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Default Load capacity of 200-amp panel

This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how many
amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I remember
something about a 200-amp main breaker actually being okay for 400 amps of
service since there are two separate circuits coming in (a 240-volt service
split into two 120-volt circuits in the panel box).



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Default Load capacity of 200-amp panel

JayB wrote:
This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how
many amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I
remember something about a 200-amp main breaker actually being okay
for 400 amps of service since there are two separate circuits coming
in (a 240-volt service split into two 120-volt circuits in the panel
box).


It all depends on voltage. A 220 amp service can in theory (you are not
supposed to use more than 80%) supply 200 amps at 240 volts OR 400 amps at
120 volts or any combination of the above.

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Default Load capacity of 200-amp panel

In article s.com, "EXT" wrote:
JayB wrote:
This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how
many amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I
remember something about a 200-amp main breaker actually being okay
for 400 amps of service since there are two separate circuits coming
in (a 240-volt service split into two 120-volt circuits in the panel
box).


It all depends on voltage. A 220 amp service can in theory (you are not
supposed to use more than 80%)


Not so. You misunderstand the 80% rule.


supply 200 amps at 240 volts OR 400 amps at
120 volts or any combination of the above.

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Default Load capacity of 200-amp panel

On Oct 22, 1:19�pm, (Doug Miller) wrote:
In article s.com, "EXT" wrote:

JayB wrote:
This came up elsewhere and I am just curious about what the answer is.


If someone has a main service panel with a 200-amp main breaker, how
many amps of service can that panel actually service?


I am probably not wording this correctly, but I thought that I
remember something about a 200-amp main breaker actually being okay
for 400 amps of service since there are two separate circuits coming
in (a 240-volt service split into two 120-volt circuits in the panel
box).


It all depends on voltage. A 220 amp service can in theory (you are not
supposed to use more than 80%)


Not so. You misunderstand the 80% rule.



supply 200 amps at 240 volts OR 400 amps at
120 volts or any combination of the above.- Hide quoted text -


- Show quoted text -


plus the 200 amp dual breaker can and will carry a percentage more
indefinetely

I had a friend who had the largest outdoor light display in the area,
the power company loved him

checking the legs of his main service, it exceeded 200 amps on either
side.

he couldnt run his dishwasher, washer dryer, or even a hair dryer as
his wife found out when the lights were on..........

her hair dryer blacked out the total home.

when his kids got bigger he quit decorating......... but geez it was
beautiful
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Default Load capacity of 200-amp panel

On Oct 22, 2:14*pm, " wrote:
On Oct 22, 1:19 pm, (Doug Miller) wrote:





In article s.com, "EXT" wrote:


JayB wrote:
This came up elsewhere and I am just curious about what the answer is.


If someone has a main service panel with a 200-amp main breaker, how
many amps of service can that panel actually service?


I am probably not wording this correctly, but I thought that I
remember something about a 200-amp main breaker actually being okay
for 400 amps of service since there are two separate circuits coming
in (a 240-volt service split into two 120-volt circuits in the panel
box).


It all depends on voltage. A 220 amp service can in theory (you are not
supposed to use more than 80%)


Not so. You misunderstand the 80% rule.


supply 200 amps at 240 volts OR 400 amps at
120 volts or any combination of the above.- Hide quoted text -


- Show quoted text -


plus the 200 amp dual breaker can and will carry a percentage more
indefinetely

I had a friend who had the largest outdoor light display in the area,
the power company loved him

checking the legs of his main service, it exceeded 200 amps on either
side.

he couldnt run his dishwasher, washer dryer, or even a hair dryer as
his wife found out when the lights were on..........

her hair dryer blacked out the total home.

when his kids got bigger he quit decorating......... but geez it was
beautiful- Hide quoted text -

- Show quoted text -



Aside from the 80% rule, you can't get 400 amps out of a 200amp
service. The service consists of two hots, and a neutral. That
means with a 200 amp service you can get 200 amps at 240V flowing
between the two hots. Or you could get say 150 amps at 240V plus 50
amps at 120V. /In the latter case you have 200 amps flowing on one
hot, 150 on the other hot, and 50 on the neutral.


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Default Load capacity of 200-amp panel


JayTKR wrote:

Thanks.

That's what I thought -- that 200 amps at 240 volts is basically 400 amps
available at 120 volts. Or, for example, if 50 of the 200 amps were for a
240 volt circuit, that would leave 150 amps at 240 which could be 300 amps
at 120 volts.


One other complicating factor is the 125A max branch circuit limitation.
Not an issue in normal residential application of course as few people
have single loads over 125A, but something to keep in mind when feeding
subpanels.
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Default Load capacity of 200-amp panel

On 2009-10-23, Pete C. wrote:

JayTKR wrote:

That's what I thought -- that 200 amps at 240 volts is basically 400 amps
available at 120 volts.


The difference is that you can't run a single 120V load at a full 400
amps. But you could run two different 120V loads at 200 amps.

One other complicating factor is the 125A max branch circuit
limitation.


The only limitation here is in the breakers for your panel. Larger
breakers may be available; they often take up more space than normal
in the panel, so as to have multiple connections to the same busbar.

Cheers, Wayne


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Default Load capacity of 200-amp panel

On Oct 23, 2:24*am, Wayne Whitney wrote:
On 2009-10-23, Pete C. wrote:



JayTKR wrote:


That's what I thought -- that 200 amps at 240 volts is basically 400 amps
available at 120 volts. *


The difference is that you can't run a single 120V load at a full 400
amps. *But you could run two different 120V loads at 200 amps.

One other complicating factor is the 125A max branch circuit
limitation.


The only limitation here is in the breakers for your panel. *Larger
breakers may be available; they often take up more space than normal
in the panel, so as to have multiple connections to the same busbar.

Cheers, Wayne


People just playing with words!

Since: Power = voltage multiplied by amperage. For example if one has
individual 20 amp 115 volt circuits the maximum power each could carry
is 115 x 20 = 2,300 watts.

A 15 amp lighting circuit, 115 x 15 = 1725 watts.

Similarly (ignoring the 80% rule for the moment) the maximum power
that a 200 amp (Standard North American 115 - 0 - 115) domestic
service can carry is 200 x 230 = 46,000 watts.

It is not possible for all the power could be loaded 'all on one 115
volt leg/side', as 115 x 400 = 46,000 watts. This would be rather like
saying one could put the total weight of a ten ton truck ALL on one
set of wheels! Or hiring two taxis to carry ten passengers, but then
putting all ten passengers in one taxi, with none in the other!

That's also why domestic loads are 'supposed' to be balanced/
distributed' across both legs. In practice rarely operating in most
situations at anything close to maximum loading. So balance not often
an issue.

A domestic service double pole main circuit protects both legs of the
incoming service. Once the trip limit of the breaker (200 amps say)
exceeded, on either leg it would operate thus disconnecting both 115
volt legs.
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Default Load capacity of 200-amp panel

On Oct 22, 12:02*pm, "JayB" wrote:
This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how many
amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I remember
something about a 200-amp main breaker actually being okay for 400 amps of
service since there are two separate circuits coming in (a 240-volt service
split into two 120-volt circuits in the panel box).


You shouldnt have more than 160 amps on any one leg or 80% of 200..

Jimmie
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Default Load capacity of 200-amp panel

I havn't heard from Clark Griswold in a while, not since
they did the movie about him.
http://www.youtube.com/watch?v=ian6NyXpszw
--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


wrote in message
...

I had a friend who had the largest outdoor light display in
the area,
the power company loved him

checking the legs of his main service, it exceeded 200 amps
on either
side.

he couldnt run his dishwasher, washer dryer, or even a hair
dryer as
his wife found out when the lights were on..........

her hair dryer blacked out the total home.

when his kids got bigger he quit decorating......... but
geez it was
beautiful


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Default Load capacity of 200-amp panel

I havn't heard from Clark Griswold in a while, not since
they did the movie about him.
http://www.youtube.com/watch?v=ian6NyXpszw

http://www.youtube.com/watch?v=8qc_RYm0ylA&NR=1
--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


wrote in message
...

I had a friend who had the largest outdoor light display in
the area,
the power company loved him

checking the legs of his main service, it exceeded 200 amps
on either
side.

he couldnt run his dishwasher, washer dryer, or even a hair
dryer as
his wife found out when the lights were on..........

her hair dryer blacked out the total home.

when his kids got bigger he quit decorating......... but
geez it was
beautiful



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Default Load capacity of 200-amp panel

I havn't heard from Clark Griswold in a while, not since
they did the movie about him.
http://www.youtube.com/watch?v=ian6NyXpszw

http://www.youtube.com/watch?v=8qc_RYm0ylA&NR=1
--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


wrote in message
...

I had a friend who had the largest outdoor light display in
the area,
the power company loved him

checking the legs of his main service, it exceeded 200 amps
on either
side.

he couldnt run his dishwasher, washer dryer, or even a hair
dryer as
his wife found out when the lights were on..........

her hair dryer blacked out the total home.

when his kids got bigger he quit decorating......... but
geez it was
beautiful





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Default Load capacity of 200-amp panel

On Oct 23, 7:38�am, "Stormin Mormon"
wrote:
I havn't heard from Clark Griswold in a while, not since
they did the movie about him.
�http://www.youtube.com/watch?v=ian6NyXpszw

� �http://www.youtube.com/watch?v=8qc_RYm0ylA&NR=1
--
Christopher A. Young



griswald is what my neighbor was called reportedly by everyone he
knew.

he lit up the neighborhood, and his power bill collected donations
for salvation army and created sometimes massive traffic jams, after
his display was featured on news.

i alwasys expected him to blow the local transformer..........

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Default Load capacity of 200-amp panel

On Oct 22, 4:10*pm, (Doug Miller) wrote:
In article , wrote:

Aside from the 80% rule,


Which doesn't apply...

you can't get 400 amps out of a 200amp
service.


Of course you can; it just depends on which circuits are in use. If you're
using only 120V circuits, you can get 200A on *each* leg.

200A @ 240V is the
same power as 400A @120V.


Yes but physically, a current of 200 amps is all that is actually
flowing. Put a meter on it and you will measure 200 amps, not 400.
It's a simple matter of Kirchoffs law.

What you are arguing is like saying a resistor that has 1 amp flowing
in it is actually carrying 2 amps, because 1 amp goes in and one amp
goes out.




*The service consists of two hots, and a neutral. * That
means with a 200 amp service you can get 200 amps at 240V flowing
between the two hots. * Or you could get say 150 amps at 240V plus 50
amps at 120V. */In the latter case you have 200 amps flowing on one
hot, 150 on the other hot, and 50 on the neutral.


Ummm....no. You could have up to 150A at 240V plus *100A* at 120V -- and if
the loads are distributed evenly across the two legs, the current in the
neutral is zero.


That is not true. If you have 150A running at 240V then you have
150A coming in on one hot, 150A going out on the other hot during each
half cycle and zero flowing through the neutral. The next half
cycle, it reverses. If you now add another 50 amps between one hot
and neutral, you now have 200A running through one hot, `150 amps
through the other hot, and 50 amps through the neutral. There is
nowhere for your extra 50 amps to come from to give you 250amps The
max current flowing is still limited to 200 amps.

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Default Load capacity of 200-amp panel

JIMMIE wrote:
On Oct 22, 12:02 pm, "JayB" wrote:
This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how many
amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I remember
something about a 200-amp main breaker actually being okay for 400 amps of
service since there are two separate circuits coming in (a 240-volt service
split into two 120-volt circuits in the panel box).


You shouldnt have more than 160 amps on any one leg or 80% of 200..


As Doug has probably been saying, the 80% limit is for continuous loads
(over 3 hours). Major loads in a house are not likely continuous. A
circuit breaker can operate at its full capacity, but may trip if at
full capacity for over 3 hours.

--
bud--
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Default Load capacity of 200-amp panel

JayB wrote:
This came up elsewhere and I am just curious about what the answer is.

If someone has a main service panel with a 200-amp main breaker, how many
amps of service can that panel actually service?

I am probably not wording this correctly, but I thought that I remember
something about a 200-amp main breaker actually being okay for 400 amps of
service since there are two separate circuits coming in (a 240-volt service
split into two 120-volt circuits in the panel box).


Do you expect to actually draw 200 amps at once, or are you adding up
the amperage value of all the circuit breakers?
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In article , JIMMIE wrote:


You shouldnt have more than 160 amps on any one leg or 80% of 200..


Incorrect. You do not understand the "80% rule". The rule applies only to
"continuous loads" which is defined by the Code as maximum current for a
period of three hours or more.


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In article , wrote:
On Oct 22, 4:10=A0pm, (Doug Miller) wrote:
In article =

..com, wrote:

Aside from the 80% rule,


Which doesn't apply...

you can't get 400 amps out of a 200amp service.


Of course you can; it just depends on which circuits are in use. If you're
using only 120V circuits, you can get 200A on *each* leg. 200A @ 240V is the
same power as 400A @120V.


Yes but physically, a current of 200 amps is all that is actually
flowing. Put a meter on it and you will measure 200 amps, not 400.
It's a simple matter of Kirchoffs law.


200 amps on _each leg_. It's a total of (up to) 400 amps at 120V.

What you are arguing is like saying a resistor that has 1 amp flowing
in it is actually carrying 2 amps, because 1 amp goes in and one amp
goes out.


It's not at all the same. You are failing to consider that the two legs of a
residential service can be treated as two *separate* parallel 120V circuits.

The service consists of two hots, and a neutral. That
means with a 200 amp service you can get 200 amps at 240V flowing
between the two hots. Or you could get say 150 amps at 240V plus 50
amps at 120V. In the latter case you have 200 amps flowing on one
hot, 150 on the other hot, and 50 on the neutral.


Ummm....no. You could have up to 150A at 240V plus *100A* at 120V -- and if
the loads are distributed evenly across the two legs, the current in the
neutral is zero.


That is not true. If you have 150A running at 240V then you have
150A coming in on one hot, 150A going out on the other hot during each
half cycle and zero flowing through the neutral. The next half
cycle, it reverses. If you now add another 50 amps between one hot
and neutral, you now have 200A running through one hot, `150 amps
through the other hot, and 50 amps through the neutral.


Right so far...

There is
nowhere for your extra 50 amps to come from


Sure there is: the other hot leg still has an extra 50A capacity.

to give you 250amps


Ahh, _there_ is the source of your misconception.

The neutral carries only the unbalanced current. When the other hot leg
carries 200A as well, the current in the neutral _drops to zero_.

The
max current flowing is still limited to 200 amps.


Suppose that the residence has no 240V loads of any sort -- gas furnace, gas
WH, gas dryer, gas stove, no large power tools, no double-pole breakers, every
circuit in the panel is a 120V circuit.

Do you maintain that the maximum power that could be drawn from this service
is 200A @ 120V = 24kVA?

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Neat. Would have liked to see that, but it sounds dangerous.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


wrote in message
...

griswald is what my neighbor was called reportedly by
everyone he
knew.

he lit up the neighborhood, and his power bill collected
donations
for salvation army and created sometimes massive traffic
jams, after
his display was featured on news.

i alwasys expected him to blow the local
transformer..........


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Default Load capacity of 200-amp panel

On Oct 23, 9:41*am, bud-- wrote:
JIMMIE wrote:
On Oct 22, 12:02 pm, "JayB" wrote:
This came up elsewhere and I am just curious about what the answer is.


If someone has a main service panel with a 200-amp main breaker, how many
amps of service can that panel actually service?


I am probably not wording this correctly, but I thought that I remember
something about a 200-amp main breaker actually being okay for 400 amps of
service since there are two separate circuits coming in (a 240-volt service
split into two 120-volt circuits in the panel box).


You shouldnt have more than 160 amps on any one leg or 80% of 200..


As Doug has probably been saying, the 80% limit is for continuous loads
(over 3 hours). Major loads in a house are not likely continuous. A
circuit breaker can operate at its full capacity, but may trip if at
full capacity for over 3 hours.

--
bud--


Its doubtfull you would ever pull more than 100 amps on a house wired
with a 200 amp panel. Worse case in my house would be WELDER, HVAC,
OVEN, and SPA running all at once. Of course if wife and daughter are
both doing their hair at the same time that may put me over the top.

Jimmie
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Default Load capacity of 200-amp panel

In article , JIMMIE wrote:
On Oct 23, 9:41=A0am, bud-- wrote:
JIMMIE wrote:

You shouldnt have more than 160 amps on any one leg or 80% of 200..


As Doug has probably been saying, the 80% limit is for continuous loads
(over 3 hours). Major loads in a house are not likely continuous. A
circuit breaker can operate at its full capacity, but may trip if at
full capacity for over 3 hours.


Its doubtfull you would ever pull more than 100 amps on a house wired
with a 200 amp panel. Worse case in my house would be WELDER, HVAC,
OVEN, and SPA running all at once.


Exactly. So why do you keep talking about the 80% rule? It doesn't apply.

Of course if wife and daughter are
both doing their hair at the same time that may put me over the top.


Do they take three hours to dry their hair? While the welder, HVAC, oven and
spa are all running? For three hours?

The 80% rule applies _only_ to continuous loads -- which is clearly and
specifically defined in the Code.

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On Oct 23, 3:54*pm, (Doug Miller) wrote:
In article , wrote:





On Oct 22, 4:10=A0pm, (Doug Miller) wrote:
In article =

..com, wrote:


Aside from the 80% rule,


Which doesn't apply...


you can't get 400 amps out of a 200amp service.


Of course you can; it just depends on which circuits are in use. If you're
using only 120V circuits, you can get 200A on *each* leg. 200A @ 240V is the
same power as 400A @120V.


Yes but physically, a current of 200 amps is all that is actually
flowing. * Put a meter on it and you will measure 200 amps, not 400.
It's a simple matter of Kirchoffs law.


200 amps on _each leg_. It's a total of (up to) 400 amps at 120V.



What you are arguing is like saying a resistor that has 1 amp flowing
in it is actually carrying 2 amps, because 1 amp goes in and one amp
goes out.


It's not at all the same. You are failing to consider that the two legs of a
residential service can be treated as two *separate* parallel 120V circuits.









The service consists of two hots, and a neutral. That
means with a 200 amp service you can get 200 amps at 240V flowing
between the two hots. Or you could get say 150 amps at 240V plus 50
amps at 120V. In the latter case you have 200 amps flowing on one
hot, 150 on the other hot, and 50 on the neutral.


Ummm....no. You could have up to 150A at 240V plus *100A* at 120V -- and if
the loads are distributed evenly across the two legs, the current in the
neutral is zero.


That is not true. * If you have 150A running at 240V then you have
150A coming in on one hot, 150A going out on the other hot during each
half cycle and zero flowing through the neutral. * * *The next half
cycle, it reverses. * * If you now add another 50 amps between one hot
and neutral, you now have 200A running through one hot, `150 amps
through the other hot, and 50 amps through the neutral. * *


Right so far...

There is
nowhere for your extra 50 amps to come from


Sure there is: the other hot leg still has an extra 50A capacity.


Yes, you are right on that point and I was wrong.




to give you 250amps *


Ahh, _there_ is the source of your misconception.

The neutral carries only the unbalanced current. When the other hot leg
carries 200A as well, the current in the neutral _drops to zero_.

The
max current flowing is still limited to 200 amps.


Suppose that the residence has no 240V loads of any sort -- gas furnace, gas
WH, gas dryer, gas stove, no large power tools, no double-pole breakers, every
circuit in the panel is a 120V circuit.

Do you maintain that the maximum power that could be drawn from this service
is 200A @ 120V = 24kVA?- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -


The issue here is what defines the current at the service. In a 200
amp service there is only 200 amps of actual physical current running
through the service conductors. The conductors are sized for 200
amps, not 400 amps.


Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. It's a 240V voltage
source powering two 120ohm resistors.




____________ 240V___________
I I
I I
I I
---------120ohm---------120ohm---------
a b c


There is only 1 amp of actual current flowing in the circuit. Across
each resistor there is 120Volts and 1 amp of current flowing. So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.

That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


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In article ,
(Doug Miller) wrote:

In article
,
wrote:

Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. It's a 240V voltage
source powering two 120ohm resistors.

____________ 240V___________
I I
I I
I I
---------120ohm---------120ohm---------
a b c


There is only 1 amp of actual current flowing in the circuit. Across
each resistor there is 120Volts and 1 amp of current flowing. So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.


What voltage do you measure between a and b? Between c and b?
What current do you measure between a and b? Between c and b?


*Immediately* above your two questions, he answered them both, Doug.
There isn't really so much disagreement going on, it's just that y'all
aren't paying attention to what the others are saying.

That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits.
200A flowing in each of two parallel circuits is 400A total, not 200A.

Consider a house with only 120V loads, no 240V circuits anywhere, and 200A
service. Suppose that one leg of the service is fully loaded, and the other
leg is unloaded. I think we'd both agree that the power being drawn is 200A
at
120V, right?

Now fully load the other leg too.

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Default Load capacity of 200-amp panel

On Oct 24, 2:35*pm, Smitty Two wrote:
In article (Doug Miller) wrote:
In article wrote:


Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. * *It's a 240V voltage
source powering two 120ohm resistors.


* * * * * * ____________ *240V___________
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * ---------120ohm---------120ohm---------
* * * * * * a * * * * * * * * * * * b * * * * * * * * * * * c


There is only 1 amp of actual current flowing in the circuit. * Across
each resistor there is 120Volts and 1 amp of current flowing. * *So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.


What voltage do you measure between a and b? Between c and b?
What current do you measure between a and b? Between c and b?


*Immediately* above your two questions, he answered them both, Doug.
There isn't really so much disagreement going on, it's just that y'all
aren't paying attention to what the others are saying.


I think the problem is that people aren't paying attention to what the
other is saying.

R


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In article , Smitty Two wrote:
In article ,
(Doug Miller) wrote:

In article
,
wrote:

Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. It's a 240V voltage
source powering two 120ohm resistors.

____________ 240V___________
I I
I I
I I
---------120ohm---------120ohm---------
a b c


There is only 1 amp of actual current flowing in the circuit. Across
each resistor there is 120Volts and 1 amp of current flowing. So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.


What voltage do you measure between a and b? Between c and b?
What current do you measure between a and b? Between c and b?


*Immediately* above your two questions, he answered them both, Doug.


He doesn't understand the implications of what he wrote, though, which is why
I'm emphasizing it.

There isn't really so much disagreement going on, it's just that y'all
aren't paying attention to what the others are saying.


Rather, vice versa. A 200A residential service supplies up to 200A _at 240V_.
This is _exactly_ equivalent to 400A at 120V -- which is precisely what you
have if each leg of the service is fully loaded at 120V.

That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits.
200A flowing in each of two parallel circuits is 400A total, not 200A.

Consider a house with only 120V loads, no 240V circuits anywhere, and 200A
service. Suppose that one leg of the service is fully loaded, and the other
leg is unloaded. I think we'd both agree that the power being drawn is 200A
at
120V, right?

Now fully load the other leg too.

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Default Load capacity of 200-amp panel

On 2009-10-24, Doug Miller wrote:

A 200A residential service supplies up to 200A _at 240V_. This is
_exactly_ equivalent to 400A at 120V -- which is precisely what you
have if each leg of the service is fully loaded at 120V.


There are a couple small differences between 400A worth of 120V loads
balanced on the two legs of a 240/120V supply, and 400A of loads on a
120V supply. First, in the former case the biggest 120V load you can
handle (without a transformer) is 200A, while in the latter case you
can handle a 400A 120V load. Second, the voltage drop on the supply
is different. V = I^2 * R, where I is 200A in the first case, and
400A in the second case.

Cheers, Wayne
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On Oct 24, 2:17*pm, (Doug Miller) wrote:
In article , wrote:







Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. * *It's a 240V voltage
source powering two 120ohm resistors.


* * * * * * ____________ *240V___________
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * I * * * * * * * * * * * * * * * * * * * * * * * * I
* * * * * * ---------120ohm---------120ohm---------
* * * * * * a * * * * * * * * * * * b * * * * * * * * * * * c


There is only 1 amp of actual current flowing in the circuit. * Across
each resistor there is 120Volts and 1 amp of current flowing. * *So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.


What voltage do you measure between a and b? Between c and b?


120 Volts
120 Volts



What current do you measure between a and b? Between c and b?


1 amp and it's THE SAME 1 AMP current. It just gets counted twice.
Which once again is my point. There is only 1 amp flowing in the
actual complete circuit, just like there is only a maximum of 200
physical amps flowing in a 200 amp service.

In a house, here's how the same thing happens. I hook a 120Volt
light bulb that draws 1 amp on one hot leg and a 120volt fan that
draws one amp on the other hot leg. The 1 amp current comes in one
leg, goes through the bulb, through the fan and out the other hot
leg. That's still an actual current of only 1 amp, though it runs
through two 1 amp loads. If you want to get techical, since it's AC,
the current direction switches each cycle.

Kapisch?


That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits..
200A flowing in each of two parallel circuits is 400A total, not 200A.


They are NOT parallel circuits. That would imply that each has it's
own seperate return path. They do not. The return path is through
the other hot conductor for the balanced part of the load and through
the shared neutral for the unbalanced portion. Again, at any point
in time there is only 200 amps moving through that service going into
the home, which is why it's called a 200 amp service.



Consider a house with only 120V loads, no 240V circuits anywhere, and 200A
service. Suppose that one leg of the service is fully loaded, and the other
leg is unloaded. I think we'd both agree that the power being drawn is 200A at
120V, right?


Yes


Now fully load the other leg too.- Hide quoted text -



And now you have 200 amps flowing from one hot and back on the other
hot. Zero flows through the neutral. Hence, again, it's only a
200 amp total current moving through the service.

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In article , wrote:
On Oct 24, 2:17=A0pm, (Doug Miller) wrote:
In article =

..com, wrote:


[...]
What voltage do you measure between a and b? Between c and b?


120 Volts
120 Volts

What current do you measure between a and b? Between c and b?


1 amp and it's THE SAME 1 AMP current. It just gets counted twice.
Which once again is my point.


Umm, no, actually, that's *my* point: it's counted twice. *Two* amps at 120V.

There is only 1 amp flowing in the
actual complete circuit, just like there is only a maximum of 200
physical amps flowing in a 200 amp service.


OK, so there's 120V @ 1A flowing between a and b = 120W. And there's 120V @ 1A
flowing between b and c = 120W. Total = 240W.

240W / 120V = 2A

In a house, here's how the same thing happens. I hook a 120Volt
light bulb that draws 1 amp on one hot leg and a 120volt fan that
draws one amp on the other hot leg. The 1 amp current comes in one
leg, goes through the bulb, through the fan and out the other hot
leg. That's still an actual current of only 1 amp, though it runs
through two 1 amp loads.


Wrong. Two 1 amp loads = *two* amps, not one.

If you want to get techical, since it's AC,
the current direction switches each cycle.

Kapisch?


I "kapisch" that you don't understand this.


That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits..
200A flowing in each of two parallel circuits is 400A total, not 200A.


They are NOT parallel circuits. That would imply that each has it's
own seperate return path. They do not. The return path is through
the other hot conductor for the balanced part of the load and through
the shared neutral for the unbalanced portion. Again, at any point
in time there is only 200 amps moving through that service going into
the home, which is why it's called a 200 amp service.


Suppose that each one had its own separate return. Does that change your
answer?

Consider a house with only 120V loads, no 240V circuits anywhere, and 200A
service. Suppose that one leg of the service is fully loaded, and the other
leg is unloaded. I think we'd both agree that the power being drawn is 200A at
120V, right?


Yes

Now fully load the other leg too.


And now you have 200 amps flowing from one hot and back on the other
hot. Zero flows through the neutral. Hence, again, it's only a
200 amp total current moving through the service.


So, according to your reasoning, since it's "only a 200 amp total current",
then 200A at 120V on only one leg of the service is the same as 200A at 120V
on *each* leg of the service.
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Doug Miller wrote:
In article , wrote:
Consider this simple circuit analogy which is exactly what you would
have with a balanced load on a 240V service. It's a 240V voltage
source powering two 120ohm resistors.

____________ 240V___________
I I
I I
I I
---------120ohm---------120ohm---------
a b c


There is only 1 amp of actual current flowing in the circuit. Across
each resistor there is 120Volts and 1 amp of current flowing. So,
yes you have 1 amp flowing in EACH load, it is supporting two 1 amp
loads, but it's the same physical current flowing through each load.
The "service" is only supplying 1 amp of actual current, not 2.


What voltage do you measure between a and b? Between c and b?
What current do you measure between a and b? Between c and b?

That's what I meant when I said a 200 amp service cannot supply 400
amps of current.


But it can. 200A at 120V on each leg is a total of 400A at 120V. The two legs
of a residential electrical service are, in effect, two parallel circuits.


.....with a common neutral wire which must provide a return path for both
circuits.

200A flowing in each of two parallel circuits is 400A total, not 200A.


As long as the neutral wire is rated for an amperage capacity of
400A...if it's not, and you try feeding 400 amps through a wire only
rated for 200A max, what do you think will happen? ;-)


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In article , propman wrote:
Doug Miller wrote:



The two legs of a residential electrical service are, in effect, two parallel circuits.


.....with a common neutral wire which must provide a return path for both
circuits.

200A flowing in each of two parallel circuits is 400A total, not 200A.


As long as the neutral wire is rated for an amperage capacity of
400A...if it's not, and you try feeding 400 amps through a wire only
rated for 200A max, what do you think will happen? ;-)


You badly misunderstand how this works. In a 240/120 residential service, the
neutral carries only the unbalanced current (the difference between the
currents in the hot legs, not their sum): if 50A is being drawn on one hot
leg, and 90A on the other, the neutral carries only 40A. If one hot leg is
carrying 200A, and the other 199A, the current in the neutral is *not* 399A --
it's 1A. And if both hot legs are loaded exactly equally, whether that's 1mA
each or 200A each, the current in the neutral is zero.

For 200A service, the neutral does *not* need to be rated for 400A. The most
it can ever carry -- if one hot leg is fully loaded, and the other is unused
-- is 200A, and if the loads are even halfway close to being balanced across
the two legs, most of the time the current in the neutral is far less than
that.
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On Oct 23, 10:34*pm, (Doug Miller) wrote:
In article , JIMMIE wrote:

On Oct 23, 9:41=A0am, bud-- wrote:
JIMMIE wrote:


You shouldnt have more than 160 amps on any one leg or 80% of 200..


As Doug has probably been saying, the 80% limit is for continuous loads
(over 3 hours). Major loads in a house are not likely continuous. A
circuit breaker can operate at its full capacity, but may trip if at
full capacity for over 3 hours.


Its doubtfull you would ever pull more than 100 amps on a house wired
with a 200 amp panel. Worse case in my house would be WELDER, HVAC,
OVEN, and SPA running all at once.


Exactly. So why do you keep talking about the 80% rule? It doesn't apply.

Of course if wife and daughter are
both doing their hair at the same time that may put me over the top.


Do they take three hours to dry their hair? While the welder, HVAC, oven and
spa are all running? For three hours?

The 80% rule applies _only_ to continuous loads -- which is clearly and
specifically defined in the Code.


At the time I read it a continuous power situation is the only thing
that made sense to me. Having the flu and taking codeine will change
ones sense quite a bit. Sorry, you are correct.
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