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A little background; the line voltage supplied here in my part of India varies as a function of the load. At dusk, the measured value is as high as 248V. Household appliances are rated at either 220V, or 240V.

A friend and I were talking; my take is the bill is for Energy (kWH). Ergo, regardless of whether the line is 220, 240, 250 - the energy consumed will be constant. His take is that the higher voltage means a lower current drawn - less heat, and less energy consumed.

How do I, as a consumer, gain or lose when the utility line voltage swings above or below the rated value?

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  • \$\begingroup\$ If your load is ohmic, then with lower voltage it will draw lower current so it will receive less power. This may mean for the same thing to do you will have to run it longer, so no net win in that case. \$\endgroup\$
    – PlasmaHH
    Feb 27, 2015 at 14:57
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    \$\begingroup\$ I'm voting to close this question as off-topic because it is nothing to do with electronic design. \$\endgroup\$
    – Leon Heller
    Feb 27, 2015 at 14:59
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    \$\begingroup\$ Energy is metered, not current, so generally you'll get the energy you paid for, not more and not less. Most major energy consuming appliances (and a lot of minor ones)- for example, an oven or a clothes dryer- will adjust their current draw on average to compensate over the course of what they do. In the case of lights you may pay a bit less in a brownout, but you'll get less light. \$\endgroup\$
    – Spehro Pefhany
    Feb 27, 2015 at 15:58
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    \$\begingroup\$ @LeonHeller: There is an interesting question behind this, of how various kinds of loads behave under varying voltage conditions. As a power engineer, I find it to be on topic. \$\endgroup\$
    – Li-aung Yip
    Feb 27, 2015 at 15:59

2 Answers 2

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The meter has a voltage coil, or measures voltage in some way, so you are only paying for the energy that passes the meter. This much is fair.

What happens next depends on your equipment, but it doesn't make much difference.

If you run predominantly switch-mode devices like computers, inverter-driven motors, LED lights, then they will take the same amount of power at any voltage. At a higher line voltage, the current will drop, and hence the power wasted in the wiring will decrease. This is probably only a 1% effect.

Resistive loads with thermostats like a hot water cylinder will show no net change - both the power of the element, and the power of wasted in the wires will go up, in proportion.

If you have a lot of light bulbs... your power consumption will go up at higher voltage. While you will get the extra light that you're paying for, you might not have wanted it. If you already have enough lights, 10% more light for 10% more money is just a waste.

There are probably other cases I haven't thought of. Induction motors... transformers.

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    \$\begingroup\$ Induction motors behave as a constant-power load. (This causes problems when the voltage drops too low; they will try to draw extra current to make up for it, which causes them to burn out if not protected against overload.) \$\endgroup\$
    – Li-aung Yip
    Feb 27, 2015 at 15:48
  • \$\begingroup\$ For thermostat-ted heaters, the reason they won't use more electricity is that although the heater uses more power, it will be on less often. \$\endgroup\$
    – user253751
    Feb 28, 2015 at 0:03
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How do I, as a consumer, gain or lose when the utility line voltage swings above or below the rated value?

If you looked at this cynically, you could imagine that the power companies could sneak a higher voltage to your house in order for you to consume more electricity in (say) your lighting - this gives them a few more dollars per house per year and could amount to the difference between profit and loss. For other appiances this usually won't make much of a difference as mentioned in another answer.

It won't make a difference to cookers because stuff will cook a bit quicker and you'll switch off the cooker sooner (or burn the cake). Heating water won't make a difference because the thermostat will stop supplying energy to the heating element when water reaches temperature and, this will be a tad quicker with a higher supply voltage.

So I don't see much in the way of gains when the voltage rises except gains for the electricity company on kWh supplied for domestic lighting. This is a loss to the consumer and, given that bulbs will probably have a reduced lifetime because of this, there is a gain for the supplier of bulbs.

At lower voltages compared to normal you'll still be charged for kWh and, because your lights are a bit dimmer you'll see a small benefit or, you'll trip over in the now-darkened-kitchen, break a leg and have a massive medical bill to pay (unless you live in the UK with the National health system).

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