Modules that integrate (in lieu of conventional screw connections) plugs for plug-in connectors or short wires with such connectors on them allow PV modules to be wired to strings in a safe and non-confusable manner. PV plug-in connectors (Figures 4.78 and 4.79) are available from numerous vendors.
Inasmuch as the ends of cables with PV plug-in connectors are not hazardous when plugged in, including when live, disconnect terminals are often unnecessary for systems that integrate quality PV plug-in connectors. If necessary, a string can simply be unplugged from the PV generator. Like disconnect terminals, PV plug-in connectors should only be touched with the system powered down and should never be used for switching purposes.
Figure 4.78 PV plug-in connectors sold by Multi-Contact, which was the first manufacturer to develop this type of connector (old, non-latched connector). The elements at the upper left are used to wire two strings to each other in parallel (Photo: Multi-Contact AG)
184.108.40.206.3 String Diodes
Inasmuch as string diodes are relatively vulnerable to power surges, which can occur in a storm even without a direct lightning strike, they are often dispensed with in today’s installations (see Sections 4.3 and 220.127.116.11 for further details on the sizing of and need for these devices). Fully protecting each and every string diode against such power surges is extremely expensive and is thus hardly ever done. A certain measure of protection against such surges can be integrated into a PV system through the use of diodes whose inverse voltage is twice that of the system’s open-circuit voltage VoCa. As current flows continuously through string diodes, they need to be cooled adequately. Schottky diodes are available for relatively low inverse voltage and thus are normally unsuitable for use as string diodes.