Voltage and energy consumption

  • 29 November 2020
  • 6 replies

Afternoon all.

I have an intermittent issue with my voltage at the moment, mainly there’s not enough of it, to the degree that my bathroom light sometimes doesn’t come on, and the shower’s sometimes stuck on cold no matter what you set the heat to.

Western Power Distribution are trying to find the issue, and it got me wondering.

If I’m receiving ‘less voltage’ - does that mean I’m using less energy, the same amount of energy, or more energy, for everything going on in my house at the moment?
Will this have any effect on my meter readings? 

6 replies

Userlevel 3

It depends on what’s consuming the power.

A switched mode power supply (which would be most modern devices) will draw more current as the voltage drops, so you’ll be consuming exactly the same amount of power no matter what your voltage is doing.

A motor will run slower. 

A heater will run slightly cooler.. if it’s a thermostatically controlled heater it’ll simply run for longer (since the heat loss through the walls will be more less constant, the energy required to heat the room will also be constant).

For the average household you wouldn’t see a whole lot of difference.


Userlevel 7
Badge +11

@Gwyndy The answer to the question is that anything resistive like heaters or showers will consume less energy if the voltage is lower and this will be reflected in your meter readings.

As @TonyHoyle  correctly says anything designed to be run with a variable voltage input will more or less consume it’s stated rated power. With a switched mode supply there will be a somewhat non-linear relationship between the power consumed and the voltage at the input depending on the electronics the item and the intended design.

In general anything designed to be run with a variable voltage input will more or less consume it’s stated rated power.

(The meter only measures real power, most cheap switched-mode electronics have a dreadful power factor and thus consume lots of apparent power which is a story for another day...)

More to the point have you measured your voltage and is anything in the area of the consumer unit or meter getting hot or smelly?

If you don’t have a meter to measure your mains voltage, just plug yourself in* and see how far across the room you (hopefully) wake up!

@woz will calculate the non-linear relationship between voltage and distance by taking into account your weight, flooring material, footwear, under-garment style, amount of sweat production and incoming supply fuse size.

*this is a bad joke and this voltage measuring technique should not be tried at home.

Userlevel 7
Badge +11

@25 quid More white space…?

or use a voltmeter and one hand behind your back...

Userlevel 7
Badge +11

Ofgem standards attached

Always have the loose hand behind your back. It creates essential (white) space.