(1) The nominal tightening torque is based on a friction coefficient of the thread of 0.14 (distributed value the thread is subjected to which, in some cases, is not
negligible). The nominal tightening torque with lubricant is according to the DIN 43673 Standards.
(2) Oil or grease. The thread and contact surfaces of the lubricated heads. Take into account the deviations from the general Standards table (for example, for
contact systems or terminals) as foreseen in the specific technical documentation. The thread and contact surfaces of the heads of bolts must be slightly oiled
or greased, so as to obtain correct nominal tightening torque.
7.7. Power circuit connections of
fixed circuit breakers
7.7.1. General recommendations
• Select the cross-section of the conductors
according to the service current and the short-
circuit current of the installation.
• Prepare special supporting insulators, near the
terminals of the fixed circuit breaker or of the
enclosure, sized according to the electrodynamic
forces deriving from the short-circuit current of the
installation.
7.7.2. Assembly of the connections
• Check that the contact surfaces of the connections
are flat, and are free of any burrs, traces of
oxidation or deformation caused by drilling or
impacts received.
• According to the conductor material and the
surface treatment used, carry out the operations
indicated in table T1 on the contact surface of the
conductor
Assembly procedure
• Put the connections in contact with the circuit
breaker terminals taking care to avoid mechanical
stresses (traction / compression) on, for example,
the conducting busbars on the terminals.
• Interpose a spring washer and a flat washer
between the head of the bolt and the connection.
• It is advisable to use bolts according to DIN class
8.8 Standards, also referring to what is indicated in
table T2.
• In the case of cable connections, strictly follow the
manufacturer’s instructions to make the terminals.
T1
T2
Bolt Recommended tightening torque (1)
Without lubricant
—
7. Installation
Bare copper Copper or silver-plated aluminium Bare aluminium
• Clean with a fine file or emery cloth.
• Tighten fully and cover the contact
• Clean with a rough dry cloth.
• Only in the case of obstinate traces of
oxidation, clean with a very fine grain
emery cloth taking care not to remove
the surface layer.
• If necessary, restore the surface
treatment.
• Clean with a metal brush or emery cloth.
• Cover the contact surfaces again
immediately with neutral grease.
• Insert the copper-aluminium bimetal
with surfaces shined (copper side in
contact with the terminal; aluminium
side in contact with the connection)
between the aluminium connection and
the copper terminal.
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