Load capacity of 200-amp panel (2024 Update)

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

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.

Right so far...

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

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_.

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?

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

Reply to
Stormin Mormon

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

Reply to
JIMMIE

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

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.

Reply to
Doug Miller

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.
Reply to
Gary H

200A @ 120V on leg 1, 200A @ 120V on leg 2.

Actually, it does.

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.
Reply to
Doug Miller

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.

Reply to
trader4

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.

Reply to
Doug Miller

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

b =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 c

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

R
Reply to
RicodJour

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.

Reply to
Doug Miller

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

Reply to
Wayne Whitney

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 I

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 c

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.
Reply to
trader4

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.

Reply to
Doug Miller

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

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? ;-)
Reply to
propman

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.

Reply to
Doug Miller

I understand Ohm's law much better than the folks who apparently believe that

200A at 240V is the same thing as 200A at 120V.
Reply to
Doug Miller

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.

Reply to
JIMMIE

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?
Reply to
Doug Miller

mitty

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.

Reply to
trader4
[snip]

That current is 200A. That 400A is obviously not in the neutral. WHERE is it?

Reply to
Sam E

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