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Posted by terry on October 23, 2009, 1:18 am
> > JayTKR wrote:
> >> That's what I thought -- that 200 amps at 240 volts is basically 400 a=
mps
> >> available at 120 volts. =A0
> The difference is that you can't run a single 120V load at a full 400
> amps. =A0But 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. =A0Larger
> 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 =3D 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 =3D 2,300 watts.
A 15 amp lighting circuit, 115 x 15 =3D 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 =3D 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 =3D 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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Posted by on October 23, 2009, 8:59 am
On Oct 22, 4:10=A0pm, spamb...@milmac.com (Doug Miller) wrote:
> In article <eac71d20-b0a7-49ff-970c-7068c6290...@l35g2000vba.googlegroups=
.com>, trad...@optonline.net 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'r=
e
> 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.
> > =A0The service consists of two hots, and a neutral. =A0 That
> >means with a 200 amp service you can get 200 amps at 240V flowing
> >between the two hots. =A0 Or you could get say 150 amps at 240V plus 50
> >amps at 120V. =A0/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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Posted by Doug Miller on October 23, 2009, 3:54 pm
trader4@optonline.net wrote:
>On Oct 22, 4:10=A0pm, spamb...@milmac.com (Doug Miller) wrote:
>> In article <eac71d20-b0a7-49ff-970c-7068c6290...@l35g2000vba.googlegroups=
>..com>, trad...@optonline.net 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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Posted by Gary H on October 24, 2009, 10:11 am
On Fri, 23 Oct 2009 19:54:26 GMT, spambait@milmac.com (Doug Miller)
wrote:
trader4@optonline.net wrote:
>>On Oct 22, 4:10=A0pm, spamb...@milmac.com (Doug Miller) wrote:
>>> In article <eac71d20-b0a7-49ff-970c-7068c6290...@l35g2000vba.googlegroups=
>>..com>, trad...@optonline.net 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.
200A on each leg. Where's the 400A?
Being able to add to numbers* doesn't mean reality works that way.
[snip]
* - Actually, that's incorrect too. The addends are out of phase, so
200 + 200 = 0.
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Posted by Doug Miller on October 24, 2009, 11:10 am
>On Fri, 23 Oct 2009 19:54:26 GMT, spambait@milmac.com (Doug Miller)
>wrote:
>>In article
> trader4@optonline.net wrote:
>>>On Oct 22, 4:10=A0pm, spamb...@milmac.com (Doug Miller) wrote:
>>>> In article <eac71d20-b0a7-49ff-970c-7068c6290...@l35g2000vba.googlegroups=
>>>..com>, trad...@optonline.net 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.
>200A on each leg. Where's the 400A?
200A @ 120V on leg 1, 200A @ 120V on leg 2.
>Being able to add to numbers* doesn't mean reality works that way.
Actually, it does.
>[snip]
>* - Actually, that's incorrect too. The addends are out of phase, so
>200 + 200 = 0.
Oh, you mean that if both legs are fully loaded, there's no current being
drawn at all?
Sorry, but you don't understand. The current in the neutral is in fact zero,
if both legs are loaded exactly equally -- and if all the loads supplied are
120V loads, then it is in fact drawing 400A @ 120V.
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