Power Meter Reactance – Will Reactive Load Register Lower Reading?


At an exhibition on home appliances, I saw this guy hawking his 'energy saver device'. The guy claimed that merely plugging his instrument into the supply would reduce the consumption reported in an energy usage meter by a fourth. He mentioned something about the load seen by the meter being non-resistive …

Not sure if this is the right forum to post the question (feel free to vote for the question to be closed)… Anyhow I find myself wondering – Is this just a sales-pitch (no warranty/guarantee on the device) or is there some fire to the smoke?

Best Answer

SCAM WARNING. These "energy saver" devices usually are simply capacitors, and they don't save you any money. Typical customer energy (usually billed in kilowatt-hours, kWh) meters are not affected by adding a capacitor.

The scam works like so:

  1. Many loads in your home are inductors (fridge motor, furnace fan)
  2. If you install a capacitor which has just the right value, the current in the power grid leading to your home is reduced.
  3. Con artists correctly claim that some energy somewhere is being saved.
  4. Con artists correctly claim that industry uses these capacitors to save money
  5. Con artist sneakily insinuates that this somehow saves YOU money
  6. As evidence, con artist supplies testimonials rather than basic lab test results.

So why doesn't this save you money? It's because, while motors do draw extra unnecessary current, the energy meter on the side of your home is designed to ignore that extra current! Adding a capacitor doesn't change your electric bill.

So energy is really being saved, right? Yes: it's energy which otherwise would heat all the power lines between the company generators and your home. The extra capacitor doesn't cause your motors to use less energy. Instead it relieves some load-current on the power grid. The electric company benefits from this ...but the homeowner doesn't!

Why then do factories use these Power-Factor Correction capacitors? Ah, for most huge industrial customers, electric utility companies install a different type of a meter: one with two dials. One dial is used to bill the customer for real energy consumed, while the other is used to bill wasted or 'reactive' energy. These industrial meters do detect the excess current drawn by induction motors. The industrial customers are charged for the unnecessary heating of the power grid. If they install just the right value of capacitor, they can reduce their electric bills.

And this brings up one last bit of info. To reduce the excess current in the power grid, the capacitor has to be just the right value!

If you have no induction motors in your home, then a PFC capacitor is less than worthless. Adding a PFC capacitor will INCREASE the wasted reactive current, not reduce it. So basically that's part of the dishonesty: selling capacitors of an unknown value in order to cancel out the effects of an unknown number of induction motors ...which aren't being billed by the electric company in the first place.

Finally, what about #6 above? The testimonials? I suspect that these are genuine. If you were to install a very expensive PFC capacitor in your home, you'd be bringing in the "stone soup effect." You'd become very aware of any wasted energy. You'd start "helping" the device: turning off lights, turning down the furnace and the air conditioning, perhaps buying better windows and installing improved insulation. The expensive and worthless "stone" has turned into "soup." But you'd save lots more money if you skipped the PFC capacitor scam and just started turning down the hot water heater in the first place.