The Wallpowers

North America uses a 3-wire system – it is Keyed (polarized) to allow for a standard plug orientation and a third wire has been added for protection against shocks.

Hot, neutral and grounding wires.

Each wire has a specific purpose and redundant safety measures are built into the overall system.

Hot wire - The narrow blade on the plug and the narrow socket on the outlet are part of the current-carrying or "hot" circuit.

Neutral wire – The thick blade on the plug and the thick socket on the outlet are part of the neutral circuit. This circuit returns to your energy provider and is grounded (connected to earth) many times along its route.

Grounding wire – in North America, the rounded prong on the plug and the rounded socket on the outlet are part of the grounding circuit. This is a special circuit that was designed to provide relief from uncontrolled and dangerous energy situations.

Cover plate screw - For most outlets, the receptacle cover screw is part of the grounding circuit. This can serve as a handy ground point for releasing ESD either by touching the screw for immediate discharge or for connecting a grounding wire.

• Most homes have what is called a "three wire service" which means that you have two 120-volt lines and a "neutral" line.

  These three lines can provide either 120 volt or 240-volt power when properly connected in your circuit breaker box.

• Many homes have "100 amp service". This means that the power lines going to your home and your circuit breaker box can handle up to 100 amps of electricity at 240 volts.

  Just for fun: If we multiply 100 amps by 240 volts, we have a maximum of 24,000 watts of power. This doesn't mean you are using all 24,000 watts all the time - just that you have the ability to draw that much power if necessary.

  The good news: that’s 16 hairdryers all running at once!

  
  

  Safety

  

  Important (and free) life-saving tip – houses are different than computers

  In AC circuits, generally, electricians use "black" wires for hot load-carrying AC circuits (white wires for neutral and green for ground).

  In DC circuits like those inside your computer, ground wires have historically been "black".

  There is an important and dangerous distinction here, especially when working with AC circuits - which have a higher voltage than your typical DC circuits.

  The black wire inside your computer is generally pretty benign, however the black wire in your household wiring can be a source of dangerous current.

   

  How much is too much?

  1 second contact with Electric Current (in amps and milliamps)	Physiological Effect
  .001A (.1 mA)	Threshold of feeling, tingling sensation.
  .005A (.5 mA)	Accepted as maximum harmless current – Possibly A+
  .01-.02A (10-20 mA)	Beginning of sustained muscular contraction ("Can't let go" current.)
  .1-.3A (100-300 mA)	Ventricular fibrillation, fatal if continued. Respiratory function continues.
  6A	Sustained ventricular contraction followed by normal heart rhythm. (Defibrillation). Temporary respiratory paralysis and possibly burns.

  
  

  Your skin is an insulator:

  • Over 100,000 ohms (ohms is a measure of resistance)
  • If your skin is moist or broken the resistance may drop to as little as 300 ohms. Conversely, if your skin is dirty, its resistance will actually increase.
  
  

  "Old electrician" tips:

  • "Hand in pocket" rule
  • Work with "right hand" rule
  
  

  Measuring Electricity

  More than likely, the "type measurements" that a PC technician will need to make will generally be AC or DC volts and continuity. You will measure:

  • AC to verify the power to the computer is adequate.
  • DC on the inside of the computer to verify that components within the computer are getting the proper amounts of power.
  • Continuity to check fuses and cables.
  
  

  Most practical electrical measurements can be taken with the following meters:

  • Ammeter - measures amps (AC and DC)
  • Ohmmeter - measures resistance and continuity (a continuous connection)
  • Voltmeter - measures voltage (AC and DC)

  Some or all of these features may be combined into a tool called a multimeter.

  Most multimeters today combine a voltmeter and an ohmmeter, while others may also include an ammeter.

  
  

  Multimeter displays may be digital or analog

  Meters may be:

  Auto-ranging – can determine the amount being measured

  Manual – the human must anticipate and set the amount being measured.

  Digital		Analog
  Manual	Auto Ranging

   

  Measuring Voltage (the Amount)

  
  

  Non-autoranging meter

  • Set these meters greater than but close to your predicted measurement amounts. Very A+
  • Facilitating this requires that you use knowledge and perhaps even some common sense before you begin the measurement process.
    • If you don’t know where to begin, it is safest for your meter to start high and work down.
  
  

  Autoranging meter

  • These meters will pick the correct range for you - still need to set type.
  • These meters are designed to figure out the range and adjust themselves accordingly.
  • The meters we use in lab are basically autoranging although you can "Range-Lock" their displays.
  
  

  Noise on the scope

  Note that when the probes are not connected to a source of energy or resistance, you may experience seemingly random numbers on the display.

  Measuring the type of stuff - AC, DC, volts, resistance, continuity or amps

  Your meter needs to know just which of these components (or which kind of current) that you want to measure.

  
  
  • DC inside the computer
  • AC to measure the electricity that is delivered to your wall outlets or into the power supply of your computer

  There are sometimes additional settings for measuring continuity, diodes, capacitors, and amps (usually in milliamps), and for these you would set your meter accordingly.

   

  The cult of continuity

  Please note that both continuity and resistance are measured when the circuit is not energized!

  
  

  Continuity

  Audible setting – beeps when there is continuity. The audible setting will buzz if there is less than (usually) 150 ohms of resistance.

  Resistance setting – If a wire or circuit doesn't have continuity, it is said to have infinite resistance.

  To check for continuity using the resistance setting, set the meter to resistance (Ω).

  When you measure resistance using a non-autoranging meter, a setting of 200 will measure resistances from as little as .1 ohm up to 200 ohms.

  On some meters the display will indicate ''OL" if the measured resistance is greater than 200 ohms.

  
  

  BIG A+ DEAL – A good fuse or a wire with continuity should measure zero resistance – 0 ohms.

  Note that on some auto ranging meters, the meter may show a nominal reading of .01 0r .02 ohms for a good fuse - however for A+ the answer is 0 ohms.

   

  Measuring Stuff

  Outside the box - wall outlets

  Here is what you can expect to measure in a typical wall outlet:

  • Between hot and neutral you should have 110-125V.
  • Between hot and ground you should have 110-125V.
  • Between neutral and grounding you should have zero volts – or nominal "noise" on the display.

  Remember that the narrow prong is hot, the wider prong is neutral and the semi-round prong is for grounding.

  
  

  NEMA 5-15	NEMA 5-30

  More

  
  

  Components – help control amounts, flow and direction of energy

  • Resistors
  • Capacitors
  • Inductors
  • Diodes
  • Fuses
  
  

  Historically A+

  Resistors

  When electrical current goes through a resistor some electrical energy is converted to heat and resistors can get warm when they resist.

  Electric stoves, toasters, Curling irons, hair dryers, and baseboard house heaters use the principal of resistance to do their jobs.

  
  

  Capacitors

  A capacitor is primarily a device for storing energy.

  A capacitor's "capacitance" is rated in farads or, more commonly, microfarads (µF - millionths of a farad). Its microfarad rating is then typically marked on it’s exterior.

  • They are often used to "smooth out" an uneven flow of energy in power supplies.
  • Another function of a capacitor (when combined with other components) is to actually block the flow of current.
    • This function is applied to what are called "filters" that extract or eliminate particular frequencies (noise) in a circuit.
  
  

  Inductor

  

  While a capacitor stores voltage as electrical energy, an inductor stores current as magnetic energy.

  Inductors can help block AC current and let DC current pass.

  
  

  Diodes

  Allow electricity to flow in one direction only

  

  Fuses

  Fuses are used to protect electrical circuits from dealing with more current than they were designed for.

  A fuse uses a thin piece of wire that, under normal circumstances, allows the current to flow through.

  When exposed to too much current, the wire will melt and thus break the electrical connection.

  "Buss" type fuses used commonly in electronics Typically 0.1 - 10 amps                          "Slo-blo" buss type fuse	Household type screwin fuse Typically 15 or 20 amps

  Fuses are rated in amps and these ratings are often labeled on the ends of the fuse itself.

  Equipment damage and possibly even fire can be the results of inappropriate fuse values.

  When called upon, a fuse creates infinite resistance – a blown fuse.

  A good fuse or a wire with continuity should measure zero resistance – 0 ohms. A bad fuse would show infinite resistance – a reading of 1 or, in some cases, OL.

  
  

  Inside the box – Your power supply

  

  • Convert wall outlet AC electrical power to suitable DC voltages - Step-down, switching transformer
  • Monitor those DC voltages
  • Remove the heat that results from the consumption of electrical power - generally blows air out of system
  • Watts up? Around 250 watts or more
  
  

  Acceptable Ranges – around plus or minus 10%

  Voltage	Acceptable Range
  - 5	- 4.5 to - 5.5
  + 5	+ 4.5 to + 5.5
  - 12	- 10.8 to - 13.2
  + 12	+ 10.8 to + 13.2
  + 3.3	+ 3.1 to + 3.5

  If a particular voltage is out of whack from the figures in the previous table, unusual errors and lockups may occur.

  Remember that (in general) on modern power supplies, red wires are +5V, the oranges are +3.3v and the yellows are +12V.

   

  (typical) P8/P9		3.3V (11)	(typical) P1	Ground (24)
  	P9	12V (12)		+5V (23)
  	(12) + 5V
  	(11) + 5V
  	(10) + 5V	+ 12V (10)
  	(9) - 5V	+ 5V Standby (9)		+ 5V (20)
  	(8) Ground			+ 5V (19)
  	(7) Ground	Power Good (8)		- 5V (18)
  		Ground (7)
  		+ 5V (6)		Ground (17)
  	P8	Groung (5)		Ground (16)
  	(6) Ground			Ground (15)
  	(5) Ground	+ 5V (4)
  	(4) - 12V	Ground (3)		PWR Sup. On (14)
  	(3) + 12V	+ 3.3V (2)
  	(2) + 5V	+3.3V (1)		Ground (13)
  	(1) Power OK			- 12V (12)
  				+ 3.3 (11)

  
  

  When good power supplies go bad - Very A+

  Problems with power supplies manifest themselves in many ways:

  • Intermittent beep codes and errors while booting
  • The system hangs for no reason and may even reboot itself
  • The system freezes while booting but after several tries it boots successfully
  • Intermittent memory errors
  • The power supply becomes too hot to touch
  • Your motherboard is damaged

  Caution - power supplies can be dangerous – they contain capacitors. Remember that A+ considers power supplies to be FRUs and should only be serviced by someone trained to work on them. Leave them closed and do all your testing on the connectors.

  
  

  Power Problems

  Noise Noise is unwanted low-level high-frequency signals found in power lines and/or data lines. Your computer's power supply is designed to filter noise out. However, greater levels of noise cannot be handled by most PC power supplies. Noise is also referred to as EMI (Electro Magnetic Interference) or, if at specific frequencies, RFI (Radio Frequency Interference).

  
  
  

  Overvoltages

  Spikes A spike is a brief, severe over-voltage situation. They are instantaneous, dramatically high levels of voltage. A typical spike may last only for a few nanoseconds.

   

  Surges A surge is an over-voltage situation. It is a short-term wave of current, potential, or power in an electric circuit. Although a surge does not supply the dramatic high-voltage of a spike, it lasts longer. A surge may last from 16 milliseconds (one AC cycle) to around a hundredth of a second.

  
  

  
  Undervoltages

  Sags A sag is an under-voltage situation. Sags are more commonly known as "brownouts" and are the most common utility power problem. Voltage sags are short-term decreases in voltage - typically lasting only a few milliseconds.

  
  

  Blackout A blackout is an instantaneous and total loss-of-voltage situation.

  
  

  
  Power Solutions

  The kind of power protection device you choose depends on what kind of power problems you might experience.

  • If you are just concerned with over-voltage and line noise you might want to purchase a surge suppressor.
  • If you are concerned with under-voltage, over-voltage, and line noise, you might choose a line conditioner.
  • If you are concerned with over-voltage, line noise, under-voltage and blackouts, you may want to purchase and uninterruptible power supply (or UPS) unit.

    Note that not all UPS units provide suppression and line conditioning capabilities.

  These devices are installed between the computer and the house current and protect the system from power anomalies.
  

  • You should occasionally inspect and test these devices. Very A+

  
  
  Surge Suppressors

  A surge suppressors acts like a sponge and absorbs excess electricity. It is best to attach the surge protector as close to the equipment being protected as possible.

  Historically surge suppressors have incorporated a component called a Metal Oxide Varistor (MOV). A MOV is an electrical component that is used to clamp surge voltage to a lower level.

  A MOV works by "shunting" (or redirecting) any excess voltage above a set voltage (called the clamping voltage) into the location’s grounding circuitry.

  Note that for this to happen, your location must be properly wired to ground. Many surge units have circuitry that senses the integrity of your wiring and then warn you of problems by lighting an LED or not allowing the unit to provide power.

  MOVs wear out!

  Joules – joules relate to the amount of electrical energy a unit can absorb before the MOVs cease to function.

  Scientists use a unit called a Joule to measure energy in what they call watt-seconds. 60 joules is equivalent to a 60-watt light bulb that is on for one second. When measuring electrical power, the term watt is just a convenient way of saying Joules of "energy flow" per second. Convenience is usually good!
  
  

• Clamping Voltage – a value is established by Underwriters Laboratories during tests conducted while evaluating a surge suppressor for listing. A UL1449 rating of 330 is UL’s current "best" rating.

  
  

  Uninterruptible Power Supplies (UPS) - Very A+

  When your system loses power from it’s primary power source (usually your AC outlet), it will draw its power from the battery reserves available in the UPS.

  Your system may be able to stay "on" anywhere from a few minutes to a few hours depending on the draw of your system and the capacity of UPS unit.

  
  
  
  
  
  
  
  "Intelligent UPS" units may optionally include software monitoring, self-diagnostics, voltage boost and voltage reduction, overload notification and a host of other features.

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Sizing your UPS / Volt-Amps and Watts

  V * A = WATTS. It turns out that this formula is great for light bulbs (or other resistive devices), but inaccurate for some computing devices – like "switching power supplies".

  UPS units have both maximum Watt ratings and maximum VA ratings. Neither the Watt nor the VA rating of a UPS may be exceeded.

  A 1000VA UPS unit will not power a 1000-Watt computing device. It will only power a 600-watt device. To size your UPS, basically take watts needed and divide by .6 (watts ratings for PCs are typically 60% of the VA rating).

  A typical modern computer (including monitor) uses around 175 watts under typical use. Note that you shouldn’t connect high-draw devices like laser printers to the battery back up portion of your UPS. Very A+

  From the "This is Goofy" Department - UPS units take AC energy from the wall, store it in batteries as DC. They then use a component called an inverter to convert battery-DC back to AC which is fed to your computer. Your PC's power supply uses a rectifier to convert it back to DC again!

  There are three basic kinds of UPS units. The difference between the three is basically how the power supplied to the system flows through the UPS unit itself.

  • Standby (or offline or SPS)
    
    

  • Online (or true) UPS
    
    

  • Line-interactive UPS

  These units simplify the power path by adding a component called an inverter/charger. Since this component is always "working", less time is needed for switching to the inverter section of the UPS.

  
  

  Line Conditioners - AKA Power Conditioners - Very A+

  Along with offering surge protection, line conditioners are devices that condition (or regulate) power during sags without offering any battery protection from blackouts. Basically, line conditioners step up low power and step down excess power.

  A line conditioner is an active device - it is always at work massaging AC power into spec. Line conditioners run from around a hundred dollars to thousands of dollars for the industrial-grade units.

  Note that that not all line conditioners protect well against spikes and they never protect the system against blackouts