Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 53)

Fig. 2.3-15
Example of a dimensional drawing stating the required safety clearances to conductive materials; the
safety clearances do not apply to connected, insulated conductors
Clearances between devices may also be necessary from a thermal viewpoint, in order to
ensure adequate heatflow and compliance with the operationally permissible temperatures.
These specifications are also available in the catalogs or on request. See also Section
6.1 .
2.3.10 Mounting position
Certain electrical devices such as contactors and circuit breakers may be subject to restrictions
with respect to the permissible mounting position (
Fig. 2.3-16 ) or their operational parameters
may change with the mounting position. Thus standing contactors (table-mounted), if this
mounting type is permissible at all, typically exhibit longer dropout times and are sensitive to
impacts in vertical direction. Suspended contactors (overhead position) may require higher pull-
in voltages, which pushes the lower limit of the tolerance range of the control voltage upward.
Fig. 2.3-16
Permissible mounting position of a contactor (example).
The gray zone on the side indicates the required clearance from grounded components.
Specifications on the permissible mounting positions can be found in the dimensional drawings
of the devices. With respect to the influence on the operational parameters of installation in
positions that differ from the standard position (suspended, upright), it is recommended to
inquire directly to the manufacturer.
2.3.11 Protective separation
For protection against electric shock in conjunction with the use of electronic control devices,
protection by SELV (Safety Extra Low Voltage) and PELV (Protective Extra Low Voltage) is
increasingly being chosen. The maximum voltage levels for SELV and PELV are 50 V a.c. and
120 V d.c. (with exception of special applications with lower limit values).
In circuits with SELV and PELV, all devices that are included in the circuit must be isolated from
other power circuits by insulation corresponding to that of a safety transformer. That means
double creepage distances and the next higher impulse voltage withstand level U
imp
. This
applies for example for auxiliary circuits of switchgear with respect to their power circuits
(
Fig. 2.3-17 ).
LVSAM-WP001A-EN-P - April 2009 2-25