IMT 140

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IMT 140

• Chapter 18
• Wiring Materials

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Nonmetallic-sheathed Cable

• Available with 2 or 3 current carrying
  conductors.
• In sizes 2 through 14 with copper conductors
  and in sizes 2 through 12 for aluminum
  conductors.

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Nonmetallic-sheathed Cable

• Color coding is black and white for 2 conductors
  and
• Red, black and white for 3 conductors.
• This type cable is available with a ground wire,
  usually an un-insulated bare wire. This is for
  grounding use only.

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Nonmetallic-sheathed Cable

• Underwriters laboratory list 2 classifications
  for this type cable
• Type NM which may be used for both exposed and
  concealed work in normally dry locations.

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Nonmetallic-sheathed Cable

• Type NMC cable which may be used in both exposed
  and concealed work in dry, moist, damp or
  corrosive locations.
• The National Electric Code lists various
  locations where these cables may not be used.
  See Article 336.

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Nonmetallic-sheathed Cable

• Both types shall be stapled or strapped not more
  than 12 inches from a box or fitting and at
  intervals not exceeding 4.5 feet.
• They can be used only in circuits of 600 volts or
  less.

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BX (Armored) Cable

• BX cable is available with 2, 3 or 4 conductors
  from sizes 1 through 14.
• Color coding is the same as non-metallic sheathed
  cable.

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BX (Armored) Cable

• Four conductor color coding is red, black, white
  and blue.
• Armored cable is required to have a grounding
  strip of copper or aluminum.

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BX (Armored) Cable

• A fiber bushing is used to prevent damage to the
  conductors when entering a box.
• BX cable can not be used underground or embedded
  in concrete or masonry.
• Other types of armored cable are types AC, ACT,
  ACL and BXL.

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Built-in clamping devices
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Flexible Metal Conduit

• Also called Greenfield tubing.
• Similar to BX cable.
• The electrician must pull wires in this conduit.
• Available in sizes from 3/8 to 4 inches in
  diameter.
• Another type of this type conduit is
  Liquidtight flexible conduit, which has a
  vinyl-like outer covering. This may be metallic
  or non-metallic.

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Fairly easy to make small bends, saves on
fittings.
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Electrical Nonmetallic Tubing

• This is a light weight and flexible tubing.
• Generally, a plastic corrugated tube.
• Known as ENT.
• This is approved for 1 and 2 family dwellings of
  3 stories or less.

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Rigid Metal Conduit

• Considered a pipe.
• Permanent installations.
• The pipe is annealed and heat treated to permit
  easy bending.
• Comes in 10 foot lengths and is galvanized for
  smoothness and for rust prevention.

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Rigid Metal Conduit

• Ends are threaded and a coupling is provided on 1
  end.
• There are many types of fittings available.
• The pipe may be coated with plastic for corrosive
  areas.
• Aluminum pipe is available where weight or
  magnetic properties are a consideration.

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Electrical Metallic Tubing

• Called EMT, this is thin-wall rigid tubing.
• Much lighter than rigid conduit pipe, thus it
  does not protect the wiring as well.
• The ends are not threaded but are used with
  compression type fittings at joints and fixtures.

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Rigid Non-metallic Conduit

• Easy to install, light weight, resistant to
  corrosion, temperature changes and impact
  resistant.
• Can be used above or below ground or embedded in
  concrete.
• Comes in various wall thickness.
• Can be bent by heating the conduit, bending and
  then cooling.

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Surface Metal Raceways

• Can be mounted to walls and ceilings.
• Generally, used in offices and public buildings
  to add to existing installations.
• Considered to be decorative in appearance.
  Comes in several colors and can be painted.
• Requires special fittings.
• Not for concealed work.
• The conduit is much smaller and the number of
  wires it can carry is limited.

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Wire Mold
For adding to existing wiring after walls and
ceiling are finished.
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Wire Mold Accessories
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Conduit Fittings
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Knock-outs allow versatility in construction and
layout.
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The ring protects wires from the sharp edge of
the conduit.
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Run armored cable and flexible conduit through
holes bored in the middle of framing members.
Where necessary, use notches. BX and Greenfield
are heavier and stiffer than nonmetallic cable,
so it will take more room every time you want to
change direction.
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Even armored sheathing can be pierced with a
nail, so anywhere that the cable is within 1-1/4
inches of the framing surface, protect it with a
nail plate designed for the purpose. For short
runs (see inset), flexible armored cable can be
left exposedcheck your local codes.
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Support metal-clad cable with specially designed
straps or staples every 4 feet or so and within
12 inches of boxes. If youre fishing through
existing walls or ceilings, secure the run as
best you can.
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Pull the brown paper surrounding the wires in BX
back about an inch inside the armor. This leaves
room to slip in a bushing. If your cable has a
bonding strip, fold it back as shown.
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Slip on a connector, making sure the bushing is
in place. Tighten the clamp or setscrew. Armored
cable and conduit are self-grounding, so you
dont need a grounding wire. Some codes require
that the bonding strip be attached to the
tightening screw.
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Slip the wires and connector into a knockout
hole, slip on a locknut, and tighten with your
fingers. As with all wiring, connections
should be made only in boxes
Locknut
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Dont use your best screwdriver!!!
Tighten the locknut with a hammer and
screwdriver. Finally, tug on the cable to make
sure everything is securely fastened.
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Measure the distance for the rundont forget to
subtract for the connector or elbow you will be
using. Cut with a tubing cutter by clamping it
to the conduit and rotating it a few times.
Tighten and rotate until the cut is made. Or
cut with a hacksaw. Hold conduit against a
cleat, or use a miter box to keep it from rolling
as you saw.
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Sharp edges can chew up wiring insulation in a
hurry. Remove all burrs and rough spots from
the inside of the conduit, using the reamer
thats attached to the tubing cutter or a file.
File rough spots on the outside as well, so the
conduit can slip easily into a connector.
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Where you have more than four turns to negotiate,
install a junction box. When its time to pull
the wires, it will let you start another run.
More boxes and few bends ease wire-pulling.
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Use an offset connector to keep the conduit flush
against the wall when its attached to a
box. The conduit can be bent to form an offset
(see Bending Conduit, Related Projects), but
adding an offset connector is easier.
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A pulling elbow makes negotiating corners easier.
Remove the cover to pull the wires through.
Dont make any connections inside a pulling
elbow wires must pass through without a break.
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To get conduit around a corner, first measure
from the box to the top of the bend (distance A).
Then subtract the bend distance and mark the
conduit. (The bend distance for 1/2-inch conduit
is 5 inches. For 3/4- and 1-inch conduit, allow
6 and 8 inches, respectively.) Slip the conduit
bender onto the tubing and align it as shown.
After making the bend, trim section B by
holding the bent conduit in place for measuring,
and cutting the end so it just reaches the box.
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With one foot on the rear of the bender, pull
slowly and steadily on the handle. Be careful.
Tugging too sharply will crimp the tubing and
youll have to start over again with another
piece. (Codes forbid installing crimped
conduit.) Making crimp-free bends takes practice,
so dont be surprised if your first efforts fail.

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When mounting conduit on a flat surface, youll
need to form an offset at each box. Offsets
must be aligned with other bends in the tubing.
A stripe painted along the length of the
conduit helps you do this. First make a
15-degree bend.
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Roll the conduit over, move the bender a few
inches farther from the end, and pull until the
section beyond the first bend is parallel to the
floor.
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Now comes the moment when you realize why codes
are so specific about bends, crimps, and burrs in
conduit. Pulling wire can be surprisingly hard
work. If you suspect that the wire is scraping
against something that might damage the
insulation, stop work, locate the trouble spot
(you can find it easily by using the wire as a
measuring device), and remove it. Purchase
pulling grease, and lubricate the wires with it
if you need to make a long pull.
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For short runs with only a couple of bends, you
can probably just push the wires from one box to
the other. Feed the wires carefully to protect
the insulation.
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If you cant push the wires, youll need a fish
tape and an assistant. Snake the fish tape
through the conduit, hook the wires to the fish
tape and secure with electricians tape. Wrap
the connection neatly, so it can slide through
the conduit.
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As one worker feeds the wire in and makes sure
there are no kinks, the other pulls. Pull the
wires with steady pressureavoid tugging. As
the wires work past bends, expect to employ more
muscle. If you have lots of wires or a long
pull, lubricate the wires with pulling grease.
Where possible, use gravity to aid the process.
Feed the wires from above and pull from below.
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This is not a time to be cheap!!!
Leave 6 to 8 inches of wire at each box. Never
splice wire inside conduitall wires must run
continuously from box to box.
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The End!!!!