The PV output circuit’s conductor should be grounded, and at one point only.
The most critical factor in PV system installation is that PV systems never
stop working during daylight hours. Even when the system is offline, the solar
panels are still producing energy.
One of the biggest hazards for workers is thinking that the system is grounded
when system maintenance is performed. It may not be grounded! “Ungrounding”
occurs frequently during inverter maintenance. In order to prevent this, PV
equipment and PV systems need continuous grounding mechanisms in place:
fail-safes for just in case. One way to do this is to install jumpers for PV equip-
ment and output conductors during inverter removal. NEC Article 690.48 and
690.49 address the conditions for jumpers.
Definitions
NEC Article 200 deals with grounding details. Grounding limits voltages from
surges, lightning, and accidental contact with lines that have higher voltages.
Lightning causes indirect effects in the area surrounding a strike, not just at
the point where it hits. During thunderstorm near-lightning strikes, the array can
act as a receiver. The array receives a coronal discharge from the lightning. The
discharge sends an electro magnetic force (EMF) through the PV system and can
damage the system. Proper grounding can offset some of these effects.
Grounding makes the earth the common reference point and stabilizes volt-
ages. Also, the path facilitates the work of overcurrent devices.
Here are a few important terms in order to understand the NEC on grounding:
An item or system that is grounded is connected to the earth or another con-
ducting body that serves the same purpose.
A grounded conductor is a wire that carries current and is grounded; this is
usually marked with white.
A grounding conductor does not normally carry current. Grounding con-
ductors connect equipment and grounding circuits to grounding systems; they
are usually marked with green or left as bare copper.
A grounding electrode conductor is a bare copper wire that connects the
equipment grounding conductor and grounding conductor to the grounding
electrode.
An ungrounded conductor is a conductor that is not connected to the
ground but does carry current.
System Grounding
In systems with two wires, connect one wire to the ground. This is called system
grounding. The NEC specifies that all systems over 50 volts must be system
grounded. [690.41] System grounding is usually the most cost-effective grounding
method and is common in systems under 50 volts as well.
192 ADVANCED PHOTOVOLTAIC INSTALLATIONS
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