On Tue, 28 Jan 2020 22:12:40 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> wrote:

>I'd like to take a moment to thank everybody that has helped me along my 
>journey to learn about Negative 48 Volts DC.  I believe that I have 
>learned, and unlearned, enough to have a acceptable decent understanding.
>
>I have learned that the terms "hot" / "common" / "return" / "ground" do 
>not correlate with the polarity without indication of "negative ground" 
>(what I'm used to) or "positive ground".
>
>In a negative ground system, the "hot" wire will be positive compared to 
>"ground" / "return".
>
>In a positive ground system, the "hot" wire will be negative compared to 
>"ground" / "return".

If you want to measure the height of something, you need to stand
somewhere and call that "zero." There is such a thing as absolute sea
level, H=0, and electrical earth ground, V=0, but they may not always
be available.

So we clip the "negative" (better called the "reference") wire of a
voltmeter to something conductive and declare that to be "ground",
namely zero volts. Chassis, car body, metal ladder that we're standing
on, most anything. Then we measure positive or negative voltages
relative to that.

We have one Tek oscilloscope with fully isolated channels. We can clip
a scope probe ground to the hot side of the AC line and then probe
relative to that.

-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

I'd like to take a moment to thank everybody that has helped me along my 
journey to learn about Negative 48 Volts DC.  I believe that I have 
learned, and unlearned, enough to have a acceptable decent understanding.

I have learned that the terms "hot" / "common" / "return" / "ground" do 
not correlate with the polarity without indication of "negative ground" 
(what I'm used to) or "positive ground".

In a negative ground system, the "hot" wire will be positive compared to 
"ground" / "return".

In a positive ground system, the "hot" wire will be negative compared to 
"ground" / "return".



-- 
Grant. . . .
unix || die

On 1/28/20 4:18 PM, jrwalliker@gmail.com wrote:
> Just to confuse things even more, the live wires in 3 phase systems in 
> Europe (including UK) are brown, black and grey.  The old UK colours 
> were black for neutral and red, yellow and blue for the phases. 
> There are many installations where both sets of colours are mixed!

Oy vey!

And I thought old four pair phone wire color codes and new four pair 
phone wiring color codes were confusing / annoying, in that they take a 
few minutes to stop, think about, and figure out.  But that is nominally 
low voltage and decidedly low current.  Much less room for catastrophic 
failure than the old & new color codes for three phase.

-- 
Grant. . . .
unix || die

On 1/28/20 2:37 PM, DecadentLinuxUserNumeroUno@decadence.org wrote:
> Some folks are simply confused when things do not match their 
> preconceived ideas.

I think it's fair to say that I was.  Hence why I started this thread.

I feel like I've gained a better understanding of what's going on.

-- 
Grant. . . .
unix || die

> I suspect that there is more to it than simply reversing the + and - 
> lead from a battery or meter.  But I can't wrap my head around it.

I think it may become crystal clear for you if you can visualize what a negative voltage is, and how the currents flow.

For me, the water analogy helped me visualize it.  Think of a voltage source (power supply output) as a water pump, which brings water uphill to a reservoir.  So a +10V supply is like pumping water up a 10 foot wall.  Then when you connect to a load, that is like dropping the water (kinetic energy); it returns to ground and has no energy left so you continue to pump it uphill.  Currents only flow downhill.

Now for the -10V supply, dig a 10 foot hole and put the pump from the bottom of the hole to ground level.  Now you connect to a load the same way as before, you drop the water down into the hole (kinetic energy) and then you pump it back up.  Currents continue to only flow downhill.

If you have a power supply with +10V and ground outputs, you can measure the current, it will always flow out the +10V and back on the ground terminal.  If your power supply has -10V and ground output, the current will flow out the ground output and return on the -10V.

It sounds like your systems use black=ground and red=hot, whether red is negative or positive.  "Hot" is a good term, since current will flow through your body if you touch the red wire and you are grounded.  Only difference for a negative voltage is the direction the current takes as it flows through you.

On Tuesday, 28 January 2020 22:04:05 UTC, upsid...@downunder.com  wrote:
> On Tue, 28 Jan 2020 11:49:56 -0800 (PST), whit3rd <whit3rd@gmail.com>
> wrote:
> 
> >In US house wiring, red would be AC high voltage.   In a computer, red is +5V,
> >and yellow is +12V.   In European AC cables, black is neutral, but in US 
> >the white is neutral.   Ground is sometimes black, sometimes green, and 
> >green/yellow stripe is almost always ground.
> 
> In AC wiring in Europe, light blue is neutral, green/yellow stripe is
> the protective earth (PE). It is forbidden to use the green/yellow
> stripe for anything else than ground/earh. If you are forced to use
> some other colord conductor for PE, the ends must be marked with
> green/yellow stripe tape.

Just to confuse things even more, the live wires in 3 phase systems
in Europe (including UK) are brown, black and grey.  The old UK colours
were black for neutral and red, yellow and blue for the phases.  There
are many installations where both sets of colours are mixed!
John

On Tue, 28 Jan 2020 11:49:56 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

>In US house wiring, red would be AC high voltage.   In a computer, red is +5V,
>and yellow is +12V.   In European AC cables, black is neutral, but in US 
>the white is neutral.   Ground is sometimes black, sometimes green, and 
>green/yellow stripe is almost always ground.

In AC wiring in Europe, light blue is neutral, green/yellow stripe is
the protective earth (PE). It is forbidden to use the green/yellow
stripe for anything else than ground/earh. If you are forced to use
some other colord conductor for PE, the ends must be marked with
green/yellow stripe tape.

On Tuesday, January 28, 2020 at 2:22:16 AM UTC-5, Rick C wrote:
> On Monday, January 27, 2020 at 11:20:11 PM UTC-5, Grant Taylor wrote:
> > On 1/27/20 8:17 PM, Rick C wrote:
> > > Positive and negative are electrical terms of physics.  It has nothing 
> > > to do with convention of colors or which polarity of common you use. 
> > > Connect the positive meter probe to the positive power line and you 
> > > will always measure a positive voltage no matter what.
> > 
> > Presuming the negative meter probe is connected to negative power line, 
> > and I agree.
> > 
> > The thing that I've learned is that there is no correlation between 
> > "hot" / "common" / "return" / "ground" with positive or negative like I 
> > have naively thought for the last 30 years.
> 
> That's because positive ground systems are the exception rather than the norm.  Telephony related gear is an exception... when powered from 48 volts, but not always even then.  I have seen gear that didn't have an internal connection to common and so could be used as positive ground or negative ground. 
> 
> 
> > > That would imply the equipment cabinet be grounded and the equipment 
> > > connected to that.  The power source can be floating and the equipment 
> > > should not care.  Do the equipment vendors define "properly grounded", 
> > > that is, any specific instructions?
> > 
> > Yes.  The better documentation calls out very specific directions on how 
> > to bond ground to the equipment.  They are quite specific about earth / 
> > safety ground.
> > 
> > > Is this strap at the power supply or the equipment being powered?
> > 
> > It is part of part of the power supply.
> 
> That surprises me a bit.  A AC/DC power supply output is typically isolated from the input power line, so common is whichever terminal you connect to... common.  Having a connection internally to the AC protective earth limits the applications with no added advantage. 

It it's a power supply supplied by the same company that makes the
gear it's connected to, or intended specifically for the application
it's being used in, they don't give a rat's ass about how it might
be used for something else.  It's not a bench power supply.




> 
> 
> > > Braided copper strap or just a regular wire?  Just curious.  As I've 
> > > said, I've not worked with this sort of equipment.
> > 
> > It is a piece of solid (what looks to be) steal that fits over the bolts 
> > of the positive terminal where wires get bolted on top, thus sandwiching 
> > the steal between the terminals and the restraining bolts.  The other 
> > end is bolted to the metal chassis.
> 
> That sounds very external then.  That makes sense.  That's not really part of the power supply.  They just provide the strap and you likely can use it on either output.  But since the positive terminal is labeled "common", maybe not. 
> 
> -- 
> 
>   Rick C.
> 
>   +++ Get 1,000 miles of free Supercharging
>   +++ Tesla referral code - https://ts.la/richard11209

DecadentLinuxUserNumeroUno@decadence.org wrote in
news:r0q8qe$1ivm$1@gioia.aioe.org: 

> Whoey Louie <trader4@optonline.net> wrote in
> news:499044a5-a46d-45a0- afbb-6984e3965ac4@googlegroups.com:
> 
>> I'm wondering what color was used on the negative/supply side of
>> the wiring in early cars that used a positive ground?  I took a
>> quick google, couldn't find anything.
>> 
>> 
> 
> 6 Volt automotive systems used black cables throughout.
> Many used terminated bare braided tinned copper cable for the
> grounded side.
> 

  Aftermarket replacements, however, are colored red for positive 
side connections.

  Lots of stuff about converting old Willys jeeps to negative ground.

  Some folks are simply confused when things do not match their pre-
conceived ideas.