Negative 48 Volts DC

[Whoey Louie]

On Saturday, January 25, 2020 at 2:28:05 PM UTC-5, George Herold wrote:

On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, 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?



--
Grant. . . .
unix || die

Right, Say you have a 48V battery.
You hook up the neg. terminal to ground, you've got +48V at the
positive terminal.
You hook up the pos. terminal to ground and it's -48V at the negative
terminal.

George H.

And the latter is his "positive ground" system. As someone else pointed
out, ground in this case just means a system reference point.
As an example, cars today have a negative ground system, the battery negative
is connected to the car metal chassis, which is used as part of the
return path for current. Some cars years ago, instead had a positive
ground system, with the battery positive connected to the chassis instead.
It's like driving on the wrong side of the road, some just had to be
different. Fortunately with grounding, I think the weirdos wised
up and AFAIK no cars have been built for decades that have positive
ground.

 

[Whoey Louie]

On Saturday, January 25, 2020 at 3:44:27 PM UTC-5, Grant Taylor wrote:

On 1/25/20 12:33 PM, Rick C wrote:
I'm at a loss to understand what you are confused about. Do you have
any specific questions???

I have a -48 VDC power supply with an unlabeled terminal and a return
terminal.

So then there is -48V between the unlabeled terminal and the return.
But you'd think they would label that unlabeled terminal -48V or supply.

Other sets of DC equipment & associated supplies (multiple small sets of
different supplies and equipment used for various things) use red and
black wire.

What is return? red or black

The red side would be positive, the black negative. Current flows from
the positive side of the source to negative. So the return would be the
black, but that terminology isn't frequently used.

What voltage should be read when connecting the meter's positive / red
lead and negative / black lead to the red & black wires from the DC supply?

Take a 12 V power supply. If you connect the red meter lead to the red
on the power supply, black to black you'd read +12V. If you connect red
to black, black to red, you'd read -12V.

How should things be wired to a piece of equipment that has the ground
symbol on one terminal and the other terminal unlabeled?

Carefully. It's a very bad idea to have things unlabeled. Better
RTFM.

My brain is having problems aggregating all of these and making
associations.

How does any of this impact using the 48 volts to supply the equipment
you list? In other words, why are you confused?

Which terminal of the DC source; unlabled and return, connects to the
ground terminal on the DC load equipment?

You have what you say is a -48V supply and it has one terminal marked
return, the other unlabeled. Let's say you have a 48V piece of eqpt
and it has a red wire and black wire coming out of it or a red terminal
and black terminal. Knowing only the above, the logical thing is that
the unmarked supply terminal goes to the black/neg and the return terminal
goes to the red/positive.

 

[Sylvia Else]

On 26/01/2020 6:21 am, 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?

In any system of connected wires at different potentials, you can
arbitrarily label one of them "ground", and then measure the potentials
of the other wires relative to your ground. You will then get some that
are positive, and some that are negative.

For some systems, such as a car, it can make some sense to label
whatever is connected to the chassis as ground, but it is still pretty
much an arbitrary choice.

And of course, with a fixed system, one can connect one point to the
soil under one's feet, and call that point ground.

But it's a naming convention, and nothing more.

In the absence of clear documentation on the system you're examining,
the only practical option is to take a multimeter to it, and make
measurements.

Sylvia

 

[Michael Terrell]

On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, 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?

A communications system that I worked on for the International Space Station ran on -48VDC.

 

[Johnny B Good]

On Sat, 25 Jan 2020 23:10:35 -0800, Michael Terrell wrote:

On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, 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?



A communications system that I worked on for the International Space
Station ran on -48VDC.

I should imagine for much the same reasons used to standardise road
vehicle ground reference polarity and telephone exchange equipment
grounding to earth - to minimise galvanic corrosion in vital metallic
structures - the inside would be a humid environment - it has to be for
the sake of the astronaut's respiratory health, providing ample
opportunity for the water vapour to condense out onto cold spots within
the structure of the ISS.

Incidentally, regarding the question of colour coding the polarity of
telecoms DC supplies, the GPO (as it was when I joined that organisation
as an apprentice in late '67) which is now known as BT (British Telecom),
the -52v "hot" (aka "Battery") exchange equipment bus bars were insulated
with blue plastic insulation (PVC afaicr) and the grounded (actually
earthed) positive bus bars were all left bare.

The fact that only the 'live' bus bars were insulated and the choice of
blue rather than black, were sufficient reminder (if a reminder was ever
needed) that the 'dangerous' pole of the 52v DC supply was negative with
respect to anything (all the exposed metalwork including the ground
return bus bars) at earth potential.

This scheme neatly eliminated any possible confusion that could arise
over which was the 'live' if the convention of red for positive and black
for negative had been followed (red for danger and black for the safety
of a conductor at ground potential failing to apply in this case).

As to whether or not this colour coding scheme was followed outside of
the UK and its dependencies (and the 48vdc power standards that came in
with the later solid state comms equipment), I know not so I'll leave
that as a question for old timers who've worked in telephone exchanges
outside of the UK to answer. ;-)

--
Johnny B Good

 

On Sun, 26 Jan 2020 13:31:52 +1100, Sylvia Else <sylvia@email.invalid>
wrote:

On 26/01/2020 6:21 am, 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?




In any system of connected wires at different potentials, you can
arbitrarily label one of them "ground", and then measure the potentials
of the other wires relative to your ground. You will then get some that
are positive, and some that are negative.

For some systems, such as a car, it can make some sense to label
whatever is connected to the chassis as ground, but it is still pretty
much an arbitrary choice.

And of course, with a fixed system, one can connect one point to the
soil under one's feet, and call that point ground.

But it's a naming convention, and nothing more.

In the absence of clear documentation on the system you're examining,
the only practical option is to take a multimeter to it, and make
measurements.

Sylvia

The universe is probably absolute ground, and also defines absolute
zero velocity.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Rick C]

On Sunday, January 26, 2020 at 10:58:11 AM UTC-5, jla...@highlandsniptechnology.com wrote:

On Sun, 26 Jan 2020 13:31:52 +1100, Sylvia Else <sylvia@email.invalid
wrote:

On 26/01/2020 6:21 am, 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?




In any system of connected wires at different potentials, you can
arbitrarily label one of them "ground", and then measure the potentials
of the other wires relative to your ground. You will then get some that
are positive, and some that are negative.

For some systems, such as a car, it can make some sense to label
whatever is connected to the chassis as ground, but it is still pretty
much an arbitrary choice.

And of course, with a fixed system, one can connect one point to the
soil under one's feet, and call that point ground.

But it's a naming convention, and nothing more.

In the absence of clear documentation on the system you're examining,
the only practical option is to take a multimeter to it, and make
measurements.

Sylvia

The universe is probably absolute ground, and also defines absolute
zero velocity.

Yeah, if we could just find the middle of it. Well, the part we can see anyway. What if we are off in a corner of the universe expanding away from the center at greater than the speed of light?

So if the universe started as a singularity and expanded from there, how could any part of it speed away and become invisible by exceeding the speed of light?

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Wond]

On Sat, 25 Jan 2020 12:21:25 -0700, 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?

In a DC system, red is positive, black is negative, by convention.
Terms such as hot, return and ground are simply descriptive, and usually
applied in distributed AC in North America, where black is hot.

 

[mpm]

On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:

A communications system that I worked on for the International Space Station ran on -48VDC.

I don't know if it is still the case, but that last (and probably only) time I had to install a two-way radio into a backhoe or bulldozer - that was a "positive ground" system.

I remember it because there was a circuit on the microphone hang-up clip that would automatically un-squelch the receiver (it used ground). But in this case, we had to isolate the chassis of the two-way radio from "ground", as to avoid a short. I forget what we did as a workaround. I think the antenna was also one of those Motorola NMO-type mounts (also "grounded"), so we had to do something to that too.

Someone earlier mentioned that "positive ground" systems tend to slow down corrosion. I don't know if that's true with backhoes, but they do spend their lives outdoors in the elements? (But so do cars, mostly.)

 

[Grant Taylor]

On 1/25/20 2:34 PM, George Herold wrote:

Voltages are about differences. You have to set 'zero' somewhere...
or we can't really talk about it. Ground is a common point (NPI)
you can float everything above ground... but it gets dangerous to touch
above ~60V (depends on source impedance)
GH.
Are you an EE?

No. I'm a systems / network administrator by trade. I'm just trying to
understand (more than wrote memory) how some of the equipment I
administer works.

There are other, more skilled people between me and connecting equipment.



--
Grant. . . .
unix || die

 

[Grant Taylor]

On 1/25/20 3:54 PM, Rick C wrote:

Unless there is a connection within the power supply to earth ground
or some other reference point such as a ground for a control signal,
the power supply is just a 48 volt power supply. One terminal is
positive and the other negative.

I naively agree with you. But the negative part of -48 VDC confuses me
on what the positive and negative lead is. :-/

When you say "return" terminal, what do you see that distinguishes
the two terminals? Is one labeled "return"?

Yes. One terminal is labeled "return" and the other terminal is unlabled.

Is that the positive terminal? If you plug it in and measure the
terminals to earth ground, what do you get? If one approximately
zero volts and the other positive or negative?

I have not yet done this test.

You may need to put a 1 kohm resistor across the meter to prevent
seeing stray voltage while you do this.

Yep. I'm familiar with this.

> In typical DC electronics, red is positive and black negative.

This matches my experience.

I don't work with -48 volt circuits a lot, so I can't say that this
applies for that.

My limited experience with -48 VDC makes me think that it does not.
Hence my desire to get a better understanding of -48 VDC.

What is the existing system using? I would go with that unless you
want to rewire the whole thing.

Sadly, the few pieces of -48 VDC equipment that I have are all using
small AC to DC power supplies for each piece of -48 VDC equipment. Both
the supplies and the equipment are unique. There's nothing really
common to look at. Save for the red and black wires. But with nothing
else common to match against, it's tough to tell.

> Is the equipment designed for -48 volts?

Yes.

> If so connect accordingly. I guess you are asking about colors.

I'm asking multiple questions in the hopes of getting a general
understanding. I'd like to have more than simple wrote memory.

I don't know convention other than in smaller gear where red is
positive and black is negative.

That's where the bulk of my experience is too.

The main thing is to not think in terms of "reference" or "ground"
but positive and negative. You won't blow up things if you keep
polarity straight.

If I put on blinders and look at just the positive / negative and what
each piece of equipment wants, I agree.

I'm trying to learn more about how the multiple pieces of equipment work
together as a system.

If the equipment is not presently connected (for you to measure and
copy), I recommend you get a manual for the equipment and find out
what polarity they are expecting. Getting that wrong can destroy
the equipment.

Yep. I know that the equipment is -48 VDC. I know that the supply
provides -48 VDC. I'm just not clear on which terminal needs to be
connected to what. Yes the manuals will be involved.



--
Grant. . . .
unix || die

 

[Rick C]

On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote:

On 1/25/20 3:54 PM, Rick C wrote:
Unless there is a connection within the power supply to earth ground
or some other reference point such as a ground for a control signal,
the power supply is just a 48 volt power supply. One terminal is
positive and the other negative.

I naively agree with you. But the negative part of -48 VDC confuses me
on what the positive and negative lead is. :-/

This seems to be the question you are asking I guess.

If you are working with a -48 volt system, the ground will be positive and the power lead will be negative. If your power supply is intended for such a system the lead labeled "return" will be positive and the other output will be negative.

It would be helpful to see some photos of the terminals and the power supply label.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote:

On 1/25/20 3:54 PM, Rick C wrote:
Unless there is a connection within the power supply to earth ground
or some other reference point such as a ground for a control signal,
the power supply is just a 48 volt power supply. One terminal is
positive and the other negative.

I naively agree with you. But the negative part of -48 VDC confuses me
on what the positive and negative lead is. :-/

Unfortunately that question is confusing to me. lol One terminal is positive and the other negative. Unless there is an internal connection to ground (like the power line safety ground - which there shouldn't be) it doesn't make any real sense to call it a -48 volt supply.

That's the part I'm not getting. Does the power supply actually say it is a -48 volt supply or just 48 volts? Or is the -48 volts just what you see in references to the supply elsewhere?

Bottom line is there's nothing unexpected going on. If it is wired for a -48 volt supply it will have the positive terminal wired to ground and the other terminal will be -48 volts. I can't tell you anything about how the terminals are labeled and I would not assume anything unless the labels on the supply are a bit more clear.

When you say "return" terminal, what do you see that distinguishes
the two terminals? Is one labeled "return"?

Yes. One terminal is labeled "return" and the other terminal is unlabled..

Is that the positive terminal? If you plug it in and measure the
terminals to earth ground, what do you get? If one approximately
zero volts and the other positive or negative?

I have not yet done this test.

The supply could very well be intended for -48 volt use with a positive ground and so the label "return" means positive. Or it could also be a typical supply with a positive output and a negative return. Is there a label with model number, maker's name, other identification? Find that and look up a data sheet.

You may need to put a 1 kohm resistor across the meter to prevent
seeing stray voltage while you do this.

Yep. I'm familiar with this.

In typical DC electronics, red is positive and black negative.

This matches my experience.

I don't work with -48 volt circuits a lot, so I can't say that this
applies for that.

My limited experience with -48 VDC makes me think that it does not.
Hence my desire to get a better understanding of -48 VDC.

When you say a better "understanding" you mean of the color code conventions? Technically it's all just wires and polarity, not much to understand.

What is the existing system using? I would go with that unless you
want to rewire the whole thing.

Sadly, the few pieces of -48 VDC equipment that I have are all using
small AC to DC power supplies for each piece of -48 VDC equipment. Both
the supplies and the equipment are unique. There's nothing really
common to look at. Save for the red and black wires. But with nothing
else common to match against, it's tough to tell.

That's what I'm asking, the wiring colors. Are they consistent?

Is the equipment designed for -48 volts?

Yes.

If so connect accordingly. I guess you are asking about colors.

I'm asking multiple questions in the hopes of getting a general
understanding. I'd like to have more than simple wrote memory.

Yes, you keep saying that, but you don't really say what is not clear. Maybe rote memory is good enough for now and a light bulb will come on later. That has happened for me in many areas.

I don't know convention other than in smaller gear where red is
positive and black is negative.

That's where the bulk of my experience is too.

The main thing is to not think in terms of "reference" or "ground"
but positive and negative. You won't blow up things if you keep
polarity straight.

If I put on blinders and look at just the positive / negative and what
each piece of equipment wants, I agree.

I don't know what you mean by "blinders". You seem to think there is some greater understanding, but in reality it's all just a matter of polarity and the conventions are just that, conventions.

I'm trying to learn more about how the multiple pieces of equipment work
together as a system.

Do you have a question?

If the equipment is not presently connected (for you to measure and
copy), I recommend you get a manual for the equipment and find out
what polarity they are expecting. Getting that wrong can destroy
the equipment.

Yep. I know that the equipment is -48 VDC. I know that the supply
provides -48 VDC. I'm just not clear on which terminal needs to be
connected to what. Yes the manuals will be involved.

Positive to positive and negative to negative. It's literally that simple. Since the vendors of the equipment seem to be fuzzy on labeling terminals, at least on the power supply, you should measure everything.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Jeff Liebermann]

On Sun, 26 Jan 2020 10:16:41 -0800 (PST), mpm <mpmillard@aol.com>
wrote:

On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:
A communications system that I worked on for the International Space Station ran on -48VDC.

Hmmm... I guess the ISS doesn't need to worry about ground leakage.

I don't know if it is still the case, but that last (and probably only) time
I had to install a two-way radio into a backhoe or bulldozer - that was
a "positive ground" system.

In 1971, after graduating college directly into a recession, the only
job I could find was working for the local 2-way radio shop. I spend
2 months installing Motorola Motrac radios in concrete trucks. I
think they were either Mack or Peterbilt but I'm not sure. Most had
positive ground system. There were also some 24 volt systems (2
batteries in series) but we were able to tap off one battery.

Somewhat later, I found myself servicing and later selling marine
radios. On larger metal hull vessels, both the positive and negative
lines are floating. Therefore, all our early marine radios had
floating grounds. Eventually, a separate 12V power system was
introduced for powering radios and such, which had a negative ground.
Eventually, we supplied positive ground 12V radios on special order,
where all the electronics was grounded to the chassis though multiple
capacitors.

I remember it because there was a circuit on the microphone hang-up
clip that would automatically un-squelch the receiver (it used ground).

Ummm... if that were Motorola, it would be called a "hangup switch".
It did have anything to do with the noise squelch but did turn off the
PL (Private Line) tone squelch decoder. Usually, the button on the
back of the microphone was connected to ground when the PL was enabled
through the "microphone hanger". However, for positive ground system,
there was an isolated leaf switch inside the "hangup switch" and the
button on the back of the microphone was not used.

But in this case, we had to isolate the chassis of the two-way
radio from "ground", as to avoid a short. I forget what we did
as a workaround.

Sounds like a later model radio that didn't have a positive ground
feature or option. I've seen radios installed on wooden platforms to
provide the necessary insulation. A plastic case microphone, isolated
hangup switch, and capacitor coupling the antenna coax ground were
also common.

I think the antenna was also one of those Motorola NMO-type mounts
(also "grounded"), so we had to do something to that too.

I've seen what happens when someone forgets about NOT ground the
antenna shield. Things mostly work ok, until someone blows the fuse
in the negative power line. That makes the only path to battery
negative through the coax cable ground. It usually works ok, until
someone keys the transmitter. The coax shield becomes hot enough to
melt the outer jacket and possibly set fire to everything nearby.

Someone earlier mentioned that "positive ground" systems tend
to slow down corrosion. I don't know if that's true with backhoes,
but they do spend their lives outdoors in the elements? (But
so do cars, mostly.)

The corrosion aspect was important for telco plant, but less so for
automotive. For cars, the manufacturers wanted to save money. Why
waste money on copper "ground" wire when they can run the current
though the body of the car. At high currents, that was also good for
re-heating all the Unibody spot welds. Usually about 10% of these
welds would fail, which was not enough to ruin the integrity of the
chassis, but was sufficient to create enough squeaks and rattles to
drive the owner nuts. With such an arrangement, it really doesn't
matter whether the chassis is positive or negative polarity. Road
salt is sufficient to guarantee that the body rots out at about the
same time as the other major components fail. I don't know why
negative ground was selected, but there are a variety of theories.
Here's one that suggests it was because the original cloth insulation
would leak current when wet and cause corrosion:
<http://www.cruisersforum.com/forums/f14/negative-ground-vs-positive-ground-history-question-184600.html>

Incidentally, Motorola decided to run two really heavy cables directly
between the trunk mounted radio and the battery under the hood.
However, they got cheap and lazy with their front and dash mounted
radios by supplying fairly short power cables with the radios.
Installers were tempted to just ground the negative to the car chassis
and were then blessed with alternator whine, generator whine, and
vibrator hash on transmit.

Not wishing to repeat all the mistakes of past attempts to color code
the power wiring, the solar power standard committees decided that it
would be better to label these in English and use the colors in their
original manner (red=danger, green=working, yellow=warning,
black=all_else). So, it is now mandatory to attach stickers on
everything including the DC power cables:
<https://www.google.com/search?tbm=isch&q=solar+power+warning+labels>
However, the DC power labels do not mention polarity. Instead the are
yellow and say "Solar Circuit". Most (not all) of the panels I've
seen use red and black color coded wires. NEC 2014 wasn't bad for a
first attempt at labeling, but did require a rewrite in 2017 to make
the English intelligible.
<https://www.solarpowerworldonline.com/2016/03/new-nec-2017-brings-clarity-solar-pv-labeling/>
I expect the next generation of labels might add multiple languages,
hieroglyphics, and icons.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[George Herold]

On Sunday, January 26, 2020 at 1:23:27 PM UTC-5, Grant Taylor wrote:

On 1/25/20 2:34 PM, George Herold wrote:
Voltages are about differences. You have to set 'zero' somewhere...
or we can't really talk about it. Ground is a common point (NPI)
you can float everything above ground... but it gets dangerous to touch
above ~60V (depends on source impedance)
GH.
Are you an EE?

No. I'm a systems / network administrator by trade. I'm just trying to
understand (more than wrote memory) how some of the equipment I
administer works.

There are other, more skilled people between me and connecting equipment.

OK, that makes sense. Good on you for trying to figure it out.
probably you can get one of the tech guys to show you the voltage on a
DMM (volt meter). (and even compare to ground on the ac plug.)

George H.

--
Grant. . . .
unix || die

 

[Grant Taylor]

On 1/26/20 1:37 PM, Rick C wrote:
> Unfortunately that question is confusing to me. lol

Sorry. I'll try restating.

I naively agree with you that one terminal is positive with respect to
the other terminal.

However, what this terminal is called, is confusing, particularly when
dealing with negative voltage.

Aside: Yes, this equipment is powered by /negative/ 48 VDC.
"Neg(ative) 48 (V(DC))" or some close variant (including the "negative
polarity) and "48" volts) is quite common phrasing as an alternate power
source in computer (particularly servers) and networking equipment.

Further Aside: I can't actually remember the last time I heard
reference to (positive) 48 VDC in computers & networking equipment.

I believe that if I hook the positive / red lead of a voltmeter to the
positive / red lead of a power supply, and the negative / black lead of
the volt meter to the negative / black 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

So what is called the positive or red lead actually is negative with
respect to what is called the negative or black lead.

I /think/ this is accurate. But I'm not sure. Nor do I actually
understand /why/ this is the way that it is. This thread is my attempt
to learn and understand. …how can a positive power wire have a
negative voltage on it?

One terminal is positive and the other negative. Unless there is an
internal connection to ground (like the power line safety ground -
which there shouldn't be) it doesn't make any real sense to call it
a -48 volt supply.

See above.

> That's the part I'm not getting.

I understand the confusion. Hence my trying to ask questions and learn.

> Does the power supply actually say it is a -48 volt supply

Simplistically, yes, the power supply does say that it's -48 VDC.

Less simplistically, the labeling may not say it in those words. It may
simply say the output is (nominally) -48 VDC. Some actually are labeled
as -48 VDC supplies.

or just 48 volts? Or is the -48 volts just what you see in references
to the supply elsewhere?

Nope. To the best of my knowledge, the "negative" is an important part
of the description. I don't think it's simply how it's connected in
relation to the 48 VDC.

Bottom line is there's nothing unexpected going on. If it is wired
for a -48 volt supply it will have the positive terminal wired to
ground and the other terminal will be -48 volts. I can't tell you
anything about how the terminals are labeled and I would not assume
anything unless the labels on the supply are a bit more clear.

The supply could very well be intended for -48 volt use with a positive
ground and so the label "return" means positive. Or it could also
be a typical supply with a positive output and a negative return.
Is there a label with model number, maker's name, other identification?
Find that and look up a data sheet.

That is my plan.

When you say a better "understanding" you mean of the color code
conventions? Technically it's all just wires and polarity, not much
to understand.

No. It's more than just color code. As you say, colors are immaterial
and simply chosen based on convention.

I want to understand how the volt meter reading described above.

I want to understand how the following AC-to-DC power supplies work:

-⏚) AC-to-DC with a connection between neutral / ground and the - output.
+⏚) AC-to-DC with a connection between neutral / ground and the + output.

If I don't know which, +⏚ or -⏚, the AC-to-DC supply is and I bond the -
output to ⏚, I'm either going to be safe (-⏚) or quite unhappy (+⏚).

> That's what I'm asking, the wiring colors. Are they consistent?

The equipment all uses red and black wires. I don't know what the
potential is between each of them to ⏚ is, much less how they are labeled.

I will need to look when I get an opportunity to, probably on Tuesday.

> Yes, you keep saying that, but you don't really say what is not clear.

I hope this message has cleared some of this up.

Maybe rote memory is good enough for now and a light bulb will come
on later. That has happened for me in many areas.

Maybe. I dislike doing such.

> I don't know what you mean by "blinders".

I'm referring to the 48 VDC supply (negative omitted on purpose) coming
in on two wires to connect to a piece of equipment. I can ignore the
color of the wires, use a volt meter to identify which is + and - and
wire it to the equipment the way that it wants. But that ignores, or is
blind to, the actual colors of the wires and how it integrates to the
rest of the system.

You seem to think there is some greater understanding, but in reality
it's all just a matter of polarity and the conventions are just that,
conventions.

I /think/ that it is more than just polarity. See the +⏚ and -⏚
examples above.

> Do you have a question?

I think I've asked, or at least alluded to, many in this thread. It's
difficult to word smith a question about a concept that is still unclear
to me. :-( I think this email has some better ""questions in the form
of "I want to understand". They aren't worded as questions per say.
But I hope they convey what I want to learn.

Positive to positive and negative to negative. It's literally
that simple. Since the vendors of the equipment seem to be fuzzy on
labeling terminals, at least on the power supply, you should measure
everything.

--
Grant. . . .
unix || die

 

[Rick C]

On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:

On 1/26/20 1:37 PM, Rick C wrote:
Unfortunately that question is confusing to me. lol

Sorry. I'll try restating.

I naively agree with you that one terminal is positive with respect to
the other terminal.

However, what this terminal is called, is confusing, particularly when
dealing with negative voltage.

That's why I would look at the documentation for the equipment/supply. 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".

Aside: Yes, this equipment is powered by /negative/ 48 VDC.
"Neg(ative) 48 (V(DC))" or some close variant (including the "negative
polarity) and "48" volts) is quite common phrasing as an alternate power
source in computer (particularly servers) and networking equipment.

Further Aside: I can't actually remember the last time I heard
reference to (positive) 48 VDC in computers & networking equipment.

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

I believe that if I hook the positive / red lead of a voltmeter to the
positive / red lead of a power supply, and the negative / black lead of
the volt meter to the negative / black 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

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

So what is called the positive or red lead actually is negative with
respect to what is called the negative or black lead.

"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.

I /think/ this is accurate. But I'm not sure. Nor do I actually
understand /why/ this is the way that it is. This thread is my attempt
to learn and understand. …how can a positive power wire have a
negative voltage on it?

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.

One terminal is positive and the other negative. Unless there is an
internal connection to ground (like the power line safety ground -
which there shouldn't be) it doesn't make any real sense to call it
a -48 volt supply.

See above.

That's the part I'm not getting.

I understand the confusion. Hence my trying to ask questions and learn.

Does the power supply actually say it is a -48 volt supply

Simplistically, yes, the power supply does say that it's -48 VDC.

Less simplistically, the labeling may not say it in those words. It may
simply say the output is (nominally) -48 VDC. Some actually are labeled
as -48 VDC supplies.

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.

or just 48 volts? Or is the -48 volts just what you see in references
to the supply elsewhere?

Nope. To the best of my knowledge, the "negative" is an important part
of the description. I don't think it's simply how it's connected in
relation to the 48 VDC.

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.

Bottom line is there's nothing unexpected going on. If it is wired
for a -48 volt supply it will have the positive terminal wired to
ground and the other terminal will be -48 volts. I can't tell you
anything about how the terminals are labeled and I would not assume
anything unless the labels on the supply are a bit more clear.

The supply could very well be intended for -48 volt use with a positive
ground and so the label "return" means positive. Or it could also
be a typical supply with a positive output and a negative return.
Is there a label with model number, maker's name, other identification?
Find that and look up a data sheet.

That is my plan.

When you say a better "understanding" you mean of the color code
conventions? Technically it's all just wires and polarity, not much
to understand.

No. It's more than just color code. As you say, colors are immaterial
and simply chosen based on convention.

I want to understand how the volt meter reading described above.

The volt meter will always tell you the voltage between the two probes assuming the red will be positive and the black negative. If that is correct the meter will show a positive voltage. I the red lead is negative it will show a negative voltage.

I want to understand how the following AC-to-DC power supplies work:

-⏚) AC-to-DC with a connection between neutral / ground and the - output.

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


> +⏚) AC-to-DC with a connection between neutral / ground and the + output.

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

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).

If I don't know which, +⏚ or -⏚, the AC-to-DC supply is and I bond the -
output to ⏚, I'm either going to be safe (-⏚) or quite unhappy (+⏚).

Why would you bond any voltage line to earth? Do your equipment systems use actual grounds anywhere? It's easy enough to measure the voltages and see if the power is connected to ground.

That's what I'm asking, the wiring colors. Are they consistent?

The equipment all uses red and black wires. I don't know what the
potential is between each of them to ⏚ is, much less how they are labeled.

I'd say a measurement is in order... with the resistor I mentioned.

I will need to look when I get an opportunity to, probably on Tuesday.

Yes, you keep saying that, but you don't really say what is not clear.

I hope this message has cleared some of this up.

Maybe rote memory is good enough for now and a light bulb will come
on later. That has happened for me in many areas.

Maybe. I dislike doing such.

I don't know what you mean by "blinders".

I'm referring to the 48 VDC supply (negative omitted on purpose) coming
in on two wires to connect to a piece of equipment. I can ignore the
color of the wires, use a volt meter to identify which is + and - and
wire it to the equipment the way that it wants. But that ignores, or is
blind to, the actual colors of the wires and how it integrates to the
rest of the system.

That's the part I don't get. Once you measure the voltages on the wires and know what the terminals of your equipment need, what else is there to know about the "system"??? The only problem that could happen is if one of the power leads is grounded to the chassis and a piece of equipment connects power to the chassis, but they are different connections. That's why you read the documentation.

You seem to think there is some greater understanding, but in reality
it's all just a matter of polarity and the conventions are just that,
conventions.

I /think/ that it is more than just polarity. See the +⏚ and -⏚
examples above.

That is all polarity, no? I'm not getting it.

Do you have a question?

I think I've asked, or at least alluded to, many in this thread. It's
difficult to word smith a question about a concept that is still unclear
to me. :-( I think this email has some better ""questions in the form
of "I want to understand". They aren't worded as questions per say.
But I hope they convey what I want to learn.

Positive to positive and negative to negative. It's literally
that simple. Since the vendors of the equipment seem to be fuzzy on
labeling terminals, at least on the power supply, you should measure
everything.

I hope that helps.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Grant Taylor]

On 1/26/20 1:41 PM, Rick C wrote:

This seems to be the question you are asking I guess.

If you are working with a -48 volt system, the ground will be positive
and the power lead will be negative.

Okay.

So what colors would you expect / assume the ground and power leads to
be? Black and red, respectively? Or red and black, respectively?

If your power supply is intended for such a system the lead labeled
"return" will be positive and the other output will be negative.

Okay.

Do you think it would be acceptable for the negative power lead to be
referred to as "hot"?

This does seem to answer part of what I'm wanting to know. I say "part"
because I think your answer likely does provide the wrote memory type of
information. And in a round about way makes it easier for me to point
to the other part that I'm trying to learn.

How did you come to saying that -48 the ground will be positive and the
power lead will be negative? What other information / knowledge did you
rely on to make that statement? That other information / knowledge is
the other part of what I'm wanting to learn and understand. The
intention being for me to learn the foundational knowledge to deduce
statements like you did without needing to rely on wrote memory. Does
that make sense?

It would be helpful to see some photos of the terminals and the power
supply label.

Agreed. I'm at home, and the equipment in question is at work. I doubt
that I'll be able to get any pictures before Tuesday.



--
Grant. . . .
unix || die

 

[Rick C]

On Sunday, January 26, 2020 at 4:50:41 PM UTC-5, Grant Taylor wrote:

On 1/26/20 1:41 PM, Rick C wrote:
This seems to be the question you are asking I guess.

If you are working with a -48 volt system, the ground will be positive
and the power lead will be negative.

Okay.

So what colors would you expect / assume the ground and power leads to
be? Black and red, respectively? Or red and black, respectively?

I don't assume something I don't know about. You'll have to measure.

If your power supply is intended for such a system the lead labeled
"return" will be positive and the other output will be negative.

Okay.

Do you think it would be acceptable for the negative power lead to be
referred to as "hot"?

Hot or power. Ground/common is typically used for the "reference" of the power. So the other lead will be positive in this system and so, hot.

This does seem to answer part of what I'm wanting to know. I say "part"
because I think your answer likely does provide the wrote memory type of
information. And in a round about way makes it easier for me to point
to the other part that I'm trying to learn.

How did you come to saying that -48 the ground will be positive and the
power lead will be negative? What other information / knowledge did you
rely on to make that statement?

Just that the definition of -48 volt power is that the negative is the power or hot lead and the positive is common.

I really shouldn't use "ground" for the common lead since ground is often used for "protective earth" which is a different concept. They may be connected, but are not the same thing, just as neutral and protective earth are connected (if all is well) but not the same thing.

If I mean protective earth I will say protective earth, otherwise ground will mean common.

That other information / knowledge is
the other part of what I'm wanting to learn and understand. The
intention being for me to learn the foundational knowledge to deduce
statements like you did without needing to rely on wrote memory. Does
that make sense?

Not really. I think you are making this a bit too complicated than it is. I'm not complaining, just stating an observation.

It would be helpful to see some photos of the terminals and the power
supply label.

Agreed. I'm at home, and the equipment in question is at work. I doubt
that I'll be able to get any pictures before Tuesday.

I expect that by the time you get to the equipment this will all be much more clear to you.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[mpm]

On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:

Grant, let me just offer this as consolation:

A few months back, we got a job to wire-up a Verizon rack.
The rectifier was an Emerson NetSure 502. (Pretty generic, in that industry).

Well.... You need a Ph.D. to understand the Installation Manual.
That manual covers so many different options and configurations it will make your head spin. The manuals (plural)are at least 3-inches thick, loaded with schematics and wiring diagrams to cover any situation and options packages known to mankind.

We sat there for about an hour with the manuals just trying to figure out where to connect the two leads from the battery. (A "-48 VDC" system.)

Getting nowhere - we finally called Emerson Tech Support.
I was mortified - how embarrassing to have to call in for this kind of stuff?!
You may as well wear a hat on your head that reads "I eat paint chips."

AN HOUR LATER - the rep was FINALLY able to tell us where to hook up!
Because even though Verizon probably buys these rectifiers by the 1000's, it's some special bus arrangement requiring the aforementioned Ph.D. to decipher the fucking manual.

Great product. Horrible manuals!
Unless all you do in life is focus on authoring manuals like that, and then of course, it's terrific.

But who has the time for that?

I guess I'm saying, don't feel bad about being confused.
Even the big guys fuck it up.