For multi-bolt joints, overall resistance is effectively the resistance of a single bolt divided by bolt count—making torque consistency even more critical. For copper busbars wider than 40 mm, use M12 bolts, 30–50 mm spacing, and torque values above 70 N·m. Failure to follow these instructions can result in injury or equipment damage. That same joint, undertorqued by 30%, runs 80–100°C above ambient within months as micro-gaps develop, contact resistance increases, and oxidation accelerates. Over-tightening may have the same consequences as under-tightening. For connecting busbars (Cu ETP-NFA51-100) to the circuit breaker, the tightening torques to be used are shown in the. * Bronze alloy bolts shall have a minimum tensile strength of 70,000 pounds per square inch. ** Bolts, cap screws, nuts, flat washers, locknuts: 18-8 alloy. Uniswitch switchgears are either fixed or withdrawable type cubicles.
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