Conduits and Fittings

8/11/2019 Conduits and Fittings

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CHAPTER 11 CONDUIT AND FITTINGS

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GENERAL

A conduit is defined as a tube or duct for enclosing electrical wires or cables.

MnDOT uses two types of conduits in signal construction:

Rigid Steel Conduit - Specification 3801.

Non-Metallic Conduit - Specification 3803.

MnDOT allows the use of either Rigid Polyvinyl Chloride (PVC) conduit (rigid sectional lengths)or High Density Polyethylene (HDPE) (continuous length) conduit. All Rigid PVC and HDPEconduit and fittings must be listed by a Nationally Recognized Testing Laboratory (NRTL).SeeContract Documents for the specific requirements for all non-metallic conduit.

CONDUITS AND FITTINGS

HDPE CONTINUOUSCONDUIT

RIGID STEELCONDUIT RIGID PVCCONDUIT


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CHAPTER 11 CONDUITS AND FITTINGS

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STANDARD SPECIFICATIONS

All conduits and fittings must be the size and type specified in the Contract Documents.

If conduit size is not specified, the minimum conduit size must be 3/4 inch (21

millimeters).

Conduit installation must be in accordance with the National Electrical Code.

The conduit in a run must be the same size and type and must be continuous from outletto outlet.

Conduit must be installed in as straight a run as practicable and will enter handhole andfoundations in line with the general direction of the conduit run.

Conduits with sharp kinks or reduced

cross section will be rejected.

The damage occurs if:

a. The conduit is bent without usingthe proper equipment.

b. An attempt is made to relocate theend of the conduit so that it lines upwith the handhole or foundation.

CONDUIT BENDS 2565.3D

Conduit bends other than those done in the factory must have a radius no less than 6 times thenormal diameter of the conduit. Bends must not damage the conduit or effectively reduce itsinternal diameter. In addition bends must not exceed 360 degrees of bend per conduit runbetween handholes or foundations.


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ABOVE GROUND 2565.3D

All cables must be run in conduits except as otherwise specifiedin the Contract Documents.

When conduits are attached to wood poles the conduit must besecured with the appropriate two hole type conduit straps thatmeet the current edition of the National Electrical Code (NEC).The conduit straps must not be more than 4 feet (1.2 meters)apart and the conduit must be supported within 3 feet (900millimeters) of the termination point or fitting.

Conduits attached to metal poles require a minimum of 3/4 inch (19 millimeters) stainless steelbindings that are spaced not more than 5 feet (1.5 meters) apart.

Conduits attached to other structures must besecured as indicated in the Contract Documentsto the satisfaction of the Engineer.

UNDERGROUND 2565.3D

Underground conduits must be placed no less than 18

inches (460 millimeters) below the surface of anyground area and not less than 24 inches (610millimeters) below any roadway surface. It should benoted that the depth of the conduit is measured fromthe top of the pipe. For example a trench for a 4 inch(100 millimeters) conduit is 22 inches (560 millimeters)from the finished ground to the bottom of the trench.


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Conduits placed under railroadtracks must be placed no less than

57 inches (1.44 meters) below thebottom of the ties or as required bythe railroad company.

For Rigid Steel Conduit (RSC) and Rigid PolyvinylChloride (PVC) conduit trenching is the accepted methodof conduit installation except when the conduits are beinginstalled under existing roadways. Conduits must not beplaced until the trench has been inspected.

Except for under existing pavements, HighDensity Polyethylene (HDPE) (continuouslength) conduit must be placed bytrenching, vibratory plow with feed blade orother method approved by the Engineer.


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If installing conduit under an existing roadway and a method other than directional boring isused, a distortion due to conduit installation in excess of one quarter-inch (6 mm) is created inthe existing roadway surface the Contractor must remove the distortion and restore at noexpense to the Department the roadway surface to its original condition.

If boring operations through a roadbed are abandoned for any reason, the voids must begrouted at the contractors expense and to the satisfaction of the Engineer.

The Contractor must install a 36 inch (91.44cm) rigidPVC conduit stub out with the appropriate end bell for alldirect buried lighting cable entering a hand hole.


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Position conduit terminating in handholes, concrete foundations and equipment pads so theconduit extends inside the handholes, pole bases, structure bases, or service cabinets asindicated in the Standard Plates or plan details. Slope the conduit away from the foundation andtoward the handhole opening for drainage.

Conduits that are stubbed out ofthe foundation for future use mustextend 18 inches to 24 inches(460 millimeters to 610millimeters) beyond the foundationor sidewalk in the directionspecified by the Engineer, andcapped on both ends withstandard pipe caps. After the capis secured, a permanent markershould be used to draw an arrow,on the cap, indicating the directionof the conduit.


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OPEN ENDS 2565.3D

The open ends of conduits that are locatedin handholes or those that extend abovefoundations must be capped until the wiringis installed.

When the RSC caps are removed an appropriate ground bushing (UL Std. 467) must be

installed with a lug compatible with a solid bare No. 6 copper bonding conductor. The lugmaterial shall consist of stainless steel, copper, brass or bronze. Each bushing must becovered with a corrosion inhibiting compound. See 2545.3.R and 2565.3.D.4.b

The open ends of conduits in acabinet or foundation must besealed in accordance with2565.3D.2.b.

After the installation of the cablesand conductors use a duct sealcompound NRTL classified undergeneral use tapes. This preventsmoisture from entering the cabinetor signal pole. The sealant alsohelps in preventing rodents fromentering the foundation throughthe conduit system. Thisrequirement applies to bothsignals and lighting systems.


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R.S.C. JOINTS 2565.3D

When standard length RSCconduit is cut the end must be

threaded and reamed toremove burrs and rough edges.Field cuts must be madesquare and true so that allends joined by coupling butttogether for the fullcircumference. This providesan electrical bonding andgrounding connectionthroughout the entire length ofthe conduit run.

If the galvanized coating on the conduit is damaged during handling or installation, the damagedareas must be painted with MnDOT approved paint to the satisfaction of the Engineer.

EXISTING CONDUITS 2565.3D

If the existing underground conduitis incorporated into a new trafficcontrol signal system it must becleaned and blown out withcompressed air before the newwires are installed. If a newhandhole is installed into anexisting conduit run the conduitmust be cut, threaded andextended into the new handhole asdirected by the Engineer. A newbushing with an integral lug andground wire must be installed andthe sides of the handhole must bemade water tight before theinstallation of any new wires.Threadless couplings and bushingsare not permitted unless otherwiseauthorized by the Engineer.


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NON-METALLIC CONDUITS 2565.3D[Rigid PVC Sectional and Continuous Length (HDPE)]

All non-metallic conduits must be listed by a Nationally Recognized Testing Laboratory (NRTL)as being compliant with the requirements of UL 514B and UL 651 for underground use.

All non-metallic conduit must be Schedule 80.

Cut ends of sectional conduit must butt or come together for the full circumference thereof.

All non-metallic conduit must be either RED or Grey color.

HDPE continuous length conduit must not be spliced under roadway surfaces.

When rigid PVC conduit sections are installed using the directional boring method the rigid PVCconduit sections must be pre-glued at least 6 hours prior to installation under roadwaysurfaces.

Long-line couplings must be used when rigid PVC conduit sections are installed under roadwaysurfaces.

The Contractor must trim the inside and outside of cut ends to remove rough edges.

Rigid PVC Conduit HDPE Continuous Length Condui t


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All open ends of non-metallic conduit must be immediately capped to keep moisture and debrisout.

Before cables and conductors are installed, standard non-metallic conduit end bells must beinstalled to prevent damage to the cables and conductors.

The Contractor must pull cables and conductors through the non-metallic conduit in such amanner as not to damage the conduit due to pull rope abrasion.

The Contractor will be required to pull a ground wire through the conduit system as required bythe Contract Documents.

HDPE Continuous length conduit must not be used between concrete foundations and thenearest handhole.

CONDUITS ATTACHED TO A BRIDGE 2565.3D

Because bridges are subjected to flexing, expansion and contraction, special expansion and

deflection conduit fittings as well as hangers are required (see special details for the installationprocedure). Improper installation of conduits can cause severe damage to the electrical systemand may cause damage to the bridge structure itself.

All conduits must be attached to bridge as specified in the Contract Documents.