Installation and Commissioning
20
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Manual SCA-340 / SCA-340-L
Example 2: Other mounting positions
For an environmental temperature of 45 °C (113 °F) and non-horizontal mounting,
using additionally a USB device with 200 mA, the power dissipation is limited to
70 %, i.e. 1.89 W. Therfore, the max. current from U
L
is:
I
L
=
0.7
P
V
– 0.7 V
×
I
USB
1 V
I
L
=
1.89 W – 0.14
W
1 V
= 1.75
A
3.2.2.5
Protective Devices of 24 V Main and Segment Supply U
M
and U
S
Surge / overvoltage: Input protective diodes (can be destroyed by permanent
overload).
Polarity reversal: Parallel diodes. In case of wrong polarity a high current is flowing
which is blowing the external fuses.
Segment supply and main supply are related to the same ground potential.
Note:
Each 24 V voltage supply must be fused externally. The power supply unit must be
capable of supplying a current four times the nominal value of the external fuse to reliably
blow the fuses in case of an error.
3.2.3
RS-485 and LON
The interface connector provides terminals for both RS-485 interfaces and (for
SCA-340-L only) the LON TP/FT-10 interface.
Fig. 3.2.3.1:
RS-485/LON Interface terminal connections