Power Wire Gage Selection - Emerson E2 Einstein Manual

5 Power Wire Gage Se-
lection
The gage of wire used to connect networked
devices to the transformer secondary also plays a sig-
nificant part in noise reduction. Most CPC control-
lers and I/O devices are powered by 24VAC
transformers. Power wiring from the transformer sec-
ondary should be either 18AWG, 16AWG, or
14AWG, depending upon the total wire length to all
devices and the total VA of all devices powered.
To determine the correct wire gage to use:
1. Add together the VA ratings of all devices that will be
powered by the transformer. Table 5-1 shows the VA
devices for the E2 controller and the most common
RS485 I/O and Echelon devices used in an E2 control
system.
Controller
E2 40
16AI 5
8RO 15
4AO 10
8DO 18
8IO/ARTC 18
MultiFlex 16 6
MultiFlex I/O 15
(except ESR)
ESR8 80
MultiFlex ESR 80
TD3 4
Gateway 5
Table 5-1 - VA Ratings for CPC I/O Devices
2. Use the total VA calculated in step 1 in the following
equations to determine the maximum wire length
allowable for each wire gage:
 
• 14AWG: 1200 VA
  
• 16AWG:
750 VA
6 • E2 Controller Wiring Practices
Center
VA VAC
Tapped?
24 No
24 Yes
24 Yes
24 Yes
24 Yes
24 No
24 Yes
24 No
24 No
24 Yes
24 No
24 Yes

(feet)
(feet)
  
• 18AWG:
462 VA
3. Estimate the total length of wire necessary to power
the devices, measured from the transformer secondary
to the last device that will be connected. Using the
maximum wire lengths calculated in step 2, choose a
gage of wire whose maximum wire length is longer
than the total length of wire you will be using.
Example: A 24VAC transformer will be used
to power three MultiFlex 168AOs. The total
length of power wire needed is 15 feet. Since
the total VA of the three MultiFlex boards is
45VA, 18AWG wire may not be used, since
462 / 45 = 10.2 feet maximum. 16AWG wire
and 14AWG wire may both be used, since
with 45VA these wires would have maximum
distances of 16.7 ft. and 26.7 ft. respectively.
(feet)
026-1903 Rev 4 19-APR-2010