Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 171)

1.5 Nm,tight:
55.1 °C
0.5 Nm, loose:
86.6 °C
Fig. 6.1-6
Picture of a device made with a thermal imaging camera. Effect of the tightening torque on terminal
heating. The various temperatures are represented with colors. At interpretation the emission factors of
the various surfaces should be considered.
With thermal imaging cameras, the temperatures of the visible surfaces can be measured.
Overheating on the inside of a device can manifest itself in the increased temperature of a
visible surface. Thus a worn out main contact can show-up through an increase in visible
surface-temperature on the associated terminal. However, by far the most common explanation
of unexpectedly high temperature on a terminal is a loose connection.
It is useful to perform temperature-rise measurements at long intervals in order to determine
changes and establish whether these changes are due to the devices, connections or with
respect to some variation in their load.
6.2 Short-circuit withstand capacity
In accordance with IEC 60439-1 verification of the short-circuit withstand capacity of a switch-
gear assembly is mandatory from a prospective short-circuit current of 10 kA
eff
or 17 kA
pk
(peak
value) upwards. Below these limit values the withstand capacity is not stated, as the stress
generated by the forces is not regarded as critical.
For auxiliary circuits that are connected to control transformers, the limits of 10 kVA at ≥ 110 V
and 1.6 kVA at < 110 V at a minimum short-circuit voltage of 4 % apply. Below these values
verification of the short-circuit withstand capacity is not required.
It is important to note that verification of the short-circuit withstand capacity is not required for
components, where the short-circuit withstand capacity for the conditions under which they are
used in the relevant switchgear assembly has been verified by type testing. Examples of these
are: busbars, busbar supports, connections to bus-bars, input and output units, switchgear etc.
In practice, this means that type-tested devices or subassemblies (for example contactors,
motor starters, motor protective devices, bus-bar systems) can be used without further verifica-
tion of their short-circuit withstand capacity, insofar as their type test includes loading in the
given switchgear assembly.
If, for example, for a two-component motor starter consisting of a circuit breaker with motor
protection characteristic and a contactor, there is a coordination table available for 400 V at a
conditional rated short-circuit current I
q
= 50 kA, then starters from this table can be used for all
applications with I
q
≤ 50 kA without further verification of the short-circuit withstand capacity.
Manufacturer instructions, where they exist, must be observed.
LVSAM-WP001A-EN-P - April 2009 6-7