Blue usually marks neutral in IEC/UK, but in the U. Wiring rules change by country, voltage, and application. In many places that follow IEC. Wire color codes indicate the purpose of each wire in a circuit. Blue doesn't mean one thing everywhere. For typical building AC circuits (commonly up to 600 volts nominal), the NEC specifies identification rules for grounded conductors (neutral), requirements. These color codes are used for electrical distribution systems, and while some are mandatory, others are optional. This is a general reference, not a substitute for proper testing.
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