If the energy meter sees a reactive load, will it register a lower reading?

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.

I think this is a perfectly legitimate question. Energy meters like on the side of your house or on the utility pole already measure real energy delivered. If you were to have a purely reactive load, like a capacitor for example, then the energy meter would not increase but you also wouldn't be getting any energy. The capacitor won't get warm.

But if you put a current meter in series with the capacitor, you'd see real current. How can this be? No laws of physics have been violated because the voltage and the current are 90 degrees out of phase, something you can't tell just be looking at either in isolation.

The utility's electric meter measures the integral of the voltage times the current, so measures only real energy delivered. The utility doesn't like highly reactive loads because it causes currents in the transmission system, which waste power by I**2 * R losses which they can't bill for. This is why large electric customers get charged in part by the power factor. This is basically a measure of how far off you'd be assuming the product of independently measured voltage and current gave you real delivered power. For a purely resistive load, the voltage and current are in phase and the power factor is 1. That's what the utilities like. The worst case are purely capacitive or purely inductive loads. The voltage and current are 90 degrees out of phase, so no real power is delivered, and the power factor is 0.

In general, the power grid looks somewhat inductive. Utilities combat this various ways. These include banks of capacitors, nagging legistlators to force appliances to have better power factors, and running their generators a little out of phase. The utility term for the latter is "reactive power". In most cases you're actually doing the utility a favor by plugging a little capacitance into your outlet.

Unfortunately there are lots of snake oil salesman ready to exploit the fact that most people don't understand that independently measured voltage times current doesn't give you delivered power. There may be some slight saving to you in presenting a better power factor, but 25% "less electricity used" sounds like pure BS, and your electric meter already measures real delivered power anyway.

It depends on the meter. If the meter reads only active power (P), then plugging in a non-resistive load wouldn't show up on the meter.

If however the meter reads the total power (S which is \$\sqrt{P^2+Q^2}\$, where Q is the reactive power), then if your house consumes a lot "inductive" power, plugging in something with "capacitive" power would indeed lower the total reactive power ("inductive" power cancels with "capacitive" power). If in the equation above you minimize Q, you would minimize S, which would minimize your bill.

I don't know how they bill electricity over in the US, but if the meter reads active power only, then this device would be a sham. If it reads S, which I highly doubt, you MAY experience a minor bill.