Section VI
General Wiring Requirements
GENERAL INFORMATION
WARNING
Do not open any junction box or device enclosure
when power is applied without first de-classifying
the hazardous area.
CAUTION
Any deviation from the recommended wiring
practices can compromise system operation.
Consult the factory if different wire types or
methods are being considered.
NOTE
All wiring must be marked per NFPA 70 Article
760.
NOTE
Specific installation requirements may differ
depending on local installation practices and
compliance with third party certifications. For local
installation practices, consult the local authority
having jurisdiction. For compliance with third party
certifications, consult the appropriate appendix in
this manual for additional specific installation
requirements.
POWER WIRING
The input voltage at the field devices must be 18 vdc
minimum to ensure proper operation of the devices.
Therefore, it is important to consider both the size
(gauge) of the power wiring and the wiring distance
from the power supply. As the wiring distance
increases, larger diameter wire is required to maintain a
minimum of 18 vdc at the device.
Refer to Table VI-1 to determine the minimum wire size
needed to prevent excessive voltage drop from power
supply to device for a given current load.
To use Table VI-1, first determine the total current load
for the circuit and the maximum allowable voltage drop.
Then look under the appropriate Amp Load column to
determine the minimum wire size that will not allow the
voltage drop to exceed the maximum allowable.
For example:
What wire size is required to power ten DCUs at a
distance of 100 feet from the power supply, assuming a
24 VDC power supply and a minimum of 18 VDC
needed to power the DCUs?
Maximum allowable voltage drop is 6 VDC.
(24 – 18 = 6)
VI-1
95-8470
AWG
1 AMP LOAD
2 AMP LOAD
3 AMP LOAD
4 AMP LOAD
5 AMP LOAD
22
3.3
6.6 9.9
13.2
16.5
20
2.1
4.1
6.2
8.3
10.4
18
1.5
3.1
4.6
6.2
7.7
16
1.0
2.0
2.9
3.9
4.9
14
0.6
1.2
1.9
2.5
3.1
12
0.4
0.8
1.2
1.5
1.9
10
0.2
0.5
0.7
1.0
1.2
8
0.2
0.3
0.5
0.6
0.8
6
0.1
0.2
0.3
0.4
0.5
4
0.1
0.1
0.2
0.2
0.3
1
0.0
0.1
0.1
0.1
0.2
1/0
0.0
0.0
0.1
0.1
0.1
Table VI-1—Voltage Drop Per Pair in Volts DC per 100 Feet from Power Supply to Device
NOTES: This table is for reference only and does not replace good engineering practice.
Use Ohms Law when designing the power distribution system.
Voltage drop and wiring distance are proportional.
Consult factory for assistance with system wiring requirements.
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