SOLAR POWER SYSTEM DESIGN
makezine.com/14/primer
M
N
perfectly with the inverter, so no wires are exposed 40 underground but must be Schedule 80 above
between the 2 units. ground. Conduit expansion joints must be used with
OutBack makes an input/output bypass (IOB) trenched conduit in cold climates above ground
assembly kit designed to work with the AC breaker level, to prevent the conduit from cracking from
enclosure, specifically for grid-tie scenarios. A bypass temperature changes. All AC cable runs are required
assembly kit is a set of breakers that can be used to to have an AC disconnect at the point of entry
isolate your inverter from the grid when maintenance to any building. This disconnect can be inside or
is required. The AC loads that the inverter normally outside of the building.
powers through separate breakers get switched to I’m using another small load center to meet the
being powered by the grid. You can see the black National Electrical Code’s point-of-entry disconnect
bypass plate and set of breakers in Figure L. requirement. You can see the black wire (Figure M),
which runs to the AC In bus bar in the Flexware
AC500 box.
Connecting to the utility grid has been one of the
most confusing parts of the whole process. The NEC
2005 code has specific requirements that regulate
the amperage load on the load center’s bus bar and
conductors. See makezine.com/go/nec for details
on the NEC 2005 Residential Utility Connection
options and requirements. Again, see “Making the
Utility Connection” at makezine.com/go/wiles2.
9. GRID CONNECTION
One of the most difficult parts of this project is
configuring the solar PV system to sell power back
to the grid. It can be beyond the realm of some solar
installers and electricians alike. You must contact
your electrical utility company to obtain permission
to connect to the grid, and figure out what needs to
be done to receive any available financial incentives,
rebates, and tax credits. I also recommend showing
your plans to a licensed electrical inspector, who
can tell you what you need to do to pass inspection.
Following are a few things I learned while working
with the local electrical inspectors. When digging
a trench from one building to another, the trench
must be 2' deep. Grey PVC pipe can be Schedule
10. AC DISCONNECT
My local electric utility requires an AC disconnect
switch (Figure N) on the outside of my workshop
or house before connecting to the grid. You can
use Square D’s DU221RB 30A 120/240V AC 2-pole
166 Make: Volume 14
