HAM Toolkit/HAM Toolkit.iso/text/arrl/faqelec1.txt

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From: [e-mail] (Chris Lewis)
Newsgroups: misc.consumers.house,rec.woodworking,sci.electronics,news.answers,misc.answers,rec.answers,sci.answers
Subject: Electrical Wiring FAQ [Part 1/2]
Summary: A series of questions and answers about house wiring
Message-ID: <[e-mail]>
Date: 13 Jan 94 06:40:26 GMT
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Archive-name: electrical-wiring/part1
Last-modified: Thu Dec  2 02:20:51 EST 1993

        Frequently Asked Questions on Electrical Wiring

                        Copyright 1991, 1992, 1993
        Steven Bellovin ([e-mail])
        Chris Lewis ([e-mail])

        Redistribution for profit, or in altered content/format
        prohibited without permission of the authors.

        Comments to (automatic if you reply to this article):
            [e-mail]

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
[e-mail] 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.  "g^|" will get you to the changed sections quickly
in most newsreaders.

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
    How do I convert two prong receptacles to three prong?
    Surges, spikes, zaps, grounding and your electronics
    Are you sure about GFCIs and ungrounded outlets?
        Should the test button work?
    What kind of outlets do I need in a kitchen?
    Where must outlets and switches be in bathrooms?
    General outlet placement rules/line capacities
    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?
    Noisy fluorescent fixtures, what do I do?
    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 should I wire my shop?
    Underground wiring
    Doorbell/telephone/cable other service wiring hints
    Aluminum wiring
    I'm buying a house!  What should I do?
|    What is this weird stuff?  Old style wiring
    Where do I buy stuff?
    Copper wire characteristics table


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.

    Note: strictly speaking, there usually is a legal way around the
    lack of a CSA sticker.  In some cases (eg: Ontario), a local hydro
    inspection prior to purchase, or prior to use, is acceptable.
    The hydro inspector will affix a "hydro sticker" to the unit, which
    is as good as CSA approval.  But it costs money - last I knew,
    $75 per unit inspected.

    ULC (Underwriters Laboratory of Canada) is an independent organization
    that, amongst other things, undertakes the quarterly inspection of
    manufacturer's to ensure continued compliance of UL Listed/Recognized
    products to Agency reports and safety standards. This work is done under
    contract to UL Inc (Follow-up Services Division). They are not
    a branch or subsidiary of UL.




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 1993.

    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 or green with a yellow stripe 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.]

    Note: do not tape, colour or substitute other colour wires for the
    safety grounding conductor.

    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.
    [This author has seen it happen.]  Breakers won'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, wet-bar
    sinks, roof outlets, 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 NEC now requires that if your replace an outlet in a
    location now requiring GFCI, you must install GFCI protection.
    Note in particular - kitchen and bathroom outlets.

    When using the "fixed appliance" rule for avoiding GFCI outlets,
    single outlet receptacles must be used for single appliances,
    duplex receptacles may be used for two 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,
    as do pools systems and jacuzzi or whirlpool pumps.

    There are many rules about GFCIs with pools and so on.  This
    is outside of our expertise, so we're not covering it in
    detail.  See your inspector.

    When replacing an outlet, it must now be GFCI-protected if
    such would now be required for a new installation.  That is,
    a kitchen outlet installed per the 1984 code need not have
    been protected, but if that outlet is ever replaced, GFCI
    protection must now be added (under NEC).  This is explicit
    in the 1993 NEC, and inspector-imposed in Canada.

    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.

    Note that the labels are mandatory for GFCI-protected-but-ungrounded
    three prong outlets according to the NEC.

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: 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 practice.
        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.
           NEC: this can only be done if the point of attachment
           is within 5 feet of where the pipe enters the ground.
        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.

    The NEC requires that three prong receptacles without ground
    that are protected by GFCI must be labelled as such.

    See the next section about computers on GFCI-protected groundless
    outlets.

Subject: Surges, spikes, zaps, grounding and your electronics (NEW)

    Theoretically, the power coming into your house is a perfect
    AC sine wave.  It is usually quite close.  But occasionally,
    it won't be.  Lightning strikes and other events will affect
    the power.  These usually fall into two general categories: very
    high voltage spikes (often into 1000s of volts, but usually
    only a few microseconds in length) or surges (longer duration,
    but usually much lower voltage).

    Most of your electrical equipment, motors, transformer-operated
    electronics, lights, etc., won't even notice these one-shot events.
    However, certain types of solid-state electronics, particularly
    computers with switching power supplies and MOS semiconductors,
    can be damaged by these occurances.  For example, a spike can
    "punch a hole" through an insulating layer in a MOS device (such
    as that several hundred dollar 386 CPU), thereby destroying it.

    The traditional approach to protecting your electronics is to use
    "surge suppressors" or "line filters".  These are usually devices
    that you plug in between the outlet and your electronics.

    Roughly speaking, surge suppressors work by detecting overvoltages,
    and shorting them out.  Think of them as voltage limiters.  Line
    filters usually use frequency-dependent circuits (inductors, capacitors
    etc.) to "tune out" undesirable spikes - preventing them from reaching
    your electronics.

    So, you should consider using suppressors or filters on your sensitive
    equipment.

    These devices come in a very wide price range.  From a couple
    of dollars to several hundred.  We believe that you can protect
    your equipment from the vast majority of power problems by selecting
    devices in the $20-50 range.

    A word about grounding: most suppressors and EFI filters require real
    grounds.  Any that don't are next to useless.

    For example, most surge suppressors use MOVs (metal oxide varistors)
    to "clamp" overvoltages.  Yes, you can have a suppressor that only
    has a MOV between neutral and hot to combat differential-mode voltage
    excursions, but that isn't enough.  You need common-mode protection
    too.  Good suppressors should have 3 MOVs, one between each pair of wires.
    Which means you should have a good solid ground.  Eg: a solidly connected
    14ga wire back to the panel.  Not rusty BX armour or galvanized pipe
    with condensation turning the copper connection green.

    Without a ground, a surge or spike is free to "lift" your entire electronics
    system well away from ground.  Which is ideal for blowing out interface
    electronics for printer ports etc.

    Secondly, static electricity is one of the major enemies of electronics.
    Having good frame grounds is one way of protecting against static zaps.

    If you're in the situation of wanting to install computer equipment
    on two wire groundless circuits take note:

    Adding a GFCI outlet to the circuit makes the circuit safe for you.
    But it doesn't make it safe for your equipment - you need a ground to
    make surge suppressors or line filters effective.

Subject: Are you sure about GFCIs and ungrounded outlets?
    Should the test button work?

    The NEC, section 210-7(d), and CEC, section 26-700(9), are quite
    explicit that GFCIs are a legal substitute for a grounded outlet
    in an existing installation where there is no ground available in
    the outlet box.

    But 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.)

--
Look on the bright side - at least the PC's reached gender parity!
Chris Lewis; [e-mail]; Phone: Canada 613 832-0541
Ferret list: [e-mail]
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