Discussion:
Why 3-prong plugs
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micky
2017-03-07 21:29:46 UTC
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Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?

And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
Retired
2017-03-07 22:00:32 UTC
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Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
I have a Toshiba Netbook with a small "black rectangular thing" that
is only 2-prong.

The Mac Mini has a large white thing that is 2 prong.
trader_4
2017-03-08 17:31:06 UTC
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Post by Retired
Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
I have a Toshiba Netbook with a small "black rectangular thing" that
is only 2-prong.
The Mac Mini has a large white thing that is 2 prong.
Same here with a Dell notebook, it has a two prong power supply.
c***@snyder.on.ca
2017-03-08 01:27:10 UTC
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Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
If the power supply were to short power could get through the
laptop, and out the USB or headphone, or whatever jacks.?
Anyway, some require grounding by code, others don'r.
Stijn De Jong
2017-03-08 04:29:30 UTC
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Post by c***@snyder.on.ca
If the power supply were to short power could get through the
laptop, and out the USB or headphone, or whatever jacks.?
Anyway, some require grounding by code, others don'r.
It's a good question, since the OP is right that a power supply seems
pretty well isolated by all that plastic encasement, and the output is low
DC at relatively low amps (< 10 or so amps most of the time).

There's no power transformers anymore due to the switching power supply
design.

And yet ... ... ...

I wonder if the electronics of the switching power supply require a really
good ground?
Ralph Mowery
2017-03-08 15:54:55 UTC
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In article <o9o1b9$1hj7$***@gioia.aioe.org>, ***@nlnet.nl
says...
Post by Stijn De Jong
Post by c***@snyder.on.ca
If the power supply were to short power could get through the
laptop, and out the USB or headphone, or whatever jacks.?
Anyway, some require grounding by code, others don'r.
It's a good question, since the OP is right that a power supply seems
pretty well isolated by all that plastic encasement, and the output is low
DC at relatively low amps (< 10 or so amps most of the time).
There's no power transformers anymore due to the switching power supply
design.
And yet ... ... ...
I wonder if the electronics of the switching power supply require a really
good ground?
The switchers do have transformers in them. They are usually after some
of the switching circuit and are very small compaired to what they are
if they were on the 60 HZ side.

The electronics will work fine without a ground. The ground is for
safety, and it does help with the filtering of the hash the switchers
generate that is fed back on the power wires.
It may also pay a small part to help prevent surges coming in from the
AC line.
Uncle Monster
2017-03-08 05:44:15 UTC
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Post by c***@snyder.on.ca
Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
If the power supply were to short power could get through the
laptop, and out the USB or headphone, or whatever jacks.?
Anyway, some require grounding by code, others don'r.
Many manufacturers put an IEC socket on the laptop power supplies because the power supplies will operate on multiple voltages. It's simple to change the cord that's shipped with the laptop depending on the area of the world it's sold in. It's the same with desktop computers. If the computer is shipped to a part of the world that uses 220vac 50hz, all you do is use a power cord that has the appropriate plug. t(ツ)_/¯

[8~{} Uncle Power Monster
h***@ccanoemail.ca
2017-03-08 12:57:47 UTC
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Post by Uncle Monster
Post by c***@snyder.on.ca
Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber?
If the power supply were to short power could get through the
laptop, and out the USB or headphone, or whatever jacks.?
Anyway, some require grounding by code, others don'r.
Many manufacturers put an IEC socket on the laptop power supplies because
the power supplies will operate on multiple voltages. It's simple to change
the cord that's shipped with the laptop depending on the area of the world it's sold in.
It's the same with desktop computers. If the computer is shipped to a part
of the world that uses 220vac 50hz, all you do is use a power cord that has
the appropriate plug. t(?)_/¯
[8~{} Uncle Power Monster
My Lenovo laptop has a 2-prong plug and the converter
is rated for 240 volts. I guess I am in mortal danger -
if "the power supply were to short" ... :-)
John T.
Ralph Mowery
2017-03-08 16:01:06 UTC
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Post by c***@snyder.on.ca
Anyway, some require grounding by code, others don'r.
Many manufacturers put an IEC socket on the laptop power supplies because the power supplies will operate on multiple voltages. It's simple to change the cord that's shipped with the laptop depending on the area of the world it's sold in. It's the same with desktop computers. If the computer is shipped to a part of the world that uses 220vac 50hz, all you do is use a power cord that has the appropriate plug. t
(?)_/¯
Post by c***@snyder.on.ca
[8~{} Uncle Power Monster
They have done that for many years, or in some cases like priners and
modems the power supply is seperte so they can just ship seperate
supplies depending on the country.

Many computers and some other devices have a switch for 120 or 240 volts
and that universal socket on the device. The suplies are really not
even that particular about the voltages, just get into the ball park
with them. Going 20 or 30 volts either way is fine.
g***@aol.com
2017-03-08 17:28:53 UTC
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On Wed, 8 Mar 2017 11:01:06 -0500, Ralph Mowery
Post by Ralph Mowery
Many computers and some other devices have a switch for 120 or 240 volts
and that universal socket on the device. The suplies are really not
even that particular about the voltages, just get into the ball park
with them. Going 20 or 30 volts either way is fine.
These days the switchers are very wide mouth and can take anything
from 100-250v at any frequency, even DC although they are not labeled
that way. The first thing that happens is the input is converted to DC
immediately anyway. Then it is chopped to something in the 10s of
thousands of hz, fed through a small toroid transformer, regulated,
rectified and comes out at the desired voltage. When went to New
Zealand, all I needed was a plug adapter to run every electronic
device I had (laptop, phone, camera, MP3 player, tablet etc) All of
the chargers were 100-250v.
c***@snyder.on.ca
2017-03-09 02:16:35 UTC
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On Wed, 8 Mar 2017 11:01:06 -0500, Ralph Mowery
Post by Uncle Monster
Post by c***@snyder.on.ca
Anyway, some require grounding by code, others don'r.
Many manufacturers put an IEC socket on the laptop power supplies because the power supplies will operate on multiple voltages. It's simple to change the cord that's shipped with the laptop depending on the area of the world it's sold in. It's the same with desktop computers. If the computer is shipped to a part of the world that uses 220vac 50hz, all you do is use a power cord that has the appropriate plug. t
(?)_/¯
Post by c***@snyder.on.ca
[8~{} Uncle Power Monster
They have done that for many years, or in some cases like priners and
modems the power supply is seperte so they can just ship seperate
supplies depending on the country.
Many computers and some other devices have a switch for 120 or 240 volts
and that universal socket on the device. The suplies are really not
even that particular about the voltages, just get into the ball park
with them. Going 20 or 30 volts either way is fine.
Power supplies with 120/240 switches are SO 1990.
Mark Lloyd
2017-03-09 05:52:14 UTC
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On 03/08/2017 08:16 PM, ***@snyder.on.ca wrote:

[snip]
Post by c***@snyder.on.ca
Power supplies with 120/240 switches are SO 1990.
WHAT is that supposed to mean? It can't mean that year, since there was
nothing special about 1990.

Also, I have a PC power supply from last year (2016). It has a 120/240
switch.
--
Mark Lloyd
http://notstupid.us/

"Think not that I am come to send peace on earth; I came not to send
peace, but a sword." [Jesus, Matthew 10:34]
g***@aol.com
2017-03-09 06:35:33 UTC
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Post by Mark Lloyd
[snip]
Post by c***@snyder.on.ca
Power supplies with 120/240 switches are SO 1990.
WHAT is that supposed to mean? It can't mean that year, since there was
nothing special about 1990.
Also, I have a PC power supply from last year (2016). It has a 120/240
switch.
The design is from 1990. I haven't seen an ATX supply that was not
"auto switching" AKA wide mouth and I have a dozen of them in my parts
cabinet.
c***@snyder.on.ca
2017-03-10 01:43:17 UTC
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Post by Mark Lloyd
[snip]
Post by c***@snyder.on.ca
Power supplies with 120/240 switches are SO 1990.
SO OLD. Virtually everything in the last20 years anyway is
"universal" or "auto switching" in the small SMPS world. Virtually
all my laptop powes supplies and switch mode wall warts are listed as
100-240 or the odd one 85-250 volts The odd PC power supply still has
a switch (Del and HP up until at least a few years ago) but Acer has
been full auto for at least that long. I've got8 nyear old acers that
are full automatic, for sure
Post by Mark Lloyd
WHAT is that supposed to mean? It can't mean that year, since there was
nothing special about 1990.
Also, I have a PC power supply from last year (2016). It has a 120/240
switch.
gregz
2017-03-08 09:11:29 UTC
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Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
And, I believe, when there's nothing more dangerous than a lamp
underneath the plastic and the rubber? Less dangerous because some
light bulbs ger really hot!
The ac can use ground as part of a filter, capacitor to ground. I have seen
ground fed to common on laptop, sometimes causes ground loop problems.

Greg
Colonel Edmund J. Burke
2017-03-08 13:59:18 UTC
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Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
Micky, I'm gonna field this one out to the expurts in Cyberland.
Take it away, Cyberland dudes...........
Mike Jones
2017-03-08 15:20:21 UTC
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Post by Colonel Edmund J. Burke
Post by micky
Why do laptop power supplies, the ones with black rectangular things in
the middle of the cord, have 3-prong plugs when everything you can touch
is plastic or "rubber"?
Micky, I'm gonna field this one out to the expurts in Cyberland.
Take it away, Cyberland dudes...........
A user might plug in an accessory such as a printer, headphone,
flash drive, etc which DOES have exposed metal parts, and the
manufacturer wants to have done everything he can to make it
safe so he won't be sued......
Diesel
2017-03-10 01:58:15 UTC
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Post by micky
Why do laptop power supplies, the ones with black rectangular
things in the middle of the cord, have 3-prong plugs when
everything you can touch is plastic or "rubber"?
Filtering perhaps? Limited surge supression components? Redundant
safety...I've got a few laptops around here that have the 3 prong and a
couple that don't. I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.
--
Sarcasm, because beating the living shit out of deserving people is
illegal.
g***@aol.com
2017-03-10 07:55:44 UTC
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Post by Diesel
I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.
That implies that the ground is connected to the DC common. Not sure
why they would want to do that unless it is just for RF filtering.
Diesel
2017-03-10 10:55:09 UTC
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Post by g***@aol.com
Post by Diesel
I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.
That implies that the ground is connected to the DC common. Not sure
why they would want to do that unless it is just for RF filtering.
I've suspected the issue is a ground loop based on prior experience
with that...I haven't tried to open one of these and take a look
inside, so it's entirely possible it is connected, but, due to some
filtering circuitry in between, I'm unable to do a simple continuity
test on it. By unable, I mean that it doesn't read as completing a
circuit when tested in that manner.


http://www.channld.com/hum.html

This works well to remedy the problem...

https://www.amazon.com/Mpow-Ground-Isolator-Stereo-System/dp/B019393MV2/ref=pd_lpo_107_bs_img_2?_encoding=UTF8&psc=1&refRID=H7D9H4F6E7CCRCVEDNNN
--
Sarcasm, because beating the living shit out of deserving people is illegal.
g***@aol.com
2017-03-10 14:55:06 UTC
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Post by Diesel
Post by g***@aol.com
Post by Diesel
I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.
That implies that the ground is connected to the DC common. Not sure
why they would want to do that unless it is just for RF filtering.
I've suspected the issue is a ground loop based on prior experience
with that...I haven't tried to open one of these and take a look
inside, so it's entirely possible it is connected, but, due to some
filtering circuitry in between, I'm unable to do a simple continuity
test on it. By unable, I mean that it doesn't read as completing a
circuit when tested in that manner.
http://www.channld.com/hum.html
This works well to remedy the problem...
https://www.amazon.com/Mpow-Ground-Isolator-Stereo-System/dp/B019393MV2/ref=pd_lpo_107_bs_img_2?_encoding=UTF8&psc=1&refRID=H7D9H4F6E7CCRCVEDNNN
Reading with a meter you will be looking through the filter so YMMV on
what kind of continuity you see but at 60hz there will be some pass
through. I have had that problem with desk tops that feed amps,
particularly if there are other things in that loop like a TV.
Diesel
2017-03-11 11:12:32 UTC
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Post by g***@aol.com
Post by Diesel
On Fri, 10 Mar 2017 01:58:15 -0000 (UTC), Diesel
Post by Diesel
I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to
external audio amplifiers while plugged into their chargers.
That implies that the ground is connected to the DC common. Not
sure why they would want to do that unless it is just for RF
filtering.
I've suspected the issue is a ground loop based on prior
experience with that...I haven't tried to open one of these and
take a look inside, so it's entirely possible it is connected,
but, due to some filtering circuitry in between, I'm unable to do
a simple continuity test on it. By unable, I mean that it doesn't
read as completing a circuit when tested in that manner.
http://www.channld.com/hum.html
This works well to remedy the problem...
https://www.amazon.com/Mpow-Ground-Isolator-Stereo-System/dp/B01939
3MV2/ref=pd_lpo_107_bs_img_2?_encoding=UTF8&psc=1&refRID=H7D9H4F6E7
CCRCVEDNNN
Reading with a meter you will be looking through the filter so
YMMV on what kind of continuity you see but at 60hz there will be
some pass through. I have had that problem with desk tops that
feed amps, particularly if there are other things in that loop
like a TV.
Same here. When I routed a friends computer thru a mixer board into a
stereo system, we had the ground loop hum issue to deal with. Oh the
joys of a semi digital recording studio.
--
Sarcasm, because beating the living shit out of deserving people is
illegal.
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