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7.6. Power circuit connections of fixed
circuit-breakers
7.6.1. General recommendations
– Select the cross-section of the conductors
according to the service current and the short-
circuit current of the installation.
– Prepare special pole insulators, near the ter-
minals of the fixed circuit-breaker or of the
enclosure, sized according to the electrody-
namic forces deriving from the short-circuit
current of the installation.
7.6.2. Assembly of the connections
– Check that the contact surfaces of the con-
nections 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 opera-
tions indicated in table T1 on the contact sur-
face of the conductor.
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 treat-
ment.
Bare aluminium
– Clean with a metal brush or emery cloth
– Cover the contact surfaces again im-
mediately with neutral grease.
– Insert the copper-aluminium bimetal with
surfaces shined (copper side in contact
with the terminal; aluminium side in con-
tact with the connection) between the
aluminium connection and the copper
terminal.
Assembly procedure
– Put the connections in contact with the circuit-
breaker terminals taking care to avoid mechani-
cal stresses (traction / compression) on, for
example, the conducting busbars on the ter-
minals.
– Interpose a spring washer and a flat washer
between the head of the bolt and the connec-
tion.
– 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 fol-
low the manufacturer’s instructions to make the
terminals.
T2
Bolt
M6
M8
M10
M12
M16
Without lubricant
10.5 Nm
26 Nm
50 Nm
86 Nm
200 Nm
Recommended tightening torque (1)
With lubricant (2)
4.5 Nm
10 Nm
20 Nm
40 Nm
80 Nm
(1) The nominal tightening torque is based on a fric-
tion 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 surfaces in con-
tact with the lubricated heads.
Take into account the deviations from the general
Standards table (for example, for systems in con-
tact or terminals) as foreseen in the specific techni-
cal documentation.
The thread and surfaces in contact with the heads
of bolts must be slightly oiled or greased, so as to
obtain correct nominal tightening torque.
T1
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