Quote:
Originally Posted by Ruffy
You're correct about vehicle systems not being technically "earthed" or "grounded". However, I don't know why you seem fixated on AC and DC systems being fundamentally different when it comes to tieing to the reference of Earth.
An AC common (often the "Neutral") might be earthed/grounded or it might not. Both can function perfectly well, especially in multi-phase systems. (An alternator output on a modern car/bike is a 3-phase AC example that works without earthing.)
Also, in non-vehicle DC it is quite normal to electrically connect one pole to Earth, for safety or EMC reasons. In that circumstance I think it would be correct to refer to it as earth/ground as well as common.
At the risk of confusing things, some systems have centre tap. E.g. an industrial 110V supply is actually +/-55V with a centre-tap earth connection in the interests of safety. The only DC-based example I can think of off the top of my head is an audio amplifier circuit - not my area of expertise but I imagine the centre 'common' connection of XLR balanced connections are actually earthed/grounded in some way too.
Your underlying original gripe is valid and shared though: Earth/Ground/Common are being treated as synonymous when they're not!  |
The best phrase I ever heard was 'don't sweat the small stuff' ...... and all this 'is it ground, common or earth' means nothing to 90% of the population who are not electrical designers or research scientists... many words and phrases creep into our wonderful language and take root, and become commonly accepted and well understood - and pretty harmless really - if you say to many 'lay' people 'check the voltage from point 'A' to earth or ground they will check it to body or frame of vehicle, they won't drive a copper stake into the ground next to vehicle and use that.
This gripe goes into 'room 101'....