Choosing Transformer Sizes; Multiflex 16 Power Wiring; Multiflex Combination Input/Output Board Power Wiring - Emerson MultiFlex Series Installation And Operation Manual

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
board products. Refer to your site controller's
manual for VA ratings of the other I/O boards
that may be powered by one of these transform-
ers.
Unit VA
MultiFlex 16 6
MultiFlex 88, 15
88AO, 168,
168AO and
168DO
Table 2-2 - Device Power Requirements

2.3.2. MultiFlex 16 Power Wiring

The MultiFlex 16 requires connection to a
transformer with a center tap such as the 56VA
(640-0056) and 80VA (640-0080) transformers
listed in Table 2-1. The 56VA and 80VA trans-
formers have quick-connects on the primary and
secondary sides for connection to line voltage
and the MultiFlex 16 board. Figure 2-4 shows
how to make those connections. Note the center
tap connection on the secondary side (CT) must
be wired to the 0V terminal on the MultiFlex 16.
Figure 2-4 - 640-0056 and 640-0080 Transformer Wiring
Powering the MultiFlex
VAC Center
tapped?
24 Yes
24 NO
2.3.3. MultiFlex Combination Input/
Output Board Power Wiring
The MultiFlex 88, 88AO, 168, 168AO, and
168DO boards do not use a center tap. Instead,
the 0V terminal on the board should be con-
nected to a separate Earth ground.
Important! The rules that must be fol-
lowed when connecting a MultiFlex Combi-
nation I/O board to a transformer are
different depending on whether you have a
"new style" MultiFlex 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 Combination I/O
board has a green power LED located next to the
24VAC connection terminal in the upper right
corner of the circuit board (see Figure 2-5 for
reference).
24 VAC
POWER LED
MultiFlex Board
(Top Left Corner)
24 VAC
NO POWER LED
MultiFlex Board
(Top Left Corner)
Figure 2-5 - New-Style vs. Old-Style MultiFlex Board
New Style
Old Style
Mounting and Powering • 7