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What should a homeowner know about electricity in the home?
February 12, 2008 12:09 PM   Subscribe

What should a homeowner know about electricity in the home?

Just looking for a general guide to electricity and an explanation of how it works and its use in homes. Basic stuff like why the outlet for the 'frig is different from a regular outlet (beside the obvious "it needs more power"), how much electricity should you plug into an outlet, the difference between volts and amps and their impact on the various circuits in the house, 15 vs 20 amp circuits, things to check for, things not to do and especially anything I'm too ignorant to even be aware of.

Yeah, I know to map the circuits if they aren't already mapped.

Note: this is not about doing any electrical work, but just a general guide for someone who knows nothing about electricity.
posted by Brandon Blatcher to Home & Garden (12 answers total) 14 users marked this as a favorite
 
I would highly recommend this book:

Wiring A House

It's got a lot of fantastic information and helped me safely wire a bathroom remodel. Lots of general theory and how's/why's as well.
posted by Pantengliopoli at 12:23 PM on February 12, 2008


The "electrical basics" books at your local giant box home Despot store are actually pretty good.
posted by notsnot at 12:33 PM on February 12, 2008


- Don't mess with it--hire a professional.
- Turn the breakers off before you mess with it.
posted by jeffamaphone at 12:39 PM on February 12, 2008


Just for a guide to basic understanding, I am sure you can find answers to the sort of questions you ask online, with out buying a book . Try howstuffworks.com. Really you need to know very little to use the house electricity. Don't change plug shapes. If something trips a circuit then don't plug it in that circuit. Don't plug to much in to a single circuit, like with extention cords and power strips. Avoid running cords under rugs and such.

The fridge has a differnt shaped plug because it requires a different (higher) voltage.

Volts is sort of like the pressure as opposed to amps which is like volume of electrons. You can plug anything in to any amp circuit so long as you don't exceed the amp rating. So you can plug in 2 five amp appliances to a 10 amp circuit but not three. But items must be rated for around the same voltage, which in practice means the plugs fit.

It is possable for an outlet to be misswired. You should get one of these at your local hardware store.

And the most important thing to know about electricity is "Don't be part of the circuit"
posted by d4nj450n at 12:45 PM on February 12, 2008


You guys are talking about electricity in general, which is fine, but looking for more practical info:

what amps or volts are residential outlets rated for?

what's the difference between the two prong and three prong outlets?

How many devices should I attach to a circuit (should it be based on the appliance volts or amps?)

How much power does a typical home have?

How can do I know how much power is coming into my house?

How many outlets should be on circuit (this is probably based on the number of appliances used on the circuit, right?)

Does it matter if a circuit extends from downstairs to upstairs?

Basically, the dumb questions someone ignorant might ask or might not know to ask.
posted by Brandon Blatcher at 12:59 PM on February 12, 2008


Basic stuff like why the outlet for the 'frig is different from a regular outlet (beside the obvious "it needs more power")

More metal is required so that it doesn't get hot from the high current draw and start a fire. (There's also the off chance your fridge works on a higher voltage than most of the house, which would have a different outlet shape to prevent mismatch.)

how much electricity should you plug into an outlet,

You should not draw more current (amps) from a circuit (which will generally be a group of several outlets, but can be only one outlet for a heavy appliance) than the circuit is rated for. This is where 15 vs 20 amps comes in. Your electronic devices may directly tell how many amps they take in, or they may only list watts. You may derive amps from watts by dividing the watt rating by the voltage of the circuit. (generally 120V, nominally, in the U.S.)

the difference between volts and amps and their impact on the various circuits in the house,

The classic analogy is that voltage is like water pressure and current is like water flow. In the household domain, your wiring is probably all one voltage except possibly for a few big appliances. That is, all the outlets should be "pushing" with the same force, and devices draw different amounts of power as different currents flow through them. Voltage can be lowered due to resistance in the wiring, and the lowering of voltage is proportional to the current load. This is what causes your lights to dim when you start up a vacuum cleaner. When voltage is lowered due to wiring resistance, the wire is heating up, so circuit breakers or fuses prevent this from reaching the point where there is a fire or the wire melts.

things to check for, things not to do and especially anything I'm too ignorant to even be aware of.


Here's a few:

-Extension cords and power strips have a maximum power rating too, and it is probably lower than that of the outlet.

-Outlets near water, e.g. the bathroom, outside, should have a Ground Fault Circuit Interrupter. This is a clever device that detects when electricity is flowing from the outlet through you and the water in the tub rather than than from the outlet, through a device, and back into the outlet, and shuts it off before you die. It cannot, however, detect when electricity is flowing from the outlet, through you, and back into the outlet, so don't go sticking your fingers into the GFCI socket. The GFCI'd outlets will have a "test/reset" button either on the outlets or on the circuit breaker. Pressing test should cause anything on that circuit to lose power, pressing reset turns it back on.

-Don't defeat the grounding, the "third pin." It's like not using your seatbelt in the car. Realistically, if you need to plug something into the ancient two prong outlet in the attic for five minutes, the chance of death is slim enough that I'd just go ahead and use the little adapter, but you definitely shouldn't be cutting the third pin off your fridge. This probably isn't an issue if your wiring isn't very old.
posted by TheOnlyCoolTim at 1:04 PM on February 12, 2008 [2 favorites]


>what amps or volts are residential outlets rated for?

Donno what outlets are rated for, but the shape of the plug is volt specific. Most US house currents are 110 to 120 volts. Circuits are rated by amp and these can be found by looking at the beakers or fuses.

>what's the difference between the two prong and three prong outlets?
The three prong outlets are grounded and thus safer. I am not going in to what grounded is here. ok to plug a two prong in to a three but not the other way around. If you must use an adapeter, be sure to screw it in to the plug plate.

>How many devices should I attach to a circuit (should it be based on the appliance volts or amps?)
Based on amps. The total amps of all the devices summed should not exceed the rating of the breaker. If it does the breaker breaks and you look for your flashlight.

>How much power does a typical home have?
100 or 200 amps usualy. You can see your amp rating at the breaker box on the main breaker.

>How many outlets should be on circuit (this is probably based on the number of appliances used on the circuit, right?)

The type more then the number. There is some code as to how to figure this out but I don't know it. For the stove or some big draw there should only be one outlet, for just living room type things like lights you would have more.

>Does it matter if a circuit extends from downstairs to upstairs?
No, but it might be bad form. You normaly want to keep circuits together. Spreading them out confuses things and uses more wire. You want to keep the wire short as possible, to minimize both cost and resistance.

Hope that helps and let me refur you once again to Howstuffworks, this time with a more direct link.
posted by d4nj450n at 1:16 PM on February 12, 2008 [1 favorite]


what amps or volts are residential outlets rated for?

You don't have to worry about what volts they're rated for unless you're wiring them up, because either you have all one voltage in your house or they're going to be different shapes if they're rated for different voltages. If you're in America, your standard two blade + ground pin socket should be rated 15 amps - meaning you can draw the entire rated current of a 15 amp circuit through a single socket. If you see a socket where one of the blades is 'T' shaped, that means it's rated for 20 amps. The 'T' shape allows you to plug both 15 and 20 amp plugs into the 20 amp socket but the 20 amp plug will not go into the 15 amp socket. More information here.


what's the difference between the two prong and three prong outlets?


Grounding, as I mentioned above. Let's say your fridge gets broken in such a way that the 120V wiring is touching the metal case of the fridge. This metal case is connected to ground through the third pin, so that if this breakage does happen, the electricity goes through the third pin and not through you.

How much power does a typical home have?

This one I don't know off the top of my head.

How can do I know how much power is coming into my house?

Your electric bill (divide the number of kilowatt-hours given by the number of hours in the billing period for your average power use in kilowatts), watching how fast the meter spins, or something like this. I imagine if you look there are whole-house meters if you really care.

How many outlets should be on circuit (this is probably based on the number of appliances used on the circuit, right?)


Pretty much, along with the current used by those appliances. So in your bedroom where you'll be plugging in Ipod chargers and light bulbs, a bunch of outlets can go on one circuit, but things like electric ovens and big air conditioners will get their own circuits.

Does it matter if a circuit extends from downstairs to upstairs?

Electrically, no. Theoretically I could wonder about the possible effects of gravity on electron flow but that's idle speculation about something ridiculously negligible.
posted by TheOnlyCoolTim at 1:25 PM on February 12, 2008


And let me say as an electrical engineer, not an electrician, I know enough to make these vague pronouncements, but I wouldn't so much as install a light fixture in a ceiling without a book telling me how to do it and for anything major I'd just have an electrician in. Practical experience has been codified and it is the electrician's job to know these codes.
posted by TheOnlyCoolTim at 1:31 PM on February 12, 2008


The bulk of your questions have been answered already. One thing I wanted to add, is that depending on the current draw through a particular circuit and the total length of the wire run, there are regulations for the gauge and type of of wire to be used. Generally, the longer then run the bigger the wire. A 220 or 240v circuit will employ very large, solid core wire, even if it's only going 2-3 feet. A 120v will use smaller wire, unless it is traveling a long distance.

The code book for this stuff is called the UGLY book. No, for real, it is.

Generally speaking, you don't want more than 5 or so plugs on a single circuit, which is often approximately one room. It's up to you to decide if you want overhead lights on this too, it's not uncommon but it's not necessarily the best thing either. These are generally 20A circuits.

Major appliances get their own, even if they use a regular plug. They ALWAYS get their own when they use a 220 or 240, and depending on the appliance these will be 40 or 60A circuits.

Plugs that could ever come into contact with fluids should always be GFCI's (ground fault circuit interrupt), OR they should be wired PAST one of these so that it will trip given a ground fault. These are the plugs with the push-button resets. Your kitchen plugs should be these, especially those around countertops and in and around sinks. Same goes for your bathroom.

Wiring's not hard, but it can be difficult. (Not so much brains as technique most of the time.)
posted by TomMelee at 1:52 PM on February 12, 2008


I'll only add that if you don't know what you are doing you shouldn't be poking around the electrical box with the cover off...there are things in there that can really mess you up if you aren't careful.
posted by mmascolino at 1:59 PM on February 12, 2008


I'd say the minimum to know is:

1. An american home is a 110volt operation. You may have a 220 volt plug for an air conditioner or some other high powered device. 220v outlets and plugs look funny. Be afraid of anything that looks funny.

2. That weird plug in your bathroom is called a GFI. It may save your life one day.

3. Powerstrips and extension cords have a wattage maximum. Thicker ones can carry more watts. A thin one with a high wattage device (hair dryer) will start a fire. Never buy thin cords, ever.

4. A three prong outlet has a "ground" connector at the bottom. This goes into the ground. If the device you are plugging in has a three prong connector you MUST use a three prong outlet. There's no such thing as a 3 to 2 prong adapter. Those exist for people who want to run their own ground wire.

5. Always call a pro. This stuff kills. Its not worth it. Especially in wet areas like kitchens or bathrooms.

I wouldnt sweat it when it comes to volts and amps. Youre always dealing with 110v (sometimes listed as 120) and should be thinking in watts. "Hey this space heater is 1000 watts, I shouldnt plug it into this 200 watt rated extension cord."
posted by damn dirty ape at 2:42 PM on February 12, 2008 [1 favorite]


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