Loop Length Calculator

Pertronic Analogue Addressable Loop Length Calculator

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Loop Number:
Site Name:
Site Address:
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Items Max per Loop No of units Unit
Apartment Module40 7 mA0 mA
Loop Relay24 6 mA0 mA
Loop Responder (Loop Powered)11 27 mA0 mA
Loop Responder (Ext Powered)11 7 mA0 mA
Conventional Smoke Detectors ++999 0.05 mA0 mA
Analogue Modules99 0.35 mA0 mA
Analogue Detectors  (F100A = 99 max)159 0.35 mA0 mA
Isolate Timer Module49 10 mA0 mA
PS2 Sounder 24V999 0.004 mA0 mA
Fan Controller, Fan Relay49 15 mA0 mA
PSB Sounder  (F100A = 99 max)159 1.5 mA0 mA
WST-XX-N Wall Mount Strobe99 0.45 mA0 mA
6500S Analogue Beam99 2 mA0 mA
Enter alarm current in mA. (1 detector = 6.5 mA)   
Total Current = TQmax Load OK65 mA
Twisted Pair Cable Size mm2
Maximum Loop Current: MUST NOT Exceed350 mA
Minimum Panel Loop Voltage22.8 Volts
Minimum Working Loop Voltage15 Volts
Maximum Loop Volt Drop = VD7.8 Volts
Cable Resistance Ω/m 0.01584 Ω/m
Maximum Allowable Loop Cable Resistance, Load Spread Evenly = 2 x (VD/TQmax) **50 Ω
Maximum Allowable Loop Cable Resistance, Load at end = VD/TQmax **50 Ω
Maximum Cable Loop Length Must Not Exceed2500 Meters
Maximum Loop Length (m) - Load Spread Evenly Over Loop2500 Meters
Maximum Loop Length (m) - Load at end of Loop2500 Meters

** To measure Analogue Loop Cable Resistance:
a) short the cable pair at one end.
b) bypass all isolators to ensure continuity (link +ve in to +ve out).
c) measure the resistance across the two conductors - red to black.

++ Include only Conventional Smoke Detectors connected to Loop
     Powered Interfaces such as Loop Responders.
2500 m
2500 m
65 mA
65 mA
Loop Calculator