120V loads only

[Bruce A. King]

It was a good discussion, also one over at INews, I think most everyone including me learned something and got another angle on it. Sometimes practical explanations and theory will cause differences but the operation from an inspectors view is the same which is what I am trying to point out.

[Bruce A. King]

Originally Posted by pbolliger

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 ..

No need, Paul Dickerson just posted a very good description on how the A/C waveform performs in this setup.

[Michael Larson]

Originally Posted by pdickerson

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.

I am in full agreement with you and never intended to indicate that one could measure more than 200 A anywhere in the system.
I very familiar with center tapped transformers which is what a 120/240 V service is being supplied from the POCO transformer.

Not sure where you got the idea that I had incorrect assumptions. Please point it out to me. I imagine its from stating you could have 400A of 120 V loads. It can never be above 200A on either hot leg(for long anyway) as the breaker will trip.

[pdickerson]

Originally Posted by mlarson

Not sure where you got the idea that I had incorrect assumptions. Please point it out to me. I imagine its from stating you could have 400A of 120 V loads.

Yes. From this statement I thought that you were making an incorrect assumption. My apologies.

[Michael Larson]

Originally Posted by pdickerson

Yes. From this statement I thought that you were making an incorrect assumption. My apologies.

No harm no foul.

How electricity works is a tough subject to wrap one's head around for many.

[pdickerson]

Originally Posted by bking

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.

It is confusing, and incorrect, to think of it as 400 amps. It is actually 200 amps doing work in two different places.

If you put two different amp clamps on the same wire with 200 amps flowing through it, both will read 200 amps. This does not mean that you have 400 amps flowing because you measured 200 in two different places.

In your example, you are using 24000 watts of power at leg A and 24000 at leg B. But the two legs are in series in this example. Imagine two waterfalls, one right after the other, in the same stream. Each waterfall represents a potential to gererate power, but the water flow in gallons per minute is same at all places in the stream.

[Michael Larson]

And no current is flowing in the neutral.

Sounds goofy but it's the truth.

Now try explaining it to a client. Good luck.

[Greg Fretwell]

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

Around here ... nothing.
My voltage remains very stable throughout the year. I have a Weston 901 plugged in all the time

[Bruce A. King]

Anyone remember that device they used to sell about 25-30 years ago that claimed energy savings for fridges?

It used SCR's or Triac's to chop off part of the AC waveform or something like that.

I guess it was hard on the equipment or were proven bogus because you never hear about them anymore.

[Greg Fretwell]

Bruce, I still see them around. It is usually called a "green plug" or something like that. Basically it is a power factor corrector. The circuit was originally designed by NASA, or so the legend goes. Unfortunately any fridge built since the Carter administration has power factor correction already and the "green plug" makes it worse, not better.
You notice, when they demonstrate these things it is always on an unloaded motor. Modern motors are designed to me most efficient at the rated load.