14-3 shared neutral

[Beeper]

I'd like some feed back on this one. When I built my house, I had a very
honest Father and Son contractor who were jack of all trades. They did the
wiring also. Sloppy but functional. A few years later, while making some
changes, I noticed they used 14-3 wiring to run 2 seperate circuits. These 2
circuits shared the neutral. I questioned them on it and they said that is
perfectly ok. I shared my concerns with them so they asked an electrical
inspector and he confirmed their beliefs. It's ok to do that. I understand
the load is such that it doesn't tax the neutral but what happens years down
the road when the homeowner throws an extra load here and an extra load
there on these circuits until the neutral is carrying more amperage than it
is designed for? The breakers don't trip because the hots are carrying just
under 15 amps each. 14.5 + 14.5 = 29. The 15 amp neutral can't carry 29
amps. I know it's probably a little far fetched but it is possible. I
have...no had 2 circuits like this in my house. Do I have OCD or what?
Residential electricians...what do you think?

 

[spudnuty]

This is true so long as someone competent does the work. I have seen
situations where someone added so much stuff on to a circuit that they
tied another breaker on to the kluged end of their mess probably
because the smaller gauge and resistive connections caused so much line
drop downstream. It took two breakers to turn off this mess! Was I
swearing. I saw this twice last week.
I also saw one where someone had replaced a 220 AC outlet with a
standard outlet. The lady wondered why her Christmas lights were the
brightest on the block and why they kept blowing out so much!

Richard

 

[Rich Grise]

On Wed, 23 Feb 2005 09:40:23 -0800, John Larkin wrote:

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

Cheers!
Rich

 

[John Larkin]

On Wed, 23 Feb 2005 21:11:22 GMT, Rich Grise <richgrise@example.net>
wrote:

On Wed, 23 Feb 2005 09:40:23 -0800, John Larkin wrote:

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

Cheers!
Rich

As I said, to see if they're in phase, merely connect them together
and see what happens. Report back and I'll interpret the experiment
for you.

John

 

[John Fields]

On Thu, 24 Feb 2005 20:28:24 GMT, Rich Grise <richgrise@example.net>
wrote:

By this logic, the positive pole of a battery is 180 degrees out of
phase with the negative pole.

---
More like the case in point, the ends of two batteries connected in
series-aiding will be out of phase with each other with respect to the
common connection between them.

--
John Fields

 

[Rich Grise]

On Thu, 24 Feb 2005 17:48:28 -0600, John Fields wrote:

On Wed, 23 Feb 2005 21:11:22 GMT, Rich Grise <richgrise@example.net

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

No, they're not.

If you use one end of the transformer secondary as a reference, the
center tap will be in phase with the other end of the winding, (that
is, one positive-going peak will occur at the same time as the other
positive-going peak) but if you use the center tap as the reference
the ends of the winding will be 180° out of phase with each other.
That is, the positive-going peak of one will occur when the
negative-going peak of the other occurs.

Let me put it this way.

A 180 degree phase-shifted sine wave is _visually indistinguishable_
from an instantaneously-inverted sine wave, that is, they _look_
exactly the same, but they are not the same, because they got
created by a different process.

To put it to an extreme example, consider a pulse train:
_ _ _ _ _ _
___| |_____| |_____| |_____| |_____| |_____| |__

Phase-shift it 180 degrees, and you get this:
_ _ _ _ _ _ _
|_____| |_____| |_____| |_____| |_____| |_____| |__

But if you invert it, you get this:
____ _____ _____ _____ _____ _____ ___
|_| |_| |_| |_| |_| |_|


You see, when you're not using a sine wave, it's very easy to tell the
difference between a phase shift and a polarity inversion.

Using a sine wave, however, they _look_ exactly the same, which is
misleading, and leads to tech school instructors (and probably college
profs) teaching their students that they _are_ the same, while in truth,
they're not.

Thanks,
Rich

 

[Michael A. Terrell]

John Larkin wrote:

On Fri, 25 Feb 2005 05:19:19 GMT, Rich Grise <richgrise@example.net
wrote:

On Thu, 24 Feb 2005 19:53:39 -0800, John Larkin wrote:
On Fri, 25 Feb 2005 02:21:57 GMT, Rich Grise <richgrise@example.net

OK. Given a reference sine wave A, please tell us how to tell the
difference between signals B and C, where

B = "A" inverted, and

C = "A" shifted 180 degrees.

It's more a matter of definition than telling them apart. Like I said,
once they're generated, they look exactly the same.

You look at where they came from.

Ah, I see now. Suppose two different computers calculate the number
"3". One adds 2+1, and the other takes the square root of 9. These 3's
are different, so there are actually two distinct kinds of "3".

Got it. Thanks.

John

John, I think this may be a better explanation:

If you use a scope to look at the unfiltered output of a full wave 60
Hz rectifier you see 120 bumps in a one second sweep. If there are not
two different phases you would see 60 with wider spaces between them.
This is like the argument of a diode in series with a resistor: Is the
power or the voltage reduced to half. Most people seem to think the
diode will reduce the voltage 50% and refuse to look at the math that
the effect voltage will be reduced from, Say, 120 VAC to an effective 84
VAC rather than 60 VAC.


--
Beware of those who post from srvinet.com!

Michael A. Terrell
Central Florida

 

[Fred Abse]

On Thu, 24 Feb 2005 21:48:13 -0800, John Larkin wrote:

Ah, I see now. Suppose two different computers calculate the number
"3". One adds 2+1, and the other takes the square root of 9. These 3's
are different, so there are actually two distinct kinds of "3".

That's only true for relatively large values of 3

;-)

--
Then there's duct tape ...
(Garrison Keillor)

 

[Fred Abse]

On Fri, 25 Feb 2005 05:19:19 +0000, Rich Grise wrote:

On Thu, 24 Feb 2005 19:53:39 -0800, John Larkin wrote:
On Fri, 25 Feb 2005 02:21:57 GMT, Rich Grise <richgrise@example.net

OK. Given a reference sine wave A, please tell us how to tell the
difference between signals B and C, where

B = "A" inverted, and

C = "A" shifted 180 degrees.

It's more a matter of definition than telling them apart. Like I said,
once they're generated, they look exactly the same.

If you substitute "phase difference" for "phase shift", I think it might
help.

Signals at the same frequency are either in phase, or they're
not. Causality is not ascertainable without additional information.

--
Then there's duct tape ...
(Garrison Keillor)

 

[Peter Bennett]

On Sat, 26 Feb 2005 23:05:03 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Method one uses more material, more labor and wires can be mixed between
the devices.

Method two uses only what is needed, takes less labor t install, and the
wiring is rather obvious to anyone capable of doing a later repair.

If it doesn't meet code the inspector can't allow it.

Think about it.

In some cases, the Canadian electrical code _requires_ that two
circuits be run in 14/3 (or 12/3).

Duplex outlets on a kitchen counter must be split, with one of the two
sockets fed from one phase, and the other from the other phase. They
must be fed by 14/3 or 12/3 cable from a two-pole breaker.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

Beeper wrote:

I'd like some feed back on this one. When I built my house, I had a
very
honest Father and Son contractor who were jack of all trades. They
did the
wiring also. Sloppy but functional. A few years later, while making
some
changes, I noticed they used 14-3 wiring to run 2 seperate circuits.
These 2
circuits shared the neutral. I questioned them on it and they said
that is
perfectly ok. I shared my concerns with them so they asked an
electrical
inspector and he confirmed their beliefs. It's ok to do that. I
understand
the load is such that it doesn't tax the neutral but what happens
years down
the road when the homeowner throws an extra load here and an extra
load
there on these circuits until the neutral is carrying more amperage
than it
is designed for? The breakers don't trip because the hots are
carrying just
under 15 amps each. 14.5 + 14.5 = 29. The 15 amp neutral can't carry
29
amps. I know it's probably a little far fetched but it is possible.
I
have...no had 2 circuits like this in my house. Do I have OCD or
what?
Residential electricians...what do you think?

The neutral carries the DIFFERENCE of those currents, not the SUM.
If the phase currents are equal, the neutral has I=0.
Wade

 

[John Larkin]

On 23 Feb 2005 08:07:34 -0800, wade_h@saber.net wrote:

Beeper wrote:
I'd like some feed back on this one. When I built my house, I had a
very
honest Father and Son contractor who were jack of all trades. They
did the
wiring also. Sloppy but functional. A few years later, while making
some
changes, I noticed they used 14-3 wiring to run 2 seperate circuits.
These 2
circuits shared the neutral. I questioned them on it and they said
that is
perfectly ok. I shared my concerns with them so they asked an
electrical
inspector and he confirmed their beliefs. It's ok to do that. I
understand
the load is such that it doesn't tax the neutral but what happens
years down
the road when the homeowner throws an extra load here and an extra
load
there on these circuits until the neutral is carrying more amperage
than it
is designed for? The breakers don't trip because the hots are
carrying just
under 15 amps each. 14.5 + 14.5 = 29. The 15 amp neutral can't carry
29
amps. I know it's probably a little far fetched but it is possible.
I
have...no had 2 circuits like this in my house. Do I have OCD or
what?
Residential electricians...what do you think?

The neutral carries the DIFFERENCE of those currents, not the SUM.
If the phase currents are equal, the neutral has I=0.
Wade

Right, so long as the two branches are on different phases. And in
office buildings where there are three separate phases of 120, that
used to be true, too. But PCs and monitors have switching power
supplies that pull a high current spike at the peak of the AC line
cycle, and the spikes from the three phases don't align in time, so
they don't cancel, and fires have resulted from the huge neutral
currents.

New directives regarding line harmonics (requiring unity-power-factor
power supplies) fix this issue.

John

 

[Terry]

Someone wrote:

" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?
The point about peak currents and being close to unity power factor seem
very valid comments.

In an industrial setting (or in a large apartment building) they MAY happen
be two 'phases'. But in most individual residence situations the two wires
which have 230 volts between them are, sort of, plus 115 volts and minus 115
volts to neutral. They are (Not quite true because we are talking AC here)
usually the two outer ends of a 230 volt 'single phase' which has a centre
tapped neutral to create the two 115 volt 'legs'. These legs are often
mistakenly called 'Phases'. They are typically Leg A (Say Black) and Leg B
(Say Red).
Thus if there is load on both 'legs' it will tend to cancel out any load in
the neutral middle conductor. However; think about this ................;
if there is load on only one side (leg) of the circuit, the neutral will
carry the same current as the hot lead on that side; and the other hot lead
will be carrying nothing; right?
It is a common mistake to think of the neutral as NOT carrying current; but
all our basic circuit training tells us that current has to flow from a
supply, through a load and return!
That return IS the neutral conductor and it better be intact and in good
shape! The fact that a good neutral is almost or only a volt or two above
ground potential means that it is doing it's job of returning the current to
the low voltage (neutral) side of the supply panel with little loss due to
the resistance of the conductor.
An open neutral is bad news and may results in electrical current trying to
return to the supply panel through whatever is available.
For example: Those so called GFIs (Ground Fault Interupters) actually work
on the currents in the hot lead and the neutral being 'balanced'. If
unbalanced due to defective neutral or a fault to ground the GFI disconnects
the outlet/s to potentially save life.
It is also bad to think of the ground wire as "Being the same as a neutral".
It is not.
The ground wire is there for safety in case something goes wrong. I would
not like to have the grounded frame of my fridge being used as the return
wire for the electric current operating the fridge compressor!
Have fun, safely!

In office buildings where there are three separate phases of 120, that
used to be true, too. But PCs and monitors have switching power
supplies that pull a high current spike at the peak of the AC line
cycle, and the spikes from the three phases don't align in time, so
they don't cancel, and fires have resulted from the huge neutral
currents.

New directives regarding line harmonics (requiring unity-power-factor
power supplies) fix this issue.

John

 

[Terry]

"Beeper" <Beeper@echoes.net> wrote in message
news:cvi83301hjc@enews3.newsguy.com...

I'd like some feed back on this one. When I built my house, I had a very
honest Father and Son contractor who were jack of all trades. They did the
wiring also. Sloppy but functional. A few years later, while making some
changes, I noticed they used 14-3 wiring to run 2 seperate circuits. These
2 circuits shared the neutral.
Beeper: I have duplex outlets in my kitchen wired this way. the upper socket

is wired, say to the red, and the lower socket of the duplex to the black.
This is not to get 230 volts between upper and lower but does allow two 115
volt loads to be plugged in, effectively doubling the current capacity of
the outlet. With 14 AWG that circuit should be fused/breakered at 15 amps. A
double pole breaker should be used to disconnect both sides 'legs' of the
supply to that circuit simultaneously.
Terry

 

[John Larkin]

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca>
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

The point about peak currents and being close to unity power factor seem
very valid comments.

In an industrial setting (or in a large apartment building) they MAY happen
be two 'phases'.

Zero degrees and 180 degrees are different phases to me. Zero and 120
are also different phases, by my standards. Zero and zero are the same
phase. A good test is to short them together and see what happens.

But in most individual residence situations the two wires
which have 230 volts between them are, sort of, plus 115 volts and minus 115
volts to neutral. They are (Not quite true because we are talking AC here)
usually the two outer ends of a 230 volt 'single phase' which has a centre
tapped neutral to create the two 115 volt 'legs'. These legs are often
mistakenly called 'Phases'.

Unless you're an engineer, in which case they are often correctly
called 'Phases.'

But definitions are personal property, so call them what you will.

John

 

[Tom Biasi]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.02.23.21.11.25.802115@example.net...

On Wed, 23 Feb 2005 09:40:23 -0800, John Larkin wrote:

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

Cheers!
Rich
Yes, they are 180 degrees out of phase "in phase."

Tom

 

[Rich Grise]

On Wed, 23 Feb 2005 18:01:06 -0500, Tom Biasi wrote:

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.02.23.21.11.25.802115@example.net...
On Wed, 23 Feb 2005 09:40:23 -0800, John Larkin wrote:

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

Yes, they are 180 degrees out of phase "in phase."

But they're the same signal! How can a signal be out of phase with itself?
Picking up a voltage from opposite ends of a transformer winding does
not introduce any phase shift, nor does center-tapping that winding and
grounding the center-tap.

If you think they're out of phase, please show me the component that
delays the signal by 1/120 second.

Sorry.
Rich

 

[Beeper]

Terry, you just said what I was hoping to hear. It is OK if the two seperate
circuits are mechanically connected(if you will) If one trips, the other one
trips also. This was not true in my case and that's why I questioned it. How
about everyone else who knows residential code. Mechanically connected? yes
or no?
"Terry" <tsanford@nf.sympatico.ca> wrote in message
news:u03Td.14418$uO.496701@news20.bellglobal.com...

"Beeper" <Beeper@echoes.net> wrote in message
news:cvi83301hjc@enews3.newsguy.com...
I'd like some feed back on this one. When I built my house, I had a very
honest Father and Son contractor who were jack of all trades. They did
the wiring also. Sloppy but functional. A few years later, while making
some changes, I noticed they used 14-3 wiring to run 2 seperate circuits.
These 2 circuits shared the neutral.
Beeper: I have duplex outlets in my kitchen wired this way. the upper
socket is wired, say to the red, and the lower socket of the duplex to the
black. This is not to get 230 volts between upper and lower but does allow
two 115 volt loads to be plugged in, effectively doubling the current
capacity of the outlet. With 14 AWG that circuit should be fused/breakered
at 15 amps. A double pole breaker should be used to disconnect both sides
'legs' of the supply to that circuit simultaneously.
Terry

 

[Rodney Kelp]

If you run two separate circuits with 14-3, I don't see the neutral sharing
aspect. Each 14-3 leg has it's own neutral.
They should have used 12-3 anyway. And if you add circuits, run new lines
from the breaker panel with a new breaker.. Don't add to existing wiring.

"Beeper" <Beeper@echoes.net> wrote in message
news:cvi83301hjc@enews3.newsguy.com...

I'd like some feed back on this one. When I built my house, I had a very
honest Father and Son contractor who were jack of all trades. They did the
wiring also. Sloppy but functional. A few years later, while making some
changes, I noticed they used 14-3 wiring to run 2 seperate circuits. These
2 circuits shared the neutral. I questioned them on it and they said that
is perfectly ok. I shared my concerns with them so they asked an
electrical inspector and he confirmed their beliefs. It's ok to do that. I
understand the load is such that it doesn't tax the neutral but what
happens years down the road when the homeowner throws an extra load here
and an extra load there on these circuits until the neutral is carrying
more amperage than it is designed for? The breakers don't trip because the
hots are carrying just under 15 amps each. 14.5 + 14.5 = 29. The 15 amp
neutral can't carry 29 amps. I know it's probably a little far fetched
but it is possible. I have...no had 2 circuits like this in my house. Do I
have OCD or what? Residential electricians...what do you think?

 

[John Larkin]

On Thu, 24 Feb 2005 02:45:07 GMT, Rich Grise <richgrise@example.net>
wrote:

On Wed, 23 Feb 2005 18:01:06 -0500, Tom Biasi wrote:


"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.02.23.21.11.25.802115@example.net...
On Wed, 23 Feb 2005 09:40:23 -0800, John Larkin wrote:

On Wed, 23 Feb 2005 13:38:01 -0330, "Terry" <tsanford@nf.sympatico.ca
wrote:

Someone wrote:
" Right, so long as the two branches are on different phases".

Err? Different 'Legs' might be a better term?

Well, I'm an electrical engineer, and we don't refer to "legs". By
"different phases" I meant that the voltages are, well, not in phase.

But with a 240V center-tapped transformer, they are exactly in phase -
simply opposite polarity, with respect to the center-tap.

Yes, they are 180 degrees out of phase "in phase."

But they're the same signal!

Then why does the power company run them in on separate wires?

How can a signal be out of phase with itself?

It can't.

Picking up a voltage from opposite ends of a transformer winding does
not introduce any phase shift, nor does center-tapping that winding and
grounding the center-tap.

If you think they're out of phase, please show me the component that
delays the signal by 1/120 second.

Take the A and B signals from a residential 120/240 circuit. Use a
time-interval counter to measure the delay from identical points and
slopes on the A and B signals, both referenced to N. You will find the
delay to be very close to 8.333 milliseconds.

Repeat experiment with a phase meter. Repeat with an oscilloscope. All
will indicate a 180 degree phase difference.

The only sensible way to refer to such a power system is "two phase."

Sorry.

John