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-   -   Why must ground & neutral be seperate in subpanel? (https://www.diybanter.com/home-repair/184059-why-must-ground-neutral-seperate-subpanel.html)

[email protected] November 27th 06 10:25 PM

Why must ground & neutral be seperate in subpanel?
 
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?

Thanks,
Joe


Jeff Wisnia November 27th 06 11:07 PM

Why must ground & neutral be seperate in subpanel?
 
wrote:

I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?

Thanks,
Joe



While I agree that what's there is correct and functional "circuit wise"
I think the reason the code requires a separate ground conductor is this:

That common ground/neutral might develop an open between the sub panel
and the main panel because of a "loose connection" at one end or the
other. If that happened currents returning on the neutrals of those
"new" branch circuits would lift the whole "ground" of the sub panel off
true ground and would create a dangerous situation by making things like
the grouning slots in recepticals rise above ground to dangerous voltage
levels.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.


Goedjn November 27th 06 11:21 PM

Why must ground & neutral be seperate in subpanel?
 
On 27 Nov 2006 13:25:38 -0800, wrote:

I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?


Essentially, because the ground wire is connected to things
that people are expected to touch.

When you connect the nuetral and ground together, you create
the possibility of the ground becoming hot, and energizing
things like the outside of your refridgerator. This is bad.
The probability of this happening goes up astronomically
if there is a nuetral/ground interconnection anywhere
but in the main service entry.

Aside from the chance of something coming loose and putting
some random voltage between 105 and 240 volts on the
outside of your bathtub, there's also the problem that
your ground wire is not zero resistance, which means that
if you touch both it and another path to ground, at least
some of whatever current is on it will choose to go through
you. (This is why, for example, you can get a shock
from the casing of a malfunctioning appliance, even if
it's grounded.)


Richard J Kinch November 27th 06 11:22 PM

Why must ground & neutral be seperate in subpanel?
 
What is the risk of my current situation?

For one thing, it puts current into the ground conductor between the
subpanel and main panel.

Phillip Devoll November 27th 06 11:43 PM

Why must ground & neutral be seperate in subpanel?
 

wrote in message
ups.com...
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?

Thanks,
Joe


The Reason is that there is current goes through a nuteral and no current
goes through a ground and if the ground and nutural are tied together they
both have current passing through them and the only time that current should
go through a ground is when there is a short or something similar...

but to make thing even moree confusing is then why is the nurural and ground
tied together at the main pannel and that is to bond the nuural to the earth
ground...



Charles Schuler November 27th 06 11:57 PM

Why must ground & neutral be seperate in subpanel?
 

wrote in message
ups.com...
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?


The neutral (white) is a return ... it carries the same current as the hot
wire (black). The ground wire is a non current-carrying safety wire (often
bare copper). The purpose of the ground wire is to reduce voltages in the
case of lightning or an accident (wires falling across other wires outside
of your home and raising the voltage with respect to ground to a dangerous
level). The ground wire only conducts current in the case of a fault.
Ground fault circuit interrupters need the ground wire to detect such faults
and open the circuit when they occur.

People are often shocked and even electrocuted with voltages with respect to
ground ... one is standing on a wet basement floor ... one is touching a
faucet ... one is in the tub or shower. The voltage with respect to ground
is the big issue here (for safety reasons).

An ungrounded electrical system in your home would allow voltages to rise to
thousands of volts above ground and fry you if you happened to be grounded
(in a tub or standing on a wet concrete floor).



Beachcomber November 28th 06 12:00 AM

Why must ground & neutral be seperate in subpanel?
 


The Reason is that there is current goes through a nuteral and no current
goes through a ground and if the ground and nutural are tied together they
both have current passing through them and the only time that current should
go through a ground is when there is a short or something similar...

but to make thing even moree confusing is then why is the nurural and ground
tied together at the main pannel and that is to bond the nuural to the earth
ground...



OK, so the ground is bonded to the neutral at the service panel.

What about the transfromer at the pole? Is the neutral center-tap in
the North American System bonded to the transformer enclosure? Is
this point often connected to a ground wire running down the pole and
into the earth?

Also, why in the US systems is the top wire on the pole the hot wire
(for the transformer primary) and the neutral is usually several feet
below this? Is this arrangement not more prone to lightning damage?

Beachcomber



Bob F November 28th 06 12:42 AM

Why must ground & neutral be seperate in subpanel?
 

"Charles Schuler" wrote in message
The neutral (white) is a return ... it carries the same current as the hot
wire (black). The ground wire is a non current-carrying safety wire

(often
bare copper). The purpose of the ground wire is to reduce voltages in the
case of lightning or an accident (wires falling across other wires outside
of your home and raising the voltage with respect to ground to a dangerous
level). The ground wire only conducts current in the case of a fault.
Ground fault circuit interrupters need the ground wire to detect such

faults
and open the circuit when they occur.


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob



bowgus November 28th 06 12:45 AM

Why must ground & neutral be seperate in subpanel?
 

wrote:
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?

Thanks,
Joe


It's not that they're to be isolated at the pony panel (we call it up
here), it's that there is to be a single connection to "ground", and
it's to be at the main panel ... kind of like it's just not right to
connect the bare copper and white in a receptacle :-) Or, that
receptacle box if wired that way could float above ground if there's
sufficient current through that bare copper ... a "potential" for ...
geez, that smarts.


Charles Schuler November 28th 06 12:48 AM

Why must ground & neutral be seperate in subpanel?
 

"Bob F" wrote in message
...

"Charles Schuler" wrote in message
The neutral (white) is a return ... it carries the same current as the
hot
wire (black). The ground wire is a non current-carrying safety wire

(often
bare copper). The purpose of the ground wire is to reduce voltages in
the
case of lightning or an accident (wires falling across other wires
outside
of your home and raising the voltage with respect to ground to a
dangerous
level). The ground wire only conducts current in the case of a fault.
Ground fault circuit interrupters need the ground wire to detect such

faults
and open the circuit when they occur.


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.


They need the ground wire.



Beachcomber November 28th 06 01:01 AM

Why must ground & neutral be seperate in subpanel?
 

I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.


They need the ground wire.


When a ground is available at an outlet with a GFCI it is preferred
(and required) that it be installed,

However, where there is no ground the NEC still recognized that a GFCI
can still provide protection by detecting an imbalance in currents
between the neutral and hot wire. In this case, the user must be
informed (with a small sticker on the outlet) that the GFCI is
ungrounded.

Beachcomber


Chris Friesen November 28th 06 01:09 AM

Why must ground & neutral be seperate in subpanel?
 
Charles Schuler wrote:
"Bob F" wrote in message


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.



They need the ground wire.


Actually, they don't.

See section 210-7(d) in the NEC, and section 26-700(9) in the CEC.

GFCIs are a legal substitute for a grounded outlet in an existing
installation where there is no ground available in the outlet box.

Chris

w_tom November 28th 06 01:49 AM

Why must ground & neutral be seperate in subpanel?
 
All household grounds must meet only at a common point for reasons
similar to why ground loops create hum in a stereo system. Neutral,
equipment ground, and earth ground that connect at a common point (main
breaker box safety ground) avoids 'ground loops' and other adverse or
surprise currents.

To explain same using a different perspective, first, all wires are
electrically different at both ends. That difference increases as more
current flows. To better explain this, we express that difference as a
separation or electrical distance.

A three prong appliance is powered from wires that are distant from
the breaker box (because they carry current). A separate safety
(equipment) ground wire connects directly (shorter) to breaker box
safety ground because it carries no current. Appliance connected
electrically shorter to breaker box means greater human safety.

Again, if safety ground and neutral wire were connected anywhere
(other than in breaker box), then that safety ground wire would be
electrically farther from breaker box (because it carries current).
Another perspective that explains why NEC demands separate neutral and
ground wires.

Another situation: suppose neutral and safety ground wire were both
carrying current. Suddenly that common wire breaks. What happens to
appliance connected to third prong safety ground? It suddenly becomes
electrically hot - directly connected to black hot wire. AND no safety
ground exists to protect human and trip circuit breaker. We want
neutral wire separated from safety ground so that any neutral wire
break always leaves appliance still connected directly to breaker box
safety ground and not connected to a neutral wire that is no longer
connected to breaker box. Just another reason why those two wires
always remain separate.

Home has its own single point safety ground inside breaker box.
Power wires connect that system to another system that has its own
single point ground - pole transformer. Pole transformer connects
primary (high voltage) ground, secondary neutral, and earth ground to a
common point. Lightning strike to primary (high voltage) wire simply
gets conducted safely to earth at transformer which is but one reason
why that primary wire can be highest on pole.

Meanwhile, household single point ground in breaker box is one ground
system centered at a single point. Transformer has its own single
point ground system. How far apart are those two grounds? As current
increases on neutral wire (transformer to house), then both grounds
become electrically more separated. Again, using a perspective of
electrical distance to explain a concept.

wrote:
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. .... The grounds and neutrals all share the common bus bar
in the sub panel. Everything has worked fine for years now. Can
someone explain why I read that ground and neutral are to be isolated
in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?



The Streets November 28th 06 02:17 AM

Why must ground & neutral be seperate in subpanel?
 
wrote in message
ups.com...
I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?

Thanks,
Joe


So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?



Mark Lloyd November 28th 06 02:35 AM

Why must ground & neutral be seperate in subpanel?
 
On Mon, 27 Nov 2006 15:42:02 -0800, "Bob F"
wrote:


"Charles Schuler" wrote in message
The neutral (white) is a return ... it carries the same current as the hot
wire (black). The ground wire is a non current-carrying safety wire

(often
bare copper). The purpose of the ground wire is to reduce voltages in the
case of lightning or an accident (wires falling across other wires outside
of your home and raising the voltage with respect to ground to a dangerous
level). The ground wire only conducts current in the case of a fault.
Ground fault circuit interrupters need the ground wire to detect such

faults
and open the circuit when they occur.


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.
--
28 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Doug Miller November 28th 06 02:44 AM

Why must ground & neutral be seperate in subpanel?
 
In article , "The Streets" wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?


There isn't one.

To make a Code-compliant connection, you must install a second bar so that you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel. Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Bob November 28th 06 03:48 AM

Why must ground & neutral be seperate in subpanel?
 

Beachcomber wrote:


What about the transfromer at the pole? Is the neutral center-tap in
the North American System bonded to the transformer enclosure? Is
this point often connected to a ground wire running down the pole and
into the earth?

Also, why in the US systems is the top wire on the pole the hot wire
(for the transformer primary) and the neutral is usually several feet
below this? Is this arrangement not more prone to lightning damage?

That was the old way - keeping the hot wire as far from people/animals
as possible. The vast majority of new installations will put the
ground wire on top.

But what about the rural Canadian systems where there is only a hot
wire with no ground at all? Are they any more susceptable to lightning
than a US hot top wire system?


krw November 28th 06 03:52 AM

Why must ground & neutral be seperate in subpanel?
 
In article ,
lid says...
On Mon, 27 Nov 2006 15:42:02 -0800, "Bob F"
wrote:


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.


No one said GFCIs did. BobF said they are "recommended in cases
where there is no ground". They are. What's your beef?

--
Keith

Mark Lloyd November 28th 06 04:39 AM

Why must ground & neutral be seperate in subpanel?
 
On Mon, 27 Nov 2006 21:52:35 -0500, krw wrote:

In article ,
says...
On Mon, 27 Nov 2006 15:42:02 -0800, "Bob F"
wrote:


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.


No one said GFCIs did.


I said that because people have. Just not in THIS thread, but in this
group.

BobF said they are "recommended in cases
where there is no ground". They are. What's your beef?


I was saying that only because some people think they provide ground.
--
28 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

[email protected] November 28th 06 04:01 PM

Why must ground & neutral be seperate in subpanel?
 

Doug Miller wrote:
In article , "The Streets" wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?


There isn't one.

To make a Code-compliant connection, you must install a second bar so that you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel. Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.


Thanks everyone, especially Doug for this post which spells it out
clearly. Please comment on this proposed "fix":
I run another wire back to the main panel (I'll probably use some 12/2
with ground) and attach all three conductors to the ground bar in the
main panel. Then, at the sub panel, I will connect all grounds to the
new cable but not to the neutral bus bar. Now all grounds will be
grounded back at the main panel, and the neutral in the sub will be
isolated from the grounds and from the sub panel chassis. (as long as I
remove the grounding screw from the neutral bus bar)
Thanks again for your responses.
Joe


krw November 28th 06 06:21 PM

Why must ground & neutral be seperate in subpanel?
 
In article ,
lid says...
On Mon, 27 Nov 2006 21:52:35 -0500, krw wrote:

In article ,
says...
On Mon, 27 Nov 2006 15:42:02 -0800, "Bob F"
wrote:


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.


No one said GFCIs did.


I said that because people have. Just not in THIS thread, but in this
group.


Then perhaps you should correct those who are mistaken?

BobF said they are "recommended in cases
where there is no ground". They are. What's your beef?


I was saying that only because some people think they provide ground.

No one in this threadlet.

--
Keith

[email protected] November 28th 06 06:32 PM

Why must ground & neutral be seperate in subpanel?
 
Doug Miller wrote:
In article , "The Streets" wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?


There isn't one.

To make a Code-compliant connection, you must install a second bar so that you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel. Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.


This is great but it doesn't mention wire size. If the ground is
smaller than the current-carrying conductors, doesn't it become a fire
hazard?

-tg






--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.



w_tom November 28th 06 07:47 PM

Why must ground & neutral be seperate in subpanel?
 
12/2 wire to power a 40 amp breaker? Not acceptable. 12/2 when, as
Doug said, four wires are required? 12/2 is not four wires and not
sufficient gauge.

wrote:
Thanks everyone, especially Doug for this post which spells it out
clearly. Please comment on this proposed "fix":
I run another wire back to the main panel (I'll probably use some 12/2
with ground) and attach all three conductors to the ground bar in the
main panel. Then, at the sub panel, I will connect all grounds to the
new cable but not to the neutral bus bar. Now all grounds will be
grounded back at the main panel, and the neutral in the sub will be
isolated from the grounds and from the sub panel chassis. (as long as I
remove the grounding screw from the neutral bus bar)
Thanks again for your responses.
Joe



Doug Miller November 28th 06 08:13 PM

Why must ground & neutral be seperate in subpanel?
 
In article .com, wrote:

Doug Miller wrote:
In article , "The Streets"

wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?


There isn't one.

To make a Code-compliant connection, you must install a second bar so that

you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel.

Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit

breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.


Thanks everyone, especially Doug for this post which spells it out
clearly. Please comment on this proposed "fix":
I run another wire back to the main panel (I'll probably use some 12/2
with ground) and attach all three conductors to the ground bar in the
main panel.


Code violation -- all conductors for a circuit must be in the same cable,
raceway, conduit, etc. You need to run a new cable, 3 conductors plus ground
as I described.

Then, at the sub panel, I will connect all grounds to the
new cable but not to the neutral bus bar.


Another violation -- you *need* a grounding bus bar in the subpanel. Among
other things, doing what you describe leaves the subpanel chassis ungrounded.

Now all grounds will be
grounded back at the main panel, and the neutral in the sub will be
isolated from the grounds and from the sub panel chassis. (as long as I
remove the grounding screw from the neutral bus bar)



--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Doug Miller November 28th 06 08:14 PM

Why must ground & neutral be seperate in subpanel?
 
In article .com, "w_tom" wrote:
12/2 wire to power a 40 amp breaker? Not acceptable. 12/2 when, as
Doug said, four wires are required? 12/2 is not four wires and not
sufficient gauge.

He's talking about using that entire cable as the grounding conductor for the
subpanel. Still not safe, still not Code-compliant... but not quite as bad an
idea as you assumed.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Doug Miller November 28th 06 08:18 PM

Why must ground & neutral be seperate in subpanel?
 
In article om, wrote:
Doug Miller wrote:
In article , "The Streets"

wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?


There isn't one.

To make a Code-compliant connection, you must install a second bar so that

you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel.

Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit

breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.


This is great but it doesn't mention wire size. If the ground is
smaller than the current-carrying conductors, doesn't it become a fire
hazard?


No. Under normal circumstances, the grounding conductor doesn't carry current
anyway. In circuits 40A and above, the grounding conductor is permitted to be
smaller than the circuit conductors; see NEC Table 250.122 for details.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

[email protected] November 28th 06 09:13 PM

Why must ground & neutral be seperate in subpanel?
 
Doug Miller wrote:
In article om, wrote:
Doug Miller wrote:
In article , "The Streets"

wrote:

So, what is the proper way to connect a 220v sub-panel that has a single
bus bar for neutral and ground to a main panel with the neutral bar bonded
to the ground bar?

There isn't one.

To make a Code-compliant connection, you must install a second bar so that

you
can separate the neutral and ground conductors for the various circuits to
separate busses. The neutral bus must be electrically insulated from the
ground bus and from the panel chassis, and the ground bus must *not* be
insulated from the chassis.

*Also* you must connect the subpanel to the main panel using *four*
conductors, e.g. black, red, white, and bare (or green). White goes from the
neutral bus bar in the main panel to the neutral bus bar in the subpanel.

Bare
(or green) goes from the ground bus bar in the main panel to the ground bus
bar in the subpanel. Black and red go from the two lugs on the circuit

breaker
in the main panel which feeds the sub, to the lugs on the main breaker in the
subpanel.


This is great but it doesn't mention wire size. If the ground is
smaller than the current-carrying conductors, doesn't it become a fire
hazard?


No. Under normal circumstances, the grounding conductor doesn't carry current
anyway. In circuits 40A and above, the grounding conductor is permitted to be
smaller than the circuit conductors; see NEC Table 250.122 for details.


But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.

I went through this exercise in running a circuit to an outbuilding. I
never quite figured out what the code meant with respect to a ground
for that building as well. There was something about livestock, but I
don't remember it now.

-tg








--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.



Doug Miller November 28th 06 09:54 PM

Why must ground & neutral be seperate in subpanel?
 
In article . com, wrote:

But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.


The breaker will trip long before the wire will melt.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Charles Schuler November 28th 06 10:20 PM

Why must ground & neutral be seperate in subpanel?
 

"Chris Friesen" wrote in message
...
Charles Schuler wrote:
"Bob F" wrote in message


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.



They need the ground wire.


Actually, they don't.


I should have said "Not a good idea."

http://members.tripod.com/~masterslic/FAQ-2/7.html

Problems are they are supposed to labeled as "ungrounded" and external
testers won't work.



Bob F November 28th 06 10:40 PM

Why must ground & neutral be seperate in subpanel?
 

"Doug Miller" wrote in message
t...
In article . com,

wrote:

But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.


The breaker will trip long before the wire will melt.


Specifically, because it is a "short" condition, rather than an
overload, which can last much longer.

Bob



Mark Lloyd November 28th 06 10:51 PM

Why must ground & neutral be seperate in subpanel?
 
On Tue, 28 Nov 2006 12:21:33 -0500, krw wrote:

In article ,
says...
On Mon, 27 Nov 2006 21:52:35 -0500, krw wrote:

In article ,
says...
On Mon, 27 Nov 2006 15:42:02 -0800, "Bob F"
wrote:

I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.

No one said GFCIs did.


I said that because people have. Just not in THIS thread, but in this
group.


Then perhaps you should correct those who are mistaken?

BobF said they are "recommended in cases
where there is no ground". They are. What's your beef?


I was saying that only because some people think they provide ground.

No one in this threadlet.


A lot of people read these things without making their presence known.
Some will make up the wrong thing.
--
27 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Mark November 28th 06 11:04 PM

Why must ground & neutral be seperate in subpanel?
 


I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.


Will the TEST BUTTON on the GFI work if it does not have a ground?

If so, how does it work?

Mark


[email protected] November 28th 06 11:13 PM

Why must ground & neutral be seperate in subpanel?
 
Doug Miller wrote:
In article . com, wrote:

But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.


The breaker will trip long before the wire will melt.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.


Again, Thanks for the input. To clarify what I should have written, my
plan was to tie my new cable into a ground bussbar which will be
secured to the metal of the subpanel. The current neutral bar either
floats or is grounded depending on one screw which makes the ground
connection. I will remove that to make it float. Regarding the guage
and being seperate from the supply, well sometimes something is better
than nothing. 3 #12 conductors all tied to the main panel ground bus
and to the sub panel ground bus is better than the current situation.
Each #12 conductor is good for 20 Amps, so in theory my ground wire(s)
can carry 60A combined, and it is only a 40A breaker. A lesser evil
than the current situation which has not been problematic so far
anyway. When I shop for the bussbar I will price a length of #4 bare
copper and consider running that to the main instead. The issue then
will be finding a lug in the main large enough to bond it to.
Regards,
Joe


Doug Miller November 29th 06 12:04 AM

Why must ground & neutral be seperate in subpanel?
 
In article . com, wrote:
Doug Miller wrote:
In article . com,

wrote:

But the ground is meant to protect against a short to the 'case', so if
a short happens, the ground will not be protected by the circuit
breaker---it will overheat.


The breaker will trip long before the wire will melt.


Or, I should have noted, long before the wire will get hot enough to cause any
kind of problem.

Again, Thanks for the input. To clarify what I should have written, my
plan was to tie my new cable into a ground bussbar which will be
secured to the metal of the subpanel.


That's better... but it's still a Code violation. All conductors for any
circuit are required to be in the same conduit, cable, raceway, etc.
Furthermore, Code also prohibits connecting conductors in parallel unless
they're (I believe) 2ga or larger.

The current neutral bar either
floats or is grounded depending on one screw which makes the ground
connection. I will remove that to make it float.


Correct.

Regarding the guage
and being seperate from the supply, well sometimes something is better
than nothing. 3 #12 conductors all tied to the main panel ground bus
and to the sub panel ground bus is better than the current situation.


Undoubtedly. But it's still a Code violation. If you're going to run a new
cable anyway, why not run the right thing, connect it up properly, and be done
with it?

Each #12 conductor is good for 20 Amps, so in theory my ground wire(s)
can carry 60A combined,


Doesn't matter -- Code doesn't permit it.

and it is only a 40A breaker. A lesser evil
than the current situation which has not been problematic so far
anyway.


Understood -- but you asked for the proper way of doing this. What you
propose is not.

When I shop for the bussbar I will price a length of #4 bare
copper and consider running that to the main instead.


It's still a Code violation, because it's not in the same cable as the
conductors supplying the subpanel. You need to replace the existing feed with
8-3 cable (given that you're using a 40A breaker) with ground, so that all of
the conductors are in the same cable. And you won't have any trouble finding a
lug in the main that you can connect #8 to.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Don Fearn November 29th 06 12:35 AM

Why must ground & neutral be seperate in subpanel?
 
I think it was "Mark" who stated:


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


Very well[*]

What it does is measure the current leaving the "hot" lead and
compares it with the current returning in the "neutral" lead. If those
are different by more than a few milliamperes, there is a Ground
Fault, that is, current is finding its way to ground through some
other path than "neutral". If that is the case, the GFCI Interrupts
(the "I" part of "GFCI") the Circuit, very, very quickly, so that no
damage is done to whatever caused the Fault (that could be a human
body). The test button simulates a fault.
[*] I had it work once for me. I didn't know it had until the
lamp I had dropped into water wouldn't come on again.

-Don
--
"What do *you* care what other people think?" --Arline Feynman

Goedjn November 29th 06 12:50 AM

Why must ground & neutral be seperate in subpanel?
 
On Tue, 28 Nov 2006 17:35:56 -0600, Don Fearn
wrote:

I think it was "Mark" who stated:


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


Very well[*]

What it does is measure the current leaving the "hot" lead and
compares it with the current returning in the "neutral" lead. If those
are different by more than a few milliamperes, there is a Ground
Fault, that is, current is finding its way to ground through some
other path than "neutral". If that is the case, the GFCI Interrupts
(the "I" part of "GFCI") the Circuit, very, very quickly, so that no
damage is done to whatever caused the Fault (that could be a human
body). The test button simulates a fault.

[*] I had it work once for me. I didn't know it had until the
lamp I had dropped into water wouldn't come on again.

-Don


Right answer to the wrong question. The GFCI will work,
but unless there's a capacitor or something in there that
I don't know about, the test button won't.




Mark Lloyd November 29th 06 04:29 AM

Why must ground & neutral be seperate in subpanel?
 
On 28 Nov 2006 14:04:29 -0800, "Mark" wrote:



I believe that GFIs are often recommended in cases where there
is no ground for safety. They do not need a ground AFAIN.

Bob


A GFCI does not need a ground. Then some people get the strange idea
that it PROVIDES one. It does not.


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


The one I examined connects a resistor between neutral on the line
side and hot on the load side. Ground is not involved.

Mark

--
27 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Mark Lloyd November 29th 06 04:34 AM

Why must ground & neutral be seperate in subpanel?
 
On Tue, 28 Nov 2006 18:50:22 -0500, Goedjn wrote:

On Tue, 28 Nov 2006 17:35:56 -0600, Don Fearn
wrote:

I think it was "Mark" who stated:


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


Very well[*]

What it does is measure the current leaving the "hot" lead and
compares it with the current returning in the "neutral" lead. If those
are different by more than a few milliamperes, there is a Ground
Fault, that is, current is finding its way to ground through some
other path than "neutral". If that is the case, the GFCI Interrupts
(the "I" part of "GFCI") the Circuit, very, very quickly, so that no
damage is done to whatever caused the Fault (that could be a human
body). The test button simulates a fault.

[*] I had it work once for me. I didn't know it had until the
lamp I had dropped into water wouldn't come on again.

-Don


Right answer to the wrong question. The GFCI will work,
but unless there's a capacitor or something in there that
I don't know about, the test button won't.



Yes, it will. The test button has nothing to do with ground. It
creates an imbalance by routing some current from the hot side of the
outlet around the GFCI to the neutral wire connected to it. This is
the same sort of imbalance caused by a wet person touching hot.
--
27 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

Don Fearn November 29th 06 04:46 AM

Why must ground & neutral be seperate in subpanel?
 
I think it was Goedjn who stated:

On Tue, 28 Nov 2006 17:35:56 -0600, Don Fearn
wrote:

I think it was "Mark" who stated:


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


Very well[*]

What it does is measure the current leaving the "hot" lead and
compares it with the current returning in the "neutral" lead. If those
are different by more than a few milliamperes, there is a Ground
Fault, that is, current is finding its way to ground through some
other path than "neutral". If that is the case, the GFCI Interrupts
(the "I" part of "GFCI") the Circuit, very, very quickly, so that no
damage is done to whatever caused the Fault (that could be a human
body). The test button simulates a fault.

[*] I had it work once for me. I didn't know it had until the
lamp I had dropped into water wouldn't come on again.

-Don


Right answer to the wrong question. The GFCI will work,
but unless there's a capacitor or something in there that
I don't know about, the test button won't.


A resistor, I believe. It shunts a small amount of current around the
balance circuit simulating an imbalance in the two sides, so if it's
working right the GFCI will interrupt the current.

-D

--
"What do *you* care what other people think?" --Arline Feynman

Mark November 29th 06 06:21 PM

Why must ground & neutral be seperate in subpanel?
 


Will the TEST BUTTON on the GFI work if it does not have a ground?


Yes.

If so, how does it work?


The one I examined connects a resistor between neutral on the line
side and hot on the load side. Ground is not involved.


OK that makes sense, and the test will work without a ground and
without a load...

thanks

Mark



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