Domestic Electric Voltages

[plugwash]

let A be the peak voltage (in volts)
let T be time (in seconds)
let F be the frequency (in hz)
let Y be the voltage at any point in time

the angle mesurement used for trig functions will be radians

Y=Asin(2(PI)FT)
let X=2(PI)FT

so Y=Asin(X)
then you just need to square this integrate it with respect to X with limits of 0 and PI and devide the result by PI to get the RMS voltage

 

[SwindonSpark]

Wazza,

see what happens when I try to explain things using simple language.

Ban-all-sheds is right when I used the term average, it was in its loosest sense.

All my brother sparks have now demonstrated mathematically the difference between an average and a root mean squared value, but are you Wazza, any the wiser?

I cannot argue with plugwash since he is right, but I get the feeling that his accurate explanation is overkill for your needs.

 

[plugwash]

oh i forgot about sqare rooting the final result

you want the root mean square voltage not the mean square voltage

 

[paulh53]

RMS Is 70.7% Of The Peak Voltage,

 

[SwindonSpark]

There you are Wazza. You'll feel happier now.

 

[pipme]

He probably would if he looked here http://www.doctronics.co.uk/rms.htm
An elegant actual answer .. using a power formula ... neat n'nice !!
Agreed anyone ?

For simple sinewave RMS = sqr root of the mean of the squares of continuous ordinates.
P
[/b]

 

[ban-all-sheds]

That just shows why you need a concept of RMS - it doesn't tell you what the RMS value for a sine wave is.

 

[BruisedThumb]

All this revision of the relationships between RMS and peak voltages is all very well but has taken us into a second page without resolving what, IMHO, was an important aspect of helping the original poster.

Namely, where did the plumber (no disrespect for plumbers in general) get this 310 Volts from? Did he measure it (them), by that I mean did he read a displayed 310 Volts off some measuring instrument? If not, did he get some other reading and multiply it by some 'fudge factor'?

If the former, what sort of measuring instrument? If he used a conventional AVO or digital multimeter, on the correct range, either it needs calibrating, or there's something seriously awry with the installation (e.g. 3-phase but I thought this was a domestic situation?) or there's some other explanation, like he'd had a pub lunch!

If the latter, what was the actual reading and does he have a rationale for the fudge factor? Without getting one or both of those things out in the open, the original poster doesn't have anything to grapple with, there's no basis for debate. How can he demonstrate that the plumber is spinning him a tale?

As things stood at the time the question was originally posted, the plumber had alleged that the poster (his customer) had a problem. Surely, we should be trying to help resolve:
a) what the problem was/is
b) whose problem it is.

 

[pipme]

Without being rude to Wazza .. the comment may have been part of a general conversation ... not enough information.

More on Wazza's problem //www.diynot.com/forums/viewtopic.php?p=89910
P

 

[Damocles]

It is not actually impossible that you have 310V RMS coming from the mains supply. Know a case where a booster transtormer had been fitted by the supply company 50 years ago, then forgotten. It was doing a grand job of boosting the output from the new supply transformer 10 yards away. Got quite hot. Explained why the quality of modern light bulbs seemed to have gone down so much. So stupid and dangerous mistakes do happen.

Most likely he was measuring DC somehow, not rms AC. My initial reaction would be to disbelieve him. Politely, just in case he turned out to be right.