System calculations
EST3 Installation and Service Manual B.21
SAC bus power
This topic provides information to help you determine whether:
A power supply must be added to the SAC bus
Adequate voltage will be available to CRCs and KPDISPs on the
SAC bus
The standby battery in each CRC is properly sized
Determining the need for a remote power supply
The need for additional power is dictated by the current drawn
by the devices on the SAC bus. Each 3-PPS/M can supply a total
of 7 A through two 3.5 A outputs. Each SAC line can therefore
draw a maximum of 3.5 A. This consists of the current drawn by
the CRCs and KPDISPs plus any readers, strikes, or maglocks.
If the load on the 3-PPS/M supply is greater than 3.5 A, you’ll
need to split the devices over two SAC busses, or add a remote
power supply.
To determine the total load on the 3-PPS/M:
1. Complete Form A (below) to calculate the system alarm and
standby load current.
2. Total the columns to determine the Total Alarm Load and
Total Amp Hours. These two totals will be used in later
calculations.
3. If the Total Alarm Load is greater than 3.5 A, the devices
must be divided between two SAC busses, each with a
separate supply—OR—a remote power supply must be
installed.
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