companies will finance an off-grid home. Those that will, typically require some
form of proof that the system is reliable enough to power the home during the life
of the mortgage.
Buildings have to comply with the NEC if they are permitted or sold. The
local authority having jurisdiction (AHJ) will typically inspect the building, and
has the ultimate authority on what is required. Its inspectors interpret the Code as
their experience directs.
Standalone PV system installers may be asked to install a service disconnect
to satisfy NEC Article 230.79. The Code requires that you first of all size the
system for the predetermined loads as presented. To quote the Code: “The service
disconnecting means shall have a rating not less than the calculated load to be
carried, determined in accordance with Part III, IV, or V of Article 220, as appli-
cable.” Planning ahead can reduce future problems. The PV system can easily be
united with a grid power source if one becomes available, and the customer
wishes to do so in the future. More important, a PV system should exceed the
existing Codes and be integrated into a structure so that the PV system is the
utility provided and nothing less.
Interior DC Wiring and Receptacles
All wiring used in PV systems has to observe the NEC. That includes interior
wiring. “The bare grounding conductor in such a cable must not be used to
carry current and cannot be used as a common negative conductor for combina-
tion 12/24-volt systems.” [NEC 2011, Article 334.108]
In a residence wired for DC and AC, separate conductors, conduits, switches,
and outlets will be required. This extra expense will probably offset any dollar
savings through efficiency that might have been achieved by using DC power.
Smoke Detectors
Smoke and fire detectors are required in all buildings. Most
building codes state that detectors should be hard-wired into
the AC power. For DC-only PV systems, this can be a problem.
There are two solutions:
Battery-operated smoke and fire detectors
Voltage regulator to drop the PV system voltage and current to the level
required by the detector(s)
Ground-Fault Circuit Interrupters
Some inverters cause ground-fault circuit interrupters (GFCI) to function
improperly. Test the GFCI. If the GFCI still does not operate as expected, examine
the conductors. The neutral conductor (white) and the mechanism-grounding
NOTE
Do not use sockets and plugs on PV
equipment. They do not conform to
NEC guidelines.
108 ADVANCED PHOTOVOLTAIC INSTALLATIONS
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