HAM Toolkit/HAM Toolkit.iso/text/arrl/faqelec2.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 2/2]
Summary: A series of questions and answers about house wiring
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Date: 13 Jan 94 06:41:11 GMT
Expires: 10 Feb 94 06:39:58 GMT
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Archive-name: electrical-wiring/part2
Last-modified: Thu Dec  2 02:22:21 EST 1993

            Copyright 1991, 1992, 1993
              Chris Lewis and Steven Bellovin

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

Subject: What kind of outlets do I need in a kitchen?

    The NEC requires at least two 20 amp ``small appliance
    circuits'' for kitchen counters.  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.

    The NEC says that switches may not be installed inside bathtubs
    or showers.  The CEC says that switches may not be installed
    "within reach" of bathtubs or showers (consult an inspector
    if you can't make it at least four feet).

Subject: General outlet placement rules/line capacities (NEW)

    We paraphrase CEC 26-702 (NEC: 210-52 through 210-63)

    Note: In laying out receptacle outlets, consideration shall be given
    to the placement of electrical baseboards, hot air registers, hot
    water or steam registers, with a view of eliminating cords having to
    pass over hot or conductive surfaces wherever possible.

    NEC:  You're not allowed to put outlets over electric baseboards.
    That, coupled with the spacing requirements, more or less mandates
    the use of baseboards with integral outlets.  Note that such outlets
    are fed by a different branch circuit than the heating elements.

    2. Except as otherwise required, receptacles shall be installed
    in the finished walls of every room or area, other than kitchens,
    bathrooms, hallways, laundry rooms, utility rooms or closests, so
    that no point along the floor line of any usable wall space is more
    than 1.8m (6') horizontally from a receptacle in that or an
    adjoining space, such distance being measured along the floor line
    of the wall spaces involved.

    Fixed dividers, counters, etc., are considered wall space.  Floor
    outlets do not satisfy the requirement unless they are ``near'' the
    wall.  Insofar as practical, outlets should be spaced equidistantly.

    3. At least one duplex receptacle shall be provided in each enclosed
    area such as a balcony or porch that is not classified as a finished
    room or area.

    [NEC doesn't seem to have this rule.]

    4. The receptacles referred to in (2) and (3) shall be duplex
    receptacles or equivalent number of single receptacles.

    5. "Usable wall space" is defined as any wall space 900mm (3', NEC 2')
    or more in width, not to include doorways, areas occupied by a door
    when fully opened, windows which extend to the floor, fireplaces or
    other permanent installations that would limit the use of the wall
    space.

    6.  See kitchen counter requirements.  At least one duplex receptacle
    in eat-in dining area.

    [We don't think the latter part is in the NEC.  Also, the NEC says that
    the two 20-amp small appliance circuits can't go outside of the kitchen,
    dining room, pantry, etc., nor can they be used for anything else,
    except for things like clock outlets, stove accessory outlets, etc.]

    7. Receptacles shall not be mounted facing up in the work surfaces or
    counters of the kitchen or dining area.

    8. No point in a hallway within a dwelling unit shall be more than
    4.5m (15', NEC 10') from a duplex receptacle as measured by the shortest
    path which the supply cord of an appliance connected to the receptacle
    would follow without passing through an openning fitted with a door.
    (vacuum-cleaner rule).

    9. At least one duplex receptacle shall be provided: in laundry
    room, utility room and any unfinshed basement area

    [NEC: see GFCI requirements.  There must be a dedicated 20 amp laundry
    receptacle, with no other outlets, plus an additional unfinished
    basement receptacle.  Any attic or crawl space with heating or air
    conditioning equipment must have a receptacle. (this is probably
    in the CEC too.)]

    10, 11, 12, 13:  See bathroom requirements, GFCI, washing machine
    outlet placement.

    14, 15. Outlets shall not be placed in ironing cabinets, cupboards,
    wall cabinets, nor in similar enclosures except where they're
    for specific non-heating appliances (including microwave) in
    the enclosure.

    [NEC: No such requirement.  Are you sure Steven?]

    16, 17. For each single-family dwelling, at least one duplex receptacle
    shall be installed outdoors to be readily available from ground level
    (see GFCI requirements).  Appendix B (additional notes) suggests front
    and back outlets to be controlled by an interior switch.

    [NEC:  One in front, one in back.  No discussion of them being switched.]

    18. At least one duplex receptacle shall be provided for each car space
    in a garage or carport.

    [NEC:  For an attached garage, or detached garage with electric service --
    but there is no requirement that detached garages have power.  This remark
    is probably relevant to CEC as well.]

    19. For the purposes of this rule, all receptacles shall be of the
    grounding type, configuration 5-15R (standard 110V/15A 3 prong).

    20. Any receptacle that is part of a lighting fixture or appliance
    that is > 1.7m (5 feet) above the floor, or in cabinets or cupboards,
    is not counted in the above rules.

    21. Where a switched duplex outlet is used in lieu of a light outlet
    and fixture, the receptacle shall be considered one of the wall mounted
    receptacles required here.

    22. At least one duplex receptacle shall be provided for a central
    vacuum system if the ducting is installed.

    [NEC:  couldn't find an equivalent rule.]

    Capacities: Knight recommends no more than 10 outlets per circuit.
    Some US references talk about a limit of 12.  There appears to be a
    wattage/area/outlet count calculation somewhere in the NEC.  20A circuits
    may have different rules.

    It is open to considerable debate whether you should mix general lighting
    and outlets on individual circuits.  Knight recommends it.  Some netters
    don't.  I tend towards the former for load balancing reasons.

    NEC: There's a new rule on outdoor outlets.  If exposed to the weather,
    and if used for unattended equipment (pool filters, outdoor lighting,
    etc.), the outlet must still be weatherproof even when the device is
    plugged in.

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 practice 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.  The 1993 NEC has many changes that bring
    it close to these rules.  These are reasonable answers to the
    vague "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
          practice 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, except were required by code [Ie: cable
          burial with shallow bedrock.].
        - 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.

    Whenever BX cable is buried in thermal insulation, 90C
    wire should be selected, but derated in current carrying
    capacity to 60C.

    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.

    Metal receptacle covers must be grounded, even on plastic
    boxes.  This may be achieved by use of a switch with ground
    connection.

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: Noisy fluorescent fixtures, what do I do?

    Many fluorescent fixtures tend to buzz, objectionably so when used in
    residential (rather than warehouse or industrial) situations.  This
    tends to be the result of magnetic/physical resonances at the
    (low) frequencies that standard fixture ballasts operate.  You
    can eliminate this problem by switching to electronic ballasts,
    which operate at a higher (inaudible) frequency.  Unfortunately,
    these are quite expensive.

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 110V motor will lose 4 times
    more power in the house wiring than a 220V motor.  This also
    means that the startup surge loss will be less, and the motor
    will get to speed quicker with 220V.  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 your motor will melt - the
|    motor is drawing far more current than its continuous rating.

    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 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: Doorbell/telephone/cable other service wiring hints.

    Auxiliary services, such as cable, telephone, doorbell, furnace
    control circuits etc. are generally considered to be "class 2"
    wiring by both the CEC and NEC.

    What this generally means is:

        1) class 2 and house power should not share conduit or
           termination boxes.
        2) class 2 and house power should be 12" apart in walls
           except where necessary.
        3) cross-over should be at 90 degrees.

    While the above may not be strictly necessary to the code, it
    is advantageous anyways - paralleling house power beside telephone
    lines tends to induce hum into the telephone.  Or could interfere
    with fancier furnace control systems.

    With telephone wiring, twisted pair can alleviate these problems,
    and there are new cable types that combine multiple services into
    one sheath.  Consult your inspector if you really want to violate
    the above recommendations.

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 practices 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 controls things that you think it
          shouldn't, for instance mysteriously removing power
          from lights or outlets in other rooms.
        - 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 (ground wire wrapped around
          the incoming cable insulation outside the box).
        - A breaker or fuse for outside wiring that is near the bottom
          of the breaker panel or in an add-on fusebox.  The outdoor
          wiring may have been homeowner-installed after the house was
          built, and was not buried deep enough or was done with the
          wrong kind of wire.

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.
        - In DC days it was common to fuse both sides, and no
          harm was done.  In fact, it was probably a Good Thing.
          The practise apparently carried over to K&T where
          you may find fused neutrals.  This is a very bad
          thing.
        - Building code does not usually permit insulation in
|          walls or ceilings that contains K&T.  Some jurisdictions
|          will allow it under some circumstances.
        - Connection to existing K&T from new circuits can be
          tricky.  Consult your inspector.
        - Modern wiring practice 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.
    It is possible for the hot conductor to short out to the cable
    jacket.  Since the jacket is rusted, it no longer presents
    a low resistance return path for the current flow, but rather
    more acts like a resistance heater.  In extreme cases the
    cable jacket will become red hot without blowing the fuse or circuit
    breaker.  The best thing to do with old style BX is to replace
    it with modern cable whenever it's encountered and there's any
    hint of the sheath rusting.

    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.

Subject: Copper wire characteristics table

    These are taken from the Amateur Radio Relay Handbook, 1985.

    AWG  dia    circ  open   cable  ft/lb   ohms/
         mils   mils  air A  Amp    bare    1000'

    10   101.9 10380    55    33    31.82   1.018
    12    80.8  6530    41    23    50.59   1.619
    14    64.1  4107    32    17    80.44   2.575

    We don't show specs for 8ga or larger because they're
    usually stranded.

    Mils are .001".  "open air A" is a continuous rating for
    a single conductor with insulation in open air.  "cable amp"
    is for in multiple conductor cables.  Disregard the amperage
    ratings for household use.

    To calculate voltage drop, plug in the values:

        V = DIR/1000'

    Where I is the amperage, R is from the ohms/1000' column
    above, and D is the total distance the current travels (don't
    forget to add the length of the neutral and hot together - ie:
    usually double cable length).  Design rules in the CEC call
    for a maximum voltage drop of 6% (7V on 120V circuit)
--
Look on the bright side - at least the PC's reached gender parity!
Chris Lewis; [e-mail]; Phone: Canada 613 832-0541
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