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Electrical conduit at a service panel (C) D Friedman T HemmElectrical Conduit Basics for Homeowners

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Electrical conduit: This article answers basic questions about installing electrical conduit. Electrical conduit is metal or plastic rigid or flexible tubing used to route electrical wires in a building.



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Page top photo courtesy of Tim Hemm.

Electrical Conduit Installation Tips for Homeowners & DIY Repairs

Electrical conduit mistakes (C) D Friedman T HemmWatch Out: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.

Even when a hot line switch is off, one terminal on the switch is still connected to the power source.

Before doing any work on the switch, the power source must be turned off by set­ting a circuit breaker to OFF or removing a fuse.

See SAFETY for ELECTRICAL INSPECTORS and ELECTRICAL WIRING BOOKS & GUIDES

Electrical conduit for wiring has some advantages in protecting wires and also in running multiple wires to a location.

The proper selection of electrical conduit materials, fittings, and installation are important for safe electrical wiring.

Our photo (above left, courtesy of Tim Hemm), shows an electrical conduit snafu along with an unsafe FPE Stab-Lok electrical sub panel. Both flexible electrical conduit and rigid conduit were used. Our arrow points to an improper "bend" made in the rigid metal electrical conduit. [3]

Cutting, Bending and Threading Electrical Conduit

Electrical conduit is often used to hold and protect house wiring. In some localities electrical conduit is required by the local code. Conduit protects building wiring from damage better than flexible steel (BX) cabling or plastic sheathing (Non metallic sheathed or NMC wire).

Electrical conduit mistakes (C) D Friedman T Hemm

However, it electrical conduit is more difficult to install and it requires both some special tools and some special knowledge about permitted bending radii and similar details.

Instead of damaging rigid electrical conduit tubing (as in the photo above) make your bends using the proper tool, use elbows and fittings, buy pre-formed bends (shown at left in plastic conduit), or use flexible metal or plastic conduit (illustrated at above left).

- Photo courtesy Galow Homes. [7]

A Photo Guide to Types of Electrical Conduit

Thin wall metal conduit (C) Daniel FriedmanThin-wall metal conduit

The most common type of electrical conduit for house wiring is the thin-wall type. Thin-wall conduit is too thin for threaded joints. It is joined to other lengths of conduit and to boxes by pressure-type fittings. Thin-wall conduit is sold in ten-foot lengths in either one-half inch or three-quarter inch (outside) diameter.

The one-half inch conduit can contain four No. 14 wires or three No. 12 wires. Three-quarter inch conduit accommodates four No. 10 or five No. 12 wires.

These wire capacities are for individual wires, not pairs. The wires used are the same as the individual conductors found in steel armor cable and plastic sheathed cable. Wires in conduit must follow standard coding. In a two-wire electrical circuit you need one black wire, one white wire, and one ground wire.

The general procedure for using thin wall conduit is similar to the use of steel armor cable. The big difference is that conduit cannot be "snaked" through openings in ceilings and walls.

You must have full access to joists and studs to install electrical conduit. So you probably won't want to use it unless your local code requires it.

Reader Comment: more wires allowed in thin wall metal conduit: NEC Table C.1

2016/08/22 Alan said:

The conduit fill listed under thin-wall metal conduit [above] is wrong. Granted, under normal conditions, you generally cannot go over 9 current carrying conductors in a conduit without needing to reduce its current carrying capacity below the size circuit for which it is generally used (e.g., #14 = 15A; #12 = 20A). A

NEC Table C.1 (for electrical metallic tubing, EMT) allows for 12 #14 and 9 #12 in 1/2" conduit, and 22 #14 and 16 #12 in 3/4" conduit.

lso, good luck pulling nine #12 wires in a 1/2" conduit, but just wanted to point out that NEC allows for more conductors than indicated above.

Also, I should note that is for THHN - other types may allow for more or less.

Spacing & Support for Rigid Metal Electrical Conduit

See NEC Table 344.30 (B)(2)

Rigid threaded electrical conduit

[Photos needed]

[Citation needed]

Plastic conduit - PVC Tubing used for Electrical Conduit: PVC-U

Rigid plastic electrical conduit (C) Daniel Friedman

Plastic electrical conduit or rigid pvc conduit, shown in our photographs here, is easier to cut; conduit sections and fittings are joined by conduit solvent cement specifically formulated for use with PVC (polyvinyl chloride) plastic conduit ducts and fittings.

Plastic conduit can be heated and bent to non-standards shapes, or pre-formed bends and elbows can be used.

Watch out: do not mix types of cements (glues) used with plastic water or drain piping with conduit cement. Conduit cement is not suitable for piping and fittings subjected to pressure.

Rigid plastic electrical conduit (C) Daniel Friedman T Hemm

Use proper fittings to join and terminate rigid plastic conduit tubing, and protect it from damage too.

Tim Hemm's photo (left) illustrates a do-it-yourself and improper PVC conduit termination (blue arrow) and a damaged, disconnected plastic conduit elbow and tubing at ground level (red arrow). [3]

Spacing & Support for Rigid PVC Electrical Conduit

Table 352.30(B) NEC shows the support requirements for Schedule. 40 & Schedule 80 PVC electrical conduit

Notes on using PVC electrical conduit:

Total weight of conduit including wires enclosed may be a factor in the requirements for conduit support

PVC electrical conduit (PVC-U) in the U.S. is sold in sizes from 1/2" to 8" in diameter and in three formulations: EPT-A-PVC, EPC-40-PBC, and EPC-80-PVC.

Plastic conduit should always be installed away from steam lines and other high heat sources.
PVC electrical conduit support straps should allow for lineal movement caused by expansion and contraction.
Maximum ambient temperature exposure for PVC electrical conduit is 122°F (50°C)

Sources:

Flexible metal electrical cvonduit

Flexible electrical conduit in an allowed outdoor use (C) D Friedman

Flexible metal conduit is sold in rolls and cut to the necessary length, joined with appropriate fittings.

Shown is Alflex™ 3/4" diameter metallic flexible conduit produced by Titan.

What's the Difference between Flexible Metal Electrical Conduit and Armored Cable or "BX" Wiring?

Armored cable, 12/3  Armorlite BX wire (C) Daniel Friedman

Flexible metal conduit sold for electrical wiring (photo above) is sold empty, and is larger in diameter than pre-wired armored cable such as the 12/3 Armorlite® armored cable shown at left.

This electrical cable is pre-wired with THHN/THWN conductors and is intended for use in cable trays and includes a green-insulated ground wire.

Watch out. Do not use set-screw type connectors with this cabling. Doing so risks pinching the cable end and cutting into the wires, causing a short circuit.

Pre-wired flexible electrical conduit whips

Flexible electrical conduit pre-wired whip for outdoor use (C) D Friedman

For special applications such as shown in our sketch (below left), flexible conduit is often used for convenience or to avoid vibration problems, but steps must be taken to prevent water from entering the conduit and/or special water-resistant wiring and fittings are required. In nearly all new installations the electrician uses a pre-wired liquid tight electrical conduit whip (photo at below right).

Flexible electrical conduit in an allowed outdoor use (C) D Friedman

Pre-wired whips in residential applications (photo above right) are found connecting air conditioner & heat pump compressor units to their outside power source. There the flexible whip avoids problems with vibration-loosened connections in the conduit. Electrical whips are also used for connecting spas and swimming pool equipment. Shown is a six-foot 3-wire Carlton Carflex™ whip assembly produced by Thomas & Betts. [5]

Damaged plastic conduit whip (C) D Friedman T Hemm

Watch out: Flexible conduit and whips are "flexible" but not to degrees that exceed the laws of physics and the properties of the materials.

If you force flexible conduit or a pre-wired conduit whip to bend too acutely over too short a radius such as at its connection to a rigid surface the conduit will eventually break, as Tim Hemm's photograph (left) illustrates.

Flexible Plastic Conduit - Electrical Nonmetallic Tubing or ENT

Flexible plastic electrical conduit (C) DanieL Friedman

Flexible plastic conduit is illustrated in our photograph (left). Shown is blue 3/4" Flex-Plus® Carlon Blue® ENT (Electrical Nonmetallic Tubing).

This electrical conduit is intended for use in residential attics up to three feet above the bottom of ceiling joists.

Sections and fittings are joined with PVC cement using a brush (not a dauber).

What tools you need and the procedures for using conduit?

Tools for Cutting Electrical Conduit

Thin-wall conduit can be cut with a special electrical conduit cutter. To use the cutter, clamp it around the conduit. To cut the conduit, tighten the knurled nut in the handle.

As you tighten, force the cutter around the conduit. The sharp cutting blade cuts a groove that deepens with each revolution, making a smooth, quick cut. After cutting through the conduit, file off any burrs around the edge of the cut.

Tools for Bending Electrical Conduit

Thin-wall electrical conduit can be readily bent by using a special tool designed to make a smooth, even bend with little effort.

The more bends in a run of conduit, the more it is to “fish” the wires through.  Plan the conduit run carefully to avoid sharp bends and to make as few bends as possible.  Never have more than four right angle bends between openings.  Follow the manufacturer’s instructions for the type of conduit bender you use.

How an electrical conduit bender works

How to thread electrical wires through conduit

A fish tape is a thin, flexible metal tape with a hook on one end. The tape is usually packaged on some type of reel. The tape is used to pull wires through conduit or through openings in walls. For conduit use, the tape is inserted in one conduit opening and worked through to the next opening. The wires to be drawn through the conduit are bent around the hook on the fish tape.

If the run is long and has a few bends it is a good idea to wrap some electrical tape around the wires to hold them on the hook.  The tape is then reeled in to draw the wires through the conduit.  A slow, steady is less likely to kink the tape or jam the wires than is a series of sharp.

Electrical codes allow multiple electrical wires to be pulled through a single conduit, but limit the number of wires allowed in a conduit run depending on the number of wires and the wire diameter or gauge.

The more wires you pull, the more crowded the conduit, so buy larger conduit---perhaps 3/4 inch instead of 1/2 inch.

More Electrical Wiring Conduit Defects Detectable by Visual Inspection

If our inspection is limited to an external, visual inspection of electrical conduit, we may not immediately be able to see safety and electrical code violations such as use of improper wire type or too many wires in a conduit, but here are some easy to spot concerns that merit further review by an expert:

Damaged electrical conduit

Damaged electrical conduit.

While electrical conduit can provide superior protection for electrical wiring, rigid conduit is also vulnerable to impact damage.

We often see a free-standing electrical junction box, perhaps holding an electrical receptacle, which has been struck and broken off. Look for conduit which has been bent, dented, crimped, cut, or broken.

Tim Hemm's photo at left shows how easily a rigid conduit mounted outdoor electrical receptacle can be kicked over and broken. This condition adds the risk of a nicked or cut wire insulation making an immediate risk of electric shock or electrocution.

Damaged electrical conduit invites leaks (C) D Friedman T Hemm

Leaks into electrical conduit can occur where improper fittings are used or where the conduit is damaged.

See ELECTRICAL WIRE STRIPPING TIPS for details on proper preparation of flexible conduit, metallic cable (MC) or "BX" cable, or armored cable (AC) wiring.

Even flexible conduit, such as the one shown in Tim Hemm's photo at left can be damaged by impact or pulling on the conduit. Such an open conduit line invites water entry, short circuits, and unsafe conditions.

Metal fencing used as electrical conduit (C) D Friedman T Hemm

Improper materials used as electrical conduit: only tubing which has been approved (NEC) and listed (UL, CSA) should be used for routing electrical wires.

In Tim Hemm's photo shown here some fool has used metal fence piping to run electrical wires, risking electrocuting someone who simply touches the fence.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions.

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