6 • MultiFlex CUB-II and CUB-TD I&O Guide
026-1705 Rev 7 06-APR-2010
Verify that neither side of the transformer
secondary is connected to earth ground before
powering the old-style MultiFlex board. A
grounded secondary will damage the MultiFlex
board.
In addition, the old-style MultiFlex CUB
boards can be powered by one of the 50VA or
75VA non-center-tapped transformers listed in
Table 2-1 on page 3
.
Figure 2-6
shows how to
wire the transformers to the MultiFlex boards.
2.3.3. Wire Types and Maximum Dis-
tances
For powering I/O boards, use only the listed
wire types from
Table 2-3
. Three-conductor non-
shielded cables are the recommended wire for
connecting between the center-tapped trans-
former and the I/O boards. Shielded cable should
not be used for power wiring. The center tap
should be wired with the third conductor to earth
ground at the controller. (Use 14AWG and keep
the length of wire short. Less than six inches is
preferred).
The wire length from the transformer and the
number of boards connected to the same wire
determines the type wire gauge used. In most
cases, the distance between the I/O boards and
the transformer that supplies power to them is
not enough to be concerned with. But it is very
important not exceed this maximum wire length
or the boards will malfunction.
Use these formulas to determine if the wire
gauge you are using fits within specification:
Sensors requiring 24VAC can be powered
from the same transformer powering the input
board as long as the resulting total load of both
the input board(s) and the sensor(s) connected to
the transformer does not exceed the trans-
former’s VA rating, and the sensors have an iso-
lated power supply. If the sensors do not have an
isolated power supply, they could be damaged if
connected with center-tapped or grounded sec-
ondary transformers.
Power Wiring Types
14 AWG
Belden 9495
18 AWG
Belden 9493
Table 2-3 - Power Wiring Types
14 AWG:
Feet = 1920/VA
18 AWG:
Feet = 739/VA
(VA is the total VA rating of the I/O boards)
For example, if you had an 80 VA load:
14 AWG: 24 ft
18 AWG: 9 ft (rounded down)
Figure 2-7 - Power Wire Lengths
