Power Supply Calculations Overview
44 MS-2/MS-4 PN 51512:D 10/18/04
SECTION 5 Power Supply Calculations
5.1 Overview
This section contains instructions and tables for calculating power supply currents in
alarm and standby conditions. This is a four-step process, consisting of the following:
1. Calculating the total amount of AC branch circuit current required to operate the
system
2. Calculating the power supply load current for non-fire and fire alarm conditions
and calculating the secondary (battery) load
3. Calculating the size of batteries required to support the system if an AC power
loss occurs
4. Selecting the proper batteries for your system
5.2 Calculating the AC Branch Circuit
The control panel requires connection to a separate, dedicated AC branch circuit, which
must be labeled FIRE ALARM. This branch circuit must connect to the line side of
the main power feed of the protected premises. No other non-fire alarm equipment may
be powered from the fire alarm branch circuit. The branch circuit wire must run contin-
uously, without any disconnect devices, from the power source to the control panel.
Overcurrent protection for this circuit must comply with Article 760 of the National
Electrical Codes as well as local codes. Use 14 AWG (2.00 mm
2
) wire with 600 volt
insulation for this branch circuit.
Use Table 5-1 , to determine the total amount of current, in AC amperes (A), that must
be supplied to the system.
TABLE 5-1:120 VAC Branch Circuit Requirements
Device Type
Number of
Devices
Current Draw
(AC amps)
Total Current
per Device
MS-2/MS-4
or
MS-2E/MS-4E
1X
2.3
1.15
=
[ ] X =
[ ] X [ ] =
Sum Column for AC Branch Current Required =
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