Calculations B
Shield Fire, Safety and Security Ltd.
Shield A-XT Releasing Fire Control Panel - Installation and Operation Manual SEXTCP-OM
Revision E01.00
83 of 127
Releasing-Circuit Wiring Length
The releasing-valve is dependant on sufficient releasing-voltage at the solenoid-terminals to provide actuation.
Releasing-valve actuation cannot occur when losses in the releasing circuit prevent sufficient voltage from occurring
at the solenoid-terminals. Installers must determine the maximum wire length that can safely provide operating
voltage at the solenoid terminals to negate losses of the releasing circuit.
Determine the maximum wire length that can safely operate a Fire Protection Service Valve.
To determine the maximum wire length of the releasing circuit:
Summary of Parameters
The table below summaries parameters for determining the maximum wire length (L
max
) of the circuit:
1 Calculate the minimum voltage (Vout
min
) at the EXTING. terminals of the Shield A-XT Releasing
Fire Control Panel.
2 Calculate the minimum operating-voltage (Vop
min
) of the Solenoid Release Valve (SRV).
3 Calculate the voltage-drop of the circuit (V
drop
) when the EXTING. output is at the minimum level (Vout
min
) and
when the operating-voltage of the SRV is at the minimum level (Vop
min
).
4 Calculate the maximum current of the circuit (I
max
) when the SRV operates at the minimum level (Vop
min
).
5 Determine the wire-resistance-per-foot of the cabling (R
wire
) in the circuit.
6 Calculate the maximum wire length (L
max
) of the circuit when connecting the SRV to the EXTING. terminals.
Parameter Description Equation
Vout
min
Minimum voltage at the EXTING. Output.
UL 864 specifies that the Shield A-XT
Releasing Fire Control Panel operate a mini-
mum output-voltage 85% below the nominal
rating.
Vout
min
= Vout
nominal
x 85%
Vop
min
Minimum operating-voltage of the SRV.
UL 429 specifies that the SRV operate a
minimum voltage 65% below the nominal
rating.
Vop
min
= VSRV
nominal
x 65%
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