2. Installation
Initiating Device Circuits
18
MS-4412B/MS-4424B Instruction Manual PN 15125:G1 10/22/02
Four-Wire Smoke Detector Connections
A maximum of 200mA is available from the 12 or 24VDC Resettable Power circuit on TB2 (VR terminals).
Any power that is drawn from the 12 or 24VDC Nonresettable Power circuit on TB2 (VNR terminals) must
be subtracted from available resettable power. See "Specifications" on page 12 and "Powering External
Devices" on page 21.
Note:
Refer to the Device Compatibility Document for suitable 4-wire smoke detectors.
Notes on Style B (Class B) field wiring:
1. The Power Supervision Relay coil leads must be connected to the last detector base 12 or 24VDC
screw terminals.
2. Calculation of the maximum allowable resistance in the 12 or 24VDC resettable power wiring:
Where:
XX.x
= 10.4 for 12VDC; 20.6 for 24VDC
Rmax
= maximum resistance of the 12 or 24VDC wires
Vom
= minimum operating voltage of the detector or end-of-line relay, whichever is greater, in volts
N
= total number of detectors on the 12 or 24VDC supply circuit
Is
= detector current in standby
Na
= number of detectors on the 12 or 24VDC power circuit which must function at the same time in alarm
Ia
= detector current in alarm
Ir
= end-of-line relay current
Figure 7 Typical Connection for Four-Wire Smoke Detectors
Rmax =
(XX.x - Vom)
(N x Is) + (Na x Ia) + (Ir)
–
–
+
+
–
–
+
+
TB2
IN #4
B+ B–
IN #3
B+ B–
IN #2
B+ B–
TB4
MS
44
B-
4w
ir
es
d.
cdr
12 or 24VDC Four-wire
Smoke Detectors
4.7K, 1/2-Watt ELR
Power
Supervision
Relay
(A77-716B)
Class B
Initiating Device Circuit
Control Panel
Power Circuit
