Temporary site floodlights

Large construction sites usually need temporary floodlight towers (in addition to the temporary lighting inside the new buildings) to provide lighting efficiently for the general movement, safety and security on the external areas of buildings under construction.

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The lighting towers will usually takes the form of fixed tower or mobile tower units. Which one to use usually depends on the siting positions available for the lighting tower units and the duration of the contract.

For contracts with construction periods of relatively short durations, it may be much more economical to use mobile tower units.

However, if contract period is long, then it may be worth some considerations to use fixed height tower units. In any case, the fixed height towers can still be reused on future projects.

Careful dismantle the fixed height static towers at the end of the contract. Then the only extra materials that are required in at the next construction site is the foundation.

Static floodlighting tower units are normally available up to 18 meter high. They can be powered from the mains supply and they can be provided with their own electric generator.

The external areas of a construction site usually need a lighting level of around 20 lux average. This is the level sufficient of for the handling of construction materials and site clearing works.

A rectangular area of 60 meter by 60 meter can be lighted up to this light level by a typical 18 m tower carrying four units of 400 watt high pressure sodium fittings.

A main contractor with larger contracts and relatively longer contract period may want to consider a more elaborate study on their site lighting requirements.

If there is enough space to mount these floodlighting tower units, a proper lighting engineering study can be carried out together with the overall temporary electrical installation. The exercise would employ the floodlight lamp data, the aiming angles of the light fittings, and the mounting heights of the individual fittings to arrive at the required overall Illuminance.

These static towers would normally employ high intensity luminaries and with the type of equipment available today, the contractor can now light areas to sufficient level so the works can continue in evenings of the darker months. This is significant because it can considerably reduce the contract time.

Light fittings used in this application would necessarily be high intensity discharge type and the high pressure sodium lantern have become the more dominant type due to its high lighting output per kW of power usage (approximately 125 lumens per watt). A tungsten halogen lamp would give only 22 lumen per watt. The capital cost of opting the hight pressure sodium equipment is considerably higher than the tungsten halogen, but the main contractor may do well to consider other factors also such as the running cost, installation cost and the lamp life.

At the end of the construction work, all these equipment except the tower foundation, can be dismantled and transported to other project sites for reuse.

Below is a picture of a small mobile floodlight unit:

Picture 1 - Mobile site floodlight unit



Read more on site electrticity at this post, Temporary Electrical Installations.

There is also more imformation on temporary lighting at this post, Temporary lighting installation.

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Temporary electric supply

What is a temporary electric supply?

A temporary electric supply is normally associated with the temporary electrical installation of a construction site. The term ‘temporary’ brings up a vision of a length of a length of twin and earth cable, or a four-core twisted cable and an undersized green earth wire, that is connected into a 30A single or 4-phase and neutral switch-fuse, trailing across the rough ground of the construction site to terminate into a seasoned self-fabricated distributed (with or without metal-clad enclosure).

On the so-called ‘distribution board’, a length of three flexible extension cord is connected to a clumsily assembled socket outlet with or without the use of a three-pin plug. How would you connect a three-core extension cord to a three-pin 13 A socket outlet? Somewhere on this blog, you can see clearly how it is done. It even has had various ways of doing it.

The extension cord run at high level near the soffit of floor slab, or some just run an the scattered floor to a temporary metalclad 13A switched socket outlet some 30 meters away.

The construction contract cost hundreds of millions, but the temporary electric supply system has been ‘engineered’ to fulfill all the site electrical requirements for the minimum price possible.

The main contractor has the responsibility to ensure the temporary electricity supply system installed is not only functional and meets all his electrical needs, but also safe for all involved in the construction work. The supply system need to be good enough to provide reliable power distribution, whether that period of the construction contract is three months or three years. Or whether the site supply requirement is 4 kVA or 3-megawatt supply.

What specifications to use for the temporary electric supply equipment?
Generally, what applied to low voltage installation is in the IEE Wiring regulations also apply to the temporary supply system. However two more British standards should be used to cover the gaps not covered there: BS 4363 (Specification for distribution units and electric supplies for construction sites and building sites) and BS 7375 (Code of practice for distribution of electricity in construction and building sites).

Source of the temporary supply

The temporary electric supply can be obtained from either the distribution network of the local electric supply authority or an independent electric generator installed at the site. Which one to use is usually just a matter of judgment on the cost involved.

However a few other factors may also need to be carefully considered which include practical problems that are usually associated with the distribution of the electric power safely and effectively throughout the site.

If the supply is taken from the local electric supply authority, a lead-time is usually required, as the authority would need time to arrange for the connection. The main contractor also need to submit sufficient details on the peak demand that will be required during the course of the contract, the positions of the point of supply intake and also the estimated contract period.

The authority usually requires enough details on the types and size of electrical load, e.g. lighting, heating, motors, etc. Motor loads usually need more details such as types of motors and the method of starting (direct-online, auto-transformer starting, etc).



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Temporary lighting installation

A construction site’s temporary electrical installation must also provide adequate lighting for the activities that are carried out at a particular workspace whether indoor or outdoor. Arguably more important than the light levels, the temporary lighting installation should be sufficiently safe for use and provided with adequate protection to prevent electrical shocks.

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1) Wire cages to prevent against mechanical damage should protect temporary light fittings at the construction sites. Damaged light fittings not only result in the repair cost, but they also present risks of electrical shocks to workers using them or those who are nearby. Precautions must be taken against the danger of electrical fires that because of damaged light fittings or the temporary supply wiring.

2) The temporary wiring supplying the lighting circuits should be connected to the special lighting section on the temporary switchboard. These circuits should be protected by 100 mA RCD (residual current circuit breakers).

3) Festoon lighting should only be used strictly in underground shafts, wells and tunnels. When this type of lights are used, the lamp holders should only be the moulded-on, non-removable type (the lamp holders are bonded or moulded to the wiring cables) and the lighting supply voltage is 32 Volts or below.

4) Either the temporary wiring or the newly installed permanent wiring may supply lift shaft temporary lighting. However, the light fittings used should be properly guarded against accidental mechanical damage and they should only be connected to the wiring using a lighting plug and socket. These lights should be installed at intervals of less than nine meters along the vertical length of the lift shaft. The control of the lift shaft lighting should be by means of two-way switches located near the shaft access points.

5) Normal duty lighting circuits are installed to provide general illumination for work and allow safe movement inside and around the construction site.

6) The installation of wiring for the temporary lighting should be carried out with proper supports and fittings to allow for wiring cables to be routed in ways that minimize obstructions, which can results in damage to the luminaries and wiring. These damages can present shock risks to the works and possibilities of electrical fires.

7) The use of lighting circuits supplied at safe extra low voltage levels (SELV - voltages less than 50 volts ac or 120 volts dc) is highly recommended for working in confined spaces where workers faces high possibilities of frequent contacts with temporary electrical equipment and wiring.

8) An illumination level of 10 lux is adequate for general movement within a building under construction. As an illustration, one length of 100 meter festoon light string fitted with 20 nos 100 watt lamps at 5 meter intervals will give a 10 lux over a rectangular area of 25 meter x 30 meter.

Read more on site electricity at this post, Temporary Electrical Installations.

You can also see a few pictures of site floodlight at this post,  Temporary site floodlights.



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Temporary electrical switchboards

All electrical switchboards used on temporary electrical installations or building construction sites should be of substantial construction. Where they are installed in outdoor locations, the switchboards should be so constructed that safe operation is not impaired by the weather. This weatherproof criteria usually means an IP rating of not less than IP 65. When the doors are opened, the degree of protection to all live parts should be no less than IP 20.

The method used for installation must have provisions so the cables and flexible extension cords coming in and out of the boards can be properly supported.

The temporary switchboards should also be provided with a door and locking facility that comply to the requirements of the electricity supply authority. Door should be designed and attached in a manner that will not damage any flexible cords connected to the board, and should protect the switches from mechanical damage. The door should be provided with a sign stating ‘KEEP CLOSED’ – ‘LEADS THROUGH BOTTOM’.

The switchboard should have an insulated slot in the bottom for the passage of leads.

The temporary switchboard should be attached to a permanent wall or other suitable portable structure, which has been designed for the purpose. Pole or post-mounted switchboards should be fixed by means of coach screws or bolted.

If the switchboard is used to supply other sub-boards downstream, every sub-board should be provided with a clearly labeled main isolating switch.

Temporary lighting outlets should be in a separate section on the switchboard and they should be clearly identified as lighting circuits. To protect from electric shock, the supply to the temporary lighting section should be provided with 100 mA residual current device (RCD), while the supply to the temporary socket outlets section should be protected by an RCD or earth leakage circuit breaker (ELCB) of sensitivity not more than 30 mA.

If too many tools are connected at the same that results in frequent tripping of the shock protection device, then the supply should splitted into multiple sections or multiple distribution boards, with each section or DB protected by a 30 mA RCD. This will prevent the shock protection device from being defeated by workers whose works have been most inconvenienced by the frequent tripping.

The electrical contractor or nominated persons should ensure that all power circuits are isolated or made accessible so as to eliminate the risk of fire, electric shock or other injury to persons after completion of the daily work.

All temporary supply mains should be protected by a circuit breaker or H.R.C. fuses.

A clearance of at least 1200 mm should be maintained in front of all switchboards and if the switchboard is located in a room, a clearance of 700 mm minimum should be provided around the other three sides. If the switchboard is also provided with rear access, then the rear of the switchboard must also have a 1200 mm clearance minimum.

Temporary switchboard should be so located that the maximum lengths of the flexible cords do not cause excessive voltage drops and impairs the normal operation of electrical equipment and portable electric tools.

The switchboard should be properly earthed and the color-coding of the protective conductors shall be done in accordance with IEC 60646.

A main earth bar should be provided inside the switchboard and it shall be connected to the temporary electrical grounding using appropriate size earthing conductor. The cross-section of the conductor shall be sufficient to carry the rated short-time withstand current of the switchgear.

All metal parts of the switchboard cubicle, and the metal parts of the components that are mounted on the switchboard including door, relays, instruments, etc shall be earthed through branch connections to the earth bar.

Frames of the draw-out circuit breakers (if they are used) shall be connected to the earth bar through a substantial plug type contact.

All temporary electrical equipment and switchgears including the switchboards should be inspected and labeled regularly by a licensed competent person before their first use and every three months thereafter.

The details of the inspection should be recorded in a logbook for inspection purposes. The details recorded in the logbook should include but not limited to the following:
a) Date of the inspection.
b) Identification no of the equipment or switchboard inspected.
c) License number of the inspecting competent person.
d) Any repair required because of the inspection.

Inspection label or sticker should be attached to the inspected switchboard showing the date of the most recent inspection. This label should carry the verification signature of the endorsing competent person.

Repair works that are required by the inspection should be carried out without delay. If the required repairs are related to safe use of the temporary switchboard, they must be properly carried out before the board is put to further use.

There is also a more detailed article on temporary electrical installation at this post, Temporary Electrical Installations.

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