230v or 240v

[gman76]

Hi chaps,

Been in the manufacturing of electrical stuff for a while now, we changed transformers from 240 to 230 a while ago - about the same time as it became compulsery to fit plug tops on all manufactured equipment.

I need to ask - if we now fall in with "Euro" 230v why do you sparks keep refering to 240v?

 

[Monkeh]

Because 240V falls within tolerance for a 230V supply, and in reality, most supplies are still 240V.

 

[1john]

same reason they say 415V instead of 400V, old habits die hard.

 

[Taylortwocities]

Originally the UK mains supply voltage was specified at 240 volts AC or, more precisely, 240 volts RMS +/-6%. The alternating current runs at a frequency of 50 Hz.

Some time ago, to allow harmonisation across Europe, the specifications were changed to 230 volts RMS +10%/-6%, also running at a frequency of 50 Hz.

Thus the mains supply voltage will remain within European Union norms (standards) even if it varies between an upper limit of 253 volts and a lower limit of 216.2 volts.

The electricity supply companies had set the supply network and have done nothing to chnage the voltage delivered as it falls within the limits set my CENELEC. Otherwise they would have to visit every substation and transformer and tweak the windings.

 

[gman76]

Is it really as stupid as that?

We sold equipment at 240 & have to label it as a voltage change as 120v & 230 as 115v

Crazy.

It will work at either!

 

[ban-all-sheds]

And most appliances still have their 240V rating as the headline figure, e.g. a 10.5kW shower sounds better than a 9.6kW....

 

[gman76]

Not a bad point BAS

Makes sense.

 

[holmslaw]

..

 

[wingcoax]

If you remember, they wanted us to change our wiring standards to EU standards a few years ago (from memory this was the second attempt)

 

[Paul_C]

Is it really as stupid as that?

Yes, it's really as stupid as that. The official 230V standard with its weird asymmetric +10/-6% tolerance is nothing more than political meddling so the government could point out what good little integrationists we're being by falling into line with another European "harmonization" directive. And all without actually changing anything on the physical network at all!

Some other European countries have done a similar trick with the tolerances the other way round, to claim adherence to the 230V standard while for all practical purposes their nominal supply voltages are still 220V.

Originally the UK mains supply voltage was specified at 240 volts AC or, more precisely, 240 volts RMS +/-6%.

And that was achieved nationwide only by the early 1970's. Before then, different districts could have slightly different nominal supply voltages, typically in the 220 to 250V range, but sometimes a little lower (especially on older systems), with corresponding 3-phase (220/380, 240/415, 250/433 etc.) and 1-phase 3-wire (220/440, 240/480 etc.) voltages.

 

[Stoday]

230V is the nominal voltage, not the average voltage.

If the LV distribution system is run for maximum efficiency, the house by the substation gets 253V whereas the house at the end has to put up with a variation between 253V when the loading is low to 216V at times of peak load. The average for everyone is ~ 240V.

 

[Taylortwocities]

230V is the nominal voltage, not the average voltage.

If the LV distribution system is run for maximum efficiency, the house by the substation gets 253V whereas the house at the end has to put up with a variation between 253V when the loading is low to 216V at times of peak load. The average for everyone is ~ 240V.

Now, England lost and Ireland lost so i am in a particularly waspish mood today.

Stoday, you are incorrect.

The average value of a sine wave is the average of all the instantaneous values during one alternation. The average value is equal to 0.636 of the peak value.

The UK mains supply is 230V AC, this means 230V RMS so the peak voltage of the mains is about 320V.
The average of a sine wave of 320V peak is 203 volts.

Could it that you mean the mean supply voltage to a group of consumers, or am I being mean?

 

[mikhailfaradayski]

230V is the nominal voltage, not the average voltage.

If the LV distribution system is run for maximum efficiency, the house by the substation gets 253V whereas the house at the end has to put up with a variation between 253V when the loading is low to 216V at times of peak load. The average for everyone is ~ 240V.

Now, England lost and Ireland lost so i am in a particularly waspish mood today.

Stoday, you are incorrect.

The average value of a sine wave is the average of all the instantaneous values during one alternation. The average value is equal to 0.636 of the peak value.

wouldn't the average value of any sine wave be zero?
can't remeber exactly, but i thought the RMS value of a sine wave was 0.7071, not 0.636. However, i've only had 1 cup of coffee this morning which is less than average. This answer may be reviewed in a bit

The UK mains supply is 230V AC, this means 230V RMS so the peak voltage of the mains is about 320V.
The average of a sine wave of 320V peak is 203 volts.

Could it that you mean the mean supply voltage to a group of consumers, or am I being mean?

ooh, id say yr being average

 

[Paul_C]

wouldn't the average value of any sine wave be zero?

Yes - But the average value of any half-cycle is 0.636 times the peak value. The RMS value, as you say, is 0.7071 times the peak value.

So 240V RMS = 340V peak = 216V average (rounded).

The RMS values of A.C. voltages & currents are used in preference to the average because across any given resistance the RMS values result in the same amount of power being dissipated as the equivalent values of D.C.

e.g.
240V D.C. across 24 ohms results in 10A and a dissipation of 2400W.
240V RMS A.C. across 24 ohms results in 10A RMS and the same dissipation.

But the point being made was not the average value of a half-cycle of sinewave, but the average of the RMS voltage delivered to a particular house over a given period of time (as in if you measured the RMS voltage at regular intervals throughout the day then added those figures together and divided by the number of readings taken to obtain a mean average).

 

[mikhailfaradayski]

wouldn't the average value of any sine wave be zero?

Yes - But the average value of any half-cycle is 0.636 times the peak value. The RMS value, as you say, is 0.7071 times the peak value.

I understand that, but from the way it was written it seemed to suggest that the average value of a sine wave was something other than zero. (excluding the possibility of some DC offset)

So 240V RMS = 340V peak = 216V average (rounded).

The RMS values of A.C. voltages & currents are used in preference to the average because across any given resistance the RMS values result in the same amount of power being dissipated as the equivalent values of D.C.

e.g.
240V D.C. across 24 ohms results in 10A and a dissipation of 2400W.
240V RMS A.C. across 24 ohms results in 10A RMS and the same dissipation.

But the point being made was not the average value of a half-cycle of sinewave,

just not written that way

but the average of the RMS voltage delivered to a particular house over a given period of time (as in if you measured the RMS voltage at regular intervals throughout the day then added those figures together and divided by the number of readings taken to obtain a mean average).

Thanks for that, its good to know that i hadn't forgotten any of that from my college days either.

Maybe we need to introduce some boolean logic into the conversation to make it far easier to understand