900 Series V5.1: Installation Guide, February 2000 21
3.4. DIN rail mounted units
The Series 950 DIN rail-mounted units are supplied in a standard housing that is clipped
on to a standard 35 mm DIN rail (DIN46277) or fixed directly to the enclosure using two
4 mm screws.
Connect the units by using plug-in terminal blocks that accept wires up to 2.5 mm²
diameter.
3.4.1. Isolators
3.4.1.1. Dual isolator – IU950D
Figure 17: Wiring connections (Dual isolator – DIN mount)
The Series 950 DIN-rail dual isolator provides, in one housing, two independent isolators
that sense and isolate short-circuits on Series 950 loops and spurs.
The isolators are loop-powered and are polarity sensitive. A maximum of 20 Series 950
detectors can be installed between isolators.
Under normal operating conditions, there is a low impedence between -IN and -OUT
terminals of each isolator channel so that power and signals are passed to the next base
in line.
If a short-circuit or abnormally low impedance occurs across the loop, the fall in voltage is
sensed and the isolator isolates the negative supply in the direction of the fault. When
this occurs, the yellow LED of the affected channel illuminates. The isolated section of
loop is tested using a current pulse every five seconds. The power is automatically
restored when the short-circuit is removed.
The two isolator channels are not interconnected internally, and operate completely
independently of one another.
Series 950 loop
Series 950 loop
CH 2 FAULT
CH 1 FAULT
Channel 2
Channel 1
Note: Polarity must be observed
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