DC PV
In a PV system, the source of energy is usually considered to be the PV module, and PV modules
have operating currents (Imp for maximum power current) in the 2 to 12 amp range depending on
the size of the cell in the module and the configuration of the internal PV module wiring. Note
that these currents are increasing as module size increases and cell technology improves. Modules
are typically connected in series strings where the operating current of the string remains the
same as that of an individual module, but the string voltage increases to maximums as high as
600, 1000, and in some newer utility-scale systems 1500 V. The strings of modules are
connected in parallel to increase the operating current and on larger utility-scale systems, these
combined string and subarray currents may reach 1000 A or higher
AC Utility
In the typical ac circuit in a residence or commercial building, the utility provides high levels of
energy from the local distribution system. The available fault currents from a utility service are
substantial compared to the typical fault currents that are available in a PV system. Molded case
circuit breakers used in ac load centers both at the branch circuit level and the main breaker level
have interrupt capabilities of 10,000-A; 22,000-A; 65,000-A and higher. Fuses used on these
circuits have interrupt capabilities even higher to deal with the very high available fault currents
from large distribution transformers.