Powering the MultiFlex Mounting and Powering • 9
Rule 2: Do not power an old-style MultiFlex
non-center-tapped board with a transformer
that is also powering a center-tapped device.
This means you cannot connect an old-style
MultiFlex non-center tapped board to a trans-
former that is powering a MultiFlex 16, 16AI,
8RO, 4AO, 8DO, a Gateway board, or any pre-
vious generation CPC board that uses center-
tapped power. Doing so will destroy the Multi-
Flex board.
Rule 3: The secondary of the transformer
must not be grounded on any side.
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 combina-
tion boards can be powered by one of the 50VA
or 75VA non-center-tapped transformers listed
in Table 2-1 on page 6. Figure 2-7 shows how to
wire the transformers to the MultiFlex boards.
2.3.4. 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 transformer.
Each MultiFlex board should have its 0V ter-
minal taken to a short, solid earth ground.
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:
Power Wiring Types
14 AWG Belden 9495 or equivalent
18 AWG Belden 9493 or equivalent
Table 2-3 - Power Wiring Types
14 AWG:
Feet = 0.40/(VA/24) x 0.005
18 AWG:
Feet = 0.40/(VA/24) x 0.013
(VA is the total VA rating of the I/O boards)
For example, if you had an 80 VA load:
14 AWG: 24 ft. (rounded down)
18 AWG: 9 ft.
Figure 2-8 - Power Wire Lengths
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