---
aliases:
  - nec-353
title: "Article 353 High Density Polyethylene Conduit: Type HDPE Conduit"
tags:
  - authorship/other
  - exclude-from-word-count
  - topic/construction/electrical
  - type/media/reference
---
# Article 353 High Density Polyethylene Conduit: Type HDPE Conduit

## Part I. General

### 353.1 Scope.

This article covers the use, installation, and construction specifications for high density polyethylene (HDPE) conduit and associated fittings.

> [!info] Informational Note:
> Refer to Article 352 for Rigid Polyvinyl Chloride Conduit: Type PVC and Article 355 for Reinforced Thermosetting Resin Conduit: Type RTRC.

### 353.2 Definition.

The definition in this section shall apply within this article and throughout the Code.

#### High Density Polyethylene (HDPE) Conduit.

A nonmetallic raceway of circular cross section, with associated couplings, connectors, and fittings for the installation of electrical conductors.

### 353.6 Listing Requirements.

HDPE conduit and associated fittings shall be listed.

## Part II. Installation

### 353.10 Uses Permitted.

The use of HDPE conduit shall be permitted under the following conditions:

* (1) In discrete lengths or in continuous lengths from a reel

* (2) In locations subject to severe corrosive influences as covered in 300.6 and where subject to chemicals for which the conduit is listed

* (3) In cinder fill

* (4) In direct burial installations in earth or concrete

    > [!info] Informational Note to (4):
    > Refer to 300.5 and 300.50 for underground installations.

* (5) Above ground, except as prohibited in 353.12, where encased in not less than 50 mm (2 in.) of concrete.

* (6) Conductors or cables rated at a temperature higher than the listed temperature rating of HDPE conduit shall be permitted to be installed in HDPE conduit, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the HDPE conduit.

### 353.12 Uses Not Permitted.

HDPE conduit shall not be used under the following conditions:

* (1) Where exposed

* (2) Within a building

* (3) In any hazardous (classified) location, except as permitted by other articles in this Code

* (4) Where subject to ambient temperatures in excess of 50°C (122°F) unless listed otherwise

### 353.20 Size.

#### 353.20(A) Minimum.

HDPE conduit smaller than metric designator 16 (trade size 1/2) shall not be used.

#### 353.20(B) Maximum.

HDPE conduit larger than metric designator 155 (trade size 6) shall not be used.

> [!info] Informational Note:
> The trade sizes and metric designators are for identification purposes only and do not relate to actual dimensions.

See 300.1(C).

### 353.22 Number of Conductors.

The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9.

Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.

### 353.24 Bends --- How Made.

Bends shall be so made that the conduit will not be damaged and the internal diameter of the conduit will not be effectively reduced.

Bends shall be permitted to be made manually without auxiliary equipment, and the radius of the curve to the centerline of such bends shall not be less than shown in Table 354.24. For conduits of metric designators 129 and 155 (trade sizes 5 and 6) the allowable radii of bends shall be in accordance with specifications provided by the manufacturer.

### 353.26 Bends --- Number in One Run.

There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes.

### 353.28 Trimming.

All cut ends shall be trimmed inside and outside to remove rough edges.

### 353.46 Bushings.

Where a conduit enters a box, fitting, or other enclosure, a bushing or adapter shall be provided to protect the wire from abrasion unless the box, fitting, or enclosure design provides equivalent protection.

> [!info] Informational Note:
> See 300.4(G) for the protection of conductors 4 AWG and larger at bushings.

### 353.48 Joints.

All joints between lengths of conduit, and between conduit and couplings, fittings, and boxes, shall be made by an approved method.

> [!info] Informational Note:
> HDPE conduit can be joined using either heat fusion, electrofusion, or mechanical fittings.

### 353.56 Splices and Taps.

Splices and taps shall be made in accordance with 300.15.

### 353.60 Grounding.

Where equipment grounding is required,
a separate equipment grounding conductor shall be installed in the conduit.

> [!important] Exception No. 1:
> The equipment grounding conductor shall be permitted to be run separately from the conduit where used for grounding dc circuits as permitted in 250.134, Exception No. 2.

> [!important] Exception No. 2:
> The equipment grounding conductor shall not be required where the grounded conductor is used to ground equipment as permitted in 250.142.

## Part III. Construction Specifications

### 353.100 Construction.

HDPE conduit shall be composed of high density polyethylene that is resistant to moisture and chemical atmospheres. The material shall be resistant to moisture and corrosive agents and shall be of sufficient strength to withstand abuse, such as by impact and crushing, in handling and during installation. Where intended for direct burial, without encasement in concrete, the material shall also be capable of withstanding continued loading that is likely to be encountered after installation.

### 353.120 Marking.

Each length of HDPE shall be clearly and durably marked at least every 3 m (10 ft) as required in 110.21. The type of material shall also be included in the marking.
