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Over-Current Protection
Each solar PV AC module will supply a small increment of
240 VAC electrical current (up to 0.9 amps). The number of
modules is limited to 17, so that no more than 15 amps is
supplied to the HVAC outdoor unit. Each microinverter
automatically limits its output current to its 0.9 amp
nameplate value. This upper limit on the number of modules
that can be used is compatible with the branch circuit
ampacity of the smallest (1.5-ton) Dave Lennox
Signature
®
Collection (DLSC) outdoor units. The Lennox® Sub-Panel
for the SunSource
®
outdoor unit has a 20 amp circuit breaker
for dedicated over-current protection of the solar power
system and branch conductors from the modules to the
outdoor HVAC unit.
Photovoltaic
Module
Microinverter
Lennox
[
Solar Sub
−
Panel
Kit
Figure 3. Components
Codes and Permits
U.S. AND CANADA CODES
In almost all United States jurisdictions, the NFPA 70
National Electrical Code
(NEC) will be cited as the authority
for electrical inspections.
In Canada, the Canadian Electrical Code (CE Code). Article
690 of the NEC covers requirements for solar photovoltaic
systems. There are a number of important requirements
regarding solar PV systems. A licensed electrician who is
knowledgeable about NEC Article 690 should supervise the
electrical installation. Because the system does not involve
high-voltage DC wiring, most of the wiring details will be
familiar: wire sizing, working space (110.26) around
electrical equipment, etc.
A few details will be new because the
system is utility-interactive:
D
The current flow on the HVAC
branch circuit is bi-directional.
Check to ensure that the HVAC
breaker in the distribution panel is
suitable for back feed. If it is not
marked with LINE and LOAD, then
it is okay.
D
HVAC breaker cannot be GCFI or
arc-fault-type breaker.
D
Route from the roof mounted solar power junction box
to vicinity of outdoor HVAC unit.
D
Install service disconnect labels (provided).
D
Connect HVAC branch circuit and solar circuit conduits
to solar sub-panel.
Main breaker plus feedback breaker less than or equal to 1.2
times bus rating.
D
Feedback breaker = 20 amp
D
Assume main breaker = bus rating (most conservative
case)
D
Solving equation for minimum main breaker rating
yields: 100 amp
