Hello all. Just a question about 220V wiring for you. I've encountered
several 3-conductor 220V circuits recently. Doing a little research, I
see that around 1965 or so it was changed to requiring 4-conductor to
seperate the ground and neutral (vs. the old two hots and the third wire
being both the ground and the neutral).

Am I correct in the above? (may only be residential NEC stuff).

Does anyone know if having the neutral and ground share a conductor is a
bad thing? Does having a seperate ground really help with safety? Is
some equipment effected by the N/G binding, or a seperate N and G?

Thanks in advance!!

Chris

Hello all. Just a question about 220V wiring for you. I've encountered
several 3-conductor 220V circuits recently. Doing a little research, I
see that around 1965 or so it was changed to requiring 4-conductor to
seperate the ground and neutral (vs. the old two hots and the third wire
being both the ground and the neutral).

Am I correct in the above? (may only be residential NEC stuff).

The three-wire cable did not "combine" the neutral and ground,
the three wire cable HAD no neutral. 220V has no neutral, it
uses two 110V wires of opposite polarity. The fourth (N) wire
is for modern equipment that also has 110V circutry in it.

Yes, it is both dangerous and forbidden to combine or interconnect
the two.

Is it just me, or do we get this question every day?

--Goedjn

According to Chris Eller :

Hello all. Just a question about 220V wiring for you. I've encountered
several 3-conductor 220V circuits recently. Doing a little research, I
see that around 1965 or so it was changed to requiring 4-conductor to
seperate the ground and neutral (vs. the old two hots and the third wire
being both the ground and the neutral).

4-conductor circuits aren't "240V circuits" per-se. They're 240V/120V
circuits. The only place where a homeowner would normally be concerned about
four-wire circuits are stoves and dryers which need both 240V and 120V. US
code now requires that new stove/dryer installations must be four wire, wheras
it used to permit 3 wire. Canadian code hasn't permitted 3 wire stoves/dryers
for several decades.

Pure 240V circuits (ie: 240W water heaters) are _still_ 3 wire. They don't
need neutrals at all.

Does anyone know if having the neutral and ground share a conductor is a
bad thing? Does having a seperate ground really help with safety? Is
some equipment effected by the N/G binding, or a seperate N and G?

Sharing the neutral and ground _can_ be quite dangerous thing, that's why
they changed the code and no longer permit it in the last remaining
exception I'm aware of in the NEC.

Ie: if you have a neutral separation in the main panel, the frame of your
stove _may_ go hot.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to :
Is it just me, or do we get this question every day?

Just about. Worse, it's the same guy telling them that neutral
and ground are the same thing every time.

I need to get the FAQ updated and into autorepost.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

"Chris Lewis" wrote in message
...
According to :
Is it just me, or do we get this question every day?

Just about. Worse, it's the same guy telling them that neutral
and ground are the same thing every time.

Maybe I am that guy!
The 240v circuits to my A/C, oven and dryer have two hots and an
"uninsulated neutral" (some manufacturers call it a "bare neutral". Say
what you what, that is the official designation. And of course, it is
attached to the chassis, so it is also the ground. Every house on my
street, and millions of others, are wired identically. What is the last
time you heard of a problem with it?

The ground and the neutral aren't the same thing, but they are the same
wire.

....
Yes, it is both dangerous and forbidden to combine or
interconnect
the two.

Is it just me, or do we get this question every day?

--Goedjn

No, it's not you, but I suspect that was rhetorical, right?
Too many people have been taught to look at these things
from a voltage standpoint, (e.g. 0Vac = 0Vac = how you get
it doesn't matter), instead of correctly considering current
flow and direction plus fault control.
I'll never forget my first encounter with ground
currents: HOW could a wire overheat and melt, when there
was 0V measured at BOTH ends of it? I watched 3 wires burst
their insulation into flames before I figured it was a
problem with me preventing knowing what went wrong! I was
an avionics TS at North Island at the time. Of course, if
I'd known to use the right meter scale, I'd have seen the
voltage diff, but ... .

Regards,

Pop

It is comforting and speaks well of this group that such
knowledge and participation exists here.

"Toller" wrote in message
...

"Chris Lewis" wrote in message
...
According to :
Is it just me, or do we get this question every day?

Just about. Worse, it's the same guy telling them that neutral
and ground are the same thing every time.

Maybe I am that guy!
The 240v circuits to my A/C, oven and dryer have two hots and an
"uninsulated neutral" (some manufacturers call it a "bare neutral". Say

I just bought a new maytag dryer they tried to hand me a 3 wire plug. I
nixed it they said it was just fine. I said if they want to complete the
order get the right part. They did and all is well. My new home circa 1999
has four wire even for the water heater. Which was good when I connected the
time clock.

what you what, that is the official designation. And of course, it is
attached to the chassis, so it is also the ground. Every house on my
street, and millions of others, are wired identically. What is the last
time you heard of a problem with it?

If there was not a problem with it why was it changed. Every time you use a
ground as a neutral you ask for problems. Granted it does not happen very
often. But it does happen.
The industry has learn a few things in the last 30 years and all that the
NEC does is set a mininum standard. When followed the installation will be
safe for all concerned.

The ground and the neutral aren't the same thing, but they are the same
wire.

Excuse me, No they are not.
A ground is a non current carrying conductor most of the time. A neutral
carries current and voltage. That is why it is insulated all of the time a
ground can be both insulated or bare.

According to Toller :

"Chris Lewis" wrote in message
...
According to :
Is it just me, or do we get this question every day?

Just about. Worse, it's the same guy telling them that neutral
and ground are the same thing every time.

Maybe I am that guy!
The 240v circuits to my A/C, oven and dryer have two hots and an
"uninsulated neutral" (some manufacturers call it a "bare neutral". Say
what you what, that is the official designation. And of course, it is
attached to the chassis, so it is also the ground. Every house on my
street, and millions of others, are wired identically. What is the last
time you heard of a problem with it?

Evidently the NEC heard of enough to change the practise.

The ground and the neutral aren't the same thing, but they are the same
wire.

Not anymore. NEC now forbids that practise in new construction.

CEC hasn't permitted it for at least 3 decades.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

If there was not a problem with it why was it changed. Every time you use
a
ground as a neutral you ask for problems. Granted it does not happen very
often. But it does happen.

So you say, but cite an incident.
I know the problem is that if the neutral connection at the breaker box
opens, the chassis is potentially hot. Aside from being unlikely (what is
the last time you had a neutral connection at the breaker box open?) it is
dumb. If the chassis is hot, it is because there is an open circuit. If
there is an open circuit, the appliance will not be working. So, you have
to have an open neutral, not notice the appliance is not working, and be
well grounded (since you will be in series with the appliance.)
Sure, with 50,000,000 such circuits out there, there is probably a problem
now and then, but you probably have a bigger risk of being hit by lightning.

The industry has learn a few things in the last 30 years and all that the
NEC does is set a mininum standard. When followed the installation will be
safe for all concerned.

The ground and the neutral aren't the same thing, but they are the same
wire.

Excuse me, No they are not.
A ground is a non current carrying conductor most of the time. A neutral
carries current and voltage. That is why it is insulated all of the time a
ground can be both insulated or bare.

Sure they are the same wire on my 240 circuits; weren't you paying
attention? Contrary to what you just said, my neutral is not insulated.

You are a fool to play with such odds. The NEC is there to reduce the
chances of you getting hurt in the case of a fault.

The combined ground/neutral can open anywhere, not only the breaker box
(surely you heard that every so often someone loses their phone connection,
water mains or gas line bursts - these happen because either the earth moves
or some cuts into them. The same can and does happen to wiring in the house.
Just check some of the safety standards UL published in the last 100+
years).

You don't need to be well grounded, just sufficiently to allow ~50 mA to
pass through your body and start giving you trouble.
People not always pay attention to how and if appliances work when they
operate them, not every person on this earth is mechanically or electrically
inclined - that is why they write all those 'XXX for Dummies' books.

You may have a circuit in your home that has the ground and neutral using
the same conductor. If undisturbed, this is still acceptable (knob & tube,
asbestos, UFFI, etc come to mind - if left alone are OK).

"Toller" wrote in message
...
If there was not a problem with it why was it changed. Every time you
use
a
ground as a neutral you ask for problems. Granted it does not happen
very
often. But it does happen.

I know the problem is that if the neutral connection at the breaker box
opens, the chassis is potentially hot. Aside from being unlikely (what is
the last time you had a neutral connection at the breaker box open?) it is
dumb. If the chassis is hot, it is because there is an open circuit. If
there is an open circuit, the appliance will not be working. So, you have
to have an open neutral, not notice the appliance is not working, and be
well grounded (since you will be in series with the appliance.)
Sure, with 50,000,000 such circuits out there, there is probably a problem
now and then, but you probably have a bigger risk of being hit by
lightning.

The industry has learn a few things in the last 30 years and all that
the
NEC does is set a mininum standard. When followed the installation will
be
safe for all concerned.

Excuse me, No they are not.
A ground is a non current carrying conductor most of the time. A neutral
carries current and voltage. That is why it is insulated all of the time
a
ground can be both insulated or bare.

Sure they are the same wire on my 240 circuits; weren't you paying
attention? Contrary to what you just said, my neutral is not insulated.

Chris Lewis wrote:
According to Toller :

"Chris Lewis" wrote in message
...
According to :
Is it just me, or do we get this question every day?

Just about. Worse, it's the same guy telling them that neutral
and ground are the same thing every time.

Maybe I am that guy!
The 240v circuits to my A/C, oven and dryer have two hots and an
"uninsulated neutral" (some manufacturers call it a "bare neutral". Say
what you what, that is the official designation. And of course, it is
attached to the chassis, so it is also the ground. Every house on my
street, and millions of others, are wired identically. What is the last
time you heard of a problem with it?

Evidently the NEC heard of enough to change the practise.

The ground and the neutral aren't the same thing, but they are the same
wire.

Not anymore. NEC now forbids that practise in new construction.

CEC hasn't permitted it for at least 3 decades.

Lots of good information in here (and some good/bad opinions).

Related then is the following; my house was built in 1965 and uses a bonded
G/N for my 110/220 outlets (stove to be precise). Everyone seems to agree
that a seperage G and N are a _good idea_, and I agree with that. Is it worth
it to run a new 4-conductor line to my stove for such a refit?

Something that may make this a moot point; mt main electrical box has bonded
neutral and ground bus-bars. So, any improvements I make up the line won't
really help as the box is old design. Probably have to replace the box as
well.

An I on target here?

Thanks in advance,
Chris

In article , Chris Eller wrote:

Something that may make this a moot point; mt main electrical box has bonded
neutral and ground bus-bars. So, any improvements I make up the line won't
really help as the box is old design. Probably have to replace the box as
well.

An I on target here?

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between
ground and neutral anywhere else.

"Toller" wrote in message
...
If there was not a problem with it why was it changed. Every time you
use
a
ground as a neutral you ask for problems. Granted it does not happen
very
often. But it does happen.

So you say, but cite an incident.
I know the problem is that if the neutral connection at the breaker box
opens, the chassis is potentially hot. Aside from being unlikely (what is
the last time you had a neutral connection at the breaker box open?)

Five years ago in my previous house. The neutral for my dishwasher was loose
at the breaker box.
It prevented the dishwasher from working at all for several years until I
got around to looking into it.

Next Question?

William

it is
dumb. If the chassis is hot, it is because there is an open circuit. If
there is an open circuit, the appliance will not be working. So, you have
to have an open neutral, not notice the appliance is not working, and be
well grounded (since you will be in series with the appliance.)
Sure, with 50,000,000 such circuits out there, there is probably a problem
now and then, but you probably have a bigger risk of being hit by
lightning.

The industry has learn a few things in the last 30 years and all that
the
NEC does is set a mininum standard. When followed the installation will
be
safe for all concerned.

The ground and the neutral aren't the same thing, but they are the
same
wire.

Excuse me, No they are not.
A ground is a non current carrying conductor most of the time. A neutral
carries current and voltage. That is why it is insulated all of the time
a
ground can be both insulated or bare.

Sure they are the same wire on my 240 circuits; weren't you paying
attention? Contrary to what you just said, my neutral is not insulated.

Doug Miller wrote:
In article , Chris Eller wrote:

Something that may make this a moot point; mt main electrical box has bonded
neutral and ground bus-bars. So, any improvements I make up the line won't
really help as the box is old design. Probably have to replace the box as
well.

An I on target here?

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between
ground and neutral anywhere else.

Definitely good to know. What I really need to do is take a few classes and
learn to not only read, but _understand_ the NEC.

As I understand it, the NEC changed the bonded N and G around the time my home
was built (1965), so somehow my stove was wired up with three conductor:
H,H,N/G. Would you say that running a new 4-conductor (H,H,N,G) line to the
stove would be beneficial? I certainly think it would be an improvement, but
is it necessary?

Thanks,
Chris

OK, here's one for you:

Our previous house had a 4-pin outlet for the dryer, but our present one
had only a 3-pin outlet, so I replaced the dryer cord by a 3-pin one
(and moved the green wire at the connection block, according to
instructions).

But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right? (And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)

Would there be any advantage in replacing the 3-pin dryer outlet by a
4-pin and replacing the 4-pin cord?

MB


On 04/20/04 08:09 pm Doug Miller put fingers to keyboard and launched
the following message into cyberspace:

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between
ground and neutral anywhere else.

In article , Chris Eller wrote:
Doug Miller wrote:
In article , Chris Eller
wrote:

Something that may make this a moot point; mt main electrical box has bonded
neutral and ground bus-bars. So, any improvements I make up the line won't
really help as the box is old design. Probably have to replace the box as
well.

An I on target here?

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between

ground and neutral anywhere else.

Definitely good to know. What I really need to do is take a few classes and
learn to not only read, but _understand_ the NEC.

As I understand it, the NEC changed the bonded N and G around the time my home
was built (1965), so somehow my stove was wired up with three conductor:
H,H,N/G. Would you say that running a new 4-conductor (H,H,N,G) line to the
stove would be beneficial? I certainly think it would be an improvement, but
is it necessary?

Does your stove have any 120V elements (clock, timer, pilot lamps to show when
things are on, etc)? If so, then it would definitely be a good idea to run a
new cable. If not, then there is no need -- the neutral is used only by 120V
circuits, and not by 240V circuits.

In article , Minnie Bannister wrote:
OK, here's one for you:

Our previous house had a 4-pin outlet for the dryer, but our present one
had only a 3-pin outlet, so I replaced the dryer cord by a 3-pin one
(and moved the green wire at the connection block, according to
instructions).

Upgrading the circuit would have been a better idea than downgrading the
appliance.

But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right?

No, not unless you also installed a bonding jumper from the frame of the dryer
to the frame of the washer. Simple contact between the two cases is not enough
to ensure a solid electrical ground.

(And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)

Might be, depending on exactly what you did at the connection block in the
dryer -- and if so, there's a potential for the dryer case to become
energized. That's why it would have been better to upgrade the circuit to
4-wire.

Would there be any advantage in replacing the 3-pin dryer outlet by a
4-pin and replacing the 4-pin cord?

Yes, there would: you ensure that no matter what happens, the case of the
dryer will *always* be at zero potential with respect to earth ground, and
thus incapable of delivering a shock. That's what the safety ground system is
for.

MB


On 04/20/04 08:09 pm Doug Miller put fingers to keyboard and launched
the following message into cyberspace:

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between

ground and neutral anywhere else.

Minnie Bannister wrote:
OK, here's one for you:

Our previous house had a 4-pin outlet for the dryer, but our present one
had only a 3-pin outlet, so I replaced the dryer cord by a 3-pin one
(and moved the green wire at the connection block, according to
instructions).

But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right? (And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)

No. Your dryer has 2 hots and a ground and no neutral. An exception in
the old code allowed you to use the ground for the unbalanced portion of
the dryer load (for the timer, buzzer, light, and maybe the motor). Your
washer has a hot, ground, and neutral, and its neutral is isolated from the
frame.

Would there be any advantage in replacing the 3-pin dryer outlet by a
4-pin and replacing the 4-pin cord?


I would leave it alone. I assume you know you cannot just replace the
outlet unless you run a big (probably #10 copper) neutral wire? This means
running a whole new cable to the dryer, unless the wires are in conduit.
If you're willing to rewire it properly, it would be marginally safer to
have 4 wires. But not much safer as long as the neutral connections are
good and tight in the 3-wire hookup.

Best regards,
Bob

According to Toller :

So you say, but cite an incident.

Do google searches on this group and misc.consumers.house. I remember seeing
at least 3-4 confirmed open main neutrals leading to extremely strange problems
being reported and discussed.

I know the problem is that if the neutral connection at the breaker box
opens, the chassis is potentially hot. Aside from being unlikely (what is
the last time you had a neutral connection at the breaker box open?) it is
dumb. If the chassis is hot, it is because there is an open circuit. If
there is an open circuit, the appliance will not be working.

Incorrect. If the main neutral opens, 240 devices (ie: stove elements) won't
notice a thing awry. If the load on the two legs is roughly equal, the
120V devices will continue to work _too_.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to zxcvbob :
Minnie Bannister wrote:

But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right? (And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)

No. Your dryer has 2 hots and a ground and no neutral. An exception in
the old code allowed you to use the ground for the unbalanced portion of
the dryer load (for the timer, buzzer, light, and maybe the motor).

Most dryers have 120V motors and timers, so they "need" neutrals.

Your
washer has a hot, ground, and neutral, and its neutral is isolated from the
frame.

Would there be any advantage in replacing the 3-pin dryer outlet by a
4-pin and replacing the 4-pin cord?

I would leave it alone. I assume you know you cannot just replace the
outlet unless you run a big (probably #10 copper) neutral wire? This means
running a whole new cable to the dryer, unless the wires are in conduit.
If you're willing to rewire it properly, it would be marginally safer to
have 4 wires. But not much safer as long as the neutral connections are
good and tight in the 3-wire hookup.

Here's something that may put this into context:

If I understand the NEC rules maze correctly, if you move into a house that
has a three wire stove connection, at most, NEC requires you to put a
receptacle on it. You do not have to upgrade to four wire. Which is why
both 3-wire and 4-wire receptacles and stove/dryer plugsets are available,
and why stoves and dryers are convertible.

In contrast, by CEC rules, if you move into a house that has a three wire
stove connection, not only do you have to install a receptacle, you must
upgrade to 4 wire. Which is why three-wire stove/dryer plugsets are _not_
available here (and three wire receptacles only available for non-dryer/stove
applications - pure 240V only - you can't feed a neutral on a 3 wire 240V
circuit).

[For compability with US standards purposes, most of our stoves and dryers
are convertible too, but it's specifically not listed in the instructions,
or there are disclaimers it doesn't apply to Canada or covered by the
generic "consult your local code!" fine print.]

The NEC doesn't think the risk is high enough to require 4-wire upgrades to
3-wire systems. The CEC does.

The NEC doesn't think the risk is high enough to require mandatory refit
on existing installations (except for new work). The CEC agrees here.

Whether you want to go to the upgrade-to-4-wire CEC rules is something you
have to answer for yourself.

I would think there's a _slightly_ increased risk with stacking a ground-neutral
bonded appliance with a ground-neutral separate appliance. But minimal at worst.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Eller wrote:
Doug Miller wrote:

In article , Chris Eller wrote:


Something that may make this a moot point; mt main electrical box has bonded
neutral and ground bus-bars. So, any improvements I make up the line won't
really help as the box is old design. Probably have to replace the box as
well.

An I on target here?


No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between
ground and neutral anywhere else.


Definitely good to know. What I really need to do is take a few classes and
learn to not only read, but _understand_ the NEC.

As I understand it, the NEC changed the bonded N and G around the time my home
was built (1965), so somehow my stove was wired up with three conductor:
H,H,N/G. Would you say that running a new 4-conductor (H,H,N,G) line to the
stove would be beneficial? I certainly think it would be an improvement, but
is it necessary?

Thanks,
Chris

Let's review what happens when the neutral goes open at any point in the
circuit between the panel and the stove. The stoves 120 volt loads will
serve as rather low resistance conductors between one of the
ungrounded conductors and the frame of the stove. Another poster has
alleged that that is not a problem because you will be in series with
the load. When two impedances are in series the largest quantity of the
voltage will be reflected across the higher impedance. In the circuit
in question the higher impedance is the human being. If the voltage
applied across that human being is higher than 30 volts there is a
likelihood that that person may be injured or killed the only thing
missing is contact with another conductive surface that happens to be
grounded. The kitchen sink, refrigerator, dishwasher, and even many
kitchen floor coverings are sufficiently conductive to provide that
conductive pathway.

It has also been alleged that it makes no difference because both
conductors terminate on the bonded buss bar of the service equipment
enclosure. That position ignores the fact that since the neutral
conductor carries current it expands and contracts with each use of the
appliance. As a result of that normal thermal cycling it's connections
are under far more stress than those of the equipment grounding
(bonding) conductor.

In the older three wire configuration any failure of the neutral
conductor energizes the frame to the potential of the circuit. In the
four wire configuration the neutral opening causes the appliance to stop
functioning but the frame will remain at zero volts relative to other
grounded surfaces.

I'm only one member of the entire nations fire service and I have
attended three accidents that were secondary to failure of neutral
terminations on three wire appliances. It is true that I have been in
active service for thity plus years. One was an electrocution. the
other two were electrical injuries that were short of being fatal. One
was a working code who then spent weeks in the hospital and was provided
with an implanted defibrillator while her injured heart muscle healed.
The other suffered a dislocated shoulder and a fractured arm as a
secondary effect of the severe muscle contractions that occur during
electric shock. In all three cases the appliance in question was an
electric clothes dryer were the frame was bonded to the neutral.

It is your house and your family so which one do you think is better.
--
Tom H

Minnie Bannister posted for all of us....

OK, here's one for you:

Our previous house had a 4-pin outlet for the dryer, but our present one
had only a 3-pin outlet, so I replaced the dryer cord by a 3-pin one
(and moved the green wire at the connection block, according to
instructions).

But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right? (And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)

Would there be any advantage in replacing the 3-pin dryer outlet by a
4-pin and replacing the 4-pin cord?

MB


On 04/20/04 08:09 pm Doug Miller put fingers to keyboard and launched
the following message into cyberspace:

No. Your main panel is just fine. The NEC *requires* the ground and neutral
bars to be bonded at the main panel, and *prohibits* *any* connection between
ground and neutral anywhere else.

How much is YOUR life or anothers worth?
--
Tekkie

Chris Lewis wrote:

According to zxcvbob :

Minnie Bannister wrote:


But we have subsequently stacked the dryer and the washer, so everything
now has a "real" ground through the washer's power cord, right? (And
doesn't that mean that the neutral and ground are now connected at a
place other than the main panel?)



No. Your dryer has 2 hots and a ground and no neutral. An exception in
the old code allowed you to use the ground for the unbalanced portion of
the dryer load (for the timer, buzzer, light, and maybe the motor).


Most dryers have 120V motors and timers, so they "need" neutrals.


They need a neutral, but a 3-wire cord doesn't give them one. It dumps
the unbalanced return voltage on the ground. A small fixed load, and a
very large low-resistance ground. [I didn't design it] Should be OK
with copper wires and tight connections; I wouldn't trust it with
aluminum wire even with proper terminations. I would use aluminum for a
4-conductor dryer or range circuit.

[now that I shot my mouth off, I gotta go doublecheck whether that
grounded wire is technically a ground or a neutral]

My dryer has an old 3-wire outlet; it's connected directly to the
service panel with a short length of rigid metal conduit, so even if the
grounded wire were to somehow come loose I'd have a good equipment
ground through the conduit so I haven't bothered to change it to 4-wires.

Best regards,
Bob

According to zxcvbob :

Most dryers have 120V motors and timers, so they "need" neutrals.

They need a neutral, but a 3-wire cord doesn't give them one. It dumps
the unbalanced return voltage on the ground. A small fixed load, and a
very large low-resistance ground. [I didn't design it] Should be OK
with copper wires and tight connections; I wouldn't trust it with
aluminum wire even with proper terminations. I would use aluminum for a
4-conductor dryer or range circuit.

[now that I shot my mouth off, I gotta go doublecheck whether that
grounded wire is technically a ground or a neutral]

This is really more of a terminology quibble than anything else, for
what really matters is what the third wire is being used _for_. The
white wire in your house isn't technically a neutral _either_. That's just
the term everyone uses. It's official name is "grounded conductor".

It's used as _both_ in the case of a 3-wire stove or dryer. It's
being used as frame ground _AND_ neutral return. This starts to become
obvious when you start looking into (older) code restrictions where, for example,
you (normally) couldn't 3-wire a stove or dryer from a subpanel that has split
neutral and ground.

My dryer has an old 3-wire outlet; it's connected directly to the
service panel with a short length of rigid metal conduit, so even if the
grounded wire were to somehow come loose I'd have a good equipment
ground through the conduit so I haven't bothered to change it to 4-wires.

This is slightly better than unconduited 3-wire, in that you
have better connections to the ground. However, if the neutral
separates in your panel or on the pole, the frame of your stove _still_
goes hot. The problem is that the frame is connected to the device neutral,
not how well it's connected to the system ground.

Because the fact of the matter is, if your neutral separates in the panel,
AND if you have a neutral-ground interconnect anywhere in your house,
_every_ grounded object in your house can potentially go to damn close to
line voltage. By NEC rules, ground electrode conductivity is not necessarily
high enough even to trip a 15A breaker, let alone the mains.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:

This is slightly better than unconduited 3-wire, in that you
have better connections to the ground. However, if the neutral
separates in your panel or on the pole, the frame of your stove _still_
goes hot. The problem is that the frame is connected to the device neutral,
not how well it's connected to the system ground.

Because the fact of the matter is, if your neutral separates in the panel,
AND if you have a neutral-ground interconnect anywhere in your house,
_every_ grounded object in your house can potentially go to damn close to
line voltage. By NEC rules, ground electrode conductivity is not necessarily
high enough even to trip a 15A breaker, let alone the mains.


That happens anyway if the service loses its neutral; the bonding screw
at the service disconnect panel will energize all the grounds in the
house. I think that's why the power company takes it so seriously if
you call them and say your service seems to have lost its neutral.
(that plus the risk of fire from one leg operating at too high a voltage.)

-Bob

According to Tom Horne :

Generally an excellent post, but I think this bears commenting on:

In the older three wire configuration any failure of the neutral
conductor energizes the frame to the potential of the circuit. In the
four wire configuration the neutral opening causes the appliance to stop
functioning but the frame will remain at zero volts relative to other
grounded surfaces.

The problem with 240V/120V appliances is that if you lose the neutral,
the appliance doesn't necessarily "completely" stop working. Regardless
of whether it's 3 or 4 wire attached.

For example, with most stoves, if you lose the neutral, the only likely
symptom is that the clock stops working (but it won't necessarily![*]),
yet, the cooktop and oven continue working. Because they don't use the
neutral.[+]

Similarly, with a dryer, the heating elements will continue to work,
but the drum and blower will stop operating.

With a stove, you may not even notice that this has happened - the stove
still cooks dinner. With a dryer, if you're not there to notice (or, you
think it finished it's cycle), you won't notice.

In and of itself, losing the neutral for a stove is harmless. With a
dryer, you may well end up having to rely on the thermal cutout preventing
a house fire.

Furthermore, if the stove or dryer is on a three wire connection, the frame
now becomes directly part of the circuit - if you touch a better ground
(like a faucet), you can get zapped by the unbalanced current flowing thru
the clock (or drum rotator motor or timer motor on a dryer).

At least with four wire, you have a vastly better chance of the frame _not_
becoming part of the circuit and you won't get zapped by the clock.
[*] the clock may continue to function but _only_ during the times that
the elements are powered up. On a dryer, the timer/motor may "work" (possibly
very badly or not at all with black smoke) when the elements are powered up.
Depends on where the break is.

[+] I encountered a similar situation. In reverse. I helped rewire a
friend's house. They had to live in the place during renovations, so,
there was always being work done. Got a call several days after I
installed (and tested) a new 4-wire stove circuit with the complaint
that "the clock's working, but nothing else is". After much
head-scratching, I managed to figure out that my friend had removed and
reinstalled the duplex breaker for the stove (because he was adding
something else). This particular panel (a FPE) alternated legs in _pairs_
(AABBAABB) not individually (ABABAB) and he had reinstalled the breaker
such that both breakers were on the same leg. _Both_ ends of the heating
elements were attached to the same leg, so the elements didn't work. But
the clock was quite happy.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.