My Dad was an electrician and a lineman for Pacific Telephone (now known as AT&T). In the 1950s, before Best Buy and Circuit City, you could order a Heathkit and build your own TV. Well that was just the thing for my Dad so he ordered a fancy black and white (no color in those days, no flat screen either) and he planned to install it in a wall opening he had made so the TV could be built in and would slide out for service (TVs had tubes back then). He got it done but had not yet put it in the wall so he set it up on a cardboard box - the electrical innards all exposed - right in the middle of the Family Room.
TVs in those days used high powered Cathode Ray Tubes (CRTs) to display the picture. They needed a high voltage to create the image on the screen. And much like the Leyden Jar old Ben used to catch the lightning, the CRT acted as a big capacitor, storing a significant jolt of electricity for hours after the TV was turned off. Now being an inquisitive fellow myself, all of 8 years old, I decided one morning to get a closer look at the inner workings of that TV. As I reached in to check out the tubes and such, my hand contacted the high voltage wire leading to the CRT and I got quite a shock! It knocked me back about 6 feet and onto the kitchen floor. You can be sure I had a new respect for electricity after that experience!
The Taming of Electricity has changed our World
But It still can pack a Deadly Punch
Treat It with the Respect It Deserves
But It still can pack a Deadly Punch
Treat It with the Respect It Deserves
When scientists talk about electricity they most often use these four terms: Amps, Watts, Volts and Ohms. A few other terms you may have heard are AC, DC, Hertz and Kilowatt-hours. If we use a common analogy, comparing an electric circuit to water flowing through a hose, the voltage is equivalent to the water pressure (or electric potential), the amps is equivalent to the flow rate (or electric current) of the water, and the ohms (electrical resistance) is like the hose size or surface area of the opening through which the water flows.
A bigger hose (or larger diameter wire) will have less resistance (fewer ohms) and will be able to move more water in a given period of time (higher current or amps) when the water pressure (volts) applied is constant. The total water moved would be like the watts of power consumed. A Watt is a unit of power having the dimensions of energy per unit of time. Thus that common term on your Electric Bill - "Kilowatt-hours" - is the total number of Kilowatts (1000 Watt chunks) you consumed divided by the number of hours you consumed them in, usually a month.
Say you used your toaster for 5 minutes every morning to brown up your breakfast bagel. In a month (30 days) you would have run it for 150 minutes or 2.5 hours. Now if your toaster is like mine, it says that at 120 volts (the common household voltage in the US) it will take 1800 watts to operate. So in that month, you used 1800 watts times 2.5 hours or 4500 watt-hours or 4.5 Kilowatt-hours of electricity. At about $0.20 per Kilowatt-hour, your favorite bagel browner costs you about $0.90 a month.
So to classify each electric term, we have:
- Watts = Power - (notated as P)
- Volts = Pressure - (V)
- Amps = Current - (I)
- Ohms = Resistance - (R)
Power = Voltage x Current (P = V * I)
or
Watts = Volts x Amps
A typical household circuit is 120 volts with a 15 amp fuse or breaker. Such a circuit can therefore handle 120V x 15a or 1800 watts, the toaster in the above illustration. If you try to run the toaster and your coffee maker on this same circuit, you will blow the fuse. However, the 1800 watts for the toaster is the maximum draw assuming that you have it set on the highest setting and your are cooking up four slices. Since this is generally not true, you should not have a problem. But you can see why the fuse will go out or the breaker will pop when your daughter has her hair dryer, curler and portable heater all plugged in at once in the bathroom!
If you run a 60 watt light bulb from the same 120 volt, 15 amps circuit, using the same equation but calculating for amps (Amps = Watts/Volts) you can see that the current in amps will only be 60w/120V or 0.5 amps. You can run quite a few 60 watt bulbs on that same circuit.
And another equation is Ohm's Law:
Resistance = Voltage / Current (R = V / I)
or
Ohms = Volts / Amps
If the resistance of the circuit is higher than the voltage applied divided by the potential current in amps, then no current will flow. This would be like the garden hose example where the faucet is shut off. The resistance to the flow of water is greater than the pressure in the hose so no water comes out. Conversely, if you have the same 120 volt - 15 amps circuit, the maximum resistance of all the appliances plugged in would be 120V/15a = 8 ohms to consume the 1800 watts the circuit can carry.
There were several other terms mentioned back in the beginning: AC, DC and Hertz. Here AC and DC are not the band (maybe with just a little heavy metal) but stand for Alternating Current and Direct Current respectively. Direct current flows in only one direction through the circuit. Alternating Current, used in the majority of homes, changes the direction of the current at a set frequency or number of times per second. The frequency is measured in hertz. One hertz means that an event repeats once per second so when the current alternates 60 times a second, it is said to have a frequency of 60 hertz (Hz).
Electricity can be Shocking!
Now electricity is great for powering your big screen TV, your Surround Sound system and your computer but it is NOT good for you should you get a jolt of it unexpectedly. Electric shock occurs when your body comes into contact with any source of electricity that causes sufficient current such that it can pass through you. Typically, electric shock is an unexpected and unwanted exposure and the effects can range from mildly irritating to deadly.
The minimum current a human can feel is about 1 mA (1 milli-amp or 1 thousandth of an amp) of AC at 60Hz, or 5 mA of DC. If the current is high enough, it can cause tissue damage or fibrillation leading to cardiac arrest. About 60 mA of AC or 300 mA of DC can cause fibrillation. A sustained electric shock from a 120 volt, 60Hz AC current is especially dangerous as it usually exceeds the let-go threshold (where your muscles contract and you can not let go of the electrical source), while not delivering enough initial energy to kick the person away. Death caused by an electric shock is called electrocution. The National Safety Council estimates that nearly 300 people die in the United States each year from electric shocks on 120V or 277V circuits. An electric shock from as little as 50V AC for as little as 1 second can disrupt the heart's rhythm, causing death in a matter of minutes.
Electric Shock is separated into four levels, depending on the physiological reaction of the body to the current.
| 10,000 ohms | 1,000 ohms | ||
Electrical Sensation: Threshold of feeling, tingling sensation. | |||
Uncomfortable Sensation: Accepted as maximum harmless current | |||
Let-Go Threshold: Beginning of sustained muscular contraction ("Can't let go" current). | | ||
| | Ventricular fibrillation: Fatal if continued. Respiratory function continues. | | |
| | | | |
While the resistance of skin and shoes are generally high, the resistance of the internal human body can be as low as 500 ohms. Thus, if the skin is broken along the path of current flow, the shock danger increases dramatically. For our purposes a body resistance of 1000 or 1500 ohms is realistic for most low to medium voltage contact with intact skin.
Shock Symptoms
Possible symptoms may include:
- Skin burns
- Numbness, tingling
- Weakness
- Muscle contraction
- Muscular pain
- Bone fractures
- Headache
- Hearing impairment
- Seizures
- Heart arrhythmias
- Cardiac arrest
- Respiratory failure
- Unconsciousness
First Aid
- Call for medical help.
- If safely possible, shut off the electrical current.
- If the current can't be turned off, use a non-conducting object to push the victim away from the source of the current. Stand on something dry and non-conducting but do not attempt to rescue a victim near active high-voltage lines.
- Once the victim is free from the source of electricity, check the victim's airway, breathing, and pulse. If either has stopped or seems dangerously slow or shallow, initiate first aid (CPR).
- If the victim has a burn, remove any clothing that comes off easily, and rinse the burned area in cool running water until the pain subsides. Give first aid for burns.
- If the victim is faint, pale, or shows other signs of shock, lay the victim down, with the head slightly lower than the trunk of the body and the legs elevated, and cover the person with a warm blanket or a coat.
- Stay with the victim until medical help arrives.
- Avoid moving the victim's head or neck if a spinal injury is suspected. Administer appropriate first aid as needed for other wounds or fractures.
- DO NOT touch the victim with your bare hands while the person is still in contact with the electrical source.
- DO NOT apply ice, butter, ointments, medications, cotton dressings, or adhesive bandages to an electrical burn.
- DO NOT get within 20 feet of someone who is being electrocuted by a high-voltage electrical current.
- DO NOT move a victim of an electrical injury unless there is immediate danger.
Jeremiah 51:15 (NIV) - "God made the Earth by His Power; He founded the World by His wisdom and stretched out the Heavens by His understanding.
James 4:7 (NIV) - Submit yourselves, then, to God. Resist the devil, and he will flee from you.
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