36
6.2.7  MTL5526 - Switch Operated Relay
Two channel, output
The MTL5526 enables two separate IS circuits in a hazardous area to be relay-contact controlled 
by two on-off switches or logic signals in a safe area. Applications include the calibration of 
strain–gauge bridges; changing the polarity (and thereby the tone) of an IS sounder; the testing 
of IS fire alarms; and the transfer of safe-area signals into an annunciator with IS input terminals 
not segregated from each other. 
The output–relay contacts are certified as non–energy–storing apparatus, and can be connected 
to any IS circuit without further certification, provided that separate IS circuits are such that 
they would remain safe if connected together.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
IS relay
IS relay
1
Vs–
Vs+
20 to 35V dc
+
–
2
+
–
Control
20 to 
35V dc
+
–
+
–
Loop
powered
Contact
inputs
All contacts shown 
in normal position
(relays de-energised)
1
2
Sw4
Hazardous area
Safe
 are
a
Terminal Function
1 IS relay output 1 (normally open)
2 IS relay output 1 (normally closed)
3 IS relay output 1 (common)
4 IS relay output 2 (common)
5 IS relay output 2 (normally closed)
6 IS relay output 2 (normally open)
8 Relay 1 control +ve
9 Relay 1 control –ve
10 Relay 2 control +ve
11 Relay 2 control –ve
13 Supply –ve
14 Supply +ve
OFF position
ON position
1 2 3 4
Table 6.3:
Switch settings
for modes
Mode Function SW1 SW2 SW3 SW4
Contact/Logic
Input
2 ch Off On On On
1in2out  On On On On
Loop Powered
2 ch Off Off Off Off
 
Figure 6.16: 
Top label  
for MTL5526