SMA SUNNY BOY 3800-US - Exchanging PV String Fuses Within the SMA DC Disconnect

SMA America, LLC Maintenance
Installation Guide SB30-40US-IUS103030 85
10.5.2 Exchanging PV string fuses within the SMA DC Disconnect
1. Turn OFF all AC and DC switches and/or breakers.
2. Wait for at least 5 minutes.
3. Open the SMA DC Disconnect as described in section 6.5”Opening the SMA DC Disconnect”
(page37).
4. Exchange the fuses having regard to the information on the next page.
5. Close the SMA DC Disconnect.
6. Turn ON all AC and DC switches and/or breakers.
PV string 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
®
requirements. Be sure to consult with
your PV module manufacturer for appropriate PV string fuse ratings.
The minimum size of fuses and wiring are calculated using the Short Circuit Current Rating (Isc) of the
PV module. The National Electrical Code
®
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.
If the Isc of the PV module equals 6.9 Adc, then the PV string fuse size is determined by
1.56 x 6.9 = 10.76. The next standard fuse size would be a 12A, 600Vdc fuse.
The fuse size per string must not be greater than the maximum fuse size rating of the PV
module. Refer to the data sheet of the PV module. If no maximum fuse size is indicated,
contact the PV module manufacturer.