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Originally Posted by David Dunlop
The bank of input terminals down the right side of the switchboard all have red, positive leads fitted to negative terminals and black negative leads fitted to positive leads and when I compare to the circuit diagram, not even the correct input terminal pairs have been connected correctly. David
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Idle thought: was it wired/rewired by a German?
(The German standard for DC wiring used Red for Earth and Black for Power, based on the original telephone and telegraph polarity where the signal wire in a Central Battery system was supplied with negative voltage to remove the risk of electrolytic corrosion, and the common Earth used a red (or brown) insulator on the top of each pole, connected to a substantial earth electrode that wouldn't be bothered by a bit of corrosion.)
The magic phrase is "Let the cat out of the bag at the CAThode" - metal ions have a positive charge so are attracted to the negative electrode, so a ground current wouldn't strip metal from the signalling wire, only the "earth return" that was much easier to replace. (Also the principle of "Cathodic Protection" on ships: zinc or magnesium electrodes are higher in the electrochemical series than iron or copper (Let alone Lead!), so will always be positive with respect to the actual vessel and will be preferentially dissolved.)
Galvanized iron (e.g. wriggly tin roofing) is the same principle, and you have to lose a LOT of the zinc protective coating before the exposed steel begins to rust. Tin cans have the opposite problem: Tin is lower than Iron, so a scratch through the very thin tin layer will cause the can to rust very rapidly if wet.
Rhode & Schwartze circuit diagrams carried warnings that Red was Negative and Black was Positive to prevent REME blowing the kit up by connecting the power supply backwards when repairing stuff.
Best,
Chris.