Negative 48 Volts DC

[Michael Kellett]

On 25/01/2020 19:21, Grant Taylor wrote:

Is anyone willing to explain Negative 48 Volts DC?

I'm trying to learn about it because we're using it for a few things at
work (servers and switch equipment) and I'd like to better understand
what we're working with than simply going through the motions that
someone else dictates.  Read:  I want to understand and not simply rely
on wrote memory.

I've learned that -48 VDC uses what is called "Positive Ground" and that
what I'm used to is called "Negative Ground".

I'm trying to correlate and understand the typical red and black wires
with them being ground / return / common / hot / etc.

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.

Can ~> will someone offer any comments that might help me understand
better?

It's a very long time since I had anything to do with +ve earth British
Post Office stuff but as I recall we used to talk about battery and
earth. (Except the Irish guy I worked with, who used battery and ert.)
I have one or two examples of things I designed then (approx 1980, as
they (PO Telephones) were morphing into British Telecom) but no diagrams.
Here's a link to what looks like a fairly typical diagram:

http://finalselector.blogspot.com/2008/02/mystery-no-longer.html

You can see the use of earth and battery symbols.


This link is to a picture of a prototype relay tester (uses an Intel
8048 and designed to look as much like traditional relay based stuff as
possible). I don't have a schematic but you can see the names we used
and the on the front panle. The ETH wires are red.


https://www.dropbox.com/s/to75xfo3ujdjraz/LF1470.JPG?dl=0

MK

 

Michael Kellett <mk@mkesc.co.uk> wrote in
news:e6SdnVob_YZ3m63DnZ2dnUU78aPNnZ2d@giganews.com:

Is anyone willing to explain Negative 48 Volts DC?

Lead acid batteries used in system UPS's are 12V. Series 4 together
and get 48 Volts. Batteries are isolated sources, so either node can
be 'fashioned' as 'ground'. The power supplies used to charge such
battery back up systems had to make more than 48 Volts to make a
charge condition occur on the bank.

Whether they had individual battery watchdog circuits I do not
know, but having a bad cell in a 4 battery 48 Volt system causes less
of a droop than having a bad cell in a single battery 12 Volt system.
So the supply could be a bit down in voltage yet still do the needed
job.
Whereas a single battery or parallel bank may not be as happy with a
burned cell in play.

So my guess is that the voltage was chosen to match the current
storage cell technology of the times, and it simply stuck even though
electrical demands to perform the same jobs reduced as solid state
matured.

 

[Whoey Louie]

On Monday, January 27, 2020 at 10:17:43 PM UTC-5, Rick C wrote:

On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote:
On 1/26/20 3:28 PM, Rick C wrote:
That's why I would look at the documentation for the equipment/supply..

That is the plan. I've not had the opportunity to do so yet.

If it is a -48 volt system it certainly would be ok to call the
positive terminal "return" or "common". It would be ok to call the
negative terminal "hot".

Okay.

I have seen some systems use a negative ground with a 48 volt power
source.

Fair enough. I've not had the exposure to (positive) 48 volt power.

Now you are talking color codes. I can't tell you what the color
code is for a -48 volt system.

I wasn't meaning to focus on the color code. Allow me to modify my
statement slightly by removing the colors from it.

I believe that if I hook the positive lead of a voltmeter to the
positive lead of a power supply, and the negative lead of the volt meter
to the negative lead of a power supply, I expect the following voltages:

Standard bench top 12 VDC power supply: + 12 VDC
Negative 48 VDC telephone power supply: - 48 VDC

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.


"Called" vs. "looks" I can't say. I never talk about the "red" lead
when dealing with power circuits. I use the other terms listed above..

Okay.

Now you have me confused again. Who talked about a positive wire with
a negative voltage??? Positive/negative are electric polarities and
don't change when your definition of the common or ground changes.

I believe it was a permutation of "hot" -> "red" -> "positive" in a
system that has negative voltage.

Let's forget color. If it is a -48 volt system the positive wire will be the common, but it will still be positive.


Ok, if they say it's a -48 volt supply with a minus sign in front
of the voltage, then it is safe to believe the hot wire will be the
negative the return/common wire will be the positive.

Okay.

Ok, because I'm willing to bet the supply is not grounded, but it
may be. If not grounded they are only calling it a -48 volt supply
because that is how most people use it. There is nothing inherent
that makes it minus vs. positive.

I had a few minutes to look at the -48 VDC power supply today.

¡ The negative terminal was connected to the red wires.
¡ The positive terminal was connected to the black wires.
¡ The positive terminal was connected to the chassis.
¡ The chassis will make electrical contact with a rack that is
connected to earth ground.

Ok, so they are using the convention that red is "hot" and black is "common". They are also grounding their common to earth ground which is likely connected to a protective earth wire.


The volt meter will always tell you the voltage between the two
probes assuming the red will be positive and the black negative.

The implication of polarity with volt meter leads doesn't help this
thread. But I generally agree with your statement.

If that is correct the meter will show a positive voltage. I the
red lead is negative it will show a negative voltage.

I believe the red lead does show a negative voltage.

I was talking about the voltmeter leads. But whatever.


That will give you a positive voltage on the positive lead with
respect to (wrt) ground.

I still need to measure, but I believe the positive lead has 0 volts to
ground.

You just said above the positive power lead is common and connected to a grounded chassis. You can't get any more zero than that. Of course you have to use common or ground as your reference (e.g. connect the black meter lead to common).


That will give you a negative voltage on the negative lead wrt ground..

Agreed.

BTW, none of these supplies should have any connection to power line
neutral. That is dangerous situation and can kill. Neutral is not
ground (protective earth).

I agree that ground and neutral (in typical 120/240 VAC 1ɸ wiring) are
separate conductors and should not be used interchangeably. However,
ground and neutral are bonded together in the main electrical panel.
(At least every main panel that I've ever looked in. Sub-panels are
decidedly different with ground and neutral isolated from each other.)
So, there is a conductive path between ground and neutral.

And that is the hazard. If the neutral connection to the panel is lost, there is no return path for the power circuit and anything touching neutral will be hot. The bond between protective earth and neutral must be connected in a way that no failure can cause the protective earth to be hot.

There is no such way. If the ground wire becomes disconnected at the panel,
or the wire is cut on it's way to the grounding electrode system and you
also have your disconnected neutral, the eqpt grounding system will become
energized through any loads.

 

[Whoey Louie]

On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote:

On 1/26/20 3:28 PM, Rick C wrote:
That's why I would look at the documentation for the equipment/supply.

That is the plan. I've not had the opportunity to do so yet.

If it is a -48 volt system it certainly would be ok to call the
positive terminal "return" or "common". It would be ok to call the
negative terminal "hot".

Okay.

I have seen some systems use a negative ground with a 48 volt power
source.

Fair enough. I've not had the exposure to (positive) 48 volt power.

Now you are talking color codes. I can't tell you what the color
code is for a -48 volt system.

I wasn't meaning to focus on the color code. Allow me to modify my
statement slightly by removing the colors from it.

I believe that if I hook the positive lead of a voltmeter to the
positive lead of a power supply, and the negative lead of the volt meter
to the negative lead of a power supply, I expect the following voltages:

Standard bench top 12 VDC power supply: + 12 VDC
Negative 48 VDC telephone power supply: - 48 VDC

"Called" vs. "looks" I can't say. I never talk about the "red" lead
when dealing with power circuits. I use the other terms listed above.

Okay.

Not okay. If you hook the red positive lead of a meter to the positive and
the black negative lead to the neg of either power supply you will see +12V

Now you have me confused again. Who talked about a positive wire with
a negative voltage??? Positive/negative are electric polarities and
don't change when your definition of the common or ground changes.

I believe it was a permutation of "hot" -> "red" -> "positive" in a
system that has negative voltage.

Ok, if they say it's a -48 volt supply with a minus sign in front
of the voltage, then it is safe to believe the hot wire will be the
negative the return/common wire will be the positive.

Okay.

Ok, because I'm willing to bet the supply is not grounded, but it
may be. If not grounded they are only calling it a -48 volt supply
because that is how most people use it. There is nothing inherent
that makes it minus vs. positive.

I had a few minutes to look at the -48 VDC power supply today.

¡ The negative terminal was connected to the red wires.
¡ The positive terminal was connected to the black wires.
¡ The positive terminal was connected to the chassis.
¡ The chassis will make electrical contact with a rack that is
connected to earth ground.

Weird and confusing to use red for the negative.

The volt meter will always tell you the voltage between the two
probes assuming the red will be positive and the black negative.

The implication of polarity with volt meter leads doesn't help this
thread. But I generally agree with your statement.

If that is correct the meter will show a positive voltage. I the
red lead is negative it will show a negative voltage.

I believe the red lead does show a negative voltage.

Yes, because it's connected to -48V.

 

On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:

A couple of years ago I helped choose colours for the input connectors
of a networking product that had 12V (automotive range) and 48V
versions. The 12V choice was easy. We were using Anderson Powerpole
connectors, so we followed the amateur radio convention for these
connectors with red for positive and black for negative in a specific
configuration.
For 48V, I looked at every standard I could find and found a mass of
conflicting recommendations. An additional constraint was that we wanted
to use the "finger safe" version of the connectors and could only use
colours available from Anderson. Most customers would use positive
ground, but some had negative ground systems.
The final outcome was that the input was isolated with no connection
between either power terminal and chassis and the positive terminal
was red and the negative terminal was blue. This seemed to be in keeping
with the spirit of most of the standards and less likely to cause
confusion than any other combination.
Pictures at the bottom of the page:
https://www.firebrick.co.uk/fb2900/

John

 

[Whoey Louie]

On Monday, January 27, 2020 at 9:28:39 PM UTC-5, Grant Taylor wrote:

On 1/27/20 9:46 AM, Whoey Louie wrote:
Why is it confusing? One terminal is the negative polarity, the other
the positive. On your supply, one terminal is marked -48V, the other
return. I would also make the -48V black, the return one red.

Having looked at the equipment earlier today, you'd be wrong.

Negative had the red wires.
Positive / ground had the black wires.

The confusion is understanding why things are wired the way that they are..

Yes, I see you said that in another post now too. And I agree, it is
confusing. I would not expect red to be the negative supply side and
black to be positive. That is confusing and asking for trouble.

but even with just -48V on one and return on the other, it's clear
which is negative, which is positive. If you had a 9V battery and
one terminal was marked -9V, or 'neg", would you be confused about
the polarity?

In a negative ground system, no, I would not be confused.

In a positive ground system, I apparently am.

Which end is designated the ground/return doesn't change the polarity
of the terminals at the power source.

Woah there Pilgrim! Are you saying on that -48V supply has a
RED terminal or wire for the -48V and BLACK for return?

Yes!!!

That is EXACTLY what I'm saying. (See above.)

Now that I would agree would be confusing.

Hence this thread.

Yes, so then it's just a color choice thing. Which raises an interesting
question. In the small minority of cars that decades ago used a positive
ground, I wonder what color the supply wires were? Possible they were
red too. I've never seen one, IDK.

I would expect black to be on the -48V, red on the return.

Nope.

I don't know what I would have expected / guessed this time last week.
I'm loath to guess, lest I confuse myself more this week.

Well, knowing that, just consider the red to be the supply side,
black to be the return. In the case of your -48V system, the red
then is the negative polarity.

It's either one polarity or the other, positive is never called negative.
What is called the "hot", the "source" or the "return" could be either
depending on the system polarity.

I'm slowly coming to the conclusion that I have naively assumed that red
≈ positive. Which is obviously wrong for positive ground systems..

Red is positive in everything I've seen, but then all of that has been
negative ground, so I share your confusion. But some of it might become
obvious, even without looking at the power supply. If there are breakers
or fuses for example, they would be on the supply/hot side, so if those
wires were red and I knew it was a -48V system, I'd start wondering.

I think I need to retrain myself that red = hot and that what is hot is
dependent on the type of system it is; negative ground or positive ground..

Yes, at least for that particular system. The question is that what
all positive ground systems do?

With one voltage, two wires like you have, it can't.

I think that I need to reword my statement to be "a hot wire has a
negative voltage … in a positive ground system".

Yes, you've got it now.

But it does make sense. That power supply is designed to be used in a
positive ground system. So the supply terminal is labeled -48V.

I checked, and one terminal is labeled "negative" and the other terminal
is labeled "positive".

So what color is the -48V terminal? Is there a color? I would expect it
to be either black or no color identification and the return to be either
red or no color.

There is no color (save for polished / chrome steal).

The red wire was connected to negative. The black wire was connected to
positive.

I've not had the opportunity to measure the voltage yet. I'm planing on
doing that tomorrow.

Why are you now adding neutral to this? Neutral is on the AC side.

I'm fairly certain that neutral and ground are bonded together somewhere
upstream. Thus I typed "neutral / ground" as "neutral or ground".
Because, from an electrical conductivity standpoint, they are at the
same potential and in some ways the same.

Yes, you have that correct too. Very normal for the return side of
eqpt to be connected to earth ground, for lightning, in case an AC
line side conductor somewhere gets shorted to the DC/low voltage side, etc.

--
Grant. . . .
unix || die

 

[Whoey Louie]

On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote:

On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:

A couple of years ago I helped choose colours for the input connectors
of a networking product that had 12V (automotive range) and 48V
versions. The 12V choice was easy. We were using Anderson Powerpole
connectors, so we followed the amateur radio convention for these
connectors with red for positive and black for negative in a specific
configuration.
For 48V, I looked at every standard I could find and found a mass of
conflicting recommendations. An additional constraint was that we wanted
to use the "finger safe" version of the connectors and could only use
colours available from Anderson. Most customers would use positive
ground, but some had negative ground systems.
The final outcome was that the input was isolated with no connection
between either power terminal and chassis and the positive terminal
was red and the negative terminal was blue. This seemed to be in keeping
with the spirit of most of the standards and less likely to cause
confusion than any other combination.
Pictures at the bottom of the page:
https://www.firebrick.co.uk/fb2900/

John

That's what I would have done too. I sure would not use red for negative
and black for positive. I was thinking about saying in the other reply
that if I decided to use black for the return in a positive ground system,
then I sure would not use red for the supply. I would use some other
color that would at least give someone looking at it reason to further
look into what's going on. When one sees just red and black in low
voltage DC system, one naturally assumes red is positive.

 

[Don Kuenz]

Whoey Louie <trader4@optonline.net> wrote:

On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote:
On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:

A couple of years ago I helped choose colours for the input connectors
of a networking product that had 12V (automotive range) and 48V
versions. The 12V choice was easy. We were using Anderson Powerpole
connectors, so we followed the amateur radio convention for these
connectors with red for positive and black for negative in a specific
configuration.
For 48V, I looked at every standard I could find and found a mass of
conflicting recommendations. An additional constraint was that we wanted
to use the "finger safe" version of the connectors and could only use
colours available from Anderson. Most customers would use positive
ground, but some had negative ground systems.
The final outcome was that the input was isolated with no connection
between either power terminal and chassis and the positive terminal
was red and the negative terminal was blue. This seemed to be in keeping
with the spirit of most of the standards and less likely to cause
confusion than any other combination.
Pictures at the bottom of the page:
https://www.firebrick.co.uk/fb2900/

That's what I would have done too. I sure would not use red for negative
and black for positive. I was thinking about saying in the other reply
that if I decided to use black for the return in a positive ground system,
then I sure would not use red for the supply. I would use some other
color that would at least give someone looking at it reason to further
look into what's going on. When one sees just red and black in low
voltage DC system, one naturally assumes red is positive.

This schematic shows red assigned to the higher potential and black
assigned to the lower, more negative, potential:

https://resources.secamerica.com/hs-fs/hubfs/Blog_Images/48vdc_for_telecom.jpg

Red is assigned to the relatively positive power rail, at least in this
schematic. What installers choose to do in the field's a whole nother
story.

That schematic originates with communications vendor:

https://www.secamerica.com/applications/communications/

Presumably the vendor knows more than most about color code usage in
the industry.

In regards to ground:

"Ground is a fantasy invented by engineers to simply
their work." - Bill Whitlock

The ground fantasy as applied to this thread seems to complicate instead
of simplify. It's probably best to leave it out.

Thank you,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

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.

 

[Whoey Louie]

On Tuesday, January 28, 2020 at 3:42:55 PM UTC-5, Don Kuenz wrote:

Whoey Louie <trader4@optonline.net> wrote:
On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote:
On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:

A couple of years ago I helped choose colours for the input connectors
of a networking product that had 12V (automotive range) and 48V
versions. The 12V choice was easy. We were using Anderson Powerpole
connectors, so we followed the amateur radio convention for these
connectors with red for positive and black for negative in a specific
configuration.
For 48V, I looked at every standard I could find and found a mass of
conflicting recommendations. An additional constraint was that we wanted
to use the "finger safe" version of the connectors and could only use
colours available from Anderson. Most customers would use positive
ground, but some had negative ground systems.
The final outcome was that the input was isolated with no connection
between either power terminal and chassis and the positive terminal
was red and the negative terminal was blue. This seemed to be in keeping
with the spirit of most of the standards and less likely to cause
confusion than any other combination.
Pictures at the bottom of the page:
https://www.firebrick.co.uk/fb2900/

That's what I would have done too. I sure would not use red for negative
and black for positive. I was thinking about saying in the other reply
that if I decided to use black for the return in a positive ground system,
then I sure would not use red for the supply. I would use some other
color that would at least give someone looking at it reason to further
look into what's going on. When one sees just red and black in low
voltage DC system, one naturally assumes red is positive.

This schematic shows red assigned to the higher potential and black
assigned to the lower, more negative, potential:

https://resources.secamerica.com/hs-fs/hubfs/Blog_Images/48vdc_for_telecom.jpg

Red is assigned to the relatively positive power rail, at least in this
schematic. What installers choose to do in the field's a whole nother
story.

That schematic originates with communications vendor:

https://www.secamerica.com/applications/communications/

Presumably the vendor knows more than most about color code usage in
the industry.

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.

In regards to ground:

"Ground is a fantasy invented by engineers to simply
their work." - Bill Whitlock

The ground fantasy as applied to this thread seems to complicate instead
of simplify. It's probably best to leave it out.

Earth ground, I would agree is just a further complication here.
But ground in general is just a system reference point and typically
the return. So if someone was working on Grant's system and hooked
a meter between -48V wiring and the return wiring, it would be common
to say that he's measuring between supply and ground.

Thank you,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[Whoey Louie]

On Tuesday, January 28, 2020 at 2:50:00 PM UTC-5, whit3rd wrote:

On Tuesday, January 28, 2020 at 10:56:17 AM UTC-8, Whoey Louie wrote:

... I agree, it is
confusing. I would not expect red to be the negative supply side and
black to be positive. That is confusing and asking for trouble.

Alas, the innards of an automobile won't teach you anything bur red = positive.
There are LOTS of color conventions, many with legal enforcement, and
one must learn not to generalize.

In US house wiring, red would be AC high voltage.

If you mean by high voltage 240/120 AC then yes that's true, red
could be used. But Grant's example is DC and 48V. You could also have
red and black in house wiring in other applications, eg HVAC,thermostats,
alarm wiring. But red for positive and black for negative in DC was
the issue and this is the first application where I've heard of red
being used for neg, black for positive.


In a computer, red is +5V,
> and yellow is +12V.

In every low voltage DC anything where there is just one voltage, I've
never seen red and black be anything other than positive and negative.
Apparently it exists, but it's not common and the convention is not
limited to cars. Buy a DC, low voltage, one speed motor, I've
never seen one where red and black did not mean pos and neg, have you?

 

whit3rd <whit3rd@gmail.com> wrote in
news:d571a9c6-95b9-4c45-be43-95644566cb96@googlegroups.com:

On Tuesday, January 28, 2020 at 10:56:17 AM UTC-8, Whoey Louie
wrote:

... I agree, it is
confusing. I would not expect red to be the negative supply side
and black to be positive. That is confusing and asking for
trouble.

Alas, the innards of an automobile won't teach you anything bur
red = positive. There are LOTS of color conventions, many with
legal enforcement, and one must learn not to generalize.

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.

I say 'almost always' because I've never seen (or used) it other
than on ground wires, but it's worth checking every time.

We designed a negative HV supply. While we would typically all
agree that black is ground, we all know that ground is not always
negative. It is most commonly always BLACK, however (AC fault return
wires do not count).

So our negative supply had a RED "HOT" wire and black was ground.
Being an isolated supply it should not matter. The signal to the
user is that red is HOT, not neccessarily positive.

 

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.

 

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.

 

[Whoey Louie]

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

 

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

 

[Grant Taylor]

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

 

[Grant Taylor]

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

 

[sea moss]

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.

 

[Grant Taylor]

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