# How stable are digital multimeters' parameters?

I live in a region where standard mains voltage is 220 volts. Recently I tried to measure it using a digital multimeter. The multimeter specs say that it has maximum error of 1,2 percent of the displayed value plus 3 units (volts in my case).

So I measured and got 241 volts which kind of scared me. According to the specs maximum error would be

241 * 1,2 / 100 + 3 = 5,892


which is about 6 volts, so the real value is in range 235..247 volts which scares me even more.

The spec further says that the maximum error is only guaranteed for the first year of the multimeter lifetime which implies that the error might be even greater as the multimeter gets older.

My question is - how much worse will the error become? The multimeter is something like 5 years old now - what measurement errors should I expect?

• What country are you in? Usually people refer to 220V (even me for long time) but it is actaully is 240Volt .. but also devices are rated 220v/240v which makes things even more confusing. But i would say 241V is normal. 247V is not normal as 227volt is not normal either. – Piotr Kula Nov 24 '11 at 12:56
• @ppumkin: That's Very Eastern Europe - the voltage is indeed 380/220 here, of course 230 volts devices work here okay. – sharptooth Nov 24 '11 at 12:58
• @shaptoohh 380? – Piotr Kula Nov 24 '11 at 12:59
• @ppumkin: It's a typical three-phase system where the voltage is 380 volts between any two phase wires and 220 volts between a phase wire and a neutral wire. Hence 380/220. – sharptooth Nov 24 '11 at 13:08

I expect your multimeter is rather more accurate than the grid voltage. Grid voltage can vary widely from the supposed nominal value. At least 10% should be assumed off the top, but more should not be surprising. 220V +-10% is 198-242V, so you're within spec. There are places in the world I would trust the power less than others, and frankly eastern Europe is in the second tier. It's not as bad as some places where outages are common, but more than 10% variation shouldn't surprise anyone.

Then there is the whole EU standardization attempt. Various countries had somewhat different power voltages, like 220V, 240V, etc. The EU wanted to standardize this. But instead of actually changing the voltages they just re-defined nominal with enough slop so everyone was within spec!

• Thanks a lot. Since that time I had the multimeter readings compared to readings from a verified multimeter in the same apartment and looks like the error is only about 4 volts. I filed a claim with the utility company and they lowered the voltage in no time. – sharptooth Mar 14 '12 at 5:49

Mains voltage usually is stable to +-10%. In Europe, the nominal voltage usually is 230V, except for Switzerland (220V) and UK (240V). This means most of Europe has a permissible voltage of 207-253 Volt.

Your grid has a nominal value of 220, at +-10%, 241 is at the upper end of the range, which is normal.

It is normal because the electricity suppliers have an incentive to run the voltage at the upper end of the range, for two reasons. If the consuming elements are unregulated (say, lightbulbs), they will draw more power, leading to more consumption. If the consuming elements are regulated (like a power supply), they will draw less current, leading to a lower loss in transportation.

Therefore, the normal expected voltage is quite a bit above the nominal voltage.

From my experience, voltage drifts somewhat over the day, sinking during main consumption time.