ABB AC 800M Manual page 175

Section 3 Configuration
To avoid the AC 800M Controller being influenced by field equipment, it is strongly
recommended that separate power supplies be installed (see
and Figure 51
Sectioning Field Equipment
If field equipment connected to an AC 800M Controller is to be sectioned into
groups – thus avoiding a power failure in one group from influencing the power to
other groups – then it is recommended to use separate power supplies for each field
equipment group.
The use of fuses in the 24 V DC distribution system is not a fail-safe measure. If a
short circuit occurs in one group, then voltage will most likely drop before a fuse
blows; consequently all groups will experience a drop in voltage.
Cable Protection
24 V DC distribution system cables must be fuse-protected. In order to allow for
overload/short circuit situations, the power supply output current is limited. Allow
the power supply an extra capacity of at least 3-4 times the rated current value of the
largest connected fuse and remember to include long cable resistance in the
calculation.
Connection Alternatives
The field equipment power supply can be connected in the same manner as that used
for connecting and powering the AC 800M units (see
Figure 62
Unit can be used to control and isolate both power supplies. Alternatively,
independent Mains Breakers can be used on each spur (see
3BSE036351-510 A
on page 148).
on page 178). However, it should be noted that the same Mains Breaker
Powering Field Equipment outside the Cabinet
Figure 61
Figure 50 on page 147
on page 177 and
Figure 62 on page 178).
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