Johnson Controls, Inc. SLC Wiring Manual —
P/N 51870:G 04/23/2009
19
Four-Wire SLC Style 6 & 7 (Class A)
Wiring Requirements
In Figure 2.1, Branches A, B, and C all begin at the SLC terminal, even though Branch B is
T-tapped.
Figure 2.1 Measuring DC Resistance of a Two-Wire SLC
2.2.2 Measuring Total Wire Length
The total wire length of all combined branches of one SLC cannot exceed the limits set forth in
each system’s instruction manual. Determine the total length in each SLC by summing all wire
segments. In Figure 2.1 above, the picture on the right shows an SLC with 3 branches. Figure 2.2
below shows the same SLC divided into segments. The total length of the SLC is determined by
adding the lengths of Segment 1 + Segment 2 + Segment 3 + Segment 4 + Segment 5. No segment
should be summed twice.
Figure 2.2 Measuring the Total Wire Length of a Two-wire SLC
2.3 Four-Wire SLC Style 6 & 7 (Class A)
2.3.1 Measuring Loop Resistance
The total DC resistance of the SLC pair exceed 50 ohms.
•
50 ohms for IFC-320, IFC2-640, IFC-640, LCM-320, LEM-320, JLIB-200A and JLIB-400.
•
40 ohms for IFC-200, IFC-300/400, and JLIB-200
Measure DC resistance as detailed and shown below:
1.
Disconnect the SLC channel B (Out) and SLC channel A (Return) at the control panel.
2.
Short the SLC at the last device and measure the resistance at SLC Out. Record resistance and
remove the short.
3.
Short the SLC at the first device and measure the resistance at SLC return. Record resistance
and remove the short.
The maximum DC resistance of the SLC is the higher of 2 and 3.
S
L
C-m
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SLC Out
Branch
Short Point
SLC Terminal
Block
B+ B–
Branch A
Branch B
Branch C
Branch A Branch B
Branch C
SL
C-
mea
s
2.
cdr
SLC Terminal Block
Segment
Two
Segment
Five
Segment
Three
Segment
Four
Segment
One