Frequently Asked Questions

Filament (incandescent and halogen) lighting loads: Reduced line voltage will save energy. How much? The answer is related roughly to the square of the reduced line voltage. For example, a10% reduction yields 90% of, or 0.9 X the original line voltage. 0 .9 squared = 0.81. Therefore, savings is approximately 19% (100% - 81%) for a 10% line reduction.

Discharge sources – fluorescent: Most electronic ballasts in use will produce some savings if line voltage is reduced. While not exactly 1 to 1, it is close. 5% lower line will produce about a 5% reduction in system input power. However, some older types (like Motorola) and many of the newest types (especially those that are now "Universal voltage") have regulating power supplies, which means they compensate for lower line voltage by drawing more current, thereby keeping the input power constant (Power being essentially voltage X current for these high power factor devices). With these types, there is no power reduction and no energy savings.

Discharge sources - HID: Savings also depends on the ballast (mostly magnetic, of course).

ˇ For standard high reactance ballasts (usually labeled HX), the regulation is poor, meaning you actually get more power reduction than line voltage reduction. For example, a 5% line voltage reduction causes a 10% lamp power reduction. Applying this at the system level, a system that was drawing 450W will now draw about 410W (assuming an HID lamp at 400W X 0.9 = 360W; add back the ballast losses of 50W, and the result is 410W for the system – a 40W savings that represents 10% of the lamp power or 9% of the system power).

ˇ HID lamps using a Constant Wattage Autotransformer (CWA) ballast will have about a 1 to 1 relationship - a 5% line voltage reduction will cause a 5% lamp power reduction. At the system level (using the same example as above) this means going from 450W to 430W.

ˇ For HID lamps operated on a Constant Wattage (CW) ballast, also known as a "three winding" or "three coil" ballast, the regulation is very good. For a 5% reduction in line, there is about a 2-1/2% reduction in lamp power. Again using the same system example, the power would be reduced from 450W to 440W.

Motor loads: For most types of HVAC motors, pump motors, refrigerators, etc., there is little or no savings since induction motors, by nature, regulate themselves by drawing more current when the line voltage drops. They are like the new ballasts noted above. A 10% low line would not cause any reduction in input watts to the motor, and therefore, no energy savings. To save energy with induction motors, devices called Variable Frequency Drives (VFD), which adjust input power based on actual motor loads, are usually applied.

Electronic devices: PCs, printers, copy machines, etc. also have regulating power supplies, so there is little if any savings with line voltage reduction.

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