On Sun, 25 Oct 2009 18:46:17 GMT, in alt.home.repair, snipped-for-privacy@milmac.com
(Doug Miller) wrote:

How can people get this so wrong? It's basic electricity, you all should
have learned this in high school.
In a 200A 240V split phase service, any SINGLE 120v load can draw up to
200A, no more. Because it is split phase, you can have two such loads. Now
the math. 200A@120V + 200A@120V = 200A@240V, NOT 400A@120V. Because two
200A 120V loads on a single split phase panel are in fact operating in
series (whether you deliberately wired them that way or not), presenting a
de facto 200A 240V load on the panel. And, yes, in that case the neutral
conductor current is zero.

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Assume you are using one leg at 200 amps, that is all the breaker
will handle that is 120 volts X 200 amps or 24,000 watts. If you
again max out the breaker with 200 amps flowing on both sides that is
240 volts x 200 amps or 48000 watts. Thats the same as 120 X 400 amps.
I think the OP wanted to know if he could get a total of 400 amps at
120VAC. Lets rephrase that to could he power 400 individual 1 amp 120
VAC loads from this box under residential conditions. The answer is
yes but that sounds a lot like a commercial installation to me where
the answer would be NO. I think this is a case of getting the right
answers to the wrong question.
Jimmie

No they are NOT 'out of phase' the two 240 'ends' are the opposite
ends of a single phase 240v winding of the distribution transformer!
they are often incorrectly referred to as 'phases. but are actually
Leg A and leg B. And when on of them is +ve the other leg is -ve with
respect to it.
The neutral is the centre tap of that distribution transformer
winding.

On Oct 23, 3:54 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

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

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.

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?

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.

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

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.

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

On Oct 24, 2:17 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

120 Volts
120 Volts

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?

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.

Yes
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.

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

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

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

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

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

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.

Perhaps you should read more carefully, then. Several posters in this thread
have insisted that the maximum capacity is 200A, period -- while ignoring the
voltage. It's 200A on *each*leg* of the service. That's 200A @ 240V, or 400A
@ 120V.

And *two* wires capable of carrying 200 amps *each* are capable of carrying
*400* amps. What's so hard to understand?

No, I've never claimed that. Rather, I've said several times that the two legs
of a residential electrical service are, in effect, two parallel circuits.
Yes, it can also be considered as a single series circuit -- IF the loads are
exactly balanced. Any unbalanced loads are parallel.
Let's try going at this from the opposite direction. Consider a single-pole
20A circuit breaker supplying a branch circuit. I believe we'd both agree that
circuit can supply a maximum of 20A at 120V.
Now consider a double-pole 20A breaker supplying a 240V circuit. I believe
we'd both agree that circuit can supply a maximum of 20A at 240V.
Re-wire that double-pole 20A breaker with two separate 12-2 cables, so that
it's supplying two 120V circuits. How many amps can that supply at 120V? 20,
or 40?
Now re-wire it with 3-wire cable, making it instead a multiwire ("Edison")
circuit supplying 120V loads instead of 240V. How many amps can that supply at
120V? 20, or 40?

On Oct 25, 7:51 am, snipped-for-privacy@milmac.com (Doug Miller) wrote:

The maximum capacity of the service is 200Amps period. As Smitty
pointed out, the current is determined by the amount of electrons
passing through a wire each second and is independent of voltage.
You are of the belief that the second hot leg carries an additional
CURRENT, which it does not. In the case of a balanced load, it only
carries the exact SAME current which is flowing in the other hot. As
I said before, the current comes in on one hot while simultaneously
exiting on the other hot. Let's say it's 150 amps. That 150 amps is
coming in on one hot and going out on the other. It reverses each
cycle. That is just like current flowing through a resistor. You
wouldn't count the current in a resistor twice would you?
Now let's add an additional 50amp unbalanced 120Volt load. Now 200
amps comes in on one hot, 150 goes back out as before on the other
hot, and 50 amps goes back via the neutral. Add that up and you
have 200 amps coming into the house and 200 amps leaving the house.
For it to work any other way, current would be piling up or
disappearing somewhere, which is a violation of Kirchoff's law.

Again, this is like saying a resistor that has 1 amp flowing in it is
carrying 2 amps because 1 amp is coming in and 1 amp is leaving.
Would you say that 14 gauge wire running to an outlet is capable of
carrying 30 amps? These two examples are the same as what is
happening with the service coming into the house.

They are not simply parallel circuits which would require they have
seperate return paths.

It's still physically supplying 20 amps because as Smitty pointed out,
that is determined by the number of electrons passing each second.
That hasn't changed. More current doesn't come out of thin air.
But what you have now is that same 20 amps passing through two
circuits. Let's hook up a 6 ohm resistor to each of the new
circuits. You now have 120V across each load, so as far as each load
is concerned, they have 120Volts and 20 amps each. Count that twice
and you have 40 amps of load at 120V driven by the same 20 amps
flowing in the circuit. Look at it at the breaker which is analogous
to the sevice point discussion and you still have 20A flowing, not 40.

Here's another example. Take a cardboard box that will be our
"house". Take an extension cord, put a 120Watt bulb on the end of
it, plug it in to a 120V outlet and put the bulb in the box. You
now have a 120volt, 1amp service to the box. 1 amp is flowing in the
circuit.
Now replace the bulb with two 60Watt bulbs in series. Across each
bulb you will have 60 volts and 1 amp will be flowing in each of
them. So, you are supporting two 1 amp loads at 60volts, But what
is flowing in that extension cord? It's still 1 amp, not 2. The
exact same scenario plays out in the 200 amp service coming into the
house, which is why only 200 amps of actual current is ever flowing.

You are wrong. It does -- in the case of 120V loads.

IF it's supplying a 240V load, yes. If it's supplying a 120V load, then it
exits on the neutral.

So is it your position that a 200A 240V service is incapable of supplying more
than 200A at 120V = 24kVA?

At 240V.

How much power can be supplied by a 200A, 240V service? 24kVa, or 48kVA?

No, it's not. It's like saying that *two* resistors IN PARALLEL with 1 amp
flowing through each have a total current of two amps. Do you disagree?

No, they are not. Keep thinking about it until you realize why those two
examples are not the same, and then you'll understand where you've made your
mistake.

Wrong again.

ON EACH CIRCUIT

You've just made current *disappear* into thin air: supplying a single 240V
circuit, it's supplying 4800W of power -- but now you claim it's supplying
only 2400W when connected to two 120V circuits. Where did that other 2400W go
to?

20 amps through each of two circuits = 40 amps.

THANK YOU. Discussion over. That's what I've been trying to tell you for three
days now.

20A in each of two parallel legs = 40 amps total. Note that these do have
separate returns...

Measured at 120V, yes. But this isn't the same situation, quite, as a
residential service. Keep the two ends of that circuit at a potential
difference of 120V, and *ground* the point in between the two light bulbs.
Then you have 60V flowing through each 60W light bulb = 1 amp *each* = 2 amps
*total* in the parallel circuits.

So you still contend that a 200A 240V service cannot supply more than 24kVA at
120V?

On Oct 25, 2:45 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Here we go again.....

False. I clearly stated here that it's a balanced load. With a
balanced 120V load, the exact same current comes in on one hot and
exists on the other. In the case of a 200 amp service, that current
is a max of 200 amps.

No and I and everyone else have tried to explain that to you. Go
back many posts to the simple circuit diagram I drew:
.
____________ 240V___________
I I
I I
I I
---------120ohm---------120ohm---------
a b c
You have a 240 volt voltage source as our "service" connected to two
120 ohm resistors in SERIES.
How much current is flowing in that circuit?
1 amp
How much current is flowing in the first resistor?
1 amp
How much current is flowing in the second resistor?
1 amp
What is the voltage across each resistor?
120V
What is the power in each resistor?
120W
So, you have 1 amp flowing in SERIES through each load, so you do have
two loads of 1 amp at 120V, but only 1 amp of current is actually
flowing in the circuit which comprises the "service"
Capishe?

Now we're back to what Smitty tried to explain to you. Current has
nothing to do with voltage. It's based on the amount of charge, ie
electrons, passing a point per second. 200 amps is still exactly
200 amps whether it's at a potential of 240V, 120V or a million volts.
And btw, the voltage is not entirely 240V in the above example I gave
either. 150amps is flowing at 240V and 50 is flowing at 120V. If it
were simply all at 240V, you'd have 48KW of power here. Actually
it's 150X240+50*120=42KW

That's been asked an answered many times in this thread. It's 48,
Now answer my question. What is the maximum current that is actually
flowing in the 3 wire cable of a 200 amp service? If you say it's
more than 200 amps, outline an example and using Kirchoff's law, trace
for us the current flowing in all 3 conductors.

Absolutely disagree. I gave you an example before. Take a 120W,
120V light bulb and place it between one hot leg and neutral. Take
a 120V fan drawing 1 amp and place it between the other hot leg and
neutral. You now have a balanced load drawing 1 amp. There is 1 amp
flowing in one hot and out the other. The neutral is carrying 0
amps. You are supporting two 1 amp, 120V loads. Total amps flowing
in the service: 1 amp. Those two loads appear in SERIES across the
two hots.

Several people in this thread say I'm right. No one is saying you are
right. So, maybe it's time that you did some more thinking.

Sigh
Again, you are somehow trying to mix current, which is measured in
amps with power and voltage.

Yes, 20 amps through two loads in series. Yes it's supporting two 20
amp loads. But what current is passing through the breaker? 20
amps

No, for 3 days you've been telling everyone here that in the case of a
service, you get more amps because there is a second hot conductor.
That is flat out wrong. Refer again to the box example later in the
thread, where there is no second hot.

Oh no, there you go again. Counting current twice. If that
breaker had 20 amps flowing through it at 240V, then it had a 12 ohm
load on it. So, now to make it into a 120V circuit, we just remove
the 12 ohm load, put two 6 ohm loads in series on it. Now across each
6 ohm resistor you have 120V, with the same 20 amps flowing
sequentially through both and suddenly the breaker is now magically
carrying 40 amps?

Again, per Smitty and the rest of the world, measuring current has
nothing to do with measuring voltage.

It is EXACTLY analogous to a residential service with a balanced 120V
load. You have a 120V, 1 amp "service" supplying two 60W, 60volt
loads. You have 1 amp flowing in series through the two loads, but
ONLY 1 AMP IS FLOWING IN THE SERVICE. If it is not the same as a
residential service, tell us exactly what the difference is and why
the exact same principles do not apply.

Good grief. If you did provide an alternative "neutral" return path
at the point between the bulbs, it would matter not a wit. Just as
in the actual residential service, the load is balanced and zero
current would flow in the neutral. That is why I left it out as I
wanted to keep it as simple as possible. If you like, I can draw you
the circuit diagram that represents a center tap 240V service, but it
doesn't change how current is counted.

Again, please stop misquoting me. Neither I nor anyone else here
ever said any such thing.
Let me restate what I've said all along:
In a 200 amp service entering a house, there is a max of 200 amps of
actual current flowing. You don't count current twice on a service
cable anymore than you would on an extension cord.
Here's a simple series of questions:
1 I have a big 240V water heater that draws 200 amps and is
connected to a 200amp service via the two hot legs.
How much current is flowing in
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house
2 Now instead of the single 240V water heater, I have two 120V water
heaters that draw 200 amps each. One is connected between hot leg 1
and neutral, the other between hot leg 2 and neutral.
How much current is flowing in:
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house
3 Is the situation in #2 above an example of a parallel circuit or a
series circuit?
4 I now disconnect the water heater that was connected to leg 2 in
the previous example. You now have one 120V, 200 amp water heater
connected to leg 1 and neutral.
How much current is flowing in:
a - Hot leg 1
b - hot leg 2
c - neutral
d - the service cable entering the house

This is the only error I picked up. The supply voltage, as stated, is
120V in both cases. In the second case the 2 60W bulbs would have to be
in parallel to give a load of 120W and 1A.
Assuming the light bulbs are linear resistances, with 60V across a 120V
bulb you would get 1/2 the rated current, or 1/4A which gives an
effective wattage in the 2nd case of 30W.
That isn't what you intended.
><....>

The arguments have gotten so twisted let me start here.

Everyone, I believe, has the same the answers (though I'm not sure what
"d" is).
The question from the OP, as I understand it, is with a panel feed at
200A 240V can you supply 200A of 120V load or 400A of 120V load.
It is case #2 above. You can supply 400A of 120V load. You can't supply
a 400A 120V load, but with the load split between the legs you can
supply a total of 400A of 120V load, half of it from each leg. In that
case the hot legs run at 200A and the neutral is zero. You don't have
400A on any wire. I assume that is not a problem for you. That is all I
read Doug as saying. I agree.
Its gotta be a point-of-view problem.

Yes, I agree. good catch.
120W bulb -> 120 ohms
60 W bulb -> 240 ohms
240W bulb -> 60 ohms
So, in my example I should have used two 240 watt bulbs in series
which would be the same resistance as the 120watt bulb. Actuallly, I
should have used a simple resistor or similar, because the resistance
of light bulbs is not a constant, temp dependent, etc.
But the example, corrected, still holds. You would have 60 volts and
1 amp flowing across each bulb.

I'm not so sure there is agreement as to the answers. And if there
is agreement, then I don't see how there can be disagreement on how
many amps are flowing on the service cable. If you have X amps
coming in and X amps going out in a circuit, then that means X amps,
no?

I don;t see it as a point of view problem at all. How many amps are
actually flowing in a 200 amp service to a house? You draw an
imaginary plane and answer the question of how many amps are flowing
in and how many are flowing out. If it is indeed 200 in, 200 out,
then that is 200 amps period. You can have 200 amps flowing between
the two hots. You can have 200 amps flowing between hot 1 and the
neutral. You can have 200 amps flowing between hot 2 hot and the
neutral, Any way you slice and dice it, it's still 200 amps.
If you can really have 400 amps of real current flow in the service,
then maybe Doug can answer this. Suppose I have a 120 volt load that
takes 400 amps. I connect it as a single 120V load to a 200 amp
service. What happens?
A - Eveything works peechy keen, because 120V* 400amps = 48KVA, at the
service limit, so 400 amps flows just fine.
B - The service cable burns up, because the only way you can supply
that 400amps is by the load being balanced, in which case it appears
as a series load and the service is actually pulling 200amps through
one hot and back the other. Which means that it would ONLY work if
you had two 200 amp, 120V loads connected to OPPOSIITE legs, and hence
acting as a SERIES circuit.

On Oct 26, 1:44 pm, snipped-for-privacy@optonline.net wrote:

QUESTION...
In a service rated as a "200 Amp service"..
What are the numbers printed on the TWO main breakers?
Are they
A) 200/200?
or
B)100/100?
That is really the only question that needs to be answered .....
The rest should be obvious.
Mark

in other words, is this:
http://homerepair.about.com/od/electricalrepair/ss/anat_elec_pnl_4.htm
considered to be a "100 amp service" or a "200 amp service?
Mark

I don't understand Doug is saying there is 400A running in any wire.
And I am not saying there is.

In example #2 there is there 200A supplied to the 120V water heater on
leg 1.
And there is 200A supplied to the 120V water heater on leg 2.
Are you not supplying 400A of 120V load (split between leg 1 and leg 2)?

I do not understand Doug ever said there was 400A in any wire. Rather
that there was 400A of total 120V load supplied - 1/2 on each leg.

You don't connect it to one leg. You split the load in half and connect
one half leg 1 to neutral. You connect the other half from leg 2 to
neutral. (In this case you reconnect the single 400A 120V load as a 200A
240V load.)
If you have 40 - 10A 120V loads (400A total at 120V) you connect 20 of
them to leg 1 (200A). You connect the other 20 to leg 2 (200A). The
neutral current is zero. You have supplied 400A of 120V loads by
splitting it and connecting half to each leg.

Which is how you connect it. I don't want to go back and reread the
thread - Doug's use of parallel may have not been the best. But I always
understood he was saying that half of a 400A load (200A) was connected
to leg 1 and the other half (200A) was connected to leg 2.
In answer to the OP's question - with a panel feed at 200A 240V can you
supply 400A of 120V load - the answer is yes.
I still think it is a point-of-view problem. You and Doug (and Smitty
and others?) all understand the underlying electrical.

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