SG3:14 Earthing of Scaffolding Structures
This NASC Guidance Note addresses the issue of earthing temporary scaffolding and the protection of
scaffolding from lightning.
In almost all circumstances scaffolding structures will have low electrical resistance.
Although the scaffolding structure is usually in contact with the ground and may have base plates and sole
boards, it should never be assumed that the structure is effectively earthed.
The Construction (Design and Management) Regulations (CDM) outlines that clients, CDM co-ordinators and
designers should consider hazards at the planning stage. This should include any requirement for earthing.
For instance, there may be a requirement for earthing to be run under the baseplates and therefore it is
important that the risk of lightning be assessed at scaffold design drawing and pre-tender stage, prior to the erection of
Electrical hazards in the form of lightning, overhead electrical lines and integral lighting and alarm systems
can affect all types of structures and if scaffolding is not properly earthed people can be killed or seriously
injured and buildings damaged.
The client or user of the scaffolding structure is responsible for ensuring that it is safe for use. The client should
ensure that expert advice is sort from a competent person (i.e. a qualified electrician) and suitable protection
EARTHING OF TEMPORARY SCAFFOLD
Where the scaffolding carries lighting, alarm or similar small power circuits, it is recommended that the
structure should be electrically bonded to the protective conductor(s) of the circuit(s) that it carries.
Bonding is not required if the operating voltage of a circuit is below 50V a.c.
For higher power circuits where bonding is required, such as goods and passenger hoists, this should be
carried out in accordance with the latest IEE regulations by a competent person in line with the risk
assessment, to ensure there is no risk of scaffold operatives being electrocuted while the scaffold is
Except where it is necessary for lightning protection purposes, scaffolding external to a structure should not
be connected to the means of earthing within the structure that is afforded by the supply authorities. If Earthing
Spikes are required, the area must be CAT Scanned by a competent person to detect underground services
etc, using equipment that has been calibrated appropriately. This will also help to ensure that any permit
conditions are complied with when in place.
It should be noted that individual scaffolding structures if not connected, must be earthed separately.
If scaffolding is next to an existing structure which has an external lightning protection system it should be
bonded to the earth termination and the air termination network of the lightning protection system by a
competent person, arranged by the client.
Where scaffolding is erected next to a building or structure which is readily accessible to the general public
and used as a working platform or erected over or as part of the common highway, the client should ensure
that it is efficiently bonded to earth.
For example, a simple method of bonding such structures consists of running a strip of metal, other than
aluminium, 20mm x 2.5mm in size, underneath and in contact with the base plates and ground carrying the
vertical members of the scaffolding and earthing at intervals not exceeding 20m. With public seating
accommodation, only the peripheral members of the structure need to be bonded to earth. Other steel
structures, such as those used for pedestrian bridges over main trunk roads, are frequently sited in isolated
situations where they may be prone to lightning strikes and should therefore be bonded to earth, particularly
at the approach points to the structure.
OVERHEAD ELECTRIC POWER LINES
Other temporary tall metallic structures may require separate earthing electrodes to afford adequate lightning
protection. This will depend on the construction of the temporary foundations and footings. BS EN62305-2
should be consulted for further guidance and expert opinion should be obtained if necessary.
When working near overhead power lines it is essential that the voltage being carried is known to determine
the likelihood of arcing and the size of any exclusion zone required. Advice should be sort from the power line
Work under overhead electric power lines should not be carried out without consultation with the owners of
the lines. Wherever possible the lines should be diverted or made dead before work begins.
Further details are contained in NASC Guidance Note SG5 Overhead Power Lines (latest edition), and HSE
Guidance Series GS6 4th Edition 2013.
SCAFFOLDING STRUCTURES AND SENSITIVE BUILDINGS
Scaffolding contractors are often asked to erect scaffolding to sensitive buildings or sites such as historic
buildings and monuments and in Atomic or Petrochemical plants. These places often have their own rules for
Earthing or Bonding and advice must be sort from the owners of the building or the Principle Contractor to
ascertain local policy, prior to the erection of scaffolding.
Additionally, special earthing requirements will be required when erecting scaffolding adjacent to power
supplies such as National Grid stations and National Rail installations, and advice and instruction must be
sought from the client, with a risk assessment made by a Senior Authorised Person prior to works
ERECTION AND USE DURING LIGHTNING STORMS
Scaffolders erecting or dismantling scaffolding and users who observe thunder storms in the distance are
strongly advised to stop work immediately and leave the scaffolding until it is clear that the storm is not
approaching or is moving away and there is no further risk of a strike.