Electrical shock from the AC neutral wire?

[Bill Bowden]

Is it possible to be shocked by touching the neutral line of a 3 wire 120
VAC system (Line, neutral, ground). Assuming all circuits are working, I
can only imagine a large voltage drop on the neutral line of maybe 50 volts
that would cause a shock. But that's a lot of current in the neutral line to
develop 50 volts.

-Bill



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[David Eather]

On Fri, 15 Aug 2014 11:52:47 +1000, Bill Bowden
<bperryb@bowdenshobbycircuits.info> wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire 120
VAC system (Line, neutral, ground). Assuming all circuits are working, I
can only imagine a large voltage drop on the neutral line of maybe 50
volts
that would cause a shock. But that's a lot of current in the neutral
line to
develop 50 volts.

-Bill



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Or a faulty eart connection with some current flowing

 

[tim]

On Thu, 14 Aug 2014 18:52:47 -0700, Bill Bowden wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire
120 VAC system (Line, neutral, ground). Assuming all circuits are
working, I can only imagine a large voltage drop on the neutral line of
maybe 50 volts that would cause a shock. But that's a lot of current in
the neutral line to develop 50 volts.

Normally? No.

For a while at a place I worked there were two different circuits,
sourced from different ends of the building, that had about 40V
difference between the grounds.

My takeaway lesson from that is to not trust nuthin'.

--
www.wescottdesign.com

 

[Helmut Wabnig]

On Thu, 14 Aug 2014 23:35:32 -0500, tim <tim@seemywebsite.com> wrote:

On Thu, 14 Aug 2014 18:52:47 -0700, Bill Bowden wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire
120 VAC system (Line, neutral, ground). Assuming all circuits are
working, I can only imagine a large voltage drop on the neutral line of
maybe 50 volts that would cause a shock. But that's a lot of current in
the neutral line to develop 50 volts.

Normally? No.

For a while at a place I worked there were two different circuits,
sourced from different ends of the building, that had about 40V
difference between the grounds.

My takeaway lesson from that is to not trust nuthin'.

Normally no, you say it.
But there is always one more bug.

w.

 

[Jim Thompson]

On Thu, 14 Aug 2014 23:35:32 -0500, tim <tim@seemywebsite.com> wrote:

On Thu, 14 Aug 2014 18:52:47 -0700, Bill Bowden wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire
120 VAC system (Line, neutral, ground). Assuming all circuits are
working, I can only imagine a large voltage drop on the neutral line of
maybe 50 volts that would cause a shock. But that's a lot of current in
the neutral line to develop 50 volts.

Normally? No.

For a while at a place I worked there were two different circuits,
sourced from different ends of the building, that had about 40V
difference between the grounds.

My takeaway lesson from that is to not trust nuthin'.

Yep. While setting up a coaxial data link between two OmniComp/GenRad
buildings in Phoenix (~1985), I found 60VAC between grounds :-(

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Bill Bowden]

"tim" <tim@seemywebsite.com> wrote in message
news:ssGdnSWM2quJE3DOnZ2dnUU7-fGdnZ2d@giganews.com...

On Thu, 14 Aug 2014 18:52:47 -0700, Bill Bowden wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire
120 VAC system (Line, neutral, ground). Assuming all circuits are
working, I can only imagine a large voltage drop on the neutral line of
maybe 50 volts that would cause a shock. But that's a lot of current in
the neutral line to develop 50 volts.

Normally? No.

For a while at a place I worked there were two different circuits,
sourced from different ends of the building, that had about 40V
difference between the grounds.

My takeaway lesson from that is to not trust nuthin'.

Yes, looks like making a good ground connection is more complicated than
just pounding a stake in the ground. Here's an interesting wiki page that
recommends installing a conductor that encircles the entire building below
the foundation. The math is fairly complicated.

http://www.electrical-installation.org/enwiki/Installation_and_measurements_of_earth_electrodes




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[ehsjr]

On 8/14/2014 9:52 PM, Bill Bowden wrote:

Is it possible to be shocked by touching the neutral line of a 3 wire 120
VAC system (Line, neutral, ground). Assuming all circuits are working, I
can only imagine a large voltage drop on the neutral line of maybe 50 volts
that would cause a shock. But that's a lot of current in the neutral line to
develop 50 volts.

-Bill



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If everything is wired correctly to code and there are no
defects, the neutral (white) wire in branch circuits (and
the neutral bus in the panel) will not rise high enough
above ground to shock you. Under normal conditions it should
be well under 5 volts above ground.

However, even with all circuits working there can be
defects.

You can be shocked by the neutral (white) wire if there
is a defect in the wiring. I'll show two examples.
The first is a wiring error with a switch wired in the white
wire to an outlet (using a bulb in the example, but it could
be a switched receptacle):

panel hot(black)---------bulb---white(neutral)---+
|
panel neutral(white)------------------[Switch]---+

The white wire in the junction box with the bulb is at
120 V when the switch is open. The white color identifies
the wire as the neutral leg, but the incorrectly wired
switch interrupts the connection back to the panel.
The circuit works just fine, but exposes you to danger.

Another example concerns a shared neutral circuit (also
called a multiwire branch circuit) like this:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)-----------+ <=== ground potential
|
[Load2]
|
Phase2 hot(red)----------+

If the neutral wire back to the panel is open, Load1
is in series with Load2 which forms a voltage divider,
raising the neutral wire potential above ground:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)---- ----+ <=== V = 240 - V_Load1
|
[Load2]
|
Phase2 hot(red)----------+

The above circuit works just fine, too if the current
drawn by the loads are roughly the same. And a bad
neutral connection at the panel can develop slowly over
time where the circuit works, but operation degrades
so slowly it is undetected. Meanwhile, bulbs burn out
more frequently and/or suddenly glow more brightly
when a heavy draw appliance turns on, so the circuit
works, but not properly.

Ed

 

[Bill Bowden]

"ehsjr" <ehsjr@mverizon.net> wrote in message
news:lsmlqv$9af$1@news.eternal-september.org...

On 8/14/2014 9:52 PM, Bill Bowden wrote:
Is it possible to be shocked by touching the neutral line of a 3 wire 120
VAC system (Line, neutral, ground). Assuming all circuits are working, I
can only imagine a large voltage drop on the neutral line of maybe 50
volts
that would cause a shock. But that's a lot of current in the neutral line
to
develop 50 volts.

-Bill



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---


If everything is wired correctly to code and there are no
defects, the neutral (white) wire in branch circuits (and
the neutral bus in the panel) will not rise high enough
above ground to shock you. Under normal conditions it should
be well under 5 volts above ground.

However, even with all circuits working there can be
defects.

You can be shocked by the neutral (white) wire if there
is a defect in the wiring. I'll show two examples.
The first is a wiring error with a switch wired in the white
wire to an outlet (using a bulb in the example, but it could
be a switched receptacle):

panel hot(black)---------bulb---white(neutral)---+
|
panel neutral(white)------------------[Switch]---+

The white wire in the junction box with the bulb is at
120 V when the switch is open. The white color identifies
the wire as the neutral leg, but the incorrectly wired
switch interrupts the connection back to the panel.
The circuit works just fine, but exposes you to danger.

Another example concerns a shared neutral circuit (also
called a multiwire branch circuit) like this:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)-----------+ <=== ground potential
|
[Load2]
|
Phase2 hot(red)----------+

If the neutral wire back to the panel is open, Load1
is in series with Load2 which forms a voltage divider,
raising the neutral wire potential above ground:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)---- ----+ <=== V = 240 - V_Load1
|
[Load2]
|
Phase2 hot(red)----------+

The above circuit works just fine, too if the current
drawn by the loads are roughly the same. And a bad
neutral connection at the panel can develop slowly over
time where the circuit works, but operation degrades
so slowly it is undetected. Meanwhile, bulbs burn out
more frequently and/or suddenly glow more brightly
when a heavy draw appliance turns on, so the circuit
works, but not properly.

Ed

Yes, the switch needs to be on the hot side, not the neutral. Not familiar
with multiphase setups but I get the idea. I experimented this morning with
two blank copper clad circuit.boards on a table with a ohm meter connected
between the boards. I wet my hands and placed one hand on each board and
pressed down and got my body resistance to drop to about 5K ohms. I was
reading somewhere that a mild shock is only about 1 milliamp, so it looks
like you could get a mild shock from just 5 volts under perfect conditions.
But an osha reference indicated wet body resistance could go as low as 200
ohms. Not sure I believe that. Maybe that's with an open wound where the
skin is broken. I hear they take great care during open heart surgery to
keep the stray voltages close to zero.

-Bill





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[Bill Bowden]

"ehsjr" <ehsjr@mverizon.net> wrote in message
news:lsmlqv$9af$1@news.eternal-september.org...

On 8/14/2014 9:52 PM, Bill Bowden wrote:
Is it possible to be shocked by touching the neutral line of a 3 wire 120
VAC system (Line, neutral, ground). Assuming all circuits are working, I
can only imagine a large voltage drop on the neutral line of maybe 50
volts
that would cause a shock. But that's a lot of current in the neutral line
to
develop 50 volts.

-Bill



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---


If everything is wired correctly to code and there are no
defects, the neutral (white) wire in branch circuits (and
the neutral bus in the panel) will not rise high enough
above ground to shock you. Under normal conditions it should
be well under 5 volts above ground.

However, even with all circuits working there can be
defects.

You can be shocked by the neutral (white) wire if there
is a defect in the wiring. I'll show two examples.
The first is a wiring error with a switch wired in the white
wire to an outlet (using a bulb in the example, but it could
be a switched receptacle):

panel hot(black)---------bulb---white(neutral)---+
|
panel neutral(white)------------------[Switch]---+

The white wire in the junction box with the bulb is at
120 V when the switch is open. The white color identifies
the wire as the neutral leg, but the incorrectly wired
switch interrupts the connection back to the panel.
The circuit works just fine, but exposes you to danger.

Another example concerns a shared neutral circuit (also
called a multiwire branch circuit) like this:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)-----------+ <=== ground potential
|
[Load2]
|
Phase2 hot(red)----------+

If the neutral wire back to the panel is open, Load1
is in series with Load2 which forms a voltage divider,
raising the neutral wire potential above ground:

Phase1 hot(black)--------+
|
[Load1]
|
Neutral(white)---- ----+ <=== V = 240 - V_Load1
|
[Load2]
|
Phase2 hot(red)----------+

The above circuit works just fine, too if the current
drawn by the loads are roughly the same. And a bad
neutral connection at the panel can develop slowly over
time where the circuit works, but operation degrades
so slowly it is undetected. Meanwhile, bulbs burn out
more frequently and/or suddenly glow more brightly
when a heavy draw appliance turns on, so the circuit
works, but not properly.

Ed

Yes, the switch needs to be on the hot side, not the neutral. Not familiar
with multiphase setups but I get the idea. I experimented this morning with
two blank copper clad circuit.boards on a table with a ohm meter connected
between the boards. I wet my hands and placed one hand on each board and
pressed down and got my body resistance to drop to about 5K ohms. I was
reading somewhere that a mild shock is only about 1 milliamp, so it looks
like you could get a mild shock from just 5 volts under perfect conditions.
But an osha reference indicated wet body resistance could go as low as 200
ohms. Not sure I believe that. Maybe that's with an open wound where the
skin is broken. I hear they take great care during open heart surgery to
keep the stray voltages close to zero.

-Bill






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[Jasen Betts]

On 2014-08-17, Bill Bowden <bperryb@bowdenshobbycircuits.info> wrote:

Yes, the switch needs to be on the hot side, not the neutral. Not familiar
with multiphase setups but I get the idea. I experimented this morning with
two blank copper clad circuit.boards on a table with a ohm meter connected
between the boards. I wet my hands and placed one hand on each board and
pressed down and got my body resistance to drop to about 5K ohms. I was
reading somewhere that a mild shock is only about 1 milliamp, so it looks
like you could get a mild shock from just 5 volts under perfect conditions.

I once did a similar experiment but with a 4.5V supply and lengths of
metal tubing, and can say that you surmise correctly. such a low voltage
can give you a surprise in ideal circumstances.

But an osha reference indicated wet body resistance could go as low as 200
ohms.

Not sure I believe that. Maybe that's with an open wound where the
skin is broken. I hear they take great care during open heart surgery to
keep the stray voltages close to zero.

Some of that resistance is actually a fixed voltage drop, 9V powered
and 1.5V powered ohm meters will give different readings,
and yeah broken skin makes a difference.

--
umop apisdn


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