5.0 APPENDIX
68 ©2000 Xantrex Technology Inc.
Multiwire Branch Circuits (continued)
Correcting Multiwire Branch Circuit Wiring
Correcting multiwire branch circuit wiring is not an easy task. There are several approaches that
can be taken, each with its advantages and disadvantages.
Rewire existing multiwire branch circuits to conventional home run wiring. This requires a
qualified electrician (knowledgeable of multiwire branch circuit wiring) and is expensive. There
may be multiple multiwire branch circuits located throughout the structure, requiring complete
rewiring.
Add a second inverter in a series stacked arrangement. This is an expensive solution, but would
restore the original 240 VAC split-phase configuration. This solution may actually be less
expensive than having an electrician re-wire the multiwire branch circuits, plus it provides
increased power backup protection and can power 240 VAC loads.
Add a T240 Autotransformer to the output of the inverter to restore the split-phase configuration.
This is the least expensive and easiest method to correct for multiwire branch circuit wiring. Refer
to Figure 53. Using this method, half of the current is supplied to one leg of the circuit and half to
the other in a split-phase arrangement (180° out-of-phase). This will restore the original
functionality and safety to the multiwire branch circuit.
Neutral
Ground
Black–Hot
Single White–Neutral
Bare–Ground
120 VAC
120 VAC
25 A
0 A
25 A
25 A
Breaker
(Ganged)
Red–Hot
Load Center
062949-004
25 A
White–Neutral
Splice
The out-of-phase
currents subtract
at this
point
25 A
Breaker
(Ganged)
Bare–Ground
Splice
Auto-
transformer
Hot–L1
Hot-L2
White–Neutral
Neutral
Hot
120 VAC
Inverter
(or generator)
L1
L2
Figure 53
Using A T240 Autotransformer in Multiwire Branch Circuit Wiring
WARNING: UNTIL ONE OF THE SOLUTIONS ABOVE IS IMPLEMENTED, A STAND-ALONE
120 VAC INVERTER (OR GENERATOR) MUST NOT BE INSTALLED WHERE MULTIWIRE
BRANCH CIRCUITS EXIST.
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