50 amp service - help - Page 3

Ed Gardiser · 08-01-2006, 06:09 PM

AKO
No need to be sarcastic or insinuate that there are people not as educated as others.I would venture to say the vast majority including you went to public schools.
Bob
Wire size was never part of the conversation.
From the beginning I only questioned how Rusty was attempting to explain himself on 240 vac 1 phase electric being used as power for a motorhome.
Ed Gardiser

Bob Hatch · 08-01-2006, 07:16 PM

While wire size may not have been a part if the conversation, it's an important part of the way it works, and why you can load a 6 gauge wire, that's rated to carry about 50 amps, with the return from a 50 amp feed on each leg. Both legs add up to 100 amps at 120 volts, or 50 amp 240 volt.

Add 10 volts to leg one cycling at 180 degrees +, and you return 10 amps across the neutral, you pointed that out yourself. Now add 10 amps to the other leg cycling at 180 degrees -, or out of phase with the first leg, and the return across the neutral is zero amps. That's why it's important to balance the loads on the bus bars. On the 50 amp rig with 2, AC's, one AC is on one leg, the second on the other, and on down the line. If balanced, with every thing in the rig running full on, your return across the neutral is maybe 10 amps or so.

Now lets say you put both bus bars on the same leg from the main service. You could do that by putting 2, 120 volt 50 amp breakers separated by one space on the main service panel, or using the same 0/00/000 wire to feed both legs in the park pedestal. You would then be using 50 amp through each breaker in your rig, but from the same leg of the service, or 100 amps of 120 volt service, and no 240. As you apply power to the different items in the rig, you would add to the load return of the neutral. Lets say each AC pulled 15 amps. Turn on both and you're at 30 amps across the neutral. Lets also assume that your converter pulls 10 amps. You're now at 40 amps to the neutral. Turn on the microwave, and you're over 50 amps across the neutral. If you were able to utilize all the items in your rig with an improperly set up service you would need a 0 gauge neutral to carry the return, because you're drawing off the same side, or cycle, of the power.

Properly configured 240 is subtractive to the neutral.

120 is additive to the neutral.

Are we there yet? If so, I'll give you an experiment to try next time you're in an RV park.

Bob Hatch · 08-01-2006, 08:12 PM

Ed, this link might help a bit.

http://science.howstuffworks.com/power9.htm

BTW, in order to simplify I indicated that one leg would be 180 +, and the other 180 -. But in fact each side cycles between 180+ and 180-. When one leg is at 180+, the other is at 180-.

rebelsbeach · 08-02-2006, 02:32 AM

Some of these 50A threads are growing faster than a Walmart thread!!

Here's a search of 50A threads...

RustyJC · 08-02-2006, 04:14 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ed Gardiser:.
Bob
Wire size was never part of the conversation. </div></BLOCKQUOTE>
No, but if the 50 amp service is wired incorrectly, the fact that the neutral conductor size is the same as the hot conductors can result in an overloaded neutral conductor, so wire size is important to the discussion.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">From the beginning I only questioned how Rusty was attempting to explain himself on 240 vac 1 phase electric being used as power for a motorhome. </div></BLOCKQUOTE>
Ed, between my explanation and Bob's, have we answered your question sufficiently?

Rusty

adj · 08-02-2006, 05:26 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RustyJC:
[QUOTE]Originally posted by adj:
If you take the center tap out you still have 240V single phase. </div></BLOCKQUOTE>
The center tap is the grounded neutral. It's present in the feed to your house as well as the feed to the RV shore power pedestal, so I don't understand the point you're trying to make.

My point is that it is a single phase with a center tap which allows us to use 2 different voltages. To acquire a phase shift using a single phase requires the use of a phase shifting network.
The use of the phrase "180 degrees out of phase" is incorrect in this application.

RustyJC · 08-02-2006, 05:30 AM

No, it is not. If you look at the voltage or current waveforms of the 2 each hot feeds on 50 amp service referenced to neutral, the waveforms are 180 degrees out of phase relative to each other. That is the significance of the center tap transformer.

Rusty

RustyJC · 08-02-2006, 06:15 AM

Referring to the drawing above, when current is flowing from top to bottom in the secondary (right side) windings of the transformer, on the V1 leg it is flowing from hot (V1) to neutral (N). Conversely, on the V2 leg, current is flowing from neutral (N) to hot (V2).

When the direction of induced current changes from bottom to top (remember, alternating current), then the opposite holds true. That's why the voltage and current in the 2 legs are 180 degrees out of phase with each other referenced to neutral.

Rusty

adj · 08-02-2006, 08:26 AM

[QUOTE]Originally posted by RustyJC:
No, it is not. If you look at the voltage or current waveforms of the 2 each hot feeds on 50 amp service referenced to neutral, the waveforms are 180 degrees out of phase relative to each other. That is the significance of the center tap transformer.
---------------------------------------------

I stand by my original statement. A transformer could have multiple taps and, as long as the primary is single phase, the secondary will have multiple single in phase output voltages. These voltages are only dependent on the number of secondary turns being tapped.
In our present example, at a given point in time, V1 can be positive, and the center tap can be positive when referenced to V2.
During a 1 Hertz time line, the voltage at all 3 reference points will vary from max+ to 0 to max-. However, it will be a single phase of voltage.

RustyJC · 08-02-2006, 08:38 AM

From Wikipedia's Open Textbook section dealing with basic electricity:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Single phase power is what is commonly available to residential and light-commercial consumers in most distribution power grids. In North America, the single phase that is supplied is developed across a transformer coil at the utility pole (for aerial drop) or transformer pad (for underground) distribution. This single coil is center tapped and the tap is grounded to develop <span class="ev_code_red">two waveforms that are 180 degrees out of phase with each other</span> with 1/2 the voltage. This then creates a 120/240 volt system that is delivered to the customer. </div></BLOCKQUOTE>

The above is consistent with what Bob and I and others have presented. Are you saying that the statement above is incorrect?

Rusty

adj · 08-02-2006, 11:00 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RustyJC:
From Wikipedia's Open Textbook section dealing with basic electricity:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Single phase power is what is commonly available to residential and light-commercial consumers in most distribution power grids. In North America, the single phase that is supplied is developed across a transformer coil at the utility pole (for aerial drop) or transformer pad (for underground) distribution. This single coil is center tapped and the tap is grounded to develop <span class="ev_code_red">two waveforms that are 180 degrees out of phase with each other</span> with 1/2 the voltage. This then creates a 120/240 volt system that is delivered to the customer. </div></BLOCKQUOTE>

The above is consistent with what Bob and I and others have presented. Are you saying that the statement above is incorrect?

Rusty </div></BLOCKQUOTE>
-----------------------------------------------
With regard to that part of the statement that says "two waveforms that are 180 degrees out of with each other" yes.
Two wave forms 180 degrees out of phase will cancel each other out and there will be no voltage (assuming they are equal).

RustyJC · 08-02-2006, 11:10 AM

The two waveforms are on two different hot legs (V1-N and V2-N in the diagram I provided). Therefore, they don't "cancel each other out", although the neutral currents (since they share a common neutral) will "cancel each other out" as Bob pointed out if the current loads in the two legs are perfectly balanced.

At this point I can only suggest that you take an oscilloscope the next time you have access to a 120/240VAC 50 amp RV shore power box and satisfy yourself that what we're saying regarding phase angles of the 2 hot legs is the truth. Obviously, I could cite more sources, but if you choose not to believe them, what would be the benefit?

Rusty

Don (W5IT) · 08-02-2006, 11:21 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Two wave forms 180 degrees out of phase will cancel each other out and there will be no voltage (assuming they are equal). </div></BLOCKQUOTE>

That is exactly what Rusty has been talking about in relation to the neutral loading.

Bob Hatch · 08-02-2006, 11:31 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Don (W5IT):
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Two wave forms 180 degrees out of phase will cancel each other out and there will be no voltage (assuming they are equal). </div></BLOCKQUOTE>

That is exactly what Rusty has been talking about in relation to the neutral loading. </div></BLOCKQUOTE>

Well of course it is. It's what we've both been saying, and what the articles say.

RustyJC · 08-02-2006, 11:40 AM

Let's take an instantaneous point in time and measure the voltage on the sine waves of both legs. The voltage on V1-N is 85V referenced to N. The voltage on V2-N is -85V referenced to N since it is 180 degrees out of phase. These do not cancel each other out - rather, the difference in potential (the definition of voltage) at that instant is 170V. If we extend this to many points, the RMS voltage of V1-N is 120VAC, but being out of phase by 180 degrees, the RMS voltage of V2-N is -120VAC (- indicating the 180 degrees phase angle shift relative to V1-N at instant of measurement), so the difference is 240VAC, the same reading you would get across V1-V2. The center tap is responsible for not only cutting the voltage in half on each secondary leg, but also for shifting the phase angle between the legs by 180 degrees.

Rusty

adj · 08-02-2006, 12:30 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RustyJC:
Let's take an instantaneous point in time and measure the voltage on the sine waves of both legs. The voltage on V1-N is 85V referenced to N. The voltage on V2-N is -85V referenced to N since it is 180 degrees out of phase. These do not cancel each other out - rather, the difference in potential (the definition of voltage) at that instant is 170V. If we extend this to many points, the RMS voltage of V1-N is 120VAC, but being out of phase by 180 degrees, the RMS voltage of V2-N is -120VAC (- indicating the 180 degrees phase angle shift relative to V1-N at instant of measurement), so the difference is 240VAC, the same reading you would get across V1-V2. The center tap is responsible for not only cutting the voltage in half on each secondary leg, but also for shifting the phase angle between the legs by 180 degrees.

Rusty </div></BLOCKQUOTE>
------------------------------------------------
In your instananeous example above, if you were to measure voltage from the neutral to V2 you would have a plus 85V.
The individual voltages induced into each secondary winding turn is additive accross the whole of the secondary. As the magnetic field expands and contracts, it induces a single sine wave of voltage into the secondary. The center tap does nothing but split secondary into 2 induividual supply legs. Without the tap, you still have a single phase 240V supply.
I'm of the opinion that we have gummed this to death. My original comments were only trying to point out that a center tap does not create a phase shift(thus, 2 phases). It only allows us to have multiple voltage sources from a single phase source.

RustyJC · 08-02-2006, 12:41 PM

What you're missing is that, at that instant of measurement, the current flow is from V1 to N in the top leg and from N to V2 in the bottom leg because of the center tap. In other words, the current is flowing in opposite directions in the two legs at any given instant. That's why the sine waves of the two legs are shifted 180 degrees relative to each other. I don't know how to make it any simpler than that. As the multiple sources point out, the waveforms of the two legs are 180 degrees out of phase with each other. That's a fact not just purported by me and others but noted in the electrical texts that have been cited.

Rusty

Tom N · 08-02-2006, 01:53 PM

IMHO, some of you guys

have had the V1 in your right hand and V2 in your left hand

a few too many times!

Ed Gardiser · 08-02-2006, 04:18 PM

Boy ! Look at all the fun I missed today.
Ed Gardiser
Escondido,Ca.
04 Vectra
87 Nissan PickUp
FMCA

Bob Hatch · 08-02-2006, 04:39 PM

[QUOTE]Originally posted by Ed Gardiser:
Boy ! Look at all the fun I missed today.
QUOTE]

Yahoo. But, did you get an answer to your question?