Confusing specification sheets and wiring diagrams can lead to instances of incorrectly wired DC isolators, so GSES has produced a clarification document for solar installers. A sample of this article is provided below; read the full PDF on the GSES website.
DC Isolators: What are the Manufacturer’s Specification Sheets Really Telling You?
Solar photovoltaic (PV) systems use rotary DC isolators with multiple current and voltage ratings more commonly than DC rated circuit breakers. However, the flexibility of these DC isolators introduces instances of incorrect wiring when manufacturer’s specifications are misunderstood, resulting in DC isolators being underrated for the PV system installed.
Determining isolator rating
Many isolator products have four to eight poles per isolator: the isolator ratings will vary according to the current and wiring configuration. It is important to correctly match the isolator rating to the wiring configuration.
Consider the two wiring configurations shown in Figure 1 and Figure 2.
Figure 1: Schematic and photo showing a single pole of the isolator used per string conductor.
Figure 2: Schematic and photo showing two poles in series used per string conductor.
The isolator rating for each string conductor individually should be at least the PV array maximum voltage. In Figure 1, only one pole of the isolator is connected to each string conductor. Therefore, the isolator’s single pole voltage rating at the current requirement must be greater than the array’s maximum voltage as calculated. In Figure 2, two poles are connected in series to each string conductor. In this example, the voltage rating of the isolator having two poles in series must be greater than the array’s maximum voltage.
Read the full PDF article on the GSES website.