Document #15668 Rev. I 04/20/98 P/N 15668:I
29
Wiring the Signaling Line Circuit
Style 4 Wiring and T-tapping
T-tapping of the SLC loop wiring is allowed for 2-wire (Style 4) configurations. The total resistance of any branch
cannot exceed 40 ohms. Measure the resistance as illustrated below. The total wire length of all combined branches
cannot exceed 10,000 feet (3,000 m).
Style 6 Wiring
T-tapping of the SLC loop wiring is not allowed for Style 6 configuration. The total resistance of the complete wire
run cannot exceed 40 ohms and total length cannot exceed 10,000 feet (3,000 m). Measure the resistance as illus-
trated below.
FIGURE 2-9:
Style 4 T-tapping and Branch Resistance
1 2 3 4 5 6
T
B
6
A B B+ A+ B- A-
Shield
Branch C
Branch D
Branch E
Branch B
Loop Out
Communication Loop Out
Branch Resistance
With power removed, short the termination
point of one branch at a time and measure
the DC resistance from the beginning of the
loop to the end of that particular branch.
The total resistance from panel to each
branch end cannot exceed 40 ohms. Repeat
this procedure for all remaining branches.
For Each Loop:
Add the lengths of all the
branches on one loop. This sum
cannot exceed 10,000 feet
(3,000 m) using 12 AWG (3.25
mm
2
) twisted, shielded wire.
Branch
In this example: Branch A + Branch B + Branch C + Branch D + Branch E = 10,000 feet (3,000 m) or less
Communication Loop Out
FIGURE 2-10:
Style 6 Wiring Requirements
1 2 3 4 5 6
T
B
6
A B B+ A+ B- A-
Shield
Loop Out
Return Loop
No T-tapping
Total length of the Communications Loop pair cannot exceed
10,000 feet (3,000 m) using 12 AWG (3.25 mm
2
) wire.
Communication Loop Return
DC Resistance of the Communications Loop pair
cannot exceed 40 ohms.
With power removed, disconnect Loop Out and
Return at the control panel, short the two leads of
Communications Loop Return and meter Loop Out.
B+ and B- = Output Loop
A+ and A- = Return Loop
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