Is ground the same thing as the black wire in DC?

• and - refers to the potential difference between the two wires. This isn't absolute - as long as the supply was designed right, you could have the -ve wire at ground+500V, and the +ve at ground+512 volts, say. But usually the -ve wire is connected to some kind of stable ground voltage, and then the positive wire is so many volts above or below that ground. You can do this the other way round - have the +ve wire at ground, and the

-ve wire at ground minus x volts. or have a split rail supply which gives ground +/- x volts.

other

not unless the table had a good connection to whatever ground your power supply is using - it might be at the right voltage to start with, but there would be no path for the current to follow to complete the circuit. so all you would do is charge up your table to ground+12V. (i.e. the table would be acting as a capacitor)

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It is a basic question and should have been cast in the basic group. What every child already knows is: For a current to flow you need a closed loop eg. from positive to the consumer and back to the other polarity. If that table is connected to the other polarity via the earth wire(red) a current will flow. Many power supplies have their 0V output connected to the earth(red or yellow/green). Any metal enclosures(computer supply) must be connected by law to prevent built-up of dangerous voltages on the chassis, and very often also the secondary side ground is connected there. In a house with metal tubing the central heating or water supply is as well connected to earth, so a gadget will sometimes work. If the power supply is isolated (plastic casing, only two conductors to the plug), there is no way of a loop and no current will flow.

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ciao Ban
Bordighera, Italy

The color of a wire is merely a matter of convenience and one should never depend on a given color to have any particular meaning or use. "Ground" is merely a reference point; one might have a current monitoring circuit with schematic showing a "ground", but the device might be umpteen feet above the earth, monitoring current in a 200KV line. Where then would you say ground is??

[snip]

I'm sure the electrons don't care, but in many applications there are

*laws* regarding the colours of wire. Still, as you say, it is prudent not to make assumptions, particularly where safety is concerned.

Regards, Allan.

... particularly in -48V DC systems, where red is sometimes used for ground and black is used for -48V. I've also seen the reverse: black used for ground and red for -48V. Check your local regulations, then measure it with a multimeter just to make sure.

Regards, Allan.

There are no laws when it comes to DC wiring. In North America, it is fairly typical to use black as the colour of a negative wire and red as positive. In Germany, it is brown for ground and black for positive. And so on.

Bottom line is that there is no absolute certainty with low voltage DC wiring.

True ground wires in an AC circuit that is UL/CDA/CE/VDE/NEMKO/SEMKO/DEMKO (etc) approved, are either green, of more commonly green with a yellow stripe. But because these are related to high voltage appliances, they come under the regulations (NOT laws!) of the above mentioned regulatory agencies.

Bob.

I read in sci.electronics.design that Bob Wilson wrote (in ) about 'Is ground the same thing as the black wire in DC?', on Mon, 26 Jul 2004:

In Europe, the colours of mains conductors ARE legal requirements. And the -MKOs are now commercial test houses, not regulatory agencies.

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Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Please elucidate.

AFAIK there are no hard and fast laws for colours. I think maybe it depends on which parts of the power path you are talking about. (Generator ------ lots of other bits----- TV)

I read in sci.electronics.design that Mjolinor wrote (in ) about 'Is ground the same thing as the black wire in DC?', on Mon, 26 Jul 2004:

Premises wiring and mains flexibles.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Agreed. My point was simply that low voltage wiring colours are not regulated.

Bob.

For purposes of human "safety and harm"...

GREEN is the ONLY ground!

If y'all are lookin for RF ground... good luck!

-- Peter Indialantic-By-the-Sea, FL

No: red positive, blue negative in low voltage DC circuits.

Thats safety ground.