7SR18 Description Of Operation
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2.4 Power Supply Unit (PSU)
Several variants of the relay PSU can be ordered: -
Ordering
Option
Auxiliary Voltage Binary Input
Threshold
M 24 V DC to 250 V DC, 100 V AC to 230 V AC 19 V DC
N 24 V DC to 250 V DC, 100 V AC to 230 V AC 88 V DC
Table 2.4-1 Power Supply Unit (PSU) options
The rated auxiliary supply voltage is clearly stated on the relay fascia rating label, see Figure 2.5-2 below.
All binary inputs are polarity conscious and will not operate if the DC supply polarity is reversed. For consistency
and safety it is advised that AC connections for auxiliary supply and binary inputs are made with the Live
connection to the +ve terminal and Neutral connection to –ve.
If the auxiliary supply voltage falls below the relay minimum operate level, the PSU will automatically switch itself
off and latch out, which prevents any PSU overload conditions occurring. The PSU is reset by switching the
auxiliary supply off and on.
The relay has a non-serviceable internal 2 A 300 V T rated fuse, soldered to the PSU PCB.
2.5 Operator Interface/ Fascia
The operator interface is designed to provide a user-friendly method of controlling, entering settings and retrieving
data from the relay.
Figure 2.5-1 Relay with Transparent cover removed
The fascia is an integral part of the relay. Handles are located at each side of the relay which allow it to be
withdrawn from the relay case. The relay should not be carried by these handles.
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