120V loads only

[Bruce A. King]

note: This does not apply to a normal residential scenario.


How many maximum amps on each leg of a regular residential 240/120V panel can you get if you only have 120V loads connected with each side balanced?

Main breaker rating is 240V, 200 amp, 48,000 watts

List the amps on each leg and total amps pulled from the service.

[Marc D. Shunk]

200 amps at 120V on leg A = 24,000va (watts)
200 amps at 120V on leg B = 24,000va (watts)
48,00va total

200 amps at 240v between A and B = 48,000va (watts)

Same diff...

[Bruce A. King]

Can you have 400 amps of load if only 120V loads are used and balanced?

[Speedy Petey]

No, you can have 200 amps on each of two legs at 120v. Or 200A @ 240v.

No, this is not equivalent to 400A @ 120v. At least not in the real world. Because no where will you every see much over 200 amps.

[Michael Larson]

Originally Posted by Speedy Petey

No, you can have 200 amps on each of two legs at 120v. Or 200A @ 240v.

No, this is not equivalent to 400A @ 120v. At least not in the real world. Because no where will you every see much over 200 amps.

But theoretically you could have 400 A total assuming balance loads correct?

[Speedy Petey]

I'm not trying to be a jerk, but what is the fascination with this 400A @ 120v thing??? So many folks pressure us to say "Yes, it is 400A at 120v.". It is not.

How come 200A @ 240v is not good enough?

[Michael Larson]

Originally Posted by Speedy Petey

I'm not trying to be a jerk, but what is the fascination with this 400A @ 120v thing??? So many folks pressure us to say "Yes, it is 400A at 120v.". It is not.

How come 200A @ 240v is not good enough?

It's an ongoing discussion somewhere else.

[Michael Larson]

Let me ask it this way.

Could you have 40 20 Amp breakers in a panel each with a 10 amp load?

[Speedy Petey]

Absolutely.
But put an amp meter on the neutral and tell me what you read.
See what I am getting at?

[Marc D. Shunk]

It's 48,000 volt-amps, regardless of how you divvy it up.

[Bruce A. King]

I agree, you can actually look at it as two 120VAC power sources and have a maximum of 48000 watts divided by 120Volts = 400 amps of 120V power.

[Paul Dickerson]

Bruce and Michael,

You are incorrect in your assumptions. In the hypothetical situation you have outlined, (200 amp balanced loads on each of the two legs), you will only measure 200 amps at any point in the system.

Lets follow the electrons. For 1/120th of a second, 200 amps will flow into the panel through Leg A, the same 200 amps will then flow through the 120V loads connected to leg A, the same 200 amps will then flow to the neutral bus, the same 200 amps will then flow through the 120V loads connected to leg B, then the same 200 amps will flow out of the panel through leg B. Then the current reverses and takes the same path backwards. It is all the same electrons.

[Bruce A. King]

Thats a good explanation of the actual operation and the reason why AC is used for power distribution instead of DC.

The highest measured current will be 200 but you have 48,000 watts of power dissipated on 120V loads. It takes the equivalent of 400 amps to produce this amount of power on 120V loads.

This "never to be found" setup in residential is best described in watts rather that amps since the voltage on the loads is not 240V.

[Michael Larson]

Originally Posted by pdickerson

Bruce and Michael,

You are incorrect in your assumptions.

What did we assume?
You mean Marc and speedy are wrong?

Your description is correct.

I thought I made it simple when I said:

40 breakers with 10 A load each.

The panel is still 120/240 @ 200 A but is capable of supplying 400 A @ 120V as long as the load is balanced.

I think we are in agreement but it's all how you look at it.

[Patrick Bolliger]

Bruce, Michael

Your looking at the concept of current, load and A/C incorrectly.

Alternating current A/C is not like DIRECT current or DC.. meaning a constantly current level..

I was going to go into a very long explanation on the theory but figured it would be best if Paul Abernathy would explain it ..

On a side note, Tangent.

By the way A/C was found to be easier to "transmit" via overhead "High" power lines over great distances. Loss factors are very high that is why we don't use DC in homes these days. Samuel Insull... He had a HUGE part in it..see......http://www.geocities.com/WallStreet/...48/insull.html
http://en.wikipedia.org/wiki/Samuel_Insull

245MKV at the towers and 12,500 volts at the wires at very top of the poles around the neighborhoods in my area to transformers 240 volts to the house...

Side note:

What happens to the voltage in the summer time when everyone runs there AC Compressors??