16
4.5.7. Power circuit connections
of fixed circuit-breakers vmax
– 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 electrodynamics forces deriving from the short-circuit
current of the installation.
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.
earthing
For the fixed version circuit-breaker, carry out earthing by
means of the special screws marked with the relative symbol
(see fig. 10).
Clean and degrease the area around the screw to a diameter
of about 30 mm and, on completion of assembly, cover the
joint again with Vaseline grease.
use a conductor (busbar or cord) with a cross section
conforming to the Standards in force.
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.
bare copper
– Clean with a fine file or emery cloth.
– Tighten fully and cover the contact surfaces with
5RX Moly type grease.
Copper or silver-plated aluminium
– 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.
bare aluminium
– 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.
T2
bolt
Recommended tightening torque (1)
without lubricant
with lubricant (2)
M6
10.5 Nm
4.5 Nm
M8
26 Nm
10 Nm
(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.
T1
