SMA DC Disconnect Switch For SB 3300-U - Manual (Page 13)

SMA America, Inc. Wiring
Installation Guide DC-Discon-U-11:SE4406 7
3 Wiring
NOTE: Use only the hole templates that are in the DC Disconnect for
making entry holes in the enclosure of the DC Disconnect.
WARNING: All electrical installation must be done in accordance with
the National Electrical Code ANSI/NFPA 70, local building codes and
the requirements of the authority having jurisdiction.
WARNING: PV arrays produce electrical energy when exposed
to light and thus create an electrical shock hazard.
3.0.1 General Information on Wiring
The output wiring terminal blocks are rated for 14 to 6 AWG wire sizes. The size of the
output conductors should be made in accordance with NEC Article 310. Conductor
size should be compensated for temperature and voltage drop considerations. Be sure
to use wire with insulation properly rated for the installation environment.
3.0.2 Fuse Sizing
In any electrical system, fuses are used to protect wiring and equipment from excessive
currents that can cause damage, heating or in extreme cases even fire. If the fuse rating
is too small it could open during normal operation. If the fuse rating is too large, it
cannot provide the needed protection. In PV systems, the minimum and maximum size
of the series fuse is determined by the electrical ratings of the PV module as well as by
UL and National Electrical Code (NEC) requirements. Be sure to consult with your PV
module manufacturer for appropriate fuse ratings.
The minimum size of fuses and wiring are calculated using the Short Circuit Current
Rating (Isc) of the PV module. The NEC requires that all fuses and wiring be sized for
a minimum of 1.56 times the Isc of the PV module used in the system.
The proper size PV string fuse is determined by calculating 1.56 x Isc (of the PV module)
and then rounding up to the next standard fuse size.
Example:
If the Isc of the PV module equals 6.9 Adc, then the fuse size is determined
by 1.56 x 6.9 = 10.76. The next standard fuse size would be a 12A,
600Vdc fuse.
WARNING: The string fuse size must not be greater than the maximum
fuse size rating of the PV module.