and protective clothing. The PPE protect skin and face from insulation. Check out
the level of safety hazard in the attic to ensure that it is a safe working space. If
not, take the appropriate steps and action to protect the employee. Also, you
should navigate the exits. An attic is not a usable working space if it can’t support
the weight of a person without risk of falling through the ceiling. An attic also
needs plenty of lighting for employees to work safely and effectively. Make sure
that workers do not stay in an attic for long periods, especially in hot weather.
Remember that you and your workers must stay hydrated.
Photovoltaic (PV) Modules
Avoid electric shock when working with PV modules. (A module is the smallest
unit in a PV array, containing many PV cells.) This is a warning to heed, especially
when there are several PV modules connected together. High voltages of 400–600
DC are frequent in strings. When exposed to sunlight or intense artificial light,
PV panels should always be treated as “hot.” The electric current can arc between
the open wire ends on modules and anything—or anyone—that will complete
the circuit.
Potential short circuits may not blow any fuses. However, the circuits might
produce a very intense DC arc between the wires. Temperature can reach as high
as 10,000 degrees Celsius (18,000 degrees Fahrenheit). DC arcs are fire and burn
hazards. They may cause ultraviolet exposure, burns, or damage to the eyes. Arcs
may surprise installers by distracting or stunning them. This could cause them to
miss a step or lose footing.
Batteries can be the most dangerous component in a PV system. When
improperly handled or installed, bad things can and often do happen. Batteries
can store thousands of amps and discharge them in seconds. A short in the bat-
tery, a cable, or damage to a terminal can cause arcs, shocks, fires, and explosions.
In addition, batteries used in PV systems give off hydrogen and other corrosive
gases. These gaseous combinations can create problems. Corrosion or explosions
can occur as a by-product if the gases become trapped and ignited by a flame.
Proper venting and charging will reduce hydrogen concentration before the mix-
ture becomes explosive.
Triple check the voltage meter’s polarity when connecting a battery or
battery groups to complete a circuit.
Vent battery containers at the top to allow an airflow path for the hydrogen
to escape.
Place batteries in a proper containment space that can hold the entire
battery and its fluids in the event of a spill or broken container.
Keep the battery storage cabinet out of the sun, and provide moderate
temperatures as recommended by the manufacturer.
Do not place batteries directly on concrete.
Keep batteries, cables, and terminals clean.
30 ADVANCED PHOTOVOLTAIC INSTALLATIONS
Electrical equipment must not be placed above batteries.
Use electrically insulated tools to reduce shock and shorting hazards.
All tools used around batteries must be counted and removed after
installation or maintenance to reduce any accidental electrical hazards.
Treat batteries with extreme caution when installing or working on or
around them.
CODE: BATTERY SAFETY
I
nsulation of Batteries of over 250 Volts. The provisions of 480.6 shall apply to storage batteries
having the cells connected so as to operate at a nominal voltage exceeding 250 volts, and, in
addition, the provisions of this section shall also apply to such batteries. Cells shall be installed
in groups having a total nominal voltage of not over 250 volts. Insulation, which can be air, shall
be provided between groups and shall have a minimum separation between live battery parts of
opposite polarity of 50 mm (2 in.) for battery voltages not exceeding 600 volts.
480.8 Racks and Trays. Racks and trays shall comply with 480.8(A) and (B).
(A) Racks. Racks, as required in this article, are rigid frames designed to support cells or trays.
They shall be substantial and be made of one of the following: (1) Metal, treated so as to be resis-
tant to deteriorating action by the electrolyte and provided with nonconducting members directly
supporting the cells or with continuous insulating material other than paint on conducting mem-
bers; (2) Other construction such as fiberglass or other suitable nonconductive materials.
(B) Trays. Trays are frames, such as crates or shallow boxes usually of wood or other noncon-
ductive material, constructed or treated so as to be resistant to deteriorating action by the
electrolyte.
480.9 Battery Locations. Battery locations shall conform to 480.9(A), (B), and (C).
(A) Ventilation. Provisions shall be made for sufficient diffusion and ventilation of the gases
from the battery to prevent the accumulation of an explosive mixture.
(B) Live Parts. Guarding of live parts shall comply with 110.27.
(C) Working Space. Working space about the battery systems shall comply with 110.26. Working
clearance shall be measured from the edge of the battery rack.
480.10 Vents.
(A) Vented Cells. Each vented cell shall be equipped with a flame arrester that is designed to
prevent destruction of the cell due to ignition of gases within the cell by an external spark or
flame under normal operating conditions.
(B) Sealed Cells. Sealed battery or cells shall be equipped with a pressure-release vent to pre-
vent excessive accumulation of gas pressure, or the battery or cell shall be designed to prevent
scatter of cell parts in event of a cell explosion.
(NEC 2011, 480.7 – 480.10)
Reprinted with permission from NFPA 70
®
, National Electrical Code
®
, Copyright© 2010, National Fire
Protection Association, Quincy, MA.
CHAPTER 2 Essential Safety Practices for Designing and Installing PV Systems 31
..................Content has been hidden....................
You can't read the all page of ebook, please click here login for view all page.