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Electrical conduit mistakes (C) D Friedman T HemmNon-Metallic Electrical Conduit Types
Plastic, ENT & LFNC electrical conduit

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Non-Metallic Electrical Conduit:

Here we describe the various types & applications of ENT or LNFC (liquid tight) non-metallic electrical conduit made of plastic, PVC.

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 conduit used to bring wires up to an electrical sub-panel was provided courtesy of Tim Hemm.



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ENT Electrical, Non-Metallic Conduit: Rigid & Flexible Plastic Electrical Conduit

Rigid plastic electrical conduit (C) Daniel Friedman

Plastic electrical conduit or rigid PVC-U pipe specified as electrical nonmetallic tubing (ENT) conduit, shown in our photographs here, is easier to cut than metallic conduit products.

Flexible plastic conduit is also sold as LFNC, liquid-tight nonmetallic conduit.

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.

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

Our photo shows Cantex® Schedule D Rigid PVC non-metallic Electrical Conduit in a Home Depot store. [Click to enlarge any image]

ENT conduit sections and fittings are joined by conduit solvent cement specifically formulated for use with PVC (polyvinyl chloride) plastic conduit ducts and fittings.

Plastic condolet connector for PVC electrical conduit (C) Daniel Friedman Low VOC PVC cement for electrical conduit (C) Daniel Friedman

Spacing & Support for Rigid PVC Electrical Conduit

A 90 degree sweep or bend using Cantex PVC nonmetallic rigid plastic electrical conduit (C) Daniel Friedman

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

Notes on using PVC electrical conduit:

Collapsing building © Daniel FriedmanTotal 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)

Our photo shows rigid PVC or ENT used to bring power to a sub panel being installed in the author's garage.

[Click to enlarge any image]

Rigid PVC Electrical Conduit Code & Standards & Sources:

Question: with 3/4" schedule 40 pvc, is the ground considered a support?

(Sept 28, 2016) Bert Deaton said:

When coming our of the ground with 3/4" schedule 40 pvc, is the ground considered a support? I have some 30" conduits that I am being told by the general I need to put strut and straps on. They go 30" from the ground to inverters. I can not find in the code book where the ground is considered a support. Thanks for any help.

Reply:

Bert:

3/4" PVC electrical conduit support spacing requirements depend on the rated operating temperature as follows:

3/4" PVC conduit at 60 degF can be supported on 5 ft. intervals

3/4" PVC conduit at 100 degF can be supported on 4 ft. intervals

3/4" PVC conduit at 140 degF can be supported on 2 1/2 ft. intervals.

I agree with you that conduit coming out of the earth might appear to be "supported" by the soil, but since soil itself can vary in hardness as water or other conditions change, I can also see why the supervising contractor thinks you need a support right at that location.

Here is a typical instruction from a PVC Conduit supplier:

"Rigid PVC conduit must be supported with straps when installed in above ground applications. These straps should be installed snugly, while allowing linear movement of the conduit. " - M Royal Electrical Solutions Co., 56400 Mound Road - Shelby Twp., MI 48316 USA, original source: www.royalbuildingproducts.com/uploadedFiles/Pipe_Microsite/Content/Products/Electrical/Rigid_Conduit_Fittings/Rigid%20PVC%20Conduit%20Installation%20Guide.pdf

The company continues, citing the NEC, 3 ft. support intervals. i.e. greater than your 30" distance. Typically support is required also within 36" of any terminus such as an electrical box or in your case to the inverter.

Note that the expert source says "above ground".

Unfortunately, the only way to close the argument about who's going to accept "earth" as a point of support is your local electrical inspector. What does he or she say?Ask also if the inspector accepts Schedule 40 below and emerging from ground. You might also see what expert Mike Holt has to say - see http://forums.mikeholt.com/

Watch out: depending on your jurisdiction, you could be asked to use metal conduit or Schedule 80 PVC below ground & at ground emergence up for some height so as to be protected from people digging about with a shovel or hit by a lawnmower.

Check out NEC '05 230.50(A)& (B) and also see (National Electrical Code 2014)

Article 352 - Rigid Polyvinyl Chloride Conduit: Type PVC

II. Installation

352.10 Uses Permitted. The use of PVC conduit shall be permitted in accordance with 352.10(A) through (H).

(F) Exposed. PVC conduit shall be permitted for exposed work. PVC conduit used exposed in areas of physical damage shall be identified for the use.

(G) Underground Installations. For underground installations, homogenous and nonhomogenous PVC shall be permitted for direct burial and underground encased in concrete. See 300.5 and 300.50.

Article 352 accepts use of Schedule 80 PVC electrical conduit where exposed and subject to physical damage

Article 352 accepts use of Schedule 40 PVC electrical conduit in exposed areas not subject to physical damage (provided you've selected the proper, listed PVC type for your application)

Article 300 - Wiring Methods

I. General Requirements

300.5 Underground Installations.

(D) Protection from Damage. Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).

(4) Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, or equivalent.

Electricians also cite
UL 651

Schedule 40, 80, Type EB and A Rigid PVC Conduit and Fittings

1.2 Schedule 40 and 80 conduit and fittings

1.2.1 Schedule 40 rigid PVC conduit and fittings are for aboveground use indoors or outdoors exposed to sunlight and weather, and for underground use by direct burial or encasement in concrete. Schedule 40 rigid PVC conduit, elbows, that are specifically marked for underground use are suitable for use underground only by direct burial or encasement in concrete.

 

ENT & LFNC Liquid-Tight Non-Metallic Flexible Conduit - Flexible Plastic Conduit

Flexible plastic electrical conduit (C) DanieL Friedman Blue Smurf figure, at Wikipedia 2017

The corrugated flexible plastic electrical conduit is illustrated in our photograph of blue tubing is blue 3/4" Flex-Plus® Carlon Blue® ENT (Electrical Nonmetallic Tubing).

Readers unfamiliar with the alphabet soup of types of electrical conduit will note that "ENT" or Electrical, Non-metallic Tubing used for conduit is thus sold in both rigid ENT and flexible ENT forms, and within flexible ENT are special whips that are waterproof or weatherproof, as we will describe below.

Flexible ENT suffers the nickname of "Smurf Tube" because of its blue color. For readers who haven't met the Smurfs, the blue Smurf shown above is discussed in Wikipedia entries and at other sources.

In residential applications in North America this electrical conduit is used

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

Watch out: flexible ENT is not permitted in all jurisdictions, and it is not used for exposed electrical work (with a few exceptions).

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

Watch 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

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