conductor (green) should be united. They should be bonded to each other and to
the ground.
If this bond is present and the GFCI is still not testing properly, take action.
Possible actions include:
Changing the brand of GFCI, which may rectify
the situation.
Upgrading to a sine-wave standalone inverter. This should
be determined during the design phase and not require
correction in the field.
Multi-Wire Branch Circuits
Most standalone PV systems are connected to structures wired for standard AC
currents. Usually these buildings have more than one circuit. The NEC terms this
kind of structure a multi-wire branch circuit. They are covered in detail in
Article 100 of the NEC.
In grid-tied PV systems and standalone systems, the
multi-wire branch circuits are limited. The currents flowing
though the multi-wire branch circuits produce uneven loads.
The currents in the common neutral should be zero; other-
wise, a neutral conductor may overload. In some instances,
the NEC requires that a multi-wire branch circuit incorporate
a two-pole circuit breaker. It has to be 15 to 20 amps or
greater, depending upon the system design and loads. The
two-pole circuit breaker shuts down both circuits at the same
time when fault conditions are present, or when the circuit
breaker needs maintenance.
As a practical matter, it is generally best, even when taking
a phased approach, to size AC components more consistently
with a grid-tied PV system. Work though the details with the
owner regarding inverter sizing, number of loads, and appli-
cation of PV to the installed loads. When customers under-
stand the process and limitations, they will be more inclined
to expand the system as required while using it more safely.
Planning and Designing Standalone
Systems
Planning and designing standalone PV systems can be tricky.
Correlating energy consumption to energy supply in stand-
alone systems is crucial and generally variable. This is especially
true if the standalone system is intended to provide energy
Whether on or off grid, prepare by
installing panels that can handle all of the
loads today and into the future.
Courtesy of PerfectPower, Inc.
TECH TIPS
NEC Article 404 is very explicit
about interior switches. “Switches rated
for AC circuits ONLY shall not be used in
DC circuits.” [404.14(A)]
CHAPTER 6 Standalone PV Systems 109
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