Thursday, December 17, 2009

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.

Copyright Temporary electrical switchboard


row anco said...

I truly appreciate you writing these as your insight has made me think a lot about this topic. Thank you!electrical switchboards

Boon Electrical said...

Very nice and informative post on electrical switchboard installation. The tips and information given is very helpful for those who are willing to change/upgrade their switchboards. Thanks for sharing this useful post with us.

Zequek Estrada said...

I also thought this post was educational. I learned a lot from it. I'm a bit curious about the installation process of temporary electrical switchboards in outdoor locations. Is it hard to meet the weatherproofing criteria?