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.  Other
  redistribution must contain this copyright notice,
  and attribution.

------------------------------
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.  If you say "loose
| neutral", they will come.

 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)
-- 
Chris Lewis: _Una confibula non sat est_
Phone: Canada 613 832-0541  Ferret list: ferret-request@ferret.ocunix.on.ca
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