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P to P value

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From the wall, for example, in the U.S.A........
Does the instantaneous voltage ever reach 340VAC.?
I can count the divisions on a scope, but is that just a theoretical number.?
If I put a DMM across the Hot and Neutral....it says 120VAC.
Can you get hit by 340 volts.?
I am trying to figure when the P-P value comes into being....
Thank You
 
From the wall, for example, in the U.S.A........
Does the instantaneous voltage ever reach 340VAC.?
I can count the divisions on a scope, but is that just a theoretical number.?
If I put a DMM across the Hot and Neutral....it says 120VAC.
Can you get hit by 340 volts.?
I am trying to figure when the P-P value comes into being....
Thank You

No you can't, it's never more than 170V peak (either positive or negative) from earth (or neutral).
 
If you measure the standard mains outlets in the US as can be seen on the bottom of this page you will measure about 120 VAC RMS. The trick becomes knowing the relationships between the RMS value of a sine wave as to peak or peak to peak. Remember a scope displays the peak to peak value.

The relationship between Vrms and Vpeak is Vpk = 1.414 * Vrms so for 120 volts RMS it becomes 120 * 1.414 = 169.68 volts peak and Vpk to pk = Vpk * 2 so 169.68 * 2 = 339.36 volts peak to peak.

Yes, you can get "hit" by 340 volts peak to peak as it is 120 volts RMS as in a wall outlet.

Be careful measuring mains voltage using a scope as if you place scope ground across mains high bad things will happen. :)

<EDIT> Nigel beat me! :) </EDIT>

Ron
 
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There is no such thing as RMS in the situation we are covering at the moment. In other words, there is not such voltage as 120v. It is a theoretical or generated value, introduced when AC overtook DC for households. It is a value that makes AC equal to DC as far as heating is concerned. The only voltage you detect when touching the "mains" is 170v.
The active line of the "AC" rises 170v higher than the neutral, then 170v lower than the neutral. But there is no way that you can get zapped by 340v (170v + 170v) as you have no means of storing or "holding onto" the -170v (with one hand) then receiving or detecting +170v.
 
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I disagree. You cannot get 340V instantaneously because it is peak-to-peak and the opposite peaks do not occur at the same time. You will get a peak of 170V in one polarity followed by a peak of 170V in the other polarity.

In your kitchen you probably have dual receptacles with one wired with one phase and the other wired with the opposite phase and it has 240V RMS or 340V peak between them. They are wired like that so you can have two appliances plugged in with each drawing 15A.
 
Thanks for the responses. I have been having a discussion/argument with a friend....he says you certainly can.....but I do not see how.....and that was my reeasonong.....I do not see where the P-P voltage occurs at the same time.....to give a 340 potential.
You guys know WAY more about this stuff than I do.....thanks for the opinions/facts.......I appreciate it.
Thanks
 
Earlier I stated:
Yes, you can get "hit" by 340 volts peak to peak as it is 120 volts RMS as in a wall outlet.

I based that on simply getting hit as in a shock. However, in reality no, as AG points out it is not instantaneous. If you look at US mains voltage of 120 VAC RMS on a scope you will see a 340 volt or so peak to peak signal. Remember, the scope is plotting amplitude against time. One full cycle (60 Hz) of AC mains power takes 16.666 mS to happen. So starting at zero volts it takes about 4.166 mS for the signal to reach a positive peak of 170 volts, then it begins a negative transition where 4.166 mS later it is crossing zero volts and 4.166 mS later it is at a negative peak of -170 volts before starting a positive transition where it will reach and cross zero volts in 4.166 mS. Deal done for a single cycle of 60 Hz. At no single point in time is there 340 volts peak to peak. The voltage is constantly changing over time. The scope makes that pretty clear to actually see. :)

Ron
 
If you look at US mains voltage of 120 VAC RMS on a scope At no single point in time is there 340 volts peak to peak. The voltage is constantly changing over time. The scope makes that pretty clear to actually see. :)
Ron

Let me ask another rudimentary question.
What if the peaks did occur at the same "time".?
Would that mean they are in-phase.?
And if so........
What would be the net voltage of +165VAC and -165VAC.?
Would that net ZERO volts.?
Thank You
 
Let me ask another rudimentary question.
What if the peaks did occur at the same "time".?
Would that mean they are in-phase.?
And if so........
What would be the net voltage of +165VAC and -165VAC.?
Would that net ZERO volts.?
Thank You

The positive and negative peaks can't occur at the same time on a regular wall outlet because it's only single phase. That would be like having a vacuum and pressure at the same time at the end of an air hose.

However, on the outlet to your electric stove, you can have 170 volts positive peak occurring on one of the hot prongs at the same time as 170 volts negative peak occurred on the other hot prong. Then between the two prongs you would have 340 volts total at that instant.
 
What if the peaks did occur at the same "time".?
Then answer this: What if full throttle forward and full throttle backward is applied to a motor simoustanely. What happends?

That question of yours simply doesn't make sense.

But - there is rectifier circuits -half phase rectifier with condensators- that can "get" Vpp minus diode drop from an AC source.
 
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You mean a 'voltage doubler' - the clue is in it's name.

I was thinking of this little fellow circuit. I'm not sure about it's corect english name.
 

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Nice day for pictures. :)

Maybe a few images will help things along. The first image is a mains power transformer pole mounted. This particular transformer feeds my house. Here the primary is single phase (one of three available) and about 7,000 VAC RMS 60 Hz. The second image is how it looks in a schematic. Here in the US mains power is delivered to most residences as 240 VAC RMS 60 Hz. split phase power. The third image is a picture of a scope screen illustrating the waveforms. Each channel has common to ground and the high sides to L1 and L2.

No, I did not use the 240 VAC mains, I used a little transformer to duplicate the one outside on the pole. In reality the waveforms are about 6.3 volts RMS. :) I managed to get bit this week by 480 volts so I am on a low voltage kick. The scope channels show the signals 180 degrees out of phase from each other, exactly as mains power enters a US residence.

Ron
 

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.................
I managed to get bit this week by 480 volts so I am on a low voltage kick.
................
That's more like a large bite.:D Glad you're still around.
 
That's more like a large bite.:D Glad you're still around.

Yeah, it wasn't one of my brighter moves or better days. I was cheating the rules and common safety logic and the tron gods punished me. Over the past few years we have stsrted placing a tremendous emphasis on safety. The ***** was right as I closed the disconnect with my right hand I had a sudden sinking realization that my left hand was across phases A and B. Knocked the hell right out of me. Can't recall the last time I did something that stupid. :(

Anyway, in keeping with the thread, attached are a few more images that better show split phase. Channel 1 illustrates L1 to Ground, Channel 2 is L2 to Ground and Channel 3 is L1 to L2. The cursor in on various peaks and valleys. The voltages for the cursor locations are seen on the right. Triggering was on Channel 1 for the images. Additionally I used a data acquisition module with isolated differential inputs. This could not be done with a scope that shared common ground inputs.

Ron
 

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