Calculations B
Shield Fire, Safety and Security Ltd.
Shield A-XT Releasing Fire Control Panel - Installation and Operation Manual SEXTCP-OM
Revision E01.00
84 of 127
Sample L
max
Calculation
The example calculation below illustrates the method for determining the maximum allowable wire length from the
EXTING. output to a Solenoid Releasing Valve (SRV).
Determine the maximum wire length (L
max
) of the circuit from the EXTING. terminals to an authorized SRV where,
• The circuit connection is provided with 18 AWG solid copper wire.
• The maximum power rating for the SRV (WSRV
max
) is 9.11 Watts.
• The nominal output-voltage for the Shield A-XT Releasing Fire Control Panel (Vout
nominal
) is 24 VDC.
• The nominal operating-voltage for the SRV (VSRV
nominal
) is 24 VDC.
• The EOL diode provides a voltage drop (
V
EOLD
) of 0.7 VDC
To determine the maximum wire length (L
max
) of the SRV circuit:
Parameter Description Equation
V
drop
Allowable voltage loss of the circuit between
the voltage source and the SRV.
V
drop
= Vout
min
- Vop
min
- V
EOLD
I
max
Maximum current of the circuit when the SRV
is operating at minimum level.
I
max
=
WSRV
max
/
Vop
min
R
wire
Resistance-per-foot of the wire gage
specified for the circuit.
Reference the wire gauge resistance table
provided in this section.
L
max
Maximum wire length of the circuit. L
max
= 1/2 [ (V
drop
/ I
max
) / R
wire
]
1 Calculate the minimum voltage (Vout
min
) at the EXTING. terminals when the voltage output is 85% of the
nominal rating.
where,
Vout
min
= Vout
nominal
x 85%
= 24 VDC x 0.85
Vout
min
= 20.4 VDC
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