Hi Folks, There's been plenty of discussion here in the past on AC wire colors and neutral. With regards to DC, NFPA 79 and UL 508 A also define BLUE for ungrounded dc control circuits and WHITE with BLUE stripe for grounded dc current-carrying control circuit conductor. EN 60204-1 defines BLACK for a.c. and d.c. power circuits and BLUE for d.c. control circuits. Machinery of course is typically comprised of AC power distribution and loads and DC controls including many sensors and actuators. Many manufacturers of 3 wire DC sensors seem to have standardized on using BROWN for DC power (I.e. 24VDC), BLUE for grounded dc current-carrying control circuit conductor (DC common), and BLACK for the signal. This seems inconsistent with the above standards. Does anyone know if there is another standard behind what the sensors are using or any reason for the discrepancy? Comments?
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