Meter Sanity Test

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  • retrotecchie's Avatar
    Level 92
    All digital electricity meters, of any flavour (smart or otherwise) have an 'Impulse Light'. This is a red LED somewhere on the front of the meter, which flashes to indicate power being used. Most meters have an impulse rate of 1000 flashes per kWh used, although some may be different. It will normally be printed on the meter next to the LED.

    The speed at which this impulse LED flashes is a way to approximate how much energy is being used at a time.

    What you need to do is either time the interval between each flash, or see how many flashes it uses over, say, a minute.

    That will give you a very good approximation of how much energy you are using. I say approximate...the impulse indicator is accurate, it's the timing that is subject to inaccuracies.

    So, if the light is flashing once a second, then that's 60 a minute or 3600 per hour. Divide that by the thousand impulses per kWh and that tells you your use is 3.6kWh over an hour.

    If it's flashing every two seconds, that implies 1.8kWh.

    Every 3 seconds, 1.2kWh. And so on and so forth.

    If your usage has doubled and you really have no idea why, then this impulse rate will assist with diagnostics. Turn off any heating appliances (heaters, cookers, immersion heaters, etc). Your light should then be flashing at the 'baseline rate'.

    See how fast the light is flashing. Then, one at a time, turn off the breakers in the consumer unit and monitor the flash rate again. If it only drops slightly, don't worry too much. If, however, you turn off a particular breaker and it slows right down, and when you turn it back on again it goes back to it's original speed, then that indicates the circuit that contains whatever is using a lot of power.

    The usual suspects are electric heaters, cooking appliances or immersion heaters, or refrigeration appliances with a failed, or always on, compressor.

    The above 'sanity tests' will hopefully enable you to narrow down the source of the higher consumption.

    Another poster on here had a problem with an electric oven which we remotely diagnosed, and I have experienced that very problem myself. Many very high consumption items like ovens, immersions, or electric heaters have very high currents being switched and the heavier the load, the more likely switch contacts are likely to burn or arc. In 50% of cases, the switch will fail open circuit, i.e. the appliance will just not work. In the other 50% of cases, the contacts will fail closed, meaning power will be flowing 24/7. Perhaps at a relatively low level if the thermostat is regulating, but still ticking over continuously.

    A piece of advice I offer to anyone is to make sure you have an accurate record of the circuits in your consumer unit. More modern installations will usually have every breaker labelled, or a numbered chart on the inside of the flap describing each circuit. Older installations may not have this information.

    If you move into a new property, or your existing property doesn't have this legending, it's easy enough to work out what's what. Turn each breaker off one at a time and see what stops working. Your lighting circuits will be on a 6A rated breaker, ring finals (sockets) on a 32A breaker, radial circuits should be on a 20A breaker and higher powered appliances like showers or cookers on a 32A or larger breaker. Label up your breakers if they aren't already, or keep a note in your consumer unit of what's what. This will assist with future faultfinding if need be.
    Last edited by retrotecchie; 10-01-23 at 23:24.
    Don't shoot me, I'm only the piano player. I DON'T work for or on behalf of EON.Next, but am willing to try and help if I can. Not on mains gas, mobile network or mains drainage. House heated almost entirely by baby dragons.
  • 2 Replies

  • gbhxu's Avatar
    Level 12
    For those of us still on the old fashioned dial meter, it will be the increase in speed that the horizontal wheel moves
  • retrotecchie's Avatar
    Level 92

    Yep. Set your watch and count how many times the little line comes round. My original post should have specified 'digital meters'. My bad.