no chances of electric wire shorting.
  • Take attachment plugs that are of the “dead front” type.
  • Don’t tin the stranded conductors before terminating.
  • For environments with dust and damp locations, use attachment plugs and connectors that offer protection from moisture.


Branch circuit conductors should come from a distribution board and a suitable device. The conductors either run as a cord or multi-conductor cable or as open wires. If conductors are open, fasten them every 10 feet at the ceiling height.

Temporary lighting

  • Keep the power tools circuits separate from the lighting circuits so that the former does not affect the latter.
  • Enclose the lighting of the fences, barricades, and sidewalk in a metal raceway. Protect available lamps from accidental damage.
  • Use heavy-duty cords for portable hand-held lamps. Do not suspend the cables of the lights unless designed so.
  • According to OSHO, if hand-held lamps work in moist or rough conditions like tanks and drums, operate them at 12 volts only. If you are using a GFCI, you can use 120-volt lights also.
  • If using non-insulated metallic lamp guards, ground them properly. Do not construct lamps with paper-lined or brass shell holders.

Power lines

Overhead wiring and cabling are always hazardous, so always call a licensed electrician to take necessary action for such power lines.

Route all the temporary power lines to not interfere with the construction process. If routing is not possible, raise the lines to sufficient height or install them underground. If it is impossible to raise existing lines, sign a warning.

Control of work practices

  • Enforce proper job rules to ensure safety at work locations and make all the workers aware of the practices.
  • You should give training to workers regarding the handling of electric conductors. They should learn mouth-to-mouth resuscitation and other methods of escaping fellow workers from the accidental sites.
  • Maintain good housekeeping and prepare a planned layout of temporary wiring to prevent incidents of shock hazards and fire hazards.
  • Workers must have personal protective equipment and should wear them strictly.


  • You must establish and religiously follow the maintenance and extension of the electrical construction installations.
  • Assign the work of complicated connections to qualified electricians.
  • Follow proper maintenance standards that reflect good quality, regular inspections, and quality equipment.
  • You must arrange the testing and repairing of tools periodically. Workers should not use defective tools.


So, you see, you need to take a lot of precautions while handling construction wiring and cables. A small error or mishandling can lead to severe accidents. Choose your construction wires and cables wisely and according to industry standards. If you want any help, our team of experts can help you. Gloom has a massive collection of high-quality construction cabling that offer superior performance.