Tuesday, March 27, 2012

Working With Wiring

The posts on Electricity were long on theory, short on practical.  There's a simple reason: personally, I'm the kind of guy who would rather you told me why I should do things some way rather than just tell me to do it that way.  That way, if I have to do something similar, I'll understand what I have to think about to do it right.  If you tell me to always use #14 wire on my boat, maybe that's because for the short distances and the current most stuff takes, the I^2*R losses are low.  If I want to do wiring, not in my boat but on a big RV, maybe that's not the right advice. 

Here's a good example.  If you have to wire in an AC outlet, always install it with the ground pin up, like this:
Why?  The plugs (left) virtually always are not completely flush when plugged in.  If you should be working on something above the outlet (usually a foot or so above the floor, right?)  and a tool drop, the ground pin will deflect it. If the two blades were unprotected, something metal might spot weld to the two pins, or cause a massive spark.  I actually had this happen to me while measuring in my kitchen and using a metal strip tape measure.  We were measuring the length of a back splash or something, when the blade slipped between the plug and the outlet, landing on the pins.  There was an enormous flash, and a loud bang.  The metal tape was blown clear, but the cellphone charger plugged into the outlet had about a 1/8" semicircle blown out of it.  A very big notch. 

Which is more likely for you to remember, someone saying to install outlets with the ground pin up, or hearing that story?  Or having it happen to you?  It's better to learn from other peoples' mistakes. 

Whenever I talk about tools, I always remember something a jeweler told me: I never buy cheap tools - they're far too expensive.  That said, you can get good quality wire cutters, strippers, long nose pliers and a meter at your favorite local home improvement store.  A good set of Stripmaster wire strippers make life easy.  My meter for most electrical work around the house is an ancient Fluke handheld digital meter.  New ones are a tiny fraction of the cost. 

Solder or solderless?  For most connections, crimp-on terminals or wire nuts (house electricians live by these) are the way to go.  A well done crimp is as reliable as a soldered joint, and has the advantage that you can do it without house power available.  I love my Metcal soldering iron, picked up used for a song at a ham radio swapmeet, and the best soldering iron I've ever owned, but without 120V AC, it's useless.  A soldering iron and knowing how to use it can be your best friend. 

Crimping tools go from the simple to the precision, and a simple one will get you there if you're not in production or a specialist.  I still have a beginner's kit like this and have just re-stocked it with new crimp terminals as needed.  For coaxial cable or for big connections, that's out of the range of this type of tool kit.  Think ratcheting and leverage.

For most house circuits, (120V 15A typical in the US), you'll use solid copper wire, usually sold in an insulated jacket under a trade name like Romex, which is a trademarked name.   Commonly in 14/3 (14 ga. 3 conductor) for light duty, and thicker 12/3 for more power.  Running 220 for a hot tub or something power hungry?  Try 10 ga., depending on the distance.  12V, @ 120A, long distances?  Start thinking large copper bars. 

There are many tables of recommended wire sizes online and in reference books; these are based on what somebody or some group decided were acceptable losses in a wire.  You might put up with more loss, or demand less, but they're a starting point. 

5 comments:

Anonymous said...

Oddly, it seems that no code requires the device to be installed ground prong up... lots of the higher voltage devices are required to be installed ground prong up.

Even most molded cords are made for the ground to be on the bottom.

Guess people just like there home outlets to resemble a 'face'.


ANYWAY - on my house I rotated all the outlets to have the ground prong up (young'uns). A friend visited and said it looked like hospital outlets...

RegT said...

SG,

I like your tip on "ground up". Makes sense and is just as easy as the other way. My first wife was an apprentice electrician until she got hurt on a large commercial job (Balboa Naval Hospital back in '86), and while I can't remember the exact reasoning (I mean, you aren't likely to grab a hot wire on purpose ;-) she said to work so that only the back of your hand could contact a live wire. That way your hand won't spasm and lock on, unable to let go. Thanks to her I also developed a taste for Klein tools (http://www.kleintools.com/). Love 'em.

Graybeard said...

I haven't done a sweep of the house - really should - but I've had to replace a few and flipped them when I put the new one in. Like you say, most molded cords don't want to go that way.

Anonymous said...

"There's a simple reason: personally, I'm the kind of guy who would rather you told me why I should do things some way rather than just tell me to do it that way. That way, if I have to do something similar, I'll understand what I have to think about to do it right. "

Exactimo.

I want to know WHY we should anything in a particular manner. Unfortunately, many instructing don't have a clue as to WHY a certain manner, only the how; and thus become agitated at the question. Knowing the theory behind the process, and therefore possessing the ability to recognize potential pitfalls can only improve the outcome particularly in areas of uncertainty.

Of course, that knowledge may be all the instructor has in terms of leverage for continued employment.

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