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With CURRENT-CARRYING ARMS, the arm body becomes the conductor between the cables and contact pad and thus conventional bus tubes are eliminated. Regardless of the design, current carrying arms are lighter in weight than conventional mast arms and have decreased maintenance requirements due to the exclusion of tubes, supports, structures and many insulated areas. Electrically, hot arms reduce resistance and reactance in the secondary circuit.

Both copper clad-steel and aluminum mast arms are repairable by a competent specialist. And while maintenance requirements are decreased, these arms do tend to accumulate sludge in much the same way as conventional arms. With this design it is particularly important to keep the internal chambers clean so the arms can be properly cooled... as excessive heating might cause problems to the dissimilar metals and weld seams.


Plates are cut to size and welded together - steel on the inside to form a water-tight box and copper on the outside to make the entire outer surface a single, uniform conductor. Thus the rectangular arm bodies are designed to perform all necessary structural and electrical functions.

These Copper Clad-Steel arms, fabricated at Erie Copper Works’ plant, are made from a carbon steel plate with explosion-bonded copper cladding.

Aluminum conductive arms are fabricated from flat or formed plates of a specific aluminum alloy. In addition to the required mechanical and structural properties, the aluminum alloy must have chemical properties, which impedes the corrosion sometimes caused by contact with water. The main advantage aluminum has over copper is its light weight and strength. The main disadvantage with aluminum compared to copper is the lower electrical conductivity. Alloy 5083 aluminum is about 30% IACS whereas deoxidized or OFHC coppers have electrical conductivities ranging between 94 and 100% IACS.

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Last Update: 03/17/2019
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