Remote receivers have to be powered all the time (Fig. 1). Otherwise, people would have to get off their couches to turn on their televisions. Early receivers had a separate power switch, so their power-hungry tube circuitry wouldn’t run up the electric bill while the family wasn’t home. (This switch worked, of course, assuming someone remembered to shut it off.)
That “indirect” power control has since widened to become today’s “soft” power switching used by just about every electronic device. The device sits poised in standby mode, pulling some current, until the power switch commands the control circuitry to get the unit up and running.
Soft power control was developed out of necessity. Devices needed to apply power in a sequence that wouldn’t cause unexpected behavior, system lockup, or even damage (see “It’s Hot, Powering, And Burning CMOS Logic Circuits”).
Soft control powers the system up and down in an orderly manner. It also lets the unit’s microprocessor (what electronic device doesn’t have one?) perform system checks and report problems. When you gripe about how long your TV takes to run through its point of service test (POST) before you can watch football from dawn to dusk, remember that it’s the price you pay for a sophisticated HD display.
Electrical Vampires Of Suburbia
Soft control leads to standby current drain, which also is known as phantom loads, leaking electricity,1 or vampire power. Most consumers aren’t aware of how many electronic devices drain power, even when they don’t seem to be on.
These vampires include remote-control systems in audio and video equipment, clocks and timers (particularly in microwave ovens, ranges, and iPod docks), computers and computer peripherals, battery chargers, and all manner of gadgets and small appliances, especially those with external power supplies.
External supplies, derisively dubbed wall warts, are notorious power drains. To reduce size and cost, most use undersized transformers with low primary inductance, drawing excessive current. They remain warm to the touch even when the device they power is shut down. Granted, the “excess” current is only 10 or 20 mA. But when a household has a dozen of these devices plugged in 24/7, there is a measurable increase in the electric bill.
Vampire power eats up approximately 5% to 10% of consumer electricity in developed countries.2 Saving this power by unplugging devices or shutting off power strips could save consumers money equal to getting “free” electricity for one month a year. It might also reduce the growth rate of new power plants.
Vampire power’s economic drain has been recognized for almost two decades. Since the 1990s, both government and industry have set goals to reduce it.3 In 2010, the International Electrotechnical Commission (IEC) set a goal to cut standby power to less than 1 W. Regulations for 2013 further reduce the draw to less than half a watt. (If half a watt doesn’t seem like a lot of power, do the math: 10 devices per home x 100,000 homes x 0.5 W per device.)
Eliminating unneeded features and functions also can reduce energy waste. Does a microwave oven’s clock have to be on when you aren’t cooking or timing? Some estimates suggest that this always-lit clock represents half the cost of operating the oven.
AC Power Vulnerability Can Really Bite
Some devices continuously draw power. That means they’re also open to abuse from glitches, transients, lightning, high voltage, and noise. Even an automobile accident or rough weather can cause a high-voltage spike that can destroy electronic appliances in our homes.
Three-phase high-voltage wiring, typically 2 kV to 30 kV, tops today’s well-equipped utility poles (Fig. 2). Transformers (the gray cylinders) step down the high voltage to 120/240 V for household and nonindustrial business use. Thin coax lines for cable TV and a heavier cable for telephone service are lower on the pole.
A windstorm, heavy snowfall, or out-of-control vehicle can break the high-voltage lines. When they fall on other lines, hundreds (or thousands) of volts surge through your appliances, telephones, or cable connection before the breakers or fuses open. Any device connected to the powerline—whether “always-on” vampires, or off, or in standby—will almost certainly be damaged. The devices drawing the vampire power are the most vulnerable.
The power grid itself can be the source of problems too. Damaging spikes and transients can occur during load balancing or when large inductive loads (motors and refrigeration equipment, in particular) are turned on and off.
Telephone companies have long histories of protecting against high-voltage wires falling down on their lines. For example, Janski and Faber’s 1916 book Principles of the Telephone4 discusses falling trolley wires, lightning arrestors, and other types of high-voltage protection. Metallic spark gaps work well, but they’re costly because they melt and require manual replacement. A better alternative uses carbon blocks, which can tolerate many strikes before needing replacement
Typically, two carbon blocks are separated with a mica sheet five-thousandths to ten-thousandths of an inch thick (Fig. 3). Arrestors also can protect a phone line from direct contact with 600-V from a trolley powerline (Fig. 4).
Both sets of fuses open when current arcs through the air around the mica spacer. The carbon block also can have an embedded low-melting-point metal slug. If arcing doesn’t blow the fuse, the metal melts and shorts the arc gap, drawing enough current to melt the fuse (Fig. 5). For lightning, the advice in the instruction manual remains sound—don’t use your wired phone during electrical storms.
Surge Protection Devices—Safeguard Or Hazard?
Always-on vampire power is particularly vulnerable to voltage transients. Enter the surge suppressor, which does bears a critical role in protecting your electronics.
Surge protection devices (SPDs), commonly called surge suppressors, protect equipment primarily by clamping voltages exceeding normal line levels.5 The “let through voltage” depends on the wire length and powerline impedance, so it can be misleading to consumers. Voltage spikes drive the clamping devices (usually metal-oxide varistors, or MOVs) into conduction, shorting out the spike. Each “event” slightly damages the MOV, and the MOV eventually fails to protect the device.
Most surge suppressors still operate as power strips, even when the suppression mechanism no longer works. The next big surge could damage equipment or so overheat a MOV that a fire starts.6 MOVs should, therefore, be paired with a thermal fuse or thermal cutoff (TCO) device to prevent these dangers.7 The suppressor also should have an indicator light to monitor the condition of the TCO and MOV, but few do.
When purchasing a surge suppressor, look for a circuit breaker to prevent overheating and fire if the power strip is overloaded; a light indicating whether the protection components are functioning; and approval by an industry, insurance, or government testing body such as Underwriters Laboratories (UL).
UL 1449 sets the minimum standards for SPDs.8 The suppressor’s joule rating (how much energy it can dissipate in a single event) isn’t considered a meaningful indicator of the suppressor’s effectiveness or longevity.9 It’s the overall design that matters. And, watch out for power strips with no surge suppression! They’re little more than elaborated extension cords.
The Ultimate Inspector
Thorough protection involves more than selecting a quality surge suppressor. Any part of the surge suppressor could fail, even the circuit breaker. It’s important, then, to regularly inspect your surge suppressors, wiring, plugs, and appliances. The stakes are high. The lives we save are our own.
If your surge suppressor has a protection light, is it on? If not, one or more of the suppression components likely has failed. Replace it. Next, is the suppressor unduly warm? If any area is hot to the touch, the suppressor should be immediately removed from service—ditto if any part of its surface is discolored.
The money that we can save by turning off the switch on the surge suppressor is our money. The thought of having free electricity for one month a year is quite an incentive to flip a switch.
References
- Student Sustainability Education Coordinators, “Phantom Load,” University of California, Berkeley, September 2005,
- “Pulling the plug on standby power,” The Economist, March 9, 2006.
- The International Electrotechnical Commission adopted an internationally sanctioned definition and test procedure for standby power (IEC 62301) in 2005 that’s now widely specified and used, www.iea.org/papers/2007/standby_fact.pdf
- Jansky, Cyril and Faber, Daniel, Principles of the Telephone, Part 1, Subscriber’s Apparatus, MaGraw-Hill, 1916, pp 120-127
- Eaton Corporation, May 2011, at IEEE/Music City Power Quality Group Meeting, “Changes to Surge Protection Device Standards.”
- Surge Protectors & Power Strips Blamed for Causing House Fires
- Littlefuse application note, “Designing with Thermally Protected TMOV Varistors in SPD and AC Line Applications.”
- Eaton Corporation, June 2007, “Eaton’s Guide to Surge Suppression: What You Need to Know About Surge Protection Devices,” page 2, Table 1.
- Ibid., page 10, “Debunking the Surge Current Myth, ‘Why Excessive Surge Current Ratings are Not Required.’”