Talk:Electricity meter/Archives/2020

Image in lead

electric meters in Kolkata

I propose this image for the lead. I just inserted it. Wikimedia Commons graded this image and ranked it as a featured picture, which is top quality. It shows meters as most of the world experiences them, which is in aggregate like this. Also the other images are becoming less relevant as they are analog, when countries which use those kinds of meters mostly have switched to remote digital meters rather than devices intended for a human to read.

If anyone has comments or wants a change then share or just do it. Thanks. Blue Rasberry (talk) 02:22, 3 March 2020 (UTC)

@Andy Dingley: Can you suggest someplace in this article to insert this image? I gave a go, what do you think? Thanks. Blue Rasberry (talk) 14:21, 3 March 2020 (UTC)

It's more about wiring, and the contrast in wiring standards in some countries vs others. It might fit into an article on theft of electricity in India (I forget the title, but we have such an article).

It might even work in this article, just not as the lead image. The lead image needs to be clear and to show a single meter (maybe two) so that we can see what a meter looks like. This might be OK in a later paragraph, about the multiplicity of meters at some residential blocks. Andy Dingley (talk) 14:30, 3 March 2020 (UTC)

Minimum load needed to make the electric meter register any usage

Mention the minimum load required, before the disc spins at all. In other words if somebody is just charging a cell phone, the only thing in used in the whole house, the meter might not even budge. Jidanni (talk) 09:18, 14 November 2020 (UTC)

I suppose there is one, but it should be pretty small. The main friction source is a magnetic field, which should be fine down to zero. Many have a usage independent charge, which should easily cover any such loss. Gah4 (talk) 11:02, 14 November 2020 (UTC)

Though you might believe this to be the case, the reality is that the disc turns (very slowly) even if there is no load on the meter. This characteristic is known as 'creep' and most, if not all, jurisdictions specify limits to its effect. The very nature of electric meters is such that it can never be zero. Any very small load (even a neon lamp of a few hundred microamps) will cause the meter to turn just a tad faster. 86.140.67.152 (talk) 17:55, 20 November 2020 (UTC)

instantaneous or power factor

The article says: rated using a lag coil.[16] This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current, voltage and phase angle (power factor) between them. I believe that this isn't right. It is the instantaneous voltage times current. Power factor comes in with RMS voltage and current. The reactive term will produce a sinusoidal force, which will average to zero. Either remove instantaneous or remove power factor. Gah4 (talk) 00:47, 11 June 2020 (UTC)

I think the problem is that it is poorly worded. It is not correct that the torque is proportional to instantaneous voltage multiplied by instantaneous current. If that were true then the meter would work on DC, which it does not. The torque is proportional to the absolute mean voltage multiplied by the absolute mean current multiplied by the power factor multiplied by the frequency. The meter is then calibrated to read correctly for the RMS of a range of sinusoidal currents and voltages at a single frequency but over a range of power factors (on the reasonable assumption that the frequency of supply remains substantially constant).

The meter will read correctly if the current is non sinusoidal because as the form factor increases the power factor decreases because the power factor is not just a function of the phase difference between current and voltage but also of the distortion of the current away from a sine wave (See Power factor#Non-sinusoidal components​. Over the AC cycle, the torque is actually constant so there is no averaging of anything. The rotor's mass is low enough that if there was any variation of torque, it would turn with a jerky movement which would generate a significant hum above that from the energising coils which it does not. -RFenergy (talk) 18:28, 21 November 2020 (UTC)