Since electrical wiring questions do turn up from time to time on sci.electronics (and the answers aren't always apparent, even to those skilled in electronics), I am hijacking the following FAQ and posting a copy here.  I've asked the writers to cross-post to sci.electronics in the future.   	--- jeh@cmkrnl.com   X-NEWS: cmkrnl news.answers: 6685 Newsgroups: misc.consumers.house,rec.woodworking,news.answers,misc.answers,rec.answers Subject: Electrical Wiring FAQ Message-ID: <wirefaq_733900891@ecicrl> From: clewis@ferret.ocunix.on.ca (Chris Lewis) Date: 4 Apr 93 05:21:49 GMT Reply-To: wirefaq@ferret.ocunix.on.ca (Wiring FAQ commentary reception) Followup-To: poster Expires: 2 May 93 05:21:31 GMT Organization: Elegant Communications Inc., Ottawa, Canada Summary: A series of questions and answers about house wiring Supersedes: <wirefaq_732691289@ecicrl> Lines: 1524  Archive-name: electrical-wiring Last-modified: Sun Feb 21 16:56:10 EST 1993  	    Frequently Asked Questions on Electrical Wiring  		Steven Bellovin (smb@ulysses.att.com) 		Chris Lewis (clewis@ferret.ocunix.on.ca)  	    Comments to (automatic if you reply to this article): 		    wirefaq@ferret.ocunix.on.ca  This FAQ is formatted as a digest.  Most news readers can skip from one question to the next by pressing ^G.  Answers to many other topics related to houses can be obtained from the misc.consumers.house archive; send an empty piece of mail to house-archive@dg-rtp.dg.com for information.  Changes to previous issue marked with "|" in left column.  Watch particularly for "NEW" in the Questions list for new or substantively changed answers.  Note that this is now a registered FAQ - cross-posted to news.answers and should appear in the FAQ list of lists.  Subject: Questions answered in this FAQ  	Introduction/Disclaimers 	What is the NEC?  Where can I get a copy? 	What is the CEC?  Where can I get a copy? 	Can I do my own wiring?  Extra pointers? 	What do I need in the way of tools? 	What is UL listing? 	What is CSA approval? 	Are there any cheaper, easier to read books on wiring? 	Inspections how and what?  Why should I get my wiring inspected? 	My house doesn't meet some of these rules and regulations. 	A word on voltages: 110/115/117/120/125/220/240 	What does an electrical service look like? 	What is a circuit? 	"grounding" versus "grounded" versus "neutral". 	What does a fuse or breaker do?  What are the differences? 	Breakers?  Can't I use fuses? 	What size wire should I use? 	Where do these numbers come from? 	What does "14-2" mean? 	What is a "wirenut"/"marrette"/"marr connector".  How are they used? 	What is a GFI/GFCI? 	Where should GFCIs be used? 	Where shouldn't I use a GFCI? 	What is the difference between a GFCI outlet and a GFCI breaker? 	What's the purpose of the ground prong on an outlet, then? 	Why is one prong wider than the other?  Polarization 	What kind of outlets do I need in a kitchen? 	Where must outlets and switches be in bathrooms? 	What is Romex/NM/NMD?  What is BX?  When should I use each? 	Should I use plastic or metal boxes? 	Junction box positioning? 	Can I install a replacement fixture? 	What does it mean when the lights brighten when a motor starts? 	What is 3 phase power?  Should I use it?  Can I get it in my house? 	Is it better to run motors at 110 or 220? 	What is this nonsense about 3HP on 110V 15A circuits? 	How do I convert two prong receptacles to three prong? 	Are you sure about GFCIs and ungrounded outlets? 	    Should the test button work? 	How should I wire my shop? 	Underground wiring 	Aluminum wiring 	I'm buying a house!  What should I do? 	What is this weird stuff?  Old style wiring 	Where do I buy stuff?   Subject: Introduction/Disclaimers  	Although we've done a fair bit of wiring, we are not 	electricians, and we cannot be responsible for what you do.  If 	you're at all uncertain about what is correct or safe, *don't 	do it*.  Contact someone qualified -- a licensed electrician, 	or your local electrical inspector.  Electricity is no joke; 	mistakes can result in shocks, fires, or electrocution.  	Furthermore, our discussion is based on the U.S. National 	Electrical Code (NEC) and the Canadian Electrical code (CEC). 	To the best of our abilities, we have confirmed every detail 	with the electrical code, but we don't quote sections 	simply to keep this thing readable.  If you think we're wrong, 	we invite you to correct us, but please - quote references!  	The NEC and the CEC do not, in and of themselves, have the 	force of law.  Many municipalities adopt it en toto.  Others, 	however, do not.  Check your with your local building 	department (and <provincial> Hydro Inspection Offices in 	Canada) to find out what applies in your area.  Also, 	your local electrical utility may also have special requirements 	for electrical service installation.  Bear in mind, too, that 	we say here applies primarily to ordinary single-family 	residences.  Multi-family dwellings, mobile homes, commercial 	establishments, etc., are sometimes governed by different 	rules.  	Also note that, contrary to popular belief in the U.S. (and in 	some parts of Canada), Canada is not a wholly-owned subsidiary 	of the U.S.  Consequently, the NEC does not apply in Canada. 	Lots of things are the same, including voltages, line 	frequencies, and the laws of physics.  But there are a number 	of crucial differences in the regulations.  Where we can, we've 	noted them, flagging the relevant passages with ``NEC'' or 	``CEC''.  	Remember that the CEC and NEC are minimal standards.  It is often 	smart to go beyond their minimal requirements.  Subject: What is the NEC?  Where can I get a copy?  	The NEC is a model electrical code devised and published by the 	National Fire Protection Association, an insurance industry group. 	It's revised every three years.  The 1993 version has been released. 	You can buy a copy at a decent bookstore, or by calling them directly 	at 800-344-3555.  The code exists in several versions.  There's the 	full text, which is fairly incomprehensible.  There's an abridged 	edition, which has only the sections likely to apply to most houses. 	And there's the NEC Handbook, which contains the ``authorized 	commentary'' on the code, as well as the full text.  That's the 	recommended version.  Unfortunately, there's no handbook for 	the abridged edition.  And the full handbook is expensive -- 	US$65 plus shipping and handling.  Subject: What is the CEC?  Where can I get a copy?  	The Canadian Standards Association is an organization made up 	of various government agencies, power utilities, insurance 	companies, electrical manufacturers and other organizations. 	The CSA publishes CSA Standard C22.1 which is updated every two 	or three years.  Each province adopts, with some amendments, 	this standard and publishes a province-specific code book. 	Since each province publishes its own slightly modified 	standard, it would be somewhat confusing to obtain the CSA 	standard itself.  In this FAQ, "CEC" really means the 	appropriate provincial standard.  In particular, this FAQ is 	derived from the Ontario Hydro Electrical Safety Code, 20th 	edition (1990).  Which is in turn based on CSA C22.1-1990 (16th 	edition).  While differences exist between the provinces, an 	attempt has been made to avoid specific-to-Ontario detail.  	The appropriate provincial code can be obtained from electrical 	inspection offices of your provincial power authority.  In 	Ontario, it's Ontario Hydro.  The Ontario Hydro book isn't 	overly fat.  It's about C$25, and includes mailed updates.  I 	hear that these standards are somewhat easier to read than the 	equivalent NEC publications.  	Don't bother asking in Quebec - DIY wiring is banned throughout 	the province.  Subject: Can I do my own wiring?  Extra pointers?  	In most places, homeowners are allowed to do their own wiring. 	In some, they're not.  Check with your local electrical 	inspector.  Most places won't permit you to do wiring on other's 	homes for money without a license.  Nor are you permitted to do 	wiring in "commercial" buildings.  Multiple dwellings (eg: duplexes) 	are usually considered "semi-commercial" or "commercial".  However, 	many jurisdictions will permit you to work on semi-commercial 	wiring if you're supervised by a licensed electrician - if you can 	find one willing to supervise.  	If you do your own wiring, an important point:  	Do it NEAT and WELL!  What you really want to aim for is a better 	job than an electrician will do.  After all, it's your own home, 	and it's you or your family that might get killed if you make 	a mistake.  An electrician has time pressures, has the skills 	and knows the tricks of the trade to do a fast, safe job. 	In this FAQ we've consciously given a few recommendations that 	are in excess of code, because we feel that it's reasonable, 	and will impress the inspector.  	The inspector will know that you're an amateur.  You have to 	earn his trust.  The best way of doing this is to spend your 	time doing as neat a job as possible.  Don't cut corners. 	Exceed specifications.  Otherwise, the inspector may get extremely 	picky and fault you on the slightest transgressions.  	Don't try to hide anything from the inspector.  	Use the proper tools.  Ie: don't use a bread knife to strip 	wires, or twist wires with your fingers.  The inspector 	won't like it, and the results won't be that safe.  And it 	takes longer.  And you're more likely to stick a hunk of 	12ga wire through your hand that way.  	Don't handle house wire when it's very cold (eg: below -10C 	or 16F).  Thermoplastic house wire, particularly older types 	become very brittle.  Subject: What do I need in the way of tools?  	First, there's the obvious -- a hammer, a drill, a few 	screwdrivers, both straight and Phillips-head.  If you're  	lucky enough to live in Canada (or find a source of CSA-approved 	devices) you need Robertson ("square recess") screwdrivers 	(#1 and #2) instead of phillips.  	For drilling a few holes, a 3/4" or 1" spade bit and 1/4" or 	3/8" electric drill will do.  If you're doing a lot, or 	are working with elderly lumber, we recommend a 1/2" drill 	(right-angle drills are wonderful.  Can be rented) and 	3/4" or 1" screw-point auger drill bits.  These bits pull 	you through, so they're much faster and less fatiguing, even 	in 90 year old hardwood timbers.  	Screw-driver bits are useful for drills, expecially if you 	install your electrical boxes using screws (drywall screws 	work well). 	 	For stripping wire, use a real wire stripper, not a knife or 	ordinary wire cutters.  Don't buy the $3 K-mart "combo stripper, 	crimper and bottle opener" types.  You should expect to pay 	$15 to $20 for a good "plier-type" pair.  It will have sized 	stripping holes, and won't nick or grab the wire - it should 	be easy to strip wire with it.  One model has a small hole in the 	blade for forming exact wire loops for screw terminals.  There 	are fancier types (autostrip/cut), but they generally aren't 	necessary, and pros usually don't use them.  	A pair of diagonal side cutter pliers are useful for clipping ends 	in constricted places.  Don't use these for stripping wire.  	You will need linesman pliers for twisting wires for wire nuts.  	You should have a pair of needle-nose pliers for fiddling 	inside boxes and closing loops, but it's better to form wire 	loops with a "loop former hole" on your wire stripper - more 	accurate.  	If you're using non-metallic cable, get a cable stripper for 	removing the sheath.  Or, do what some pros do, they nick the 	end of the sheath, grab the ground wire with a pair of pliers, 	and simply rip the sheath back using the ground wire as a 	"zipper", and cut the sheath off.  You shouldn't try to strip 	the sheath with a knife point, because it's too easy to 	slash the insulation on the conductors.  Apparently Stanley 	utility knives fitted with linoleum cutters (hooked blades) 	can be used to strip sheath, but there is still the possibility 	that you'll gouge the conductors.  	For any substantial amount of work with armored cable, it's well 	worth your while to invest in a rotary cable splitter (~US$ 18). 	Hack saws are tricky to use without cutting into the wire 	or the insulation.  	Three-prong outlet testers are a quick check for properly-wired 	outlets.  About $6.  Multimeters tell you more, but are a lot more 	expensive, and probably not worth it for most people.  A simple 	voltage sensor, which can detect potential through an insulated 	wire not supplying any devices, is extremely helpful; they cost 	about US$ 10 at Radio Shack.  	You should have a voltage detector - to check that the wires are 	dead before doing work on them.  Neon-bulb version are cheap ($2-3) 	and work well.  If you get more serious, a "audible alarm" type is 	good for tracing circuits without a helper.  (Though I've been known 	to lock the drill on, and hit breakers until the scream stops ;-)  	For running wires through existing walls, you need fish tape. 	Often, two tapes are needed, though sometimes, a bent hanger or 	a length of thin chain will suffice.  Fish tapes can be rented.  	Electrical tape.  Lots of it ;-)  Seriously, a good and competent 	wiring job will need very little tape.  The tape is useful for 	wrapping dicy insulation in repair work.  Another use is to wrap  	around the body of outlets and switches to cover the termination 	screws - I don't do this, but drywall contractors prefer it (to 	prevent explosions when the drywall knife collides with a live outlet 	that has no cover plate).  Subject: What is UL listing?  	The UL stands for "Underwriters Laboratory".  It used to be 	an Insurance Industry organization, but now it is independent 	and non-profit.  It tests electrical components and equipment 	for potential hazards.  When something is UL-listed, that means 	that the UL has tested the device, and it meets their requirements 	for safety - ie: fire or shock hazard.  It doesn't necessarily 	mean that the device actually does what it's supposed to, just 	that it probably won't kill you.  	The UL does not have power of law in the U.S. -- you are 	permitted to buy and install non-UL-listed devices.  However, 	insurance policies sometimes have clauses in them that will 	limit their liability in case of a claim made in response to 	the failure of a non-UL-listed device.  Furthermore, in 	many situations the NEC will require that a wiring component 	used for a specific purpose is UL-listed for that purpose. 	Indirectly, this means that certain parts of your wiring 	must be UL-listed before an inspector will approve it and/or 	occupancy permits issued. 	 Subject: What is CSA approval?  	Every electrical device or component must be certified by the 	Canadian Standards Association before it can be sold in 	Canada.  Implicit in this is that all wiring must be done 	with CSA-approved materials.  They perform testing similar to 	the UL (a bit more stringent), except that CSA approval is 	required by law.  	Again, like the UL, if a fire was caused by non-CSA-approved 	equipment, your insurance company may not have to pay the 	claim.  	In Canada, there is a branch organization of the UL, called ULC 	(UL of Canada).  ULC does not have power of law, and seems to 	be more a liason group between the CSA and insurance 	companies.  Subject: Are there any cheaper, easier to read books on wiring?  	USA: The following three books were suggested by our readers  	    Residential Wiring 	    by Jeff Markell, 	    Craftsman Books, 	    Carlsbad CA for $18.25. ISBN 0-934041-19-9.  	    Practical Electrical Wiring 	    Residential, Farm and Industrial,  Based on the National 	    Electrical Code    ANSI/NFPA 70 	    Herbert P. Richter and W. Creighton Schwan 	    McGraw-Hill Book Co.  	    Wiring Simplified 	    H. P. Richter and W. C. Schwan 	    Park Publishing Co. 	 	Try to make sure that the book is based on the latest NEC 	revision.  Which is currently 1990.  	Canada: P.S. Knight authors and publishes a book called 	"Electrical Code Simplified".  There appears to be a version 	published specific to each province, and is very tied into the 	appropriate provincial code.  It focuses on residential wiring, 	and is indispensible for Canadian DIY'ers.  It is better to get 	this book than the CEC unless you do a lot of wiring (or answer 	questions on the net ;-).  	It is updated each time the provincial codes are.  This book is 	available at all DIY and hardware stores for less than C$10.  Subject: Inspections how and what?  Why should I get my wiring inspected?  	Most jurisdictions require that you obtain a permit and 	inspections of any wiring that is done.  Amongst other more 	mundane bureaucratic reasons (like insurance companies not 	liking to have to pay claims), a permit and inspections 	provides some assurance that you, your family, your neighbors 	or subsequent owners of your home don't get killed or lose 	their homes one night due to a sloppy wiring job.  	Most jurisdictions have the power to order you to vacate your 	home, or order you to tear out any wiring done without a 	permit.  California, for instance, is particularly nasty about 	this.  	If fire starts in your home, and un-inspected wiring is at 	fault, insurance companies will often refuse to pay the damage 	claims.  	In general, the process goes like this: 		- you apply to your local inspections office or building 		  department for a permit.  You should have a sketch or 		  detailed drawing of what you plan on doing.  This is 		  a good time to ask questions on any things you're not 		  sure of.  If you're doing major work, they may impose 		  special conditions on you, require loading 		  calculations and ask other questions.  At this point 		  they will tell you which inspections you will need. 		- If you're installing a main panel, you will need to 		  have the panel and service connections inspected 		  before your power utility will provide a connection. 		  This is sometimes done by the local power authority 		  rather than the usual inspectors. 		- After installing the boxes and wiring, but before 		  the insulation/walls go up, you will need a 		  "rough-in" inspection. 		- After the walls are up, and the wiring is complete, 		  you will need a "final inspection".  Subject: My house doesn't meet some of these rules and regulations. 	Do I have to upgrade?  	In general, there is no requirement to upgrade older dwellings, 	though there are some exceptions (ie: smoke detectors in some 	cases).  However, any new work must be done according to the 	latest electrical code.  Also, if you do ``major'' work, you 	may be required to upgrade certain existing portions or all 	of your system.  Check with your local electrical inspector.  Subject: A word on voltages: 110/115/117/120/125/220/240  	One thing where things might get a bit confusing is the 	different numbers people bandy about for the voltage of 	a circuit.  One person might talk about 110V, another 117V 	or another 120V.  These are all, in fact, exactly the same 	thing...  In North America the utility companies are required 	to supply a split-phase 240 volt (+-5%) feed to your house. 	This works out as two 120V +- 5% legs.  Additionally, since there 	are resistive voltage drops in the house wiring, it's not 	unreasonable to find 120V has dropped to 110V or 240V has dropped 	to 220V by the time the power reaches a wall outlet.  Especially 	at the end of an extension cord or long circuit run.  For a number 	of reasons, some historical, some simple personal orneryness, 	different people choose call them by slightly different numbers. 	This FAQ has chosen to be consistent with calling them "110V" and 	"220V", except when actually saying what the measured voltage will 	be.  Confusing?  A bit.  Just ignore it.  	One thing that might make this a little more understandable 	is that the nameplates on equipment ofen show the lower (ie: 110V 	instead of 120V) value.  What this implies is that the device 	is designed to operate properly when the voltage drops that 	low.  	208V is *not* the same as 240V.  208V is the voltage between 	phases of a 3-phase "Y" circuit that is 120V from neutral to any 	hot.   480V is the voltage between phases of a 3-phase "Y" 	circuit that's 277V from hot to neutral.  	In keeping with 110V versus 120V strangeness, motors intended 	to run on 480V three phase are often labelled as 440V...  Subject: What does an electrical service look like?  	There are logically four wires involved with supplying the 	main panel with power.  Three of them will come from the utility 	pole, and a fourth (bare) wire comes from elsewhere.   	The bare wire is connected to one or more long metal bars pounded  	into the ground, or to a wire buried in the foundation, or sometimes  	to the water supply pipe (has to be metal, continuous to where 	the main water pipe entering the house.  Watch out for galvanic 	action conductivity "breaks" (often between copper and iron pipe)). 	This is the "grounding conductor".  It is there to make sure that 	the third prong on your outlets is connected to ground.  This wire 	normally carries no current.  	One of the other wires will be white (or black with white or 	yellow stripes, or sometimes simply black).  It is the neutral wire. 	It is connected to the "centre tap" (CEC; "center tap" in the 	NEC) of the distribution transformer supplying the power.  It 	is connected to the grounding conductor in only one place (often 	inside the panel).  The neutral and ground should not be connected 	anywhere else.  Otherwise, weird and/or dangerous things may happen.  	Furthermore, there should only be one grounding system in 	a home.  Some codes require more than one grounding electrode. 	These will be connected together, or connected to the neutral 	at a common point - still one grounding system.  Adding additional 	grounding electrodes connected to other portions of the house 	wiring is unsafe and contrary to code.  	If you add a subpanel, the ground and neutral are usually 	brought as separate conductors from the main panel, and are 	not connected together in the subpanel (ie: still only one 	neutral-ground connection).  However, in some situations  	(certain categories of separate buildings) you actually do 	have to provide a second grounding electrode - consult your 	inspector.  	The other two wires will usually be black, and are the "hot" 	wires.  They are attached to the distribution transformer as 	well.  	The two black wires are 180 degrees out of phase with each 	other.  This means if you connect something to both hot wires, 	the voltage will be 220 volts.  If you connect something to the 	white and either of the two blacks you will get 110V.  	Some panels seem to only have three wires coming into them. 	This is either because the neutral and ground are connected 	together at a different point (eg: the meter or pole) and one 	wire is doing dual-duty as both neutral and ground, or in some 	rare occasions, the service has only one hot wire (110V only 	service).  Subject: What is a circuit?  	Inside the panel, connections are made to the incoming wires. 	These connections are then used to supply power to selected 	portions of the home.  There are three different combinations: 		1) one hot, one neutral, and ground: 110V circuit. 		2) two hots, no neutral, and ground: 220V circuit. 		3) two hots, neutral, and ground: 220V circuit + neutral, 		   and/or two 110V circuits with a common neutral.  	(1) is used for most circuits supplying receptacles and 	lighting within your house.  (3) is usually used for supplying 	power to major appliances such as stoves, and dryers - they 	often have need for both 220V and 110V, or for bringing several 	circuits from the panel box to a distribution point.  (2) is 	usually for special 220V motor circuits, electric heaters, or 	air conditioners.  	[Note: In the US, the NEC frequently permits a circuit similar 	to (2) be used for stoves and dryers - namely, that there 	are two hot wires, and a wire that does dual duty as neutral 	and ground, and is connected to the frame as well as providing 	the neutral for 110V purposes - three prong plugs instead 	of four (*only* for stoves/dryers connected to the main panel. 	When connected to most sub-panels, 4 prong plugs and receptacles 	are required).  In our not-so-humble opinion this is crazy, but 	the NFPA claims that this practice was re-evaluated for the 1992 NEC, 	and found to be safe.  Check your local codes, or inquire as to 	local practice -- there are restrictions on when this is 	permissible.]  	(1) is usually wired with three conductor wire: black for hot, 	white for neutral, and bare for grounding.  	(2) and (3) have one hot wire coloured red, the other black, a 	bare wire for grounding, and in (3) a white wire for neutral.  	You will sometimes see (2) wired with just a black, white and ground 	wire.  Since the white is "hot" in this case, both the NEC and CEC 	requires that the white wire be "permanently marked" at the ends 	to indicate that it is a live wire.  Usually done with paint, nail 	polish or sometimes electrical tape.  	Each circuit is attached to the main wires coming into the 	panel through a circuit breaker or fuse.  	There are, in a few locales, circuits that look like (1), (2) 	or (3) except that they have two bare ground wires.  Some places 	require this for hot tubs and the like (one ground is "frame ground", 	the other attaches to the motor).  This may or may not be an 	alternative to GFCI protection.  Subject: "grounding" versus "grounded" versus "neutral".  	According to the terminology in the CEC and NEC, the 	"grounding" conductor is for the safety ground, i.e., the green 	or bare wire.  The word "neutral" is reserved for the white when 	you have a circuit with more than one "hot" wire.  Since the white 	wire is connected to neutral and the grounding conductor inside the 	panel, the proper term is "grounded conductor".  However, the 	potential confusion between "grounded conductor" and "grounding 	conductor" can lead to potentially lethal mistakes - you should 	never use the bare wire as a "grounded conductor" or white wire 	as the "grounding conductor", even though they are connected 	together in the panel.  	[But not in subpanels - subpanels are fed neutral and ground 	separately from the main panel.  Usually.]  	In the trade, and in common usage, the word "neutral" is used 	for "grounded conductor".  This FAQ uses "neutral" simply to 	avoid potential confusion.  We recommend that you use "neutral" 	too.  Thus the white wire is always (except in some light 	switch applications) neutral.  Not ground.  Subject: What does a fuse or breaker do?  What are the differences?  	Fuses and circuit breakers are designed to interrupt the power 	to a circuit when the current flow exceeds safe levels.  For 	example, if your toaster shorts out, a fuse or breaker should 	"trip", protecting the wiring in the walls from melting.  As 	such, fuses and breakers are primarily intended to protect the 	wiring -- UL or CSA approval supposedly indicates that the 	equipment itself won't cause a fire.  	Fuses contain a narrow strip of metal which is designed to melt 	(safely) when the current exceeds the rated value, thereby 	interrupting the power to the circuit.  Fuses trip relatively 	fast.  Which can sometimes be a problem with motors which have 	large startup current surges.  For motor circuits, you can use 	a "time-delay" fuse (one brand is "fusetron") which will avoid 	tripping on momentary overloads.  A fusetron looks like a 	spring-loaded fuse.  A fuse can only trip once, then it must be 	replaced.  	Breakers are fairly complicated mechanical devices.  They 	usually consist of one spring loaded contact which is latched 	into position against another contact.  When the current flow 	through the device exceeds the rated value, a bimetallic strip 	heats up and bends.  By bending it "trips" the latch, and the 	spring pulls the contacts apart.  Circuit breakers behave 	similarly to fusetrons - that is, they tend to take longer to 	trip at moderate overloads than ordinary fuses.  With high 	overloads, they trip quickly.  Breakers can be reset a finite 	number of times - each time they trip, or are thrown 	when the circuit is in use, some arcing takes place, which 	damages the contacts.  Thus, breakers should not be used in 	place of switches unless they are specially listed for the 	purpose.  	Neither fuses nor breakers "limit" the current per se.  A dead 	short on a circuit can cause hundreds or sometimes even 	thousands of amperes to flow for a short period of time, which 	can often cause severe damage.  Subject: Breakers?  Can't I use fuses?  	Statistics show that fuse panels have a significantly higher 	risk of causing a fire than breaker panels.  This is usually 	due to the fuse being loosely screwed in, or the contacts 	corroding and heating up over time, or the wrong size fuse 	being installed, or the proverbial "replace the fuse with a 	penny" trick.  	Since breakers are more permanently installed, and have better 	connection mechanisms, the risk of fire is considerably less.  	Fuses are prone to explode under extremely high overload.  When 	a fuse explodes, the metallic vapor cloud becomes a conducting 	path.  Result? from complete meltdown of the electrical panel, 	melted service wiring, through fires in the electrical 	distribution transformer and having your house burn down. 	Breakers don't do this.  	Many jurisdictions, particularly in Canada, no longer permit 	fuse panels in new installations.  The NEC does permit new 	fuse panels in some rare circumstances (requiring the special 	inserts to "key" the fuseholder to specific size fuses)  	Some devices, notably certain large air conditioners, require fuse 	protection in addition to the breaker at the panel.  The fuse 	is there to protect the motor windings from overload.  Check the 	labeling on the unit.  This is usually only on large permanently 	installed motors.  The installation instructions will tell you 	if you need one.  Subject: What size wire should I use?  	For a 20 amp circuit, use 12 gauge wire.  For a 15 amp circuit, 	you can use 14 gauge wire (in most locales).  For a long run, 	though, you should use the next larger size wire, to avoid 	voltage drops.  12 gauge is only slightly more expensive than 	14 gauge, though it's stiffer and harder to work with.  	Here's a quick table for normal situations.  Go up a size for 	more than 100 foot runs, when the cable is in conduit, or 	ganged with other wires in a place where they can't dissipate 	heat easily:  		Gauge		Amps 		14		15 		12		20 		10		30 		8		40 		6		65 	 	We don't list bigger sizes because it starts getting very dependent 	on the application and precise wire type.  Subject: Where do these numbers come from?  	There are two considerations, voltage drop and heat buildup. 	The smaller the wire is, the higher the resistance is.  When 	the resistance is higher, the wire heats up more, and there is 	more voltage drop in the wiring.  The former is why you need 	higher-temperature insulation and/or bigger wires for use in 	conduit; the latter is why you should use larger wire for long 	runs.  	Neither effect is very significant over very short distances. 	There are some very specific exceptions, where use of smaller 	wire is allowed.  The obvious one is the line cord on most 	lamps.  Don't try this unless you're certain that your use fits 	one of those exceptions; you can never go wrong by using larger 	wire.  Subject: What does "14-2" mean?  	This is used to describe the size and quantity of conductors 	in a cable.  The first number specifies the gauge.  The second 	the number of current carrying conductors in the wire - but 	remember there's usually an extra ground wire.  "14-2" means 	14 gauge, two insulated current carrying wires, plus bare ground.  	-2 wire usually has a black, white and bare ground wire.  Sometimes 	the white is red instead for 220V circuits without neutral.  In 	the latter case, the sheath is usually red too.  	-3 wire usually has a black, red, white and bare ground wire. 	Usually carrying 220V with neutral.  Subject: What is a "wirenut"/"marrette"/"marr connector"?  How are they 	used?  	A wire nut is a cone shaped threaded plastic thingummy that's used 	to connect wires together.  "Marrette" or "Marr connector" 	are trade names.  You'll usually use a lot of them in DIY wiring.  	In essence, you strip the end of the wires about an inch, twist them 	together, then twist the wirenut on.  	Though some wirenuts advertise that you don't need to twist the 	wire, do it anyways - it's more mechanically and electrically 	secure.  	There are many different sizes of wire nut.  You should check 	that the wire nut you're using is the correct size for the 	quantity and sizes of wire you're connecting together.  	Don't just gimble the wires together with a pair of pliers or 	your fingers.  Use a pair of blunt nose ("linesman") pliers, 	and carefully twist the wires tightly and neatly.  Sometimes 	it's a good idea to trim the resulting end to make sure it 	goes in the wirenut properly.  	Some people wrap the "open" end of the wirenut with electrical 	tape.  This is probably not a good idea - the inspector may 	tear it off during an inspection.  It's usually done because 	a bit of bare wire is exposed outside the wire nut - instead 	of taping it, the connection should be redone.  Subject: What is a GFI/GFCI?  	A GFCI is a ``ground-fault circuit interrupter''.  It measures 	the current current flowing through the hot wire and the 	neutral wire.  If they differ by more than a few milliamps, the 	presumption is that current is leaking to ground via some other 	path.  This may be because of a short circuit to the chassis of 	an appliance, or to the ground lead, or through a person.  Any 	of these situations is hazardous, so the GFCI trips, breaking 	the circuit.  	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.  All of the current that passed from the hot 	lead into you would return via the neutral lead, keeping the 	GFCI happy.  	The two pairs of connections on a GFCI outlet are not symmetric. 	One is labeled LOAD; the other, LINE.  The incoming power feed 	*must* be connected to the LINE side, or the outlet will not be 	protected.  The LOAD side can be used to protect all devices 	downstream from it.  Thus, a whole string of outlets can be 	covered by a single GFCI outlet.  Subject: Where should GFCIs be used?  	The NEC mandates GFCIs for 110V, 15A or 20A single phase 	outlets, in bathrooms, kitchens within 6' of the sink, garages, 	unfinished basements or crawl spaces, outdoors, near a pool, or 	just about anywhere else where you're likely to encounter water 	or dampness.  There are exceptions for inaccessible outlets, 	those dedicated to appliances ``occupying fixed space'', 	typically refrigerators and freezers, and for sump pumps and 	laundry appliances.  	The CEC does not mandate as many GFCIs.  In particular, there 	is no requirement to protect kitchen outlets, or most garage or 	basement outlets.  Basement outlets must be protected if you 	have a dirt floor, garage outlets if they're near the door to 	outside.  Bathrooms and most exterior outlets must have GFCIs.  	Even if you are not required to have GFCI protection, you may 	want to consider installing it anyway.  Unless you need a GFCI 	breaker (see below), the cost is low.  In the U.S., GFCI 	outlets can cost as little as US$8.  (Costs are a bit higher in 	Canada:  C$12.)  Evaluate your own risk factors.  Does your 	finished basement ever get wet?  Do you have small children? 	Do you use your garage outlets to power outdoor tools?  Does 	water or melted snow ever puddle inside your garage?  Subject: Where shouldn't I use a GFCI?  	GFCIs are generally not used on circuits that (a) don't pose a 	safety risk, and (b) are used to power equipment that must run 	unattended for long periods of time.  Refrigerators, freezers, 	and sump pumps are good examples.  The rationale is that GFCIs 	are sometimes prone to nuisance trips.  Some people claim that 	the inductive delay in motor windings can cause a momentary 	current imbalance, tripping the GFCI.  Note, though, that most 	GFCI trips are real; if you're getting a lot of trips for no 	apparent reason, you'd be well-advised to check your wiring 	before deciding that the GFCI is broken or useless.  Subject: What is the difference between a GFCI outlet and a GFCI breaker?  	For most situations, you can use either a GFCI outlet as the 	first device on the circuit, or you can install a breaker with 	a built-in GFCI.  The former is generally preferred, since GFCI 	breakers are quite expensive.  For example, an ordinary GE 	breaker costs ~US$5; the GFCI model costs ~US$35.  There is one 	major exception:  if you need to protect a ``multi-wire branch 	circuit'' (two or more circuits sharing a common neutral wire), 	such as a Canadian-style kitchen circuit, you'll need a 	multi-pole GFCI breaker.  Unfortunately, these are expensive; 	the cost can range into the hundreds of dollars, depending on 	what brand of panel box you have.  But if you must protect such 	a circuit (say, for a pool heater), you have no choice.  	One more caveat -- GFCI outlets are bulky.  You may want to use 	an oversize box when installing them.  On second thought, use 	large (actually deep) boxes everywhere.  You'll thank yourself for it.  	Incidentally, if you're installing a GFCI to ensure that one 	specific outlet is protected (such as a bathroom), you don't 	really have to go to all of the trouble to find the first 	outlet in the circuit, you could simply find the first outlet 	in the bathroom, and not GFCI anything upstream of it.  But 	protecting the whole circuit is preferred.  	When you install a GFCI, it's a good idea to use the little 	"ground fault protected" stickers that come with it and mark 	the outlets downstream of the GFCI.  You can figure out which 	outlets are "downstream", simply by tripping the GFCI with the 	test button and see which outlets are dead.  Subject: What's the purpose of the ground prong on an outlet, then?  	Apart from their use in electronics, which we won't comment on, 	and for certain fluorescent lights (they won't turn on without 	a good ground connection), they're intended to guard against 	insulation failures within the device.  Generally, the case of 	the appliance is connected to the ground lead.  If there's an 	insulation failure that shorts the hot lead to the case, the 	ground lead conducts the electricity away safely (and possibly 	trips the circuit breaker in the process).  If the case is not 	grounded and such a short occurs, the case is live -- and if 	you touch it while you're grounded, you'll get zapped.  Of 	course, if the circuit is GFCI-protected, it will be a very 	tiny zap -- which is why you can use GFCIs to replace 	ungrounded outlets (both NEC and CEC).  	There are some appliances that should *never* be grounded.  In 	particular, that applies to toasters and anything else with 	exposed conductors.  Consider:  if you touch the heating 	electrode in a toaster, and you're not grounded, nothing will 	happen.  If you're slightly grounded, you'll get a small shock; 	the resistance will be too high.  But if the case were 	grounded, and you were holding it, you'd be the perfect path to 	ground...  Subject: Why is one prong wider than the other?  Polarization  	Nowadays, many two-prong devices have one prong wider than the 	other.  This is so that the device could rely (not guaranteed!) 	on one specific wire being neutral, and the other hot. 	This is particularly advantageous in light fixtures, where the 	the shell should neutral (safety), or other devices which want to 	have an approximate ground reference (ie: some radios).  	Most 2-prong extension cords have wide prongs too.  	This requires that you wire your outlets and plugs the right 	way around.  You want the wide prong to be neutral, and the 	narrow one hot.  Most outlets have a darker metal for the 	hot screw, and lighter coloured screw for the neutral. 	If not, you can usually figure out which is which by which 	prong the terminating screw connects to.  Subject: What kind of outlets do I need in a kitchen?  	The NEC requires at least two 20 amp ``small appliance 	circuits'' for kitchens.  The CEC requires split-duplex 	receptacles.  Outlets must be installed such that no point is more 	than 24" (NEC) (900 mm CEC) from an outlet.  Every counter wider 	than 12" (NEC) or 300 mm (CEC) must have at least one outlet. 	The circuit these outlets are on may not feed any outlets except 	in the kitchen, pantry, or dining room.  Furthermore, these circuits 	are in addition to any required for refrigerators, stoves, microwaves, 	lighting, etc.  Non-dedicated outlets within 6' of a sink *must* be 	protected by a GFCI (NEC only).  	Split duplex receptacles are fed with a 220V circuit.  The tab 	is broken on the hot side of the outlet, and one hot goes to 	the upper outlet, and the other hot goes to the lower outlet. 	The neutral connects to both outlets through one screw.  When 	"carrying through" to another outlet, the neutral must be 	pigtailed, such that removing the outlet, or having the neutral 	connection fall off doesn't cause the neutral to disconnect 	from downstream outlets.  Subject: Where must outlets and switches be in bathrooms?  	There must be at least one outlet in each bathroom, adjacent to 	the sink, in addition to any outlet that may be incorporated in 	the light fixture.  All such outlets *must* be GFCI-protected.  Subject: What is Romex/NM/NMD?  What is BX?  When should I use each?  	Romex is a brand name for a type of plastic insulated wire. 	Sometimes called non-metallic sheath.  The formal name is NM. 	This is suitable for use in dry, protected areas (ie: inside 	stud walls, on the sides of joists etc.), that are not subject 	to mechanical damage or excessive heat.  Most newer homes are 	wired almost exclusively with NM wire.  There are several 	different categories of NM cable.  	BX cable -- technically known as armored cable or "AC" has a 	flexible aluminum or steel sheath over the conductors and is 	fairly resistant to damage.  	TECK cable is AC with an additional external thermoplastic 	sheath. 	 	Protection for cable in concealed locations: where NM or AC cable 	is run through studs, joists or similar wooden members, the outer 	surface of the cable must be kept at least 32mm/1.25" (CEC & NEC) 	from the edges of the wooden members, or the cable should be protected 	from mechanical injury.  This latter protection can take the form of 	metal plates (such as spare outlet box ends) or conduit.  	[Note: inspector-permitted practise in Canada suggests that armored 	cable, or flexible conduit can be used as the mechanical protection, 	but this is technically illegal.]  	Additional protection recommendations (these are rules in the 	Canadian codes - they are reasonable answers to the vague 	references to "exposed to mechanical damage" in both the NEC 	and CEC):  	    - NM cable should be protected against mechanical damage 	      where it passes through floors or on the surface of walls 	      in exposed locations under 5 feet from the floor. 	      Ie: use AC instead, flexible conduit, wooden guards etc. 	    - Where cable is suspended, as in, connections to furnaces 	      or water heaters, the wire should be protected.  Canadian 	      practise is usually to install a junction or outlet 	      box on the wall, and use a short length of AC cable 	      or NM cable in flexible conduit to "jump" to the appliance. 	      Stapling NM to a piece of lumber is also sometimes used. 	    - Where NM cable is run in close proximity to heating 	      ducts or pipe, heat transfer should be minimized by 	      means of a 25mm/1" air space, or suitable insulation 	      material (a wad of fiberglass). 	    - NM cable shall be supported within 300mm/1' of every box 	      or fitting, and at intervals of no more than 1.5m/5'. 	      Holes in joists or studs are considered "supports". 	      Some slack in the cable should be provided adjacent to 	      each box.  [while fishing cable is technically in violation, 	      it is permitted where "proper" support is impractical] 	    - 2 conductor NM cable should never be stapled on edge. 	      [Knight also insists on only one cable per staple, referring 	      to the "workmanship" clause, but this seems more honoured 	      in the breach...] 	    - cable should never be buried in plaster, cement or 	      similar finish. 	    - cable should be protected where it runs behind baseboards. 	    - Cable may not be run on the upper edge of ceiling joists 	      or the lower edges of rafters where the headroom is more 	      than 1m (39").  	Whenever BX cable is terminated at a box with a clamp, small 	plastic bushings must be inserted in the end of the cable to 	prevent the clamps forcing the sharp ends of the armor through 	the insulation.  	BX is sometimes a good idea in a work shop unless covered by 	solid wall coverings.  	In places where damage is more likely (like on the back wall of 	a garage ;-), you may be required to use conduit, a 	UL- (or CSA-) approved metal pipe.  You use various types of 	fittings to join the pipe or provide entrance/exit for the 	wire.  	Service entrances frequently use a plastic conduit.  	In damp places (eg: buried wiring to outdoor lighting) you will 	need special wire (eg: CEC NMW90, NEC UF).  NMW90 looks like 	very heavy-duty NMD90.  You will usually need short lengths of 	conduit where the wire enters/exits the ground.  [See underground 	wiring section.]   	Thermoplastic sheath wire (such as NM, NMW etc.) should not be  	exposed to direct sunlight unless explicitly approved for that  	purpose.  	Many electrical codes do not permit the routing of wire through 	furnace ducts, including cold air return plenums constructed 	by metal sheeting enclosing joist spaces.   The reason for this 	is that if there's a fire, the ducting will spread toxic gasses 	from burning insulation very rapidly through the building. 	Teflon insulated wire is permitted in plenums in many areas. 	  	Canada appears to use similar wire designations to the US,  	except that Canadian wire designations usually include the  	temperature rating in Celsius.  Eg: "AC90" versus "AC". 	In the US, NM-B is 90 degrees celcius.  	NOTE: local codes vary.  This is one of the items that changes 	most often.  Eg: Chicago codes require conduit *everywhere*. 	There are very different requirements for mobile homes. 	Check your local codes, *especially* if you're doing anything 	that's the slightest out of the ordinary.  	Wire selection table (incomplete - the real tables are enormous, 	uncommon wire types or applications omitted)  	Condition			Type	CEC	NEC  	Exposed/Concealed dry		plastic	NMD90	NM 					armor	AC90	AC 						TECK90  	Exposed/Concealed damp		plastic	NMD90	NMC 					armor	ACWU90 						TECK90  	Exposed/Concealed wet		plastic	NMWU90 					armor	ACWU90 						TECK90 	 	Exposed to weather		plastic	NMWU 						TW etc. 					armor	TECK90 	 	Direct earth burial/		plastic	NMWU*	UF 	Service entrance			RWU 						TWU 					armor	RA90 						TECK90 						ACWU90 	[* NMWU not for service entrance]  Subject: Should I use plastic or metal boxes?  	The NEC permits use of plastic boxes with non-metallic cable 	only.  The reasoning is simple -- with armored cable, the box 	itself provides ground conductor continuity.  U.S. plastic 	boxes don't use metal cable clamps.  	The CEC is slightly different.  The CEC never permits cable 	armor as a grounding conductor.  However, you must still 	provide ground continuity for metallic sheath.  The CEC also 	requires grounding of any metal cable clamps on plastic boxes.  	The advantage of plastic boxes is comparatively minor even for 	non-metallic sheathed cable -- you can avoid making one ground 	connection and they sometimes cost a little less.  On the other 	hand, plastic boxes are more vulnerable to impacts.  For 	exposed or shop wiring, metal boxes are probably better.  Subject: Junction box positioning?  	A junction box is a box used only for connecting wires together.  	Junction boxes must be located in such a way that they're accessible 	later.  Ie: not buried under plaster.  Excessive use of junction 	boxes is often a sign of sloppy installation, and inspectors may 	get nasty.  Subject: Can I install a replacement light fixture?  	In general, one can replace fixtures freely, subject to a few 	caveats.  First, of course, one should check the amperage 	rating of the circuit.  If your heart is set on installing half 	a dozen 500 watt floodlights, you may need to run a new wire 	back to the panel box.  But there are some more subtle 	constraints as well.  For example, older house 	wiring doesn't have high-temperature insulation.  The excess 	heat generated by a ceiling-mounted lamp can and will cause the 	insulation to deteriorate and crack, with obvious bad results. 	Some newer fixtures are specifically marked for high 	temperature wire only.  (You may find, in fact, that your 	ceiling wiring already has this problem, in which case 	replacing any devices is a real adventure.)  	Other concerns include providing a suitable ground for some 	fluorescent fixtures, and making sure that the ceiling box and 	its mounting are strong enough to support the weight of a heavy 	chandelier or ceiling fan.  You may need to install a new box 	specifically listed for this purpose.  A 2x4 across the ceiling 	joists makes a good support.  Metal brackets are also available 	that can be fished into ceilings thru the junction box hole and 	mounted between the joists.  	There are special rules for recessed light fixtures such as 	"pot" lamps or heat lamps.  When these are installed in insulated 	ceilings, they can present a very substantial fire hazard. 	The CEC provides for the installation of pot lamps in insulated 	ceilings, provided that the fixture is boxed in a "coffin" (usually 	8'x16"x12" - made by making a pair of joists 12" high, and covering 	with plywood) that doesn't have any insulation.  (Yes, that's 8 *feet* 	long)  	NEC rules are somewhat less stringent.  They require at least 3" 	clearance between the fixture and any sort of thermal insulation. 	The rules also say that one should not obstruct free air movement, 	which means that a CEC-style ``coffin'' might be worthwhile. 	Presumably, that's up to the local inspector.  [The CEC doesn't 	actually mandate the coffin per-se, this seems to be an inspector 	requirement to make absolutely certain that the fixture can't get 	accidentally buried in insulation.  Ie: if you have insulation blown 	in later.]  	There are now fixtures that contain integral thermal cutouts and 	fairly large cases that can be buried directly in insulation.  They are 	usually limited to 75 watt bulbs, and are unfortunately, somewhat 	more expensive than the older types.  Before you use them, you should 	ensure that they have explicit UL or CSA approval for such uses. 	Follow the installation instructions carefully; the prescribed location 	for the sensor can vary.  	There does not yet appear to be a heat lamp fixture that is approved 	for use in insulation.  The "coffin" appears the only legal approach.  Subject: What does it mean when the lights brighten when a motor starts?  	This usually means that the neutral wire in the panel is 	loose.  Depending on the load balance, one hot wire may end up 	being more than 110V, and the other less than 110V, with 	respect to ground.  This is a very hazardous situation - it can 	destroy your electronic equipment, possibly start fires, and in 	some situations electrocute you (ie: some US jurisdictions 	require the stove frame connected to neutral).  	If this happens, contact your electrical authority immediately 	and have them come and check out the problem.  	Note: a brief (< 1 second) brightening is sometimes normal with 	lighting and motors on the same 220V with neutral circuit.  A 	loose main panel neutral will usually show increased brightness 	far longer than one second.  In case of doubt, get help.  Subject: What is 3 phase power?  Should I use it?  Can I get it in my house?  	Three phase power has three "hot" wires, 120 degrees out of 	phase with each other.  These are usually used for large motors 	because it is more "efficient", provides a bit more starting torque, 	and because the motors are simpler and hence cheaper.  	You're most likely to encounter a 3 phase circuit that shows 	110 volts between any hot and ground, and 208 volts between 	any two hots.  The latter shows the difference between a normal 	220V/110V common neutral circuit, which is 240 volts between the 	two hots.  There are 3 phase circuits with different voltages.  	Bringing in a 3 phase feed to your house is usually 	ridiculously expensive, or impossible.  If the equipment you 	want to run has a standard motor mount, it is *MUCH* cheaper to 	buy a new 110V or 220V motor for it.  In some cases it is 	possible to run 3 phase equipment on ordinary power if you have 	a "capacitor start" unit, or use a larger motor as a 	(auto-)generator.  These are tricky, but are a good solution if 	the motor is non-standard size, or too expensive or too big to 	replace.  The Taunton Press book ``The Small Shop'' has an 	article on how to do this if you must.  	Note that you lose any possible electrical efficiency by using 	such a converter.  The laws of thermodynamics guarantee that.  Subject: Is it better to run motors at 110 or 220?  	Theoretically, it doesn't make any difference.  However, there 	is a difference is the amount of power lost in the supply 	wiring.  All things being equal, a 220V motor will lose 4 times 	less power in the house wiring than a 110V motor.  This also 	means that the startup surge loss will be less, and the motor 	will get to speed quicker.  And in some circumstances, the 	smaller power loss will lead to longer motor life.  	This is usually irrelevant unless the supply wires are more 	than 50 feet long.  Subject: What is this nonsense about 3HP on 110V 15A circuits?  	It is a universal physical law that 1 HP is equal to 746 	watts.  Given heating loss, power factor and other inefficiencies, 	it is usually best to consider 1 HP is going to need 1000-1200 	watts.  A 110V 15A circuit can only deliver 1850 watts to a motor, 	so it cannot possibly be more than approximately 2 HP.  Given rational 	efficiency factors, 1.5HP is more like it.  	Some equipment manufacturers (Sears in particular, most router 	manufacturers in general ;-) advertise a HP rating that is far 	in excess of what is possible.  They are giving you a "stall 	horsepower" or similar.  That means the power is measured when 	the motor is just about to stop turning because of the load. 	What they don't mention is that if you kept it in that 	condition for more than a few seconds hopefully your breaker 	will trip, otherwise the motor will melt -- it's drawing far 	more current than it can continuously.  	When comparing motors, compare the continuous horsepower.  This 	should be on the motor nameplate.  If you can't find that figure, 	check the amperage rating, which is always present.  Subject: How do I convert two prong receptacles to three prong?  	Older homes frequently have two-prong receptacles instead 	of the more modern three.  These receptacles have no safety 	ground, and the cabling usually has no ground wire.  Neither 	the NEC or CEC permits installing new 2 prong receptacles anymore.  	There are several different approaches to solving this: 	    1) If the wiring is done through conduit or BX, and the 	       conduit is continuous back to the panel, you can connect 	       the third prong of a new receptacle to the receptacle 	       box.  NEC mainly - CEC frowns on this practise. 	    2) If there is a copper cold water pipe going nearby, and 	       it's continuous to the main house ground point, you can 	       run a conductor to it from the third prong. 	    3) Run a ground conductor back to the main panel. 	    4) Easiest: install a GFCI receptacle.  The ground lug 	       should not be connected to anything, but the GFCI 	       protection itself will serve instead.  The GFCI 	       will also protect downstream (possibly also two prong 	       outlets).  If you do this to protect downstream outlets, 	       the grounds must not be connected together.  Since it 	       wouldn't be connected to a real ground, a wiring fault 	       could energize the cases of 3 prong devices connected 	       to other outlets.  Be sure, though, that there aren't 	       indirect ground plug connections, such as via the sheath 	       on BX cable.  	The CEC permits you to replace a two prong receptacle with a three 	prong if you fill the U ground with a non-conducting goop. 	Like caulking compound.  This is not permitted in the NEC.  Subject: Are you sure about GFCIs and ungrounded outlets? 	Should the test button work?  	We're sure about what the NEC and CEC say.  Remember, though, 	that your local codes may vary.  As for the TEST button -- there's 	a resistor connecting the LOAD side of the hot wire to the LINE 	side of the neutral wire when you press the TEST button.  Current 	through this resistor shows up as an imbalance, and trips the GFCI. 	This is a simple, passive, and reliable test, and doesn't require 	a real ground to work.  If your GFCI does not trip when you press 	the TEST button, it is very probably defective or miswired.  Again: 	if the test button doesn't work, something's broken, and potentially 	dangerous.  The problem should be corrected immediately.  	The instructions that come with some GFCIs specify that the ground 	wire must be connected.  We do not know why they say this.  The 	causes may be as mundane as an old instruction sheet, or with the 	formalities of UL or CSA listing -- perhaps the device was never 	tested without the ground wire being connected.  On the other hand, 	UL or CSA approval should only have been granted if the device 	behaves properly in *all* listed applications, including ungrounded 	outlet replacement.  (One of us called Leviton; their GFCIs are 	labeled for installation on grounded circuits only.  The technician 	was surprised to see that; he agreed that the NEC does not require 	it, and promised to investigate.)  Subject: How should I wire my shop?  	As with any other kind of wiring, you need enough power for all 	devices that will be on simultaneously.  The code specifies 	that you should stay under 80% of the nominal capacity of the 	circuit.  For typical home shop use, this means one circuit for 	the major power tools, and possibly one for a dust collector or 	shop vac.  Use at least 12 gauge wire -- many power tools have 	big motors, with a big start-up surge.  If you can, use 20 amp 	breakers (NEC), though CEC requires standard 20A receptacles 	which means you'd have to "replug" all your equipment.  Lights 	should either be on a circuit of their own -- and not shared 	with circuits in the rest of the house -- or be on at least two 	separate circuits.  The idea is that you want to avoid a 	situation where a blade is still spinning at several thousand 	RPM, while you're groping in the dark for the OFF switch.  	Do install lots of outlets.  It's easier to install them in the 	beginning, when you don't have to cut into an existing cable. 	It's useful if at least two circuits are accessible at each 	point, so you can run a shop vac or a compressor at the same 	time as the tool you really want.  But use metal boxes and 	plates, and maybe even metal-sheathed cable; you may have 	objects flying around at high speeds if something goes a bit 	wrong.  	Note that some jurisdictions have a "no horizontal wiring" 	rule in workshops or other unfinished areas that are used 	for working.  What this means is that all wiring must be 	run along structural members.  Ie: stapled to studs.  	Other possible shop circuits include heater circuits, 220V 	circuits for some large tools, and air compressor circuits. 	Don't overload circuits, and don't use extension cords if you 	can help it, unless they're rated for high currents.  (A coiled 	extension cord is not as safe as a straight length of wire of 	the same gauge.  Also, the insulation won't withstand as much 	heat, and heat dissipation is the critical issue.)  	If your shop is located at some remove from your main panel, 	you should probably install a subpanel, and derive your shop 	wiring from it.  If you have young children, you may want to 	equip this panel with a cut-off switch, and possibly a lock. 	If you want to install individual switches to ``safe'' 	particular circuits, make sure you get ones rated high enough. 	For example, ordinary light switches are not safely able to 	handle the start-up surge generated by a table saw.  Buy 	``horsepower-rated'' switches instead.  	Finally, note that most home shops are in garages or unfinished 	basements; hence the NEC requirements for GFCIs apply.  And 	even if you ``know'' that you'd never use one of your shop 	outlets to run a lawn mower, the next owner of your house might 	have a different idea.  	Note: Fine Woodworking magazine often carries articles on shop 	wiring.  April 1992 is one place to start.  Subject: Underground Wiring  	You will need to prepare a trench to specifications, use 	special wire, protect the wire with conduit or special plastic 	tubing and possibly lumber (don't use creosoted lumber, it rots 	thermoplastic insulation and acts as a catalyst in the corrosion 	of lead).  The transition from in-house to underground wire is 	generally via conduit.  All outdoor boxes must be specifically 	listed for the purpose, and contain the appropriate gaskets, 	fittings, etc.  If the location of the box is subject to immersion 	in water, a more serious style of water-proof box is needed.  And 	of course, don't forget the GFCIs.  	The required depths and other details vary from jurisdiction to 	jurisdiction, so we suggest you consult your inspector about 	your specific situation.  	A hint: buy a roll of bright yellow tape that says "buried power 	line" and bury it a few inches above where the wire has been placed.  Subject: Aluminum wiring  	During the 1970's, aluminum (instead of copper) wiring became 	quite popular and was extensively used.  Since that time, 	aluminum wiring has been implicated in a number of house fires, 	and most jurisdictions no longer permit it in new installations. 	We recommend, even if you're allowed to, that do not use it for new 	wiring.  	But don't panic if your house has aluminum wiring.  Aluminum 	wiring, when properly installed, can be just as safe as copper. 	Aluminum wiring is, however, very unforgiving of improper 	installation.  We will cover a bit of the theory behind potential 	problems, and what you can do to make your wiring safe.  	The main problem with aluminum wiring is a phenomenon known as 	"cold creep".  When aluminum wiring warms up, it expands.  When 	it cools down, it contracts.  Unlike copper, when aluminum goes 	through a number of warm/cool cycles it loses a bit of tightness each 	time.  To make the problem worse, aluminum oxidises, or corrodes 	when in contact with certain types of metal, so the resistance 	of the connection goes up.  Which causes it to heat up and corrode/ 	oxidize still more.  Eventually the wire may start getting very hot, 	melt the insulation or fixture it's attached to, and possibly even 	cause a fire.  	Since people usually encounter aluminum wiring when they move 	into a house built during the 70's, we will cover basic points of 	safe aluminum wiring.  We suggest that, if you're considering purchasing 	a home with aluminum wiring, or have discovered it later, that you 	hire a licensed electrician or inspector to check over the wiring 	for the following things:  	    1) Fixtures (eg: outlets and switches) directly attached to 	       aluminum wiring should be rated for it.  The device will 	       be stamped with "Al/Cu" or "CO/ALR".  The latter supersedes 	       the former, but both are safe.   These fixtures are somewhat 	       more expensive than the ordinary ones.  	    2) Wires should be properly connected (at least 3/4 way around 	       the screw in a clockwise direction).  Connections should be 	       tight.  While repeated tightening of the screws can make the 	       problem worse, during the inspection it would pay off to snug 	       up each connection.  	       Note that aluminum wiring is still often used for the 	       main service entrance cable.  It should be inspected.  	    3) "push-in" terminals are an extreme hazard with aluminum wire. 	       Any connections using push-in terminals should be redone with 	       the proper screw connections immediately.  	    4) There should be no signs of overheating: darkened connections, 	       melted insulation, or "baked" fixtures.  Any such damage should 	       be repaired. 	     	    5) Connections between aluminum and copper wire need to be 	       handled specially.  Current Canadian codes require that the 	       wire nut used must be specially marked for connecting 	       aluminum to copper.  The NEC requires that the wire be 	       connected together using special crimp devices, with an 	       anti-oxidant grease.  The tools and materials for the latter 	       are quite expensive - not practical to do it yourself unless 	       you can rent the tool.  	    6) Any non-rated receptacle can be connected to aluminum wiring 	       by means of a short copper "pigtail".  See (5) above. 	     	    7) Shows reasonable workmanship: neat wiring, properly stripped 	       (not nicked) wire etc.      	If, when considering purchasing a home, an inspection of the wiring 	shows no problems or only one or two, we believe that you can consider 	the wiring safe.  If there are signs of problems in many places, 	we suggest you look elsewhere.  If the wrong receptacles are used, 	you can replace them with the proper type, or use pigtails - having 	this professionally done can range from $3 to $10 per receptacle/switch. 	You can do this yourself too.  Subject: I'm buying a house!  What should I do?  	Congratulations.  But...  It's generally a good idea to hire 	an inspector to look through the house for hidden gotchas. 	Not just for wiring, but plumbing and structural as well.  If an 	inspection of the wiring shows no problems or only one or two minor 	ones, we believe that you can consider the wiring safe (after any 	minor problems are fixed).  If there are signs of problems in many 	places, we suggest you look elsewhere.  	Here's some hints on what to look for:  	Obvious non-code wiring can include:  		- Zip cord wiring, either concealed or nailed to walls 		- Hot wiring on the identified (neutral) conductor without 		  proper marking. 		- Ungrounded grounding outlets (except when downstream of 		  a GFCI) 		- Splices hanging in mid-air (other than proper knob-and-tube) 		- Switched neutrals 		- Unsecured Romex swinging about like grapevines  	Certain wiring practises that are actually to code (or were at one 	time) sometimes reveal DIY wiring that may have hidden violations:  		- Switches that seem to control nothing (abandoned, perhaps 		   not properly terminated wiring) 		- A wall switch that shuts off a group of lights that are 		  separately controlled by other wall switches.  (except when 		  it's *really* convenient ;-) 		- Switches and outlets in bizarre locations 		- Great numbers of junction boxes without outlets or lamps 		- Junction boxes with great numbers of wires going into them 		- Wiring that passes through a closet instead of a wall or 		  ceiling 		- Backwrapped grounding wires  Subject: What is this weird stuff?  Old style wiring 	 	In the years since Edison "invented" electricity, several different 	wiring "styles" have come and gone.  When you buy an older home you 	may encounter some of this stuff.  This section describes the old  	methods, and some of their idiosyncrasies.  	The oldest wiring system you're likely to encounter is called 	"knob and tube" (K&T).  It is made up of individual conductors with 	a cloth insulation.  The wires are run along side structural 	members (eg: joists or studs) using ceramic stand-offs (knobs). 	Wire is run through structural members using ceramic tubes.  Connections 	were made by twisting the wire together, soldering, and wrapping 	with tape.  Since the hot and neutral were run separately, 	the wiring tends to be rather confusing.  A neutral often runs 	down the centre of each room, with "taps" off to each fixture. 	The hot wire tended to run from one fixture to the next.  In some 	cases K&T isn't colour-coded, so the neutral is often the same 	colour as the hot wires.  	You'll see K&T in homes built as late as the 40's.  	Comments on K&T:  		- the people installing K&T were pretty paranoid about 		  electricity, so the workmanship tends to be pretty good. 		- The wire, insulation and insulators tend to stand up 		  very well.  Most K&T I've seen, for example, is in 		  quite good condition. 		- No grounding.  Grounding is usually difficult to install. 		- boxes are small.  Receptacle replacement (particularly with 		  GFCI) can be difficult.  No bushing on boxes either, 		  so wiring changes need special attention to box entry. 		- Sometimes the neutral isn't balanced very well between 		  separately hot circuits, so it is sometimes possible to 		  overload the neutral without exceeding the fusing on 		  any circuit. 		- Building code does not permit insulation in walls 		  that contain K&T. 		- Connection to existing K&T from new circuits can be 		  tricky.  Consult your inspector. 		- Modern wiring practise requires considerably more 		  outlets to be installed than K&T systems did. 	 	Since K&T tends to be in pretty decent condition it generally isn't 	necessary to replace it simply because it's K&T.  What you should 	watch out for is renovations that have interfered with it and 	be cautious about circuit loading.  In many cases it's perfectly 	reasonable to leave existing K&T alone, and add new fixtures on 	new circuits using modern techniques. 	 	After K&T, they invented multi-conductor cable.  The first type 	you will see is roughly a cloth and varnish insulation.  It looks 	much like the romex cable of the last decade or two.  This stuff was 	used in the 40's and 50's.  Again, no grounding conductor. 	It was installed much like modern wiring.  Its major drawback 	is that this type of insulation embrittles.  We've seen whole 	systems where the insulation would fracture and fall off at 	a touch.  BX cable of the same vintage has similar problems.  	This stuff is very fragile, and becomes rather hazardous if 	the wires become bare.  This wiring should be left untouched as 	much as possible - whenever an opportunity arises, replace it. 	A simple receptacle or switch replacement can turn into a several 	hour long frustrating fight with electrical tape or heat-shrink 	tubing.  	After this wiring technique, the more modern romex was invented. 	It's almost a asphalt impregnated cloth.  Often a bit sticky. 	This stuff stands up reasonably well and doesn't present a hazard 	and is reasonably easy to work with.  It does not need to be 	replaced - it should be considered as safe as the "modern" stuff - 	thermoplastic insulation wire.  Just don't abuse it too much.  Subject: Where do I buy stuff?  	Try to find a proper electrical supply outlet near you.  Their 	prices will often be considerably better than chain hardware stores or 	DIY centres, have better quality materials, have wider variety 	including the "odd" stuff, and have people behind the counter that 	know what you're talking about.  Cultivate friendly knowledgeable 	sales people.  They'll give you much valuable information.