4 • MultiFlex CUB-II and CUB-TD I&O Guide
026-1705 Rev 7 06-APR-2010
2.3.1. Choosing Transformer Sizes
In most site installations, a single trans-
former will power multiple devices. Choose a
transformer with a VA rating large enough to
power all devices that will be attached to it.
Table 2-2
gives the VA ratings of the MultiFlex
CUB in conjunction with other MultiFlex
boards. Refer to your site controller’s manual for
VA ratings of the other I/O boards that may be
powered by one of these transformers.
2.3.2. MultiFlex CUB Power Wiring
The MultiFlex CUB boards do not use a cen-
ter tap. Instead, the 0V terminal on the board
should be connected to a separate earth ground.
Important! The rules that must be fol-
lowed when connecting a MultiFlex CUB
board to a transformer are different depend-
ing on whether you have a "new style" Multi-
Flex board with an isolated power supply (all
MultiFlex boards shipped after November 1,
2002) or an "old style" MultiFlex board (all
MultiFlex boards shipped before November
1, 2002).
A new-style MultiFlex board has a green
power LED located next to the 24VAC connec-
tion terminal in the upper right corner of the cir-
cuit board (see
Figure 2-4
for reference).
If there is a green power LED next to the
connector, your MultiFlex is a
new-style Multi-
Flex --
refer to
Section 2.3.2.1., New-Style Mul-
tiFlex CUB Boards (With Isolated Power
Supply)
for power wiring instructions.
If there is no green power LED next to the
connector, your MultiFlex is an
old-style Multi-
Flex
-- refer to
Section 2.3.2.2., Old-Style Multi-
Flex CUB Boards (No Isolated Power Supply)
for power wiring instructions.
Unit
VA
VAC
Center-
Tapped?
MultiFlex 16
6
24
Yes
MultiFlex 88,
88AO, 168,
and 168AO
15
24
NO
MultiFlex RTU
15
24
NO
MultiFlex CUB
15
24
NO
Table 2-2 - Device Power Requirements
Figure 2-4 - New-Style vs. Old-Style MultiFlex Board
POWER LED
New Style
MultiFlex Board
(Top Left Corner)
NO POWER LED
Old Style
MultiFlex Board
(Top Left Corner)
24 VAC
24 VAC
