Home Electrical Basics: Terms and Safety

Tim says:

Don’t you just hate it when outlets and lights don’t work or sparks fly randomly from an outlet?  Many look on in despair, knowing the call to the local electrician means $80/hr plus scheduling hassles.  I’d like to show you how easily, and more importantly safely, these problems can be fixed.  Before we get into that, let’s have a little review of the basics.

As Heather is so apt to point out when I talk shop : “Not everyone is an engineer…”.  Fair enough, but for most repairs or upgrades only a basic understanding is necessary.   First and foremost is Safety.  Forgive me if I start sounding like a broken record, but an electrical fire or severe electrical shock can really mess up Sunday Brunch.

Basic Terms

Ma’am…your problem seems to be caused by voltage fluctuations caused by either a load imbalance or improper grounding on your 120/240vac distribution system.  Poor contacts in your light switch is also creating a high resistance hot spot…”

Wha…what??? Esoteric Lingo…gotta love it.  Here’s an overview of some basic terms that you may come across in dealings with all things electrical:

Voltage: Expressed in Volts, this represents the electrical potential between two points.

Current:  Measured in units called Amps, this represents the electrical current flow between two points.

Power:  Expressed in Watts, is the the total electrical energy being used. Calculated easily by Current x Voltage = Power.

Resistance:  Expressed in Ohms, this is a measurement of the resistance to current flow through a conductor.

Conductor: Material that has a low resistance and easily allows current to flow through it (e.g. copper, aluminum, iron…)

Insulator: Material that has a high resistance to current flow, such as glass, wood, plastic, etc…

Direct Current: Abbreviated as DC is current that flows in only one direction.  Batteries are a good example of this.

Alternating Current: Abbreviated as AC is current that changes direction many times a second.

Hertz: The frequency at which AC alternates. Measured in Hertz.  Here in the US, it’s 60Hz.

Load: This is any device which consumes power in an electrical system from a source.  The source would be an outlet or distribution panel.   Toasters, vacuums, A/C, and dishwashers, etc… are all examples of loads.

A good analogy of electricity would be to think of electricity like a river.

Where current would be how deep and wide the river is, and voltage would be how fast the river is flowing.  Resistance would be akin to a log jam, slowing down the flow (current).  Given enough logs, no water (current) would flow until the speed of the river (voltage)  increased enough to overcome it. Although this isn’t a perfect analogy, it does make it easier to visualize how all those little electrons are acting.

How does all this relate to safety?

Well, most conductors are metals like the copper wire in your house,  but given enough voltage anything can become a conductor including the human body.  On average, it only takes 100ma (milliamps) or one tenth of an amp to cause the human heart to stop beating.  That’s not much!  Consider your average toaster oven can have over 5 amps running through it at breakfast.  So, why is it that most times when we get an electric shock we don’t just keel over and die?  Because our body’s resistance is usually is well over 1Mohm (one million ohms). This means the current flowing through us would be less than one milliohm and be felt as nothing more than a slight tingle.  Things that affect our internal resistance include sweat, hydration, and our current health.  When we’re sick, our bodies resistance to current is much lower.  So, with that in mind, here’s the Golden Rule for all Electrical Work:

Never Work On Energized Equipment!!!

In case you’re just skimming through this I’ll say it one more time:

Never Work On Energized Equipment!!!

What this means is that before working on your washing machine, you would unplug it.  If you needed to change an outlet or light switch you’ll need to identify the correct circuit breaker and turn it off.  Even if you simply needed to change a light bulb, the best thing you could do is make sure the switch is off.  Sound paranoid?  Think of this:  Let’s say your simply changing a light bulb, but in the process of unscrewing the old one the glass bulb breaks.  Now you’ve just exposed yourself to 120 volts that are still present on the light’s filaments – Ouch!

In my next article we’ll go over how to verify power is off (Obvious for a light bulb, not so with an outlet).  We’ll also cover the surprisingly short list of tools required to cure most household electrical ailments.

Submit questions to Tim@home-ec101.com.


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  2. Keter on January 25, 2011 at 8:23 pm

    The way Ohms (units of electrical resistance, pronounced like what you say at yoga) are written is…
    0-999.9… Ohms (Ohms is often written as a symbol – the Greek letter Omega)
    1-999.9… K Ohms (K, read kil- (keel) or kilo-, in scientific notation means 10 cubed or 1000, add 3 zeros behind the number before the K)
    1-999.9… M Ohms (M, read meg (like Meg Ryan)- or mega-, in scientific notation means 10 raised to the 6th power or 1 million, add 6 zeros behind the number before the M)

    The actual resistance of the human body is rather lower than stated: dry skin has a resistance of about 1,000-495,000 Ohms (1K ohm to 495K ohms). I have resistors that are the size of a pencil lead with more resistivity. ;o)


    • TimSolos on January 25, 2011 at 10:37 pm

      Human electrical resistance: Well, here's the thing: There are so many variables involved that pinning down an exact amount is akin to trying to nail jell-o to the wall. For a few more examples:
      – Relative humidity and temperature
      – Relative body hydration
      – Individual BMI (Body Mass Index)
      – Electrical contact entrance and exit points
      – Pressure applied to both electrical contact points
      – Epidermal thickness and cleanliness
      – Individuals personal Karma Rating (only half kidding)

      Thats not even getting into relative body impedance based off source frequency, which I have some thoughts to share with the folks at the U of I… (Then again, folks do seem more "thin skinned" these days than back when I was studying all this…).

      Considering that 120VAC kills more people each year than any other voltage level, the actual fatality per shock rate is quite low. Reasoning is, a lot of folks don't take "light bulb" voltage seriously (usually electricians) and forgo the necessary precautions they would if they were working on something higher (Say 34.5kv).
      What this all boils down to is that on any given day if someone gets shocked by household 120VAC we're more likely to hear curse words than a eulogy reading.

  3. ThatBobbieGirl on January 25, 2011 at 7:04 pm

    Nice to meet you, Mr. Heather! I'm Bobbie — may I call you Mr. Heather?

    Oh. All right then.

    Hi Tim. *grumble*

    This post is such a great idea. I had to change out a GFCI outlet last month, and while I mangaged it on my own and without starting any fires or dying very much, it took me forever to do it. I was so paranoid about doing it safely that I double, triple and quadruple checked EVERYTHING before doing it. I'm fairly confident about jumping in and doing repairs myself, if I can figure it out, but electricity is scary stuff.

    • TimSolos on January 25, 2011 at 10:53 pm

      Tim, Timmy, Timbo, and many others Heather wouldn't like to see typed out here…They're all good 🙂
      I'm glad you enjoyed the post…although I admit it's a rather dry subject at first. Wait till we get into ground loops, open neutrals, phase matching, and inductive load calculations…then it'll get FUN! Oh wait….

      I'm glad you were successful at swapping out your GFCI and avoiding any unnecessary fires or inconvenient dying. You got ahead of me though….that's a not too distant future post!

  4. imabug on January 25, 2011 at 2:50 pm

    yay tim!

  5. Kathy on January 25, 2011 at 9:04 am

    I really enjoyed reading today's post by Tim. I think it was very well written. Especially glad to see the safety reminders for everyone, as well. By the way, what would be some potential causes for the lights in a home to occasional flicker or dim? Great work!

    • TimSolos on January 25, 2011 at 2:43 pm

      Thank you for the nice comment. Flickering and/or dimming of lights will most likely be a whole post by itself. The quick and short of it is most problems have nothing to due with your household electrical system and are caused by service fluctuations from switching being performed at various Power Company's substations (Bringing a generator on/off line…). If it is determined to be isolated to one's house, then the culprit could be anything from improper grounding, loose connections, or a load imbalance in the distribution panel. Again, I think this may make a great future topic (especially for anyone having trouble sleeping…), but I wanted to get the basics and safety out of the way first.

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