Menu

Commercial & site work

Temporary power supplies for sites and events

Building sites and refurbishments need power long before the permanent installation is ready, in conditions a finished building never sees: mud, rain, plant, dust and a layout that keeps changing. We install the temporary distribution and wiring that power the tools, site lighting and welfare cabins, alter them as the work moves on, and take them out when the job is finished.

Request a quote 020 3883 1321
Portable tools
Usually 110 V, centre-tapped to earth
Before first use
Inspected, tested and certified
As the site changes
Outlets moved or added, and each change tested

  1. The cut-out and incoming cable belong to the network operator, and the meter to the energy supplier. The site installation starts after the meter.

  2. A main isolator and the protective devices for each outgoing circuit, including RCDs where the circuit needs them, in an enclosure built for site conditions.

  3. Steps 230 V down to 110 V for tools and lighting. The centre of the output winding is earthed, so neither conductor is more than 55 V from earth.

  4. Outlets and connectors for portable tools and site lighting. They are colour-coded by voltage, and their pin layout stops them being plugged into an outlet at a different voltage.

  5. Protective conductors meet at the main earthing terminal. How the site is earthed is decided for each site and tested before anything is used.

  6. A separate 230 V circuit with its own protective devices supplies the cabin’s equipment, such as its lighting, heating and water heater.

Fig. 1 — From the incoming supply to 110 V site equipment and the welfare cabin, shown as a simplified schematic (Illustration)

Sound familiar?

When a temporary supply is needed

A site installation is laid out differently from the wiring in a house. The supply feeds a site distribution assembly, which protects each outgoing circuit. Portable tools and site lighting usually run at 110 V from a transformer whose output is centre-tapped to earth, which limits the voltage of a shock, while cabins have 230 V circuits of their own. The drawing follows that route, from the supply to the tools and the cabin.

If a site cable, plug or outlet is damaged, stop using it, keep people away, do not touch the damaged part and tell whoever runs the site. If an RCD or circuit breaker trips, reset it once at most; if it trips again, leave it off and call an electrician. Urgent electrical problems.

  • Work on a new build or extension is due to start before the permanent supply is connected
  • A refurbishment means the building’s own wiring will be isolated or stripped out
  • Welfare cabins, a site office or a drying room need power, heating and lighting
  • Trades are running extension leads from a house or a neighbouring building
  • The site has grown or moved on, and the outlets are no longer where the work is
  • A periodic inspection of the site installation is due, or the principal contractor has asked for test records
  • An event needs temporary power and lighting, and you want to know what is involved

Who this helps

  • Builders and principal contractors

    Power for tools, lighting and welfare from groundworks to handover, extended and moved as the build goes up.

  • Refurbishment and strip-out contractors

    A supply for the trades while the building’s own wiring is isolated, stripped out or replaced.

  • Homeowners running their own build

    When the house is being gutted or extended and the trades need somewhere to plug in other than an extension lead from the kitchen.

  • Event organisers and venues

    Temporary power and lighting for an event, which follows different guidance from a building site. Ask us first whether we can help.

Planning

What to send us before a site supply

The more of this we have before the site visit, the closer the first layout will be to what the site actually needs. Provisional answers are fine.

Dates and programme
When power is first needed, how long the site will run, and when the permanent supply is expected to take over.
Where the supply is
An existing supply, a new connection on order from the network operator, or a generator you are arranging, and where it is or will be.
Loads and equipment list
What will be connected: hand tools, site lighting, heaters, pumps, mixers, hoists or anything three-phase, with ratings where you have them.
Cabins and welfare
How many cabins, offices, canteens and drying rooms, and what is in them, such as heaters, water heaters and kettles.
Phases of work
How the site will change, from strip-out or groundworks through each floor or area, so the outlets can follow the work.
Principal contractor and site rules
Who the principal contractor is, who our contact on site will be, and the induction, permit and access arrangements we need to follow.

Step by step

How the work is done

Before we quote

Most site supplies need a visit before we can quote. We look at where the supply is, or will be, where the work and the cabins will be at each stage, how cables can reach them, kept clear of vehicle routes, walkways and storage or protected where they have to cross, and what is likely to change as the job goes on.

The equipment list decides most of the layout. The loads determine how many distribution points, transformers and outlets the trades will need, and whether the supply can carry them all. Three-phase equipment, heaters in the cabins and long cable runs all make a difference, so tell us about them early.

  1. Site visit and layout

    The layout is agreed on site with you or your site manager: where the distribution, transformers, outlets and cabin supplies will go at each phase of the work.

  2. Written quote

    The quote lists what will be installed and connected, and what is left to others, such as the supply connection or equipment hire. Nothing goes ahead until you approve it.

  3. Install and connect

    The site distribution is installed and connected to the supply, cables are routed and protected to suit the site, and each cabin is connected to its own circuit.

  4. Inspect and test before use

    Before anyone plugs in, the installation is inspected and tested, including the earthing and the RCDs, and you receive an Electrical Installation Certificate.

  5. Alter as the site changes

    When the work moves on, outlets and cables are moved or extended. Each alteration is inspected, tested and certified before it is used.

  6. Inspect at intervals

    On longer jobs, the installation is inspected and tested again at regular intervals, and each inspection is recorded on an Electrical Installation Condition Report.

  7. Disconnect and remove

    When the permanent installation takes over or the job ends, the temporary installation is disconnected and taken out.

Scope

What is included

Included

  • Agreeing the layout of distribution, transformers, outlets and cabin supplies with you
  • Installing and connecting the site distribution and cable runs set out in the quote
  • Separate circuits to welfare cabins and site offices
  • Inspection and testing before first use, with an Electrical Installation Certificate
  • Disconnection and removal of the temporary installation at the end of the job

Depends on what we find

  • Whether the supply you have, or have applied for, can carry the tools, cabins and heating you plan to run
  • How many distribution points, transformers and outlets the site needs, and where they can be placed
  • How cables can be routed and protected across the site
  • How the installation will be earthed, which depends on the type of supply and the site
  • How many alterations the phases of work will need

Afterwards

  • Keep the certificate and any later inspection reports with your site records
  • Ask everyone to look over tools, leads and plugs for damage before each use, and take anything damaged out of use
  • Tell us before adding cabins, heaters or large equipment, so the supply and protection can be checked first
  • Book periodic inspections for as long as the site runs

Not covered by this service: New connections and supply upgrades, which are arranged with the network operator and an energy supplier; Generator supply and the hire of site equipment: tell us what you already have or plan to hire; Testing of portable tools and leads, which is a separate service.

The paperwork you may receive

  • Electrical Installation Certificate

    New installations, rewires and new circuits.

    • What was installed and the design details
    • A schedule of test results for each circuit
    • Signatures for design, installation and inspection

  • Minor Electrical Installation Works Certificate

    Small additions and alterations that do not add a new circuit, such as an extra socket on an existing circuit.

    • A description of the work
    • Test results for the circuit that was altered
    • The signature of the person responsible

  • Electrical Installation Condition Report

    Periodic inspection and testing of an existing installation.

    • Observations coded C1, C2, C3 or FI
    • A schedule of test results
    • An overall assessment and the recommended date of the next inspection

Simplified outline, not a real certificate (Illustration)

Standards and regulations

We are a NICEIC Approved Contractor, registration number 619998000, and fully insured. How to check our registration and insurance.

  • REFBS 7671, the IET Wiring Regulations, including Section 704 for construction and demolition site installations
  • REFBS 7375, the code of practice for the distribution of electricity on construction and demolition sites
  • REFThe Construction (Design and Management) Regulations 2015: where necessary to prevent danger, energy distribution installations on site must be suitably located, periodically checked and clearly indicated
  • REFThe Electricity at Work Regulations 1989: electrical systems must be maintained, so far as is reasonably practicable, to prevent danger

Questions

Questions about temporary power

Why do site tools run on 110 V?

A 110 V supply from a centre-tapped transformer has its midpoint connected to earth, so neither conductor is more than 55 V from earth. A shock from a damaged lead or tool is then at a much lower voltage than from a 230 V supply, which reduces the risk of serious injury. The yellow 110 V connectors also cannot be plugged into a 230 V outlet.

Can we use 230 V tools on site?

In some cases, but 110 V is the usual choice for hand tools. BS 7671 allows 230 V socket outlets on a construction site where they have additional protection from an RCD. BS 7375 and HSE guidance, however, prefer 110 V for portable tools and hand lamps. Cabins and fixed plant are normally supplied at 230 V or 400 V, and the voltage for each area is agreed when the layout is planned.

How often does the site installation need inspecting?

IET Guidance Note 3 recommends that a construction site installation is inspected and tested at least every three months, with routine checks much more often in between. That is far shorter than for a finished building, because site cables and equipment are moved, driven over and left out in the weather. The people using tools and leads should also look them over before each use.

We do not have a supply yet. Who arranges one?

The connection is applied for with the network operator for the area, normally by the property owner, developer or principal contractor, and an energy supplier fits the meter. The network operator sets its own timescale, which can be long, so apply as early as you can. Once the supply and meter are in, the site installation is connected after the meter.

Can the builders just use the power in the house?

Sometimes, on a small job in an occupied home. The trades may be able to work from the existing installation, often through a portable 110 V transformer, depending on the condition of the installation, its RCD protection and the extra load. Once the house wiring is being stripped out, or on a larger job, a separate temporary installation is usually needed. Describe the work when you get in touch and we can advise which applies.

Who is responsible for the site supply once it is in?

Day to day, whoever controls the site: usually the principal contractor, or the builder on a smaller job. That means keeping cables protected, making sure tools and leads are checked and arranging the periodic inspections. Only a competent electrician should add to or move the installation, and each change needs testing before it is used.

How much notice do you need?

There is no fixed period: it depends on the size of the site. A site visit and quote come first, any equipment you are hiring has to be booked, and a new connection from the network operator usually takes longest of all, so apply for it before anything else. If the programme moves, tell us as soon as it does.

Can you provide power for an event?

It depends on the event. Event power is different work from a building site: temporary systems for entertainment have their own code of practice, BS 7909, and BS 7671 has separate sections for exhibitions, shows and fairgrounds. Send us the venue or site, the dates, what needs power and where the supply or generator will come from, and we will confirm whether it is work we take on.

Often needed alongside

Next step

Plan your site supply

Send the programme and the equipment list as soon as you have them, with photos of any supply already on site. Power is far more likely to be where the trades need it on their first day if the layout is planned before they arrive.

What to send us

  • The site address or postcode
  • What the job is: new build, extension, refurbishment, strip-out or event
  • When power is needed, and roughly for how long
  • The tools, plant and cabins that will need power
  • Whether there is a supply on site already, with photos of it if so
  • A site plan or layout sketch, if you have one

An enquiry is not a booking: we contact you first, and you see a written quote before anything goes ahead.

We list towns in London and surrounding areas, Kent, Essex, East Sussex and West Sussex. Check your postcode.

Call or email us for a free quote

Tell us the postcode and a little about the job. We will contact you to discuss it, and you get a written quote before any work starts. Quotes are free. Some survey or diagnostic visits may be charged: ask when you book.

Call 020 3883 1321 Email us

Our email address: support@dualcurrent.co.uk

Helpful to include

  • The postcode of the property
  • What the job is, or what is going wrong
  • Photos, if you have them, taken without removing any covers
Call us Request a quote