Domestic Electric Voltages

[wazza]

I am in need of help. I am currently discussing a Central Heating problem on this forum, but i am confused by a comment made by a plumber recently whilst trying to resolve this problem.

Basically he is saying that i have a voltage of 310 Volts to the central heating control box, from the fuse board.

Is this possible, as i thought domestic voltage was only 220-240 Volt ??

Any comments would be good.

 

[pipme]

....... Any comments would be good.

Still raining here.

 

[SwindonSpark]

He's referring to the fact that AC voltages change over time. Well you knew that didn't you.

The peak to peak voltage of domestic AC is plus and minus 325 volts (or 310 in your friend's opinion).

To work out the domestic voltage we take the AVERAGE value of the changing voltage, called the root mean squared value.

Which just happens to be 230 volts.

Easy eh?

 

[wazza]

Thanks Swindonsparky.
Sorry but Electrics are not my forte. It just sounded wrong that there could be higher voltage present than the 240 volts i know of.
So the fact that he got this reading is perfectly normal i presume.
I was told that no work could be carried out on my broken boiler until i got this voltage problem sorted out.
Was this a way of gettig out of solving the problem by the plumber i wonder ???

 

[BruisedThumb]

<he got this reading>

So your plumber measured a value of 310 Volts, did he?

I'd like to know what instrument he used; an oscilloscope maybe?!?

 

[pipme]

 

[plugwash]

To work out the domestic voltage we take the AVERAGE value of the changing voltage, called the root mean squared value.

Which just happens to be 230 volts.

Easy eh?

rms is not the average voltage

 

[pipme]

What if our Plumber measured 219 V ac (4.8% below the 230V, or 8.8% below 240 V, therefore likely ?)
In conversation related the amplitude as 310 V ? by using the sinusoidal peak factor 2^1/2 times the measured voltage say 1.414 x 219 V = 310 V ????

P

 

[ban-all-sheds]

rms is not the average voltage

Yes it is.

The word "average" has a generic meaning. It does not imply any particular "average" calculation, it could be used to mean mean (arithmetic or geometric), median, mode, or, indeed, RMS.

 

[breezer]

pipme, is it still raining?

 

[pipme]

West country's awash ! Want some ?

 

[pipme]

wazza.

Far better description here :- http://www.kpsec.freeuk.com/acdc.htm

 

[Damocles]

I was just itching to say that.

Just an average day then.

What does average mean there?

 

[plugwash]

anyone here fancy doing the maths to show that for a sine wave peak=rms*sqrt(2)

 

[pipme]

I think I am right in saying .... If we look at a sinewave only.
The peak factor or, max value divided by rms value is 1.414 which is the square root of 2.
PF = Max / rms therefore Max / PF = rms.

Proof of the stated relationship can be shown by the use of integration ... and the stnd expression for ac voltage .... ugh!! (cannot remember that stuff )

But here is an excellent electrically based description with a little math :-
http://www.doctronics.co.uk/rms.htm

Raining again !!

P