Wiring solution for Arc Fault Circuit Interrupter
Publication Date: 2015-Oct-07
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With the introduction of the Standard UL1699B, US photovoltaic inverters are equipped with an Arc-Fault Circuit Interrupter device (AFCI).
The purpose of that protection is detecting and extinguish arc-fault conditions in the input DC side, which may result from loose connection or improper disconnection of the DC power under load condition.
These devices are usually adapted to detect broad-band noise on the input Differential-Mode current of the DC input circuit.
For this reason, the risk of nuisance tripping could be significantly higher if external or internal noise sources interfere with the detector.
The detector is typically interested to analyze only Differential-Mode disturbances, but the presence of a parasitic capacitance from the DC circuits to ground may induce the circulation of a disturbed Common-Mode component overlapped to the Differential-Mode current. The detector in this case may be subjected to noise which is not related to arcing condition, and so the risk of nuisance tripping increases.
Figure 1 shows the paths of the Differential-Mode current and the Common-Mode current through the AFCI. It's evident how one half of the entire Common-Mode current flows inside the AFCI current sensor.
The total amount of current is the sum of the two Differential-Mode and the half Common-Mode components. In Figure 2 there is illustrated a proposed solution, where the return wire of the DC input runs into the AFCI current sensor accordingo...