If you’ve seen claims that some device is going to slash your electricity bill by 10% to 25%, you may be in for a disappointment. The fact is, these Electric Energy Saving Devices, while they cut measured electricity consumption for some older electrical motors, barely put a dent in most people’s electricity bill.

These devices are usually called Electric Energy Saving Device, power factor correctors, or power saving devices. They contain a capacitor, which is an electrical device that stores electrical energy for short periods between two conductors.

You’ll read sales pages for these devices that refer to improving the power factor of inductive loads. The idea is that voltage on an alternating current line fluctuates in wave form between positive and negative, sixty times a second. A capacitor can improve the power factor (the proportion of current in the wave form that the motor actually uses) so that more of the energy you draw from the grid actually gets used to do useful work, and less gets wasted because it wasn’t needed at that precise instant. (It can be saved in the capacitor and released some tiny increment of time later.)

Devices marketed as Electric Energy Saving Device or power saving capacitors are real, working devices, but claims that they might cut your power bill are misleading. The sellers usually hint at gains of 10-25% but actually guarantee nothing, and in reality your savings may only be 1-5%, not nearly enough to cover the expense of installing one of these units.

There are two main types of electrical loads: resistive loads, such as lights, or anything producing heat; and inductive loads (such as an electrical motor, or anything involving electromagnetism). Unfortunately, these devices only work on inductive loads – typically electric motors – and only those that don’t already have a capacitor built into them. And if you do a load estimate for your house just by scanning all the devices you use and guessing at their wattage and hours of use per day, you’ll soon discover that inductive loads make up a fairly small proportion of your overall load – perhaps 25% or less. (You don’t run your washing machine more than a few hours a week, but some lights are on 12 hours a day or more.) So the savings you’re being promised will only apply to that small percentage of your total electrical bill.

Manufacturers have been adding capacitors to anything with an electric motor for a number of years, because it’s one easy and inexpensive way to increase energy efficiency of those motors, thereby making the price to efficiency ratio more appealing to consumers. If you own an ENERGY STAR appliance containing an electric motor, chances are it already has a capacitor and you won’t save any electricity on that device with one of these power saving units.

The sales pages for these power saving devices usually hint at potential savings but they don’t actually guarantee any particular level of savings. You’ll see claims of a range: a drop of 10 to 25% in your electrical bills. But if you look closely, you’ll see there’s no guarantee of that. Even assuming you did see a gain of 10 or 25%, how would you know whether the gain came from that or from something else?

Look for the testimonials provided on these sites. Do customers claim to have cut power use consistently month after month while using these devices? Or is there just a claim that power use dropped by X% after the first month? Here’s an interesting scenario: say one hundred people buy such a device and install it in their home.

Since everyone’s power use fluctuates month by month, even if the capacitor does no good at all, some people are bound to see a drop in power use from one month to the next, while others will see an increase. Those who see an increase in power consumption may ask for a refund for their Electric Energy Saving Device. Those who see a small gain will be moderately happy, or at least won’t complain, while the small number who, for reasons unrelated to their energy saving capacitor, see major gains, will write a glowing testimonial. The testimonial gets published, and the person who asked for the refund gets their money back but doesn’t get anything published about how badly the system ‘appeared’ to work for them. (We’re assuming, of course, that the published testimonials aren’t fabricated.)

Another point in favor of this scenario (namely, where the small percentage who miraculously cut energy costs while using such a device, are the ones whose testimonials get published) is the fact that often people create the result they want to see. For example, it is well established that one of the best ways to get people to cut their electricity usage is to get them to measure their electricity usage. That’s exactly what helped my family cut our electricity usage by 50% or more: measuring our usage with an electrical power monitor (a much cheaper device, by the way, that will save you far more electricity than a power factor corrector) allowed us to see where we were wasting electricity, and we easily cut most of that waste. If you install one of these so called power saving devices expecting it will save you energy, chances are, you’ll start measuring your electricity use on a more regular basis (even just by looking at the outdoor power meter). And chances are reasonably good that your increased awareness of your electricity use will cause you or your cohabitants to be more careful about turning off lights and avoiding other big energy using activities.

Some Electric Energy Saving Device even come with a money back guarantee. That’s great, but again, think of the hundred-customer scenario.

If by fluke (or because they’re more carefully monitoring their energy use, and therefore they subconsciously cut out waste) some people see their energy use drop, they’ll keep the device, and the seller keeps the money. Others who don’t see a gain may decide not to bother asking for the refund (some people feel embarrassed when they’ve been duped) while others will get their money back. Considering that these devices are very cheap to manufacturer, a seller can profit handsomely on a 0 to 0 device even if 90% of the devices are returned. (And of course the returned devices may be redeployed to others.)

As far as testimonials go, look closely at the context. One website included a testimonial from a company that ran several large water pumps. Of course, these pumps are probably inductive motors that do not have their own built in capacitor, so significant savings should be expected.