voltage drop

[timtheenchanter]

Im looking at the voltage in my house, and seems on the high side.

My UPS reports an average of 244V, some peaks of 248V for hours at a time.

The concerning thing is the UPS is on the end of a radial, wired in 2.5mm T&E, approx 15m cable run from the CU.

By my calculations, there is an approx 4v drop on the length to the end, meaning the voltage at my CU 248V on average, with 252V at peak times.

this is JUST under the max of 253V, as I understand it, can anyone confirm my calculations.

 

[Adam_151]

Is the radial always loaded to the design current?....
When did the UPS last go for calibration?

 

[ericmark]

At zero amps the voltage at the consumer unit will be same as at UPS.
Although at max amps approx 20 for twin and earth volt drop could be calculated the cable temperature would also need measuring and compensation made. At 18mV/A/m then that's 0.27V/A so if UPS was drawing 13A it would be 3.5V so likely 251.5V max which is under 230V x 10% = 253V the drop of 1.4V from 240V+/-6% to 230V +10%-6% it was really only a paper exercise.

In real terms lighting is main problem. With old tungsten bulbs high voltage reduced life and low voltage change the colour temperature as well as becoming dimmer. But with inductance controlled discharge lamps (florescent) over voltage significantly increases the current draw I found with experiment a 60W fitting can draw 100W when the voltage is at upper limit and at low voltage it can fail to strike.

The HF fittings with electronic ballast do not have this problem.

So if your lighting is working OK then don't worry.

 

[electronicsuk]

As already mentioned, you can't trust the voltage reported by the UPS to be 100% accurate. If it worries you, get a multimeter (admittedly it's unlikely you'll have that calibrated either, but I'd trust it over the UPS) and then take a voltage reading directly at the main isolator on the consumer unit. That is, if you feel confident removing the cover - there will be exposed live parts in there.

 

[timtheenchanter]

Is the radial always loaded to the design current?....

Doh, forgot that bit, thats why I wanted to check my thinking/figures.

I dont have a calibrated multimeter, but it is only a couple of months old, and a good one, so should be fine.

Im quite happy poking around live stuff, Im working towards my C&G.
I will have a look, see what I get.

the UPS is capable of the full 13A, but not loaded up to anywhere near its full load, about an amp according to the readout. I trust the voltage reading a bit, its a god quality HP UPS, not some no named rubbish.

Ive not had any problems with lighting, all is either CFL, 12V LED or 12V halogen, no premature deaths, infact not replaced any in the 2 years I have lived here.

 

[Taylortwocities]

Even if its not calibrated, you can check the voltage at the origin end of the cable and at the UPS end.

I'll bet there's not that much difference.

 

[Stoday]

A peak voltage of 252V and an average of 244V is just about what you should expect if your house were fed from the end of a fully loaded feeder from the nearest substation.

The declared voltage of 230V (+10%, -6%) is NOT the average voltage. If the feeder were fully loaded, the end would reach 253V at times of virtually no load and 216V at times of peak load. The average of that, assuming an overall residential load variation with time, is 242V. The average voltage for a house nearer the substation would be even higher.

 

[timtheenchanter]

If Im on the nearest substation to me, its about 12 houses at the end of my road. so I would be one of the closest to the station.

is there a search to find my feeding substaion?? just out of interest.

Thanks Stoday, that makes perfect sense, I must have been being really dense of course the voltage goes up on light loading, not down. (this is why Im still in training!!)

Im looking for some more reading on distribution on a whole if anyone knows any good sites/books
Ill have to talk to the chap up the road, he used to work on live overhead lines (sounds fun)

 

[Paul_C]

Remember too that the 230V declared nominal voltage is really a charade anyway, with the tolerances meddled with just so that we could officially declare the U.K. to be 230V.

For all practical purposes, the majority of supplies are still the old standard of 240V +/-6%, and if you are near the transformer on a feeder which carries a fairly heavy load during peak times, it's not unusual for the taps to have been set so that your actual voltage during low-load periods will be rather higher.

 

[Stoday]

The one practical purpose when the new standard applies is when the DNO responds to a complaint of low voltage.

The DNO won't act now unless the voltage falls below 216V whereas before the main would be reinforced if the voltage fell below 226V.

 

[ban-all-sheds]

Not so - the other practical purpose is that it allows lamp manufacturers to sell products in the UK which are officially OK but will have short lives, thus increasing their sales.

 

[skenk]

And if fluorescents (except HF) draw more current then won't we be getting charged more on our energy bills?