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Electrical conduit at a service panel (C) D Friedman T HemmMetallic Electrical Conduit Types

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Metallic Electrical Conduit:

Here we describe the various types & applications of metallic electrical conduit, flexible and rigid, or conduit made of aluminum, galvanized steel, PVC-coated steel, and stainless steel. We include ips for installing & inspecting electrical conduit in homes and electrical conduit cutting, bending, installing suggestions

This article series describes both metallic electrical conduit and plastic or non-metallic electrical conduit products, and 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.

The page top photo showing rigid conduit used to bring wires up to an electrical sub-panel was provided courtesy of Tim Hemm.



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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]

Electrical Conduit Types, Applications, Codes, Standards, Sources

Thin wall metal conduit (C) Daniel Friedman

Photo above: EMT, thin walled electric metal conduit. [Click to enlarge any image]

Steel electrical conduit and tubing (EMT) have been used for many decades to protect electrical wiring from mechanical damage and to provide electromagnetic field or electromagnetic interference shielding for circuits and wiring of various types.

Vendors of EMT point to both its high re-cycled content (63%) and its recyclability at the end of its life. EMT is produced either in a basic oxygen furnace (BOF) or an electric arc furnace (ARF). - (NEMA 2017)

The range of electrical conduit materials and properties is large and is designed both for special applications such as corrosion or moisture resistance.

EMT, Electrical Metallic Tubing, Thin-wall metal conduit

IMC metal conduit in a New York home (C) Daniel FriedmanThe 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.

EMT Conduit is sold in two metallic types:

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.

In the U.S. manufacturers of EMT or Electrical Metallic Tubing include Allied, Calbrite, and Granger-Approved brands.

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)

EMT Resources, Sources, Standards

FMC, Flexible metal electrical conduit

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

Flexible metal conduit or FMC, is a helically-wound flexible metal electrical wiring conduit, often made using aluminum such as the ALFlex™ conduit shown here.

Flexible metallic electrical conduit is used principally in commercial and industrial construction world wide. In residential applications you may find FMC used to connect an electric oven or electric cooktop.

This conduit is also sold as LFMC or liquid-tight flexible metal conduit.

LFMC is described in the U.S. National Electrical Code NEC® Article 350 and must comply with UL 360 in the U.S. or CSA C22.2 No. 56 in Canada.

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.

[Click to enlarge any image]

Pre-Wired Flexible Electrical Conduit Whips

Armored cable, 12/3  Armorlite BX wire (C) Daniel FriedmanWhat's the Difference between Flexible Metal Electrical Conduit and Armored Cable or "BX" Wiring?

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

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.

FMC and LFMC Standards, Codes, Installation Guidelines

The following Standards govern FMC and LFMC

Rigid and flexible metallic electrical conduit in an older home (C) Daniel Friedman

Photo above: rigid and flexible metallic electrical conduit in an older home.

In addition, NEMA, the National Association of Electrical Equipment and Medical Imaging Manufacturers has produced a number of standards and installation procedures, bulletins and guides for FMC and LFMC including

Contact NEMA at

IMC Intermediate Metal Conduit

Intermediate Metallic Conduit or IMC is lighter weight, metallic conduit and is rated as stronger than other rigid conduit. IMC was first produced by Allied Tube & Conduit.

IMC, provided in both threaded IMC and non-threaded IMC forms, is a rigid metallic conduit tubing, typically hot-dipped galvanized steel or stainless steel. The interior of galvanized steel IMC is usually coated with an anti-corrosion layer.

Threaded IMC is joined by threaded couplings, C condulets, sweeps and bends. The tubing is cut with a pipe cutter or tubing cutter, and then threads cut using a thread cutting tool. When cutting IMC, take care to remove burrs on the tubing interior that would otherwise damage electrical wires being pulled through the conduit.

IMC is typically used in hazardous locations, and in its stainless steel formulation, IMC is widely used in the food and beverage industry, in chemical plants, in cosmetic and pharmaceutcial industries, in refineries, in pulp and paper mills, in marine and coastal sites, in other corrosive environments.

An advantage of IMC is its larger interior diameter compared with RMC of the same nominal sizes, making it easire to pull wires.

IMC is sold in these forms

IMC Standards, Certifications, Suppliers, Product Resources

Calbrite™ stainless steel IMC Coupling - at InspectApedia.com

Non-threaded IMC is joined by compression fit type couplings like the stainless steel Calbrite™ IMC coupling shown here.

LFMC: Liquid Tight Flexible Metallic Conduit Whips, Pre-Wired

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

In nearly all new installations the electrician uses a pre-wired liquid tight electrical conduit whip (photo above) to connect outdoor electrical equipment exposed to the weather, such as an air conditioner or heat pump compressor/condenser unit.

Shown is a six-foot 3-wire Carlton Carflex™ whip assembly produced by Thomas & Betts. [5]

[Click to enlarge any image]

For special applications such as shown in our sketch (below), 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.

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.

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.

LFMC Resources

RMC Rigid Metal Electrical Conduit - threaded metal electrical conduit

Bending-over RMC electrical conduit at a residential masthead (C) DanieL FriedmanRigid metal conduit is a heavier gauge steel electrical conduit using threaded couplings and fittings and is the thickest, or stiffest of the conduit materials used for electrical wiring.

A typical RMC and often the only RMC residential application is to enclose the electrical service entry wiring from the electrical company's overhead wires at the mast-head down to the electrical panel mounted on the building wall.

Our photo shows a damaged, bent-over RMC masthead over a private home in New York. This sort of damage can happen when a tree falls on the electrical wires between pole and masthead.

[Click to enlarge any image]

RMC is sold in both straight lengths and into pre-formed sweeps and bends at 90° and 45° angles.

Rigid metal conduit and its necessary couplings, bends, sweeps, and Condulets that permit wiring insertion & splicing are sold in the following forms and metals:

[Photos needed - use the page top or bottom CONTACT link]

Grainger (https://www.grainger.com) lists a full inventory of types of metal and non-metallic conduit products as you may also find at your local electrical contractor-supplier and at some building supply stores such as Lowes & Home Depot.

RMC Rigid Metal Conduit Resources

Calbrite™ Brand stainless steel C Condulet at InspectApedia.com contact information for Calbrite is in the article where this image appearsThe stainless steel C Condulet shown here and used for snaking or connecting electrical wires inside of RMC is a Calbrite™ product - contact information is given below. Stainless steel RMC is used where corrosive environments will exceed the limitations of aluminum, fiberglass, rigid steel, PVC, & PVC Coated conduit. (Calbrite 2017).

Galvanized RMC meets these standards in the U.S. & Canada

RMC Suppliers, North America

Tools you and procedures for bending, cutting, installing, electrical conduit

This discussion has moved to a separate aritcle at ELECTRICAL CONDUIT BEND CONNECT TOOLS

Electrical Wiring Conduit Defects Found by Visual Inspection

This discussion has moved to a separate aritcle at ELECTRICAL CONDUIT DEFECTS & DAMAGE

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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Continue reading at ELECTRICAL CONDUIT, NON-METALLIC or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ELECTRICAL WIRING BOOKS & GUIDES

Or see ELECTRICAL CODE BASICS

Or see SAFETY for ELECTRICAL INSPECTORS.

Or see SEWER SEPTIC GAS CONDUIT LEAKS - odors carried into a home through its electrical conduit

Or see these

Electrical Conduit Types, Applications, Codes, Standards, Sources



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