Some photovoltaic (pv) inverter manufacturers have designed and built transformer-less inverters to add to their existing line of transformer-type inverters for installation in the United States. Transformer-less inverters have been popular in Europe for quite some time. In comparison to the heavier same-wattage transformer-style inverters, they weigh much less, ultimately cost less, do not suffer the same energy losses, and are usually installed as ungrounded systems. However, some issues with transformer-less inverters must be understood, because they may affect the decision to install them or instead go with the conventional grounding-type transformer inverters. Section 690.35 of the 2014 National Electrical Code (NEC) provides requirements for the installation and application of ungrounded PV direct current (DC) source and DC output circuits. Source-circuit conductors are defined as the circuits between modules or from the modules to the DC system's common connection points, such as the combiner box. PV-output circuits are the circuit conductors between the source circuit (modules) and the inverter, such as the combiner box to the inverter.
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