Electronics Safety
Class _____ fires occur in or near electrical equipment such as motors, switchboards, and electrical wiring.
C
Which type of extinguisher could you use on an electrical fire?
Carbon dioxide and/or Dry chemical
What occurs when a small, specific amount of electrical current flows through the hear for 1 to 3 seconds? (for instance: 0.006-0.2 Amps of current flowing through the heart disrupting the normal coordination of heart muscles. These muscles loose their vital rhythm and begin to fibrillate.)
Electrocution
True or False: A GFCI (ground-fault circuit interrupter) measures the current flowing through the hot wire and the neutral wire, and trips if they differ more than a few milliamps. When installing a GFCI you should connect its "line" terminal to your load, and its "load" terminal to the 120V ac power line.
False
True or False: If your home stereo has blown a fuse, it is safer to replace the 2 amp blown fuse with a new 7 amp slow-blow fuse.
False
True or False: Whenever electronic devices are unplugged from the 120V power-line source they are completely safe to work on and never have charged components.
False
Short-circuit protection devices can be...
Fuses, GFCIs, Breakers
Which would be the proper first aid for a victim who has been electrocuted?
Get a doctor/ambulance immediately, the only treatment is CPR.
Is the resistance value of an open circuit high or low?
High
What is the difference between ground and earth?
In Britain, people have 'earth' and in Northern America they have 'ground'. They are exactly the same thing, only different terms are used in different countries.
Which would be the correct way to free a person from electrical shock?
Locate the line wire or source of electrical current and disconnect. Do not take hold of the persons body with your bare hand. Decide if it's easier to move the person or the conductor. Use a dry stick to move the conductor, or layers of paper or cloth to move the person. Grab the person with the insulator in hand, and pull him/her free by their arm or leg.
Back in the early days equipment and appliances fitted with the two wire power plug were readily accepted to be safe from shock hazard because
The metal housing/chassis was not connected to either wire of the line cord (called floating case)
Pulsating DC is more harmful than a steady DC source. People have killed themselves from accidentally discharging high voltage _________ with their bodies.
capacitors
In lab, if you see the end of a wire laying on a table you...
carefully look for the other end to see if it's plugged into something.
ESD is more common in ___ and ____ weather.
cold and dry
It is important to wear safety glasses when working with electronics because....
components such as capacitors and ICs can explode, causing chemical and/or pieces of semiconductor material to become airborne. You could drop a soldering iron or screw driver into a higher amperage capacity connection and have molten metal and/or sparks explode into your eyes.
Salt water is more ______ than ordinary tap water
conductive
________ is the most commonly used conductor on printed circuits boards (PCBs) and wires, extension cords, speaker wire, etc.
copper
Does the electrical resistance of the human body increase or decrease with moisture such as sweat?
decrease
Name at least three sources of electrical defects you may find in wiring or electronic devices:
dirty components, rotten or old style insulation, missing 3rd conductor or safety ground.
A copper wire is conductive. It can conduct electricity. The earth is conductive. It can conduct electricity. The human body is conductive. It can conduct _______.
electricity
A circuit or wire that is "hot" or "live" is
electronically ON
OSHA stands for "Occupational Safety and Health Administration" and they...
enforce federal occupational safety and health legislation
Today's modern (U.S.) mains cable consists of three separate wires: black, white, and ________
green
How could a circuit NOT fail?
ground and neutral touch
If a human has provided a conductive path between a "hot" (energized) toaster chassis and ground a(n) __________ is occurring.
ground fault
A shorted circuit has the potential to produce ______ amounts of electrical current.
high or excessive
_____ and _____ are two other common terms that also mean an electrical circuit is on.
hot and live
Add any _______ to water to make it more conductive (which reduces the water's resistance).
impurities
Use _______ tools such as screwdrivers, pliers, and ladders when working with electricity.
insulated
Grounding provides an alternative path around the electrical system of your home or workplace and minimizes damage from
lightning, line surges, or unintentional contact with higher voltage lines
Very briefly explain "lock out tag out"
lock electrical service panel after turning off power supply with one key and lock before working on a piece of equipment.
Is the resistance of a shorted circuit high or low?
low
What are the two main causes of electrical accidents.
misuse and carelessness
Is the human body more or less conductive when you sweat?
more
In order to make sure the equipment is off
move the power switch to "off" and unplug the device
Why are some common items such as some radios, TVs, fans, etc fitted with the 2-wire (hot/neutral) electrical connections and not the 3-wire connection which includes a safety/chassis ground?
not conductive (plastic or polymers)
PPE is
personal protective equipment
Which would indicate signs that wiring is NOT out-of-date?
receptacles have a third conductor
________ is the best electrical conductor, but its cost and tarnishing characteristics make it sometimes a less preferred conductor to gold, which has less corrosive/tarnishing characteristics.
silver
The purpose of the three wire system is to provide a separate ground path which will effectively eliminate...
the possibility of shock
Power lines in your neighborhood are typically in the range of
1 to 3 phase, 7,200 volts each
In order to feel an electric shock from touching something like a doorknob, the voltage difference between your body and the object must be in excess of
1,800 volts
Class _____ fires occur in ordinary combustible materials such as wood, rags, and rubbish.
A
Which one kills?
Amperes current
Class _____ fires occur with flammable liquids such as gasoline, oil grease, paint, and thinners.
B
True or False: Don't touch electric tools, equipment, or cords that are wet, or with wet hands.
True
True or False: GFCIs do not protect against all kinds of electric shocks. If, for example, you simultaneously touched the hot and neutral leads of a circuit, and no part of you was grounded, a GFCI wouldn't help.
True
True or False: High voltage power lines transmit voltages up to 300 miles, typically in the range of 155,000 to 765,000 volts, in order to reduce line loss.
True
True or False: In case of failure, the equipment should not be of danger to the user.
True
True or False: When you power down the equipment, wait some time to let the dangerous voltage carrying capacitors discharge. Later discharge them if necessary
True
If you are purchasing an electronic device and would like to know that it has been tested for safety, look for a(n) __________ sticker on the product.
UL (Underwriters Laboratories, INC.)
Antistatic and conductive floors, wheels, wrist straps, and work pads would most likely protect which of the following from electrostatic voltages
a computer's video card
ESD (electro static discharge is most likely destructive to
all electronic equipment
DC (direct current like from a car battery) is less likely to cause electrocution, but sometimes still does. Unlike DC, AC (alternating current like what is present in power lines) has the special ability to make you unable to let go of a conductor, and also ________.
burn you
If you must troubleshoot a "live" circuit, use a mains isolation transformer work on a less conductive floor such as wood or carpet if possible, and...
work with one hand in the circuit, the other behind your back so electricity would flow only between your arm and feet if you get shocked.
Wearing a long necklace could kill you if:
you leaned over a live circuit, plugged into a 120 V AC source.
The sign at the gas station says to never return to your car until you're finished refueling because
your body could become "charged" from the interior and seat of the car, a spark could then occur when you remove the nozzle. (Especially in dry weather)
Why would electricity flowing from one arm to the other be most hazardous to your body? Because...
your heart is the path for current
