Load capacity of 200-amp panel (2024 Update)

[Doug Miller]

Very good. Now divide 48kVA by 120V and tell me what you get.

[Doug Miller]

Now divide 48kVA by 120V and tell me what you get.

Which is exactly what I've been telling you for the last three days. Glad you finally figured it out.

[Sam E]

True, although it happens in examples, such as the ones used here.

IF those 2 legs have identical voltages, the difference between them is 0 (that's what "identical" means). In that case, 120V loads should be OK but 240V loads would get nothing.

That's some strange reality. In this one voltage and current are different things, and you can't change one into another with arithmetic.

There is still no 400A at any voltage.

I notice you ignored mine. You have yet to show any non-imaginary location of that 400A.

48KW. Of course we were talking about CURRENT.

That would be 400A. Of course that's only in your imagination since the math is invalid (120V is obtained by splitting the service into 2 separate halves, each of which is only 24KW).

[Doug Miller]

Exactly so.

200A each. Total of 400A of 120V loads -- as you said.

[JIMMIE]

It seemed like it should in this case per the OP's description . What's he doing, growing pot in his attic? Even if technically an installation is residential commercial rules should apply if the situation warrants it. I would say the described situation could fit such a case.

Jimmie

[JIMMIE]

Where in the box can you measure 400 amps? If the panel is controlling

48KW there will be no current on the neutral because the currents will be balanced. The current that flows through one half of the breaker is the same current that flows through the other half of the breaker. In this case what you have is two 200 amp breakers in series. Doug you have more current coming into the box than going out and that shouldnt happen.

[Steve N.]

The power is coming in from a transformer secondary winding that is center-tapped. Let's call the 3 wires Line 1, the neutral & Line 2 (seee the link below that shows a transformer secondary at the bottom of the page). When you put 120V loads across Line 1 & neutral, they are independent of Line 2. In effect, you're only using half of the transformer secondary, so you're only going thru the Line 1 half of the main breaker. The current path is from the Line 1 side of the secondary winding, thru the Line 1 side of the main breaker, thru the load, and back thru the neutral to the Line 1 half of the secondary winding. If you also put a 120V load across Line 2 and the neutral, then the current path is from the Line 2 side of the secondary winding thru the Line 2 side of the main breaker, thru the load, and back thru the neutral (in the opposite direction of current flow of the Line 1 current thru the neutral) and back to the Line

2 side of the secondary winding. Both loads form their own circular loops that are independent of each other, except for sharing the neutral (in opposite directions) to complete their separate circuits. Here is a great explanation of the transformer secondary, using the battery analogy which the author (not me) originally designed to show balanced loads, but is also useful in showing how 120V loads form independent circuits on each side of the secondary. You can even close the various switchs and see the effect.

[terry]

The answer is obvious; 200 amps. Although one working current recommendation is to not exceed (I guess that's at any one time) some

80% of the maximum capacity. So say 160 amps.

It's rather like saying how many passengers can a 60 seater bus carry (seated of course)!

The wire connections, bus bars (to which the individual circuit breakers attach) are rated for 200 amps. Do not exceed. BTW 200 amps at 230 volts is 230 x 200 =3D 46,000 watts (46 kilowatts).And 80% of that is about 37 kilowatts. That's usually plenty for all but the biggest homes. To get maximum capability that load should be balanced over the two 115 volt legs. Because if all the loads were on only one leg the maximum capacity would be 115 x 200 =3D

23,000 watts (23 kilowatts) and 80% of that is about 18 -19 kilowatts.

[Steve N.]

I need to make a correction - the Line 2 current flow would be down the neutral, thru the load, up thru the Line 2 half of the breaker, back to the Line 2 side of the transformer. The currents flow in the same direction thru the transformer secondary "halves", and in opposite directions thru the neutral.

[HeyBub]

Think heat.

[JIMMIE]

LOL

[trader4]

Again, this has been answered here repeatedl, so I don't see why you keep asking.. One more time, it's obviously 400 amps.

Also, you only get those 400 amps if the load is balanced so that it appears as a series load. The 200 amp current flows in one hot and out the other. If you had a single 120V 400 amp load, it would sit between one hot leg and neutral, where the capacity is limited to 200 amps and the cables would melt. Gee, I wonder why? Could it be because the actual current in a 200 amp service circuit is only 200 amps?

You can divide and get any answer you want. I could divide 48KVA by

10volts and get 4800 amps. So a 200 amp service could support a total 4800 amp, 10 volt load too. But how much max current is actually flowing in the service cable entering the house? Exactly the same as always, 200 amps. If you believe otherwise, please tell us what currents are flowing in each of the three conductors.

[terry]

Jimmie: I think the reason this thread has gone so long is that some do not really understand current flow, especially AC (Alternating Current) single phase and may be confusing current flow (amperes) with power (watts/kilowatts).

In some countries also they have only two wires coming into a domestic service (plus ground/earth). So they have a concept of only the two wires of a single phase 230 volt service. One of which is neutral (essentially at zero volts!) and the other at 230 volts (often 50 hertz) to neutral and ground. the size of those dermines the ampere capacity of the service.

Was looking at distribution along a street in Malta; which was attached to the face of the buildings. It comprised four wires. One of which was ground/earth. I think it was green? One of the remaining three was neutral. The other two were most likely 230+ and 230- as it were of a single phase. Or they might have been two phases of a a 3 phase delta/star transformer sub-station secondary at end of the street. The house services along the street were connected alternately to these last two. In other words all services were two wire single phase 230 volt, plus a ground/earth.

Again in one of the Gulf States it was also essentially 230 volts 50 hertz. BUT; in that instance there were the three phases and neutral etc. coming into every residence unit and the circuit breaker panel or CU (Consumer Unit) had three sections one for each phase. The fact that there were some seven large 230 volt 50 hertz AC units in each unit probaly required a heavy service! Residentially didn't see any 3 phase equipment although it could have been hooked up. It was mainly UG.

Other areas of the world may vary; in Sri Lanka for example it was hard to tell what was going on viewing some of the lash-ups on some of the service poles!

Anyway the point of all this is that it's best to understand, no matter where one is, what the electrical service arrangement is. Also that with two wires (plus ground) there can be no doubt .................. a 200 amp service (or whatever it's rated) is just that, 200 amps.

No more (unless overloaded) no less (subject to the recommended 80% rule for prolonged use). Nothing magic about it!

[trader4]

That was precisely my point. That to support a 400 amp 120V load, the load must be perfectly balanced. And that is because only a max of 200 amps is flowing in the service cable and the 400 amp, 120V load must appear as two 200 amp, 120V loads in SERIES.

It's a very basic and simple electrical question as to how many amps are flowing in that 200 amp service cable and it's 200 amps. You could support all kinds of loads of varying voltages off it, including

400 amps at 120V, provided the load is perfectly balanced. I could further break it down to support a total load of 800 amps at 60volts, etc. That doesn't change the physical current in the service cable from being limited to 200 amps? If you put a current meter on it you would measure 200 amps flowing into the house, 200 amps flowing out.

Do we agree?

And none of that has anything to do with claims that were made here that you get 400 amps because there is a second conductor. Or that the service is a parallel circuit. I showed in the box with light bulbs how the exact same thing can be done running various loads/ voltages off just a 2 wire 120V outlet.

I'm not so sure, as I have yet to hear Doug acknowledge that there is actually only a 200 amp current flowing in that service cable. When asked that by others he has replied with answers that try to link it to voltage, ie 200 amps at 240V or 400 amps at 120V. And that is simply wrong. Amps and voltage are two different things. There is never more than 200 amps flowing in that service cable circuit.

[trader4]

Agree.

If you also put a 120V load across Line 2 and the neutral, then

Don't agree with this. If the second load on line 2 is equal to the load already on line 1, then the current flow is in on line 1 and back out on line 2. No current flows in the neutral.

If the second load on line 2 were half the size of the load on line 1, then half the current from line 1 would flow back out on line 2 and half the current from line 1 would flow back out the neutral.

The key here is look at that service cable coming from the transformer and you have a circuit running a max of 200 amps. Agree?

[bud--]

The answer is obvious; 400 amps.

Don't know about Canada, but in the US 80% only applies to "continuous loads" (over 3 hours). In a house service, if you could get a 200 amp peak it wouldn't last long. Loads cycle on and off. It is called "diversity". Because of diversity the service wires (in the US) can usually be 'undersized' with a residential derate. Can't do that in commercial, where you turn on lights and they are on all day long ("continuous").

And when you balance the load over the two 115 volt legs you get - lets see - 46,000 watts divided by 115 volts - um - 400 amps of 115 volt load. Even in Canada. That is what the OP asked.

[Doug Miller]

Which is exactly what I've been telling you for the last four days: a 200A

240V service will support 400A of 120V loads. I'm glad you finally figured it out.

[trader4]

Thank you. That's exactly what I've been saying all along.

Here's a circuit diagram of a fully loaded, balanced 200 amp service:

-------------- 240 volt source----------- I I a I I b I I I------------------2.4 ohmRes-----------I I I I-----1.2 ohmR-----1.2 ohmR--------I

How much current is flowing in the "service", which is through the voltage source? 200 amps. It supporting one 240Volt 100 amp load and two 120volt 100 amp loads. By every circuit concept I've ever heard of there is but 2 amps flowing in the service cable here. Yet, some would have you believe it 3 amps.

If we want to include the neutral then it looks like this:

• -- + -- I------------120V----I-------120V--------- I I I I I I I I I I-----1.2ohms------I--------1.2ohms---I I I I-------------------2.4 ohms---------------I

The service now consists of 3 wires. In this case, because it's balanced no current is flowing in the neutral. You can unbalance it, do anything you like and still with a 200 amp service there is only

200 amps flowing in, 200 amps flowing out. And it;s not a "parallel circuit either as Doug has claimed.

[trader4]

That has never been in dispute. What has been is how many physical amps are flowing in the service cable circuit of a 200 amp service? Here's a hint: Try answering this simple physics question without refering to voltage or power.

[Steve N.]

You're right. If the the two 120V loads are perfectly balanced, then it's the equivalent to two 120V 0.6 ohm loads in series across 240V each pulling

200 amps, and you can disregard the neutral or even disconnect it. The neutral is there to hold the voltage on each leg or side to 120V when the loads aren't perfectly balanced.

True

No, the main breaker would open long before any melting

A whole bunch for a few microseconds. A breaker isn't instantaneous.