Negative 48 Volts DC

[Grant Taylor]

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

 

[George Herold]

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.

 

[Rick C]

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?

I'm at a loss to understand what you are confused about. Do you have any specific questions???

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

--

Rick C.

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

 

On Sat, 25 Jan 2020 11:28:01 -0800 (PST), George Herold
<ggherold@gmail.com> 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.

I had a British car once with positive ground.

I had to replace the battery and, instinctively, strapped the negative
lug to the chassis. When I connected the other cable and got a big
spark, I understood the situation in milliseconds. Too many
milliseconds!

I blew out all the diodes in the alternator, and replaced them with a
couple of big Motorola bridge rectifiers. Luckily, the radio was off
at the time.

I'm working with alternators again, FADEC power supplies. You short a
PM alternator to regulate the output.

I think positive ground has some sort of corrosion advantage.



--

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"

 

[Jeff Liebermann]

On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> wrote:

>Is anyone willing to explain Negative 48 Volts DC?

Sure. It goes back to telegraphy and telephony. The power to run the
telegraphs and telephones came from batteries. One terminal of the
battery went to earth ground. The other terminal went to the wires
between stations. The problem was, which is better? Positive ground
or negative ground.

It was decided to use positive ground. The battery positive terminal
went to ground, while the negative terminal went to the stations and
wires resulting in a -48VDC system. The selection of polarity was NOT
arbitrary. A positive ground offers better protection against
corrosion:
<https://en.wikipedia.org/wiki/Tip_and_ring#Polarity>
To provide cathodic protection against corrosion of line
wires, operating potential of telephone lines is typically
negative with respect to ground, and the tip side is
generally close to the ground potential. Thus, all power
supplies for telecommunication equipment are designated to
supply a negative voltage.

When the internet was being built, data communications went via
telephone company services and lived in telephone company owned
central offices. These offices were powered by -48VDC power. It made
sense for the new internet services, switches, muxs, termination
equipment, PoE, etc to be powered by the same -48VDC power.

Please note that red=positive and black=negative is an color
automotive standard. Color codes are VERY different in other
industries.

Also, 48VDC is considered "safe" and suitable for using "low voltage
insulation". Any higher voltage requires additional protection.
However, in the electric power industry less than 50V is consider
"extra low voltage" while anything under 1000V is considered "low
voltage". Sigh.



--
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

 

[Grant Taylor]

On 1/25/20 12:28 PM, George Herold wrote:
> Right, Say you have a 48V battery.

Okay.

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.

This seems to assume that you hook the negative terminal of your meter
to ground and the positive terminal of your meter to the other battery
terminal.

So with a positive ground system, the meter's negative terminal is
hooked to the batteries positive terminal and the meter's positive
terminal is hooked to the batteries negative terminal.

This I think that "ground" / "common" is largely irreverent in this
scenario. The only way that I think it starts to make any difference is
if you don't measure at the batteries terminals and instead measure off
of a different circuit in the car reference to common.



--
Grant. . . .
unix || die

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

> I think positive ground has some sort of corrosion advantage.

Not in cars. For telephone wires, it's a different story.

It's simnple high school chemistry. Electrolysis liberates metal ions at the
positive terminal and produces OH- at the negative terminal.

when copper is at the positive terminal, copper ions are released. This
corrodes the copper.

When copper is at the negative terminal, there is only OH- produced. There is
no corrosion.

Telephone companies can drive a large ground rod into the soil to take care
of the loss of ions at the positive terminal. This protects the positive
copper terminal from corrosion. Since there is no corrosion at the negative
terminal, the copper wires are protected and can remain buried forever.

 

[Grant Taylor]

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.

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

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?

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

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?



--
Grant. . . .
unix || die

 

[Michael Nagel]

Am 25.01.20 um 20:57 schrieb Jeff Liebermann:

On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor
gtaylor@tnetconsulting.net> wrote:

Is anyone willing to explain Negative 48 Volts DC?

Sure. It goes back to telegraphy and telephony. The power to run the
telegraphs and telephones came from batteries. One terminal of the
battery went to earth ground. The other terminal went to the wires
between stations. The problem was, which is better? Positive ground
or negative ground.

It was decided to use positive ground. The battery positive terminal
went to ground, while the negative terminal went to the stations and
wires resulting in a -48VDC system. The selection of polarity was NOT
arbitrary. A positive ground offers better protection against
corrosion:
https://en.wikipedia.org/wiki/Tip_and_ring#Polarity
To provide cathodic protection against corrosion of line
wires, operating potential of telephone lines is typically
negative with respect to ground, and the tip side is
generally close to the ground potential. Thus, all power
supplies for telecommunication equipment are designated to
supply a negative voltage.

When the internet was being built, data communications went via
telephone company services and lived in telephone company owned
central offices. These offices were powered by -48VDC power. It made
sense for the new internet services, switches, muxs, termination
equipment, PoE, etc to be powered by the same -48VDC power.

Please note that red=positive and black=negative is an color
automotive standard. Color codes are VERY different in other
industries.

Also, 48VDC is considered "safe" and suitable for using "low voltage
insulation". Any higher voltage requires additional protection.
However, in the electric power industry less than 50V is consider
"extra low voltage" while anything under 1000V is considered "low
voltage". Sigh.

Amen.

A few additions:

The terminology is TNV-x (TNV-1 or TNV-2 or TNV-3).
Here is a nice tutorial:
https://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf

The IEC/EC/UL 60950-1 is past its DoW.
It has been replaced with the IEC 62368-1.
Many standards still refer to the 60950-1 and it will take at least
another decade until this has changed.

Michael

 

Michael Nagel <m_nagel@muenchen [remove this] -mail.de> wrote in
news:r0i8pk$eq9$1@news-1.m-online.net:

Am 25.01.20 um 20:57 schrieb Jeff Liebermann:
On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor
gtaylor@tnetconsulting.net> wrote:

Is anyone willing to explain Negative 48 Volts DC?

Sure. It goes back to telegraphy and telephony. The power to
run the telegraphs and telephones came from batteries. One
terminal of the battery went to earth ground. The other terminal
went to the wires between stations. The problem was, which is
better? Positive ground or negative ground.

It was decided to use positive ground. The battery positive
terminal went to ground, while the negative terminal went to the
stations and wires resulting in a -48VDC system. The selection
of polarity was NOT arbitrary. A positive ground offers better
protection against corrosion:
https://en.wikipedia.org/wiki/Tip_and_ring#Polarity
To provide cathodic protection against corrosion of line
wires, operating potential of telephone lines is typically
negative with respect to ground, and the tip side is
generally close to the ground potential. Thus, all power
supplies for telecommunication equipment are designated to
supply a negative voltage.

When the internet was being built, data communications went via
telephone company services and lived in telephone company owned
central offices. These offices were powered by -48VDC power. It
made sense for the new internet services, switches, muxs,
termination equipment, PoE, etc to be powered by the same -48VDC
power.

Please note that red=positive and black=negative is an color
automotive standard. Color codes are VERY different in other
industries.

Also, 48VDC is considered "safe" and suitable for using "low
voltage insulation". Any higher voltage requires additional
protection. However, in the electric power industry less than 50V
is consider "extra low voltage" while anything under 1000V is
considered "low voltage". Sigh.

Amen.

A few additions:

The terminology is TNV-x (TNV-1 or TNV-2 or TNV-3).
Here is a nice tutorial:
https://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf

The IEC/EC/UL 60950-1 is past its DoW.
It has been replaced with the IEC 62368-1.
Many standards still refer to the 60950-1 and it will take at
least another decade until this has changed.

Michael

Great link... thanks.

 

[George Herold]

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.

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

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?

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

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?



--
Grant. . . .
unix || die

Go to harbor freight (assuming you live in US) buy the cheap DMM
and measure it! Otherwise you have no idea how red and black are set.
GH

 

[George Herold]

On Saturday, January 25, 2020 at 3:38:40 PM UTC-5, Grant Taylor wrote:

On 1/25/20 12:28 PM, George Herold wrote:
Right, Say you have a 48V battery.

Okay.

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.

This seems to assume that you hook the negative terminal of your meter
to ground and the positive terminal of your meter to the other battery
terminal.

So with a positive ground system, the meter's negative terminal is
hooked to the batteries positive terminal and the meter's positive
terminal is hooked to the batteries negative terminal.

This I think that "ground" / "common" is largely irreverent in this
scenario. The only way that I think it starts to make any difference is
if you don't measure at the batteries terminals and instead measure off
of a different circuit in the car reference to common.



--
Grant. . . .
unix || die

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?

 

[Dean Hoffman]

On 1/25/20 2:42 PM, Steve Wilson wrote:

jlarkin@highlandsniptechnology.com wrote:

I think positive ground has some sort of corrosion advantage.

Not in cars. For telephone wires, it's a different story.

It's simnple high school chemistry. Electrolysis liberates metal ions at the
positive terminal and produces OH- at the negative terminal.

when copper is at the positive terminal, copper ions are released. This
corrodes the copper.

When copper is at the negative terminal, there is only OH- produced. There is
no corrosion.

Telephone companies can drive a large ground rod into the soil to take care
of the loss of ions at the positive terminal. This protects the positive
copper terminal from corrosion. Since there is no corrosion at the negative
terminal, the copper wires are protected and can remain buried forever.

I guess pipeline companies bury old pipe out in fields then send
some current out to the buried pipe. That protects the actual pipeline
they want to use.

 

[Grant Taylor]

On 1/25/20 1:42 PM, Steve Wilson wrote:

Telephone companies can drive a large ground rod into the soil to take
care of the loss of ions at the positive terminal. This protects the
positive copper terminal from corrosion. Since there is no corrosion
at the negative terminal, the copper wires are protected and can
remain buried forever.

Interesting. So the ground rod is for more than just safety. It's
actually used to control / prevent corrosion too.



--
Grant. . . .
unix || die

 

[Grant Taylor]

On 1/25/20 12:57 PM, Jeff Liebermann wrote:

Please note that red=positive and black=negative is an color automotive
standard. Color codes are VERY different in other industries.

All of the -48 VDC equipment that I've seen used have used red, black,
and maybe green for a safety ground.

I think that red is the "hot" wire with -48 VDC with reference to the
black "common" wire. But I'm not sure.

See my other message ~5 minutes ago for more details.



--
Grant. . . .
unix || die

 

On Sat, 25 Jan 2020 13:44:29 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> 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.

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

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?

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

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?

Ignore ricky. He doesn't want to help, he wants to insult.

Most of what he says translates to "you are stupid."



--

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"

 

On Sat, 25 Jan 2020 13:38:41 -0700, Grant Taylor
<gtaylor@tnetconsulting.net> wrote:

On 1/25/20 12:28 PM, George Herold wrote:
Right, Say you have a 48V battery.

Okay.

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.

This seems to assume that you hook the negative terminal of your meter
to ground and the positive terminal of your meter to the other battery
terminal.

So with a positive ground system, the meter's negative terminal is
hooked to the batteries positive terminal and the meter's positive
terminal is hooked to the batteries negative terminal.

This I think that "ground" / "common" is largely irreverent in this
scenario. The only way that I think it starts to make any difference is
if you don't measure at the batteries terminals and instead measure off
of a different circuit in the car reference to common.

One almost always connects a meter negative terminal to ground. That
way, you can see if the voltage you're measuring is positive or
ground.



--

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"

 

[mpm]

On Saturday, January 25, 2020 at 3:49:25 PM UTC-5, Grant Taylor wrote:

On 1/25/20 12:57 PM, Jeff Liebermann wrote:
Please note that red=positive and black=negative is an color automotive
standard. Color codes are VERY different in other industries.

All of the -48 VDC equipment that I've seen used have used red, black,
and maybe green for a safety ground.

I think that red is the "hot" wire with -48 VDC with reference to the
black "common" wire. But I'm not sure.

Here is the DC color code used by two very large US wireless carriers (i.e., cell phone providers) at their cell sites (and, signal sources like HetNet that act like "mini-cell sites"):

Coming off the batteries to the rectifier: (Input to the rectifier)
(The rectifier keeps the batteries charged.)
Black = Negative
Red = +48 VDC

Output of the rectifier feeding all the radio & other cell site equipment:
(Note: This is usually the input to a PDU, which is a fused Power Distribution Unit - a fancy name for a fused distribution block, panel-mount.)
And everything at many cell sites is 48 VDC, including the overhead lights, and sometimes even the air conditioning.

Black = Negative 48 VDC
There is a saying in the industry: "Black to the breaker."

Grey (or White) = Return (this is 0-VDC potential relative to Earth ground), and at the rectifier, is bonded to..

Green = Earth Ground (i.e., the main facility ground bus bar)
The equipment racks are also connected to ground using Green cable.

The cables used are typically TelcoFlex-III, 600 Volt. ($$ expensive cable)
I've seen anywhere from #10 AWG to #2 AWG, depending on how many cell site radios are installed.

 

[Rick C]

On Saturday, January 25, 2020 at 5:31:54 PM UTC-5, jla...@highlandsniptechnology.com wrote:

On Sat, 25 Jan 2020 13:44:29 -0700, Grant Taylor
gtaylor@tnetconsulting.net> 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.

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

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?

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

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?

Ignore ricky. He doesn't want to help, he wants to insult.

Most of what he says translates to "you are stupid."

Notice the troll likes to demean and doesn't actually help much himself.

--

Rick C.

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

 

[Rick C]

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.

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.

When you say "return" terminal, what do you see that distinguishes the two terminals? Is one labeled "return"? 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? You may need to put a 1 kohm resistor across the meter to prevent seeing stray voltage while you do this.

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

In typical DC electronics, red is positive and black negative. I don't work with -48 volt circuits a lot, so I can't say that this applies for that.

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?

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

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

Is the equipment designed for -48 volts? If so connect accordingly. I guess you are asking about colors. I don't know convention other than in smaller gear where red is positive and black is negative.

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

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.

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?

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.

--

Rick C.

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