In brief
The Regulation on OHS in Construction Work requires a suitable residual current device on the main and sub-distribution panels on site, panels kept in locked cabinets, no connections made with bare cable ends and no worn cables in use. After the temporary installation is set up, it should be checked by an authorised person before it is energised and reviewed regularly as the site progresses.
Why does construction site electrical safety deserve its own heading?
A factory's electrical installation stays in the same place for years. A temporary electrical installation on a construction site changes every week: as floors go up the sub-panel is moved upwards, as excavation progresses the cable route changes, and each new subcontractor runs their own extension lead. On top of that, the installation is exposed to rain, mud, the wheels of construction machinery and formwork nails. Construction site electrical safety therefore cannot be managed with a "set it up and forget it" mindset.
Part (A) of Annex 4 of the Regulation on OHS in Construction Work sets out these basic rules for the energy distribution installation:
Part (B) of Annex 4 requires, for energy distribution installations in open areas, that existing installations be identified before construction work starts, that a sufficient safety distance be kept from overhead lines and that the installation be checked and maintained regularly (Section II, Art. 15).
Site distribution board: main and sub-panel layout
On a construction site, power is usually taken from a single main panel and distributed to sub-panels per floor or zone. Sockets are fed not directly from the main panel but from sub-panels close to the work area. The relevant standard for construction site panels is TS EN 61439-4; when buying or renting a panel, ask about compliance with this standard and a protection rating suitable for outdoor use.
| Panel | Function | What to check on site |
|---|---|---|
| Main panel | Grid connection, main breaker, distribution to sub-panels | Locked cover, main residual current protection, earthing connection, single-line diagram, labelled outgoing circuits |
| Sub (floor) panel | Distribution to the zone, supply to sockets and equipment | Locked cover, residual current protection on every socket group, sound enclosure, mounting raised off the ground |
| Socket box | Connection of hand tools and lighting | Industrial-type plugs and sockets, sockets with covers, no cracks or burn marks |
The panel key is held not by just anyone but by the site's authorised electrician and the site manager. Leaving the panel cover open "to make things easier" cancels out the locked cabinet rule. The area in front of the panel is kept clear of stacked materials, and the panel is mounted on a raised stand or on a wall so that water does not collect around it.
Construction site residual current device: which rating, how to test?
The regulation says "a suitable residual current device" and leaves the rating to the design. Devices used to protect human life have a rated residual current of 30 mA; this value is the basis for socket circuits feeding hand tools and lighting. On the main panel, protection is designed to provide selectivity with the sub-panels, so that a leak in one hand tool does not black out the whole site.
Having the device is not enough; it must also be shown regularly that it works:
- Test button: Tests the device's mechanism. Because panels are moved frequently on a construction site, we recommend setting up a routine of testing and recording more often than the manufacturer recommends, for example weekly.
- Test with an instrument: Only a test carried out with a measuring instrument shows that the device trips at the correct current and quickly enough. This test is carried out at installation, whenever the panel is moved and during the periodic inspection.
- Bridged device: A device that has been bridged or disabled because it trips frequently is the most dangerous finding on a construction site. Frequent tripping indicates a leak; the source is found, and the device is not disabled.
We explain in detail how earthing and the residual current device work together in our article on earthing and residual current devices.
Construction site cable safety: protection from the ground and water
Construction site cable safety means protecting cables from three enemies: wheels, water and sharp edges.
- Lift cables off the ground: At pedestrian and vehicle crossings, cables are suspended or routed under a cable bridge (protective ramp). A cable lying on the ground is both crushed and a trip hazard.
- Keep them away from water: Cables and joints are routed so that they do not run into puddles, formwork water or concrete pouring areas. No joints are left in wet areas.
- Protect them from sharp edges: Formwork edges, rebar starter bars and door frames cut the cable sheath; protective conduit or trunking is used at these points.
- Do not make joints: Cables are not joined by wrapping them in tape; a suitable connector or a new cable is used. Pushing a bare cable end into a socket is prohibited by the regulation.
- Choose suitable cable: On construction sites, flexible, rubber-sheathed, heavy-duty cables (for example H07RN-F) are preferred; thin household extension leads are not suitable for a construction site.
- Fully unwind the reel: A device drawing high power heats up cable left wound on the reel. When using a reel extension lead, unwind the cable completely.
Overhead lines and existing installations
Electrical risk on a construction site does not come only from the installation you set up. The regulation requires existing installations on site to be identified, checked and clearly marked before construction work begins. A sufficient safety distance is kept near overhead power lines; when this distance is determined, the swaying of the wires in the wind is also taken into account. If the distance cannot be maintained, the route of the line is changed or it is de-energised; permission is obtained from the relevant authorities for this. Barriers and warning signs are used for work under lines, and concrete pumps are not operated under power transmission lines (Annex 4 B, Section II).
Before excavation, the location of underground cables is obtained from the utility authorities and marked. For excavation and collapse risks, see our construction site OHS checklist article.
Post-installation check and periodic inspection
After the temporary installation is set up, and before it is energised, it should be checked by an authorised electrician or electrical engineer. This check includes at least the following:
- Earth continuity and earth resistance measurement
- Trip test of residual current devices with a measuring instrument
- Insulation check and tightness of connections inside the panel
- Consistency of panel labels and the single-line diagram with the site
Annex III of the Regulation on Health and Safety Requirements for the Use of Work Equipment requires the electrical installation and earthing to be inspected at least once a year by authorised persons registered on EKİPNET (the Ministry's register of authorised inspection personnel), unless the standards specify a shorter period, and the installation design is requested during this inspection. Annex III also states that inspection frequency may be increased depending on factors such as environmental conditions and intensity of use. A construction site is an environment where all of these factors come together; when the installation changes significantly, when panels are moved to a new floor, or after an incident such as flooding or cable damage, repeat the inspection without waiting for the annual schedule. You can track inspection dates with the OHS calendar; for the legal intervals, see our article on periodic inspection intervals for work equipment.
The steps for isolating the supply and verifying the absence of voltage in electrical work are covered in our article on the 5 safety rules in electrical work; the additional risks of wet floors and heater use in the winter months are covered in our article on workplace safety in winter. On construction sites, we carry out on-site supervision of temporary installations as part of our OHS specialist service, and planning of installation and earthing inspections as part of our periodic inspection service. For other sector-specific topics, see our construction page.
Frequently Asked Questions
Is a residual current device mandatory on every sub-panel on a construction site?
Yes. The Regulation on OHS in Construction Work requires a suitable residual current device on the main panel and sub-distribution panels on the construction site. For socket circuits, 30 mA devices for the protection of life are the basis.
Can the cover of a site distribution board be left open?
No. Panels accessible to workers are kept in a locked cabinet or compartment. The key is held by the authorised electrician and the site manager.
Can we join an extension lead with tape?
No. The regulation requires suitable connectors to be used and old or worn cables not to be used. A damaged cable is replaced or repaired by an authorised electrician with a suitable jointing component.
When is the periodic inspection of a temporary installation carried out?
Annex III requires the electrical installation and earthing to be inspected at least annually. Because the installation changes frequently on a construction site, it should also be inspected after installation, after significant changes and after damage incidents.
A certified specialist matched to your hazard class: site inspections, approved logbook, training plan, annual plan and report follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.