Special (Double) Insulation (Protection Class II)

In cases where a solar generator and particularly its modules meet protection class II insulation requirements, in keeping with the current interpretation of the applicable standards it is considered to be unnecessary to implement further electrical safety measures against touch voltage, including for high- voltage and/or grid-connected systems. For a number of years now, solar modules that meet protection class II requirements have been available from numerous vendors.

That said, I find the above take on the applicable standards to be somewhat risky. Inasmuch as solar module glass is relatively thin and fragile and the active devices behind it, which exhibit hazardously elevated potential, are continuously exposed to the elements, these devices are not provided with the same level of long-term protection as for example a protection class II drill with a thick, robust-plastic power cord that is only used indoors, or outdoors in dry weather only. Hence it seems that the widespread use of PV systems, particularly in buildings, calls for an additional electrical safety barrier via elements such as the following:

• Ungrounded solar generators that are electrically isolated from the low-voltage grid (see Figure 4.87).

• Additional fault current monitoring (DC-FI) for grounded solar generators or in installations with transformerless inverters that are wired to the low-voltage grid (integrated into most such inverters nowadays).

• Physical separation as described in Section 4.5.7.2.

Updated: August 8, 2015 — 4:59 am