Undersized component

An undersized component is a part picked at the design stage with too little capacity for the current it must carry. Examples are a bypass diode or a DC cable that is too small for the job. An undersized bypass diode can fail as an open circuit because it cannot handle a continuous flow of current. Diodes that run hot all the time fail more often, and this can happen when partial shading is frequent. A failed bypass diode can cause substring loss, overheating, reverse-bias stress, arcing risk and lower module output. Open-circuit diode failures usually go undetected. Check for them with IV curve signatures, infrared thermography, inspection for burn marks and junction box checks. For cables, check with visual inspection, insulation resistance testing, thermal inspection and string current comparison. Replace damaged runs and confirm the insulation is intact after the repair. Where diodes have failed, replace the affected modules or qualified diode assemblies, fix the mismatch or shading that caused them, and confirm the string behaves normally after the repair.

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• sentence 5: support check: partial - Passages say open circuit failures are normally not detected (not 'usually undetected' exactly, fine), and list detection methods, but the methods are for open or shorted diodes generally, not specifically for open-circuit ones. -->