Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 54)

Fig. 2.3-17
Protective separation between power and control circuits
This is usually achieved by a reduction in the rated operational voltage. This means that for
example a contactor suitable for 690 V can be used at 400 V in SELV and PELV circuits. The
approval of SELV and PELV circuits requires design features that guarantee that protective
separation is maintained even in the event of faults (for example broken parts). When selecting
switchgear for SELV and PELV circuits attention must be expressly paid to the declaration of
protective separation at the respective operational voltage.
2.3.12 Site altitude
The site altitude and hence the air density play a role with respect to the cooling conditions, the
dielectric withstand voltage and electric arc extinction. A site altitude of up to 2000 m is consid-
ered as normal in accordance with IEC 60947. For higher altitudes, some performance data of
the devices must be reduced. With power electronics devices in many cases load reductions
already apply from 1000 m. In the product catalogs specifications should be found about the site
altitudes on which the performance data is based.
For contactors, bimetallic thermal overload relays and circuit breakers with bimetallic tripping
mechanisms, approximate values for the reduction of ratings at altitudes above 2000 m are
provided in
Tab. 2.3-6 .
Altitude above sea level [m]
[ft]
2000
6600 3000
10000
4000
13000
5000
16500
Contactors
Reduction factor for I
AC-1
n·I
e
1.0 0.95 0.9 0.85
up to 415 V n·I
e
1.0 0.95 0.9 0.85
up to 500 V n·I
e
1.0 0.93 0.85 0.78
Reduction factor
for I
AC-2
, I
AC-3
, I
AC-4
up to 690 V n·I
e
1.0 0.87 0.77 0.65
Bimetal overload relays 1)
Adjustment factor on the
rated operational current of
the motor 2) n·I
e
1.0 1.06 1.11 1.18
1) Also applies for circuit breakers with bimetal tripping mechanisms. The trip characteristics of electronic protective
relays usually do not change with the site altitude
2) Reduction of the rated operational currents of motors in relation to the site altitude in accordance with specifica-
tions of the motor manufacturer to be considered additionally
Tab. 2.3-6
Correction factors for applications at altitudes over 2000 m
2.3.13 Shock and vibration
Low-voltage switchgear is designed and tested for loading by shock and vibration for normal
industrial usage. This includes the usual stress in operation, for example, as a consequence of
vibrations during switching of contactors.
LVSAM-WP001A-EN-P - April 2009 2-26