• Function of a pole is to provide mechanical support to conductor at a safe distance from ground.
• But the function of a cross arm is to keep conductors at a safe distance from each other and from pole.
• It’s a cross piece fitted at the top end of a pole by means of brackets known as pole brackets.
• These also used for supporting insulators.
• Cross arms of various types such as MS channel, angle iron and wooden.
• These are of different shapes such as U-shaped, Vshaped or zigzag shaped.
• Wooden cross arms are used on 11kv and 33kv lines.
• Wooden cross arms are preferred because of their insulating properties.
• This insulating property provides safety to the line staff and minimizes the flash over.
• Cross section of wooden cross arms are 1) for 11kv-1.5mx125mmx125mm 2) for33kv – 2.1mx125mmx125mm.
• Steel cross arms are stronger and use in steel poles.
• The length of the cross arms shall be suitable for the spacing of the conductors.
• To avoid bridge on HT line V shaped cross arms used with pin insulators.
• Straight cross arms used with disc insulators.
• Cross arm is fixed to Pole in such a manner that the load of the conductor is taken by cross arm not by the any bolt that fixes the cross arm to the pole.
• To prevent the arcing the construction of the cross arms should be such that under the worst condition , the spacing between the conductor when swinging should never be less than
6.6kv-76mm
11kv- 101mm
33kv- 190mm
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