Harrington Signal Tracker T8000 - Install Manual - Manual (Page 41)

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HSI #780-0867 FireSpy Tracker Installation Manual
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Appendix C. Wire Selection
C.1 General wiring guidelines
Induced noise (transfer of electrical energy from one wire to another) can interfere with the
communication and may cause false alarms. To avoid induced noise, follow these guidelines:
•
Isolate input wiring from high current output and power wiring. Do not pull one multi conductor cable
for the entire panel. Instead, separate the wiring as follows:
•
High voltage
•
Notification appliance Circuits (NAC)
•
Signal Line Circuits (SLC)
•
Network circuits
•
Relay circuits
•
Do not pull wires from different zones through the same conduit. If you must run them together, do so
for as short a distance as possible or use shielded cable. Connect the shield to the terminal earth
(RS485 terminal) at the panel. You must route high and low voltages separately.
•
Route the wiring around the inside perimeter of the cabinet. It should not cross the circuit board
where it could induce noise into the sensitive microelectronics or pick up unwanted RF noise from the
high speed circuits.
•
High frequency noise, such as that produced by the inductive reactance of a speaker or bell, can be
reduced by running the wire through ferrite shield beads or by wrapping it around a ferrite.
•
“T-tapping” and “starring” are not recommended.
C.2 Wire length calculations
Note: These calculations account for cable resistance only. Refer to the ratings of
the source circuit and installed devices to determine other parameters that
may need to be considered.
The equation below can be used to estimate maximum recommended wiring distances. The equation
assumes all of the load is at the end of the line, which is true for a single device load, but is a worst-case
scenario if you have many devices. The best case scenario, devices distributed evenly along the entire
length of the wire, results in twice the available length than the worst case scenario. A typical
configuration has a segment with no devices followed by a segment loaded with devices. The wire length
for the typical job will be somewhere between the worst case and the best case.
Eq. C-1 Worst case wire length, simple form
Vdrop
Length_w.c. = ------------------------
Idraw x (Rcable x DF2)
Length_w.c. is the worst case length of wire (distance from panel) in feet
Vdrop is the maximum voltage drop in volts. Use 2.4 to assume 10% voltage drop on a 24V circuit.
Idraw is the total current draw of the circuit in Amps
Rcable is the total resistance of the cable in ohms