raceway

ELECTRICAL TECHNICAL PROCEDURE

TITLE: E-207 RACEWAY SYSTEMS

NO.: 39BCC-07 REV.: 1 PAGE 1 OF 29

Rev. 3 Rev. 2 Rev. 1 Rev. 0 Rev. No.

Date

Approval

This document contains proprietary information belonging to S&W and is to be returned upon request. Its contents may not be copied, disclosed to third parties, or used for other than the express purpose for which it has been provided without the written consent of S&W.

STANDARD DESIGN CRITERIA

for

RACEWAY SYSTEMS

UNCONTROLLEDWHEN REPRODUCED




TABLE OF CONTENTS

1.0 PURPOSE & SCOPE ......................................................................................................................... 3 2.0 DEFINITIONS.................................................................................................................................... 3 3.0 RACEWAY DESIGN CRITERIA ..................................................................................................... 4

3.1 General............................................................................................................................................ 4 3.2 Electrical Requirements .................................................................................................................. 4 3.3 Civil-Structural Interface ................................................................................................................ 5 3.4 Structural and Mechanical Requirements ....................................................................................... 6 3.5 Raceway Service Level Description ............................................................................................... 7 3.6 Raceway Identification and Numbering Requirements .................................................................. 8 3.7 Unsupported Cable Length ........................................................................................................... 10

4.0 CABLE TRAY SYSTEM DESIGN CRITERIA.............................................................................. 11 4.1 Cable Tray Material Selection ...................................................................................................... 11 4.2 Cable Tray Type ........................................................................................................................... 11 4.3 Cable Tray Fill .............................................................................................................................. 12 4.4 Cable Tray Arrangement............................................................................................................... 12 4.5 Cable Tray Supports ..................................................................................................................... 13 4.6 Cable Tray Fittings ....................................................................................................................... 13 4.7 Tray Grounding............................................................................................................................. 14 4.8 Tray Barriers ................................................................................................................................. 15 4.9 Cable Tray Clearance to Isolated Phase Bus ................................................................................ 15

5.0 CONDUIT SYSTEM DESIGN CRITERIA..................................................................................... 17 5.1 Conduit Type and Material Selection ........................................................................................... 18

5.1.1 Rigid Metal Conduit ............................................................................................................. 19 5.1.2 Electrical Metallic Tubing .................................................................................................... 19 5.1.3 Liquidtight Flexible Metal Conduit ...................................................................................... 20 5.1.4 Conduit Fittings .................................................................................................................... 20 5.1.5 Conduit Supports .................................................................................................................. 21

6.0 RACEWAY PENETRATIONS DESIGN CRITERIA .................................................................... 22 6.1 Design Considerations for Electrical Fire Stop Penetrations........................................................ 22 6.2 Penetrations for Cables in Trays ................................................................................................... 22 6.3 Penetrations for Cables in Conduit ............................................................................................... 24

7.0 UNDERGROUND DUCT SYSTEM DESIGN CRITERIA............................................................ 25 7.1 Underground Ductbanks ............................................................................................................... 25 7.2 Cable Trench System .................................................................................................................... 27

8.0 REFERENCES ................................................................................................................................. 28 9.0 CODES AND STANDARDS........................................................................................................... 29 10.0 ATTACHMENTS..........................................................................Error! Bookmark not defined.




1.0 PURPOSE & SCOPE

The purpose of this procedure is to provide technical direction for the conceptual and detailed design of the electrical cable raceway systems and method of cable installation in the various raceways, including tray and conduit systems. This procedure will also provide direction for the design of cable raceway fire stops.

The raceway system shall provide a safe and orderly means of routing electrical cables, and supporting cable runs between electrical equipment including sufficient spare raceways for future additions and modifications. The system, as a minimum, shall conform to the NEC recommendations and requirements detailed in the NEC and IEEE 422.

2.0 DEFINITIONS

Accessories Devices that are used to supplement the functions of the raceway system, such as dropouts, end plates, conduit clamps, tray cover clamps, etc.

Anchorages The connection between the building and the raceway support.

Cable Tray A prefabricated metal raceway with or without covers, consisting of side rails and bottom support sections of the ladder, trough or solid type for use with wire and cable.

Cable Tray System

An assembly of metallic cable tray sections, fittings, supports, anchorages, and accessories that form a structural system to hold and support wire and cable.

Cable Trench A below grade raceway with concrete walls and metal or concrete covers at grade level for use with wire and cable.

Conduit A raceway of circular cross-section with couplings, connectors, and fittings for use with wire and cable.

Conduit System An assembly of conduit sections, fittings, supports, anchorages and accessories that form a structural system to hold and support wire and cable.

Corrosive Soil In general, soils producing severe corrosive effects are characterized by low resistivity of less than 2000ohm-cm.

Fittings Raceway sections jointed to other raceway sections for the purpose of coupling together or changing the size or the direction of the raceway system.

NEC National Electrical Code (NFPA-70).




Raceway Any channel designed and used expressly for holding and supporting wire and cable. Raceways may be of metallic or nonmetallic material, and include rigid tubing (EMT), cable tray, underground duct , cable trench, flexible conduit, intermediate metallic conduit (IMC), and rigid metallic conduit.

Raceway Penetration

A wall or floor opening to permit passage of raceway and cable from one side to the other.

Raceway Support

An assembly of structural members whose function is to provide structural stability for raceways.

Underground Duct System-

Metallic or nonmetallic conduit enclosed in reinforced concrete or directly buried in earth, including access points, such as manholes and handholes.

Cable Raceway Firestop

A method of sealing penetrations through walls or floors in order to bring the wall or floor back to its original fire rating.

3.0 RACEWAY DESIGN CRITERIA

3.1 General

The Electrical Design Criteria for Raceway Systems shall be used for input to specifications and for developing construction drawings.

3.2 Electrical Requirements

The design of the cable tray system shall initially be performed at a conceptual level based on equipment arrangements, preliminary project one lines, tray service level projections and allowances for future growth and changes during detailed design.

Note: The importance of developing an accurate, cost-effective conceptual design cannot be over-emphasized to minimize costly future redesign activities or excessive unused tray capacity. After a conceptual design is finalized, detailed design activities can proceed.

The raceway system shall be adequately sized and have provisions to accommodate reasonable future changes or additions needed. Approximately 20 percent spare ducts in a duct bank shall be provided.

Metallic raceways shall be grounded and electrical continuity between conduit and equipment shall be provided in accordance with the 39BCC-06 "Grounding and Lightning Protection Design Criteria" (Ref. 8.1).




Design interfaces include:

1) Develop drawings of proposed tray configurations to indicate design, arrangement, and location.

2) Stipulate testing requirements in the cable tray specification for Vendor supplied hardware and monitor vendor conformance to those requirements. Cable tray connector plates between tray sections shall be specified to develop the same or higher strength as the rails they connect to. If the tray is used as an equipment grounding conductor, ensure requirements of NEC are specified in the cable tray specification.

3) Provide details or references as necessary on Electrical drawings to convey information concerning cable trays which are required by vendors and construction forces.

4) Perform interdiscipline interference checks and submit sketches and/or drawings to other disciplines for interference and compatibility reviews. The sketch submittal may not be required on CAD produced drawings.

5) Ensure that local codes or regulations impose no restrictions in the use of cable trays or conduits for the project.

6) Establish the extent and usage of tray covers and types of covers. In nuclear plants and some industrial facilities, fire barriers must be considered. Derating of power cables may be required when solid covers are used. However, most tray covers are side or top ventilated, accordingly, no derating is required.

3.3 Civil-Structural Interface

Standard support details should be used for tray/conduit supports. However, the Civil- Structural Engineer should be consulted when a standard detail does not apply due to physical limitations of cable tray supports and tray span/type. When a Standard detail does not fit the application, identify “special” non-standard applications and submit them to Civil-Structural project personnel for development and/or approval.




3.4 Structural and Mechanical Requirements

The routing of raceways shall avoid conflict with passageways or access to equipment required for operation, removal, or maintenance. Wherever practical, raceway systems shall be routed to run either parallel or perpendicular to building walls or structures.

In congested areas where cable trays are stacked more than three high a clear floor to ceiling area, three ft wide, shall be reserved adjacent to the trays to allow for fire-fighting activities.

All trays and conduit near piping shall be located with sufficient clearance between the raceway and the pipe to permit the application of heat insulation on the pipe and permit unobstructed movement of pipe during normal operation. Install raceways and cable trays at least 6 inches away from flues and steam and hot water pipes. If insulated, maintain 6 inches from the outer edge of the insulation. Minimum of 12 in. clearance is recommended before pipe insulation is installed.




3.5 Raceway Service Level Description

The design phase includes developing the raceway identification requirements for the project. Power, control, and instrument cables are installed in separate raceway systems for safety and electrical considerations. This is commonly referred to as service level separation. The tray system identification for service level separation shall be J, H, JH, L, K, LK, C, and X. The conduit and duct system identification for service level separation shall be J, H, L, K, C,and X. Table 5-1, provides service level tray and conduit identification and permitted cable construction, size and installation method for each tray system.

Raceways shall be given letter designations according to service as follows:

• "J" trays shall be used for power cable with rated voltage 5,001V to 15 kV.

• "H" trays shall be used for power cable with rated voltage 601 to 5,000 V.

• "L" trays, if used, shall contain large 600 V power cables (4/O and larger) installed one layer across with 1/4 to 1.0 cable diameter between cables. L trays would include bus ties, secondary leads of auxiliary transformers, large motors and MCC feeders.

• "K” trays shall be used for power cable with rated circuit voltage up to 600 V. Maximum tray fill shall be 40 percent of the cross-sectional area of a 3 in. loading depth.

• "C" trays shall be used for control cables up to 250 V operating voltage. Maximum fill shall be 50 percent of cross-sectional area. Control cables may be installed in K trays to avoid the use of partially filled "C" trays to isolated locations. Maximum fill shall be 50% of cross sectional area, unless solid bottom trays are used, where maximum fill is limited to 40%.

• "X" trays shall be used for low level signal instrument, thermocouple extension or control (50 V or less) shielded cables. Maximum fill shall be 50% of cross sectional area, unless solid bottom trays are used, where maximum fill is limited to 40%.

Tray type “JH” allows the installation of 5 kV, 8 kV and 15 kV in the same tray. This is permitted by NEC [Section 318-6(f)] and IEEE 422 [ 4.2.1]. Use of the “JH” tray system is intended to simplify the design process. If tray type “JH” is used, then tray type “J” and “H” would not in general be used for the same route.

Tray type “LK” combines “L” tray, larger power cables spaced in trays with “K” tray, smaller cables installed in random fill. Stone & Webster’s Cable, Equipment and Instrument Database System (CEIDS) will calculate the proper fill for the LK tray. Separate “L” and “K” trays where cable quantities for each type of cable justify additional trays.




3.6 Raceway Identification and Numbering Requirements

Conduit shall be identified at each end of the conduit and on both sides of a wall that the conduit passes through.

Tray shall be identified at each end, on either side when passing through blockouts in walls, and also on both sides of the tray, if side is not against a wall, at approximately 50ft intervals.

Sleeves shall be identified at each end of the sleeve.

The preferred numbering system for raceways consists of a composite alpha-numeric number, as follows:

1) Unit Number 2) Raceway Type

a) T= Tray b) C = Conduit c) D = Duct d) F = Floor Sleeve e) W = Wall Sleeve

3) Tray Service Level (C, X, etc) 4) Separation Code (A, B, etc.) Separation code is optional if no redundancy requirement exists. 5) Unique number, which also identifies building or area, e.g. 001 - 500 = Turbine Building,

501 - 600 = Control Building, etc.

Using the numbering system, a “C” tray in the turbine building (T) for the second unit of a power generating station for an “A” bus, would be numbered:

2 T C A - 100

Unique Number Separation Code Service Level Raceway Type Unit Number




TABLE 1 RACEWAY IDENTIFICATION, CABLE TYPE & INSTALLATION

Raceway Identification

Cable Type & Rated Cable Voltage

(ICEA)7

Cable Type & Rated Cable Voltage (IEC)

Uo/U (Um)8

Rated Circuit Voltage

Conductor Size Method of Cable Installation-Tray

J 8 kV Power 15 kV Power

6/10 (12) kV Power 8.7/15(17.5) kV Power

6,900V 13,800V

All 1 layer maintained spacing or touching5

H 5 kV Power 3.6/6 (7.2) kV Power 4,160V All 1 layer maintained spacing or touching5

JH (Tray Only)

5 kV Power 8 kV Power 15 kV Power

3.6/6 (7.2) kV Power 6/10 (12) kV Power

8.7/15(17.5) kV Power

4,160 V 6,900V

13,800V

All 1 layer maintained spacing or touching5

L 600 V Power 0.6/1 kV Power 0 to 600V All 1 layer maintained spacing or touching5

K 600 V Power 600 V Control

1

0.6/1 kV Power 0.6/1 kV Control1

0 to 600V 0 to 250V

3/C 12 - 1; 1/C or Triplex 1/O - 3/O

14-4 AWG

Random Fill - 40 %2

LK (Tray Only)

600 V Power 600 V Control1

0.6/1 kV Power 0.6/1 kV Control1

0 to 600V 0 to 250V

a) 3/C 12 - 1; 1/C or Triplex 1/O - 3/O

b) 1/C or Triplex 4/O kcmil & Larger c) 14-4 AWG

a) Random Fill - 40 %2

b) 1 layer maintained spacing2,3

c) Random Fill - 40 %2

C 600 V Control 0.6/1 kV Control 0 to 250V 14-4 AWG Random fill 50%2 X 300 V Instrument,

300 V Thermocouple Extension, Fiber

Optic, Coaxial and 600 V control4,6

150/250 V Instrument, 150/250 V Thermocouple Extension, Fiber Optic, Coaxial and 0.6/1 kV

Control4,6

50V and less 14 AWG and smaller Random Fill 50%2




Notes to Table 1: 1) Control cable in K raceway or LK tray is permitted where small quantities of C cables are

installed along the route and a separate C raceway is not available.

2) Tray fill by area calculated on the basis of using a 3 inch (76 mm) deep tray (inside dimension), which is in agreement with the NFPA-70 (NEC). When deeper trays are still used, tray fill shall be based on a 3 inch (76 mm) tray, resulting in reduced percentage fill.

3) LK tray type permits 4/O AWG and larger conductor sizes to be installed 1 layer maintained spaced on one side of the tray and on the other side of the tray, 3/O and smaller cables are installed random filled. This design is permitted by NEC.

4) Control cable in X raceway must have an operating voltage of 50 V or less, contain low level signals and be shielded.

5) Project should consider one layer touching installation method for tray because of potential cost savings and limited impact on cable sizing. Cable sizing charts in 39BCC-08 "Wire and Cable Design Criteria" (Ref. 8.2) are based on L-tray touching.

6) Digital signal instrument cable must be shielded.

7) Insulated Cable Engineers Association (ICEA) nominal line-line voltage rating for cable.

8) International Electrotechnical Commission (IEC), where U0/U (Um) is nominal line to ground/nominal line to line (maximum line to line) voltages.

3.7 Unsupported Cable Length

Unsupported cable is defined as that portion of cable that runs outside of raceways or conduits. In general, the maximum unsupported length of cable should not exceed 4 ½ ft for electrical considerations.

Where power (J, H, or L) cables are spaced for heat dissipation purposes, the unsupported cable length should not exceed 3 ft.

Additionally, structural considerations with regard to raceway and/or associated supports may dictate unsupported cable lengths that are more restrictive.

This unsupported cable length requirement does not apply to cable lengths inside of equipment.




4.0 CABLE TRAY SYSTEM DESIGN CRITERIA

The cable tray system is provided for holding and supporting wire and cable with different voltage levels.

Drawings developed early in the project that depict the major tray routes shall be distributed to other disciplines for review.

Cable trays shall conform to NEMA VE 1 and FG 1as applicable

4.1 Cable Tray Material Selection

Materials of construction include galvanized steel, aluminum, stainless steel, and non-metallic designs. Galvanized steel tray is available in pre-galvanized (hot dipped mill-galvanized) and hot-dip galvanized after fabrication (HDGAF) with varying coating thickness. HDGAF tray should be specified if steel tray is used.

Hot dipped galvanized steel tray (HDGAF) is the preferred choice. Aluminum tray has been used on some projects based on construction preference.

All metal cable trays shall be manufacturer's standard.

Careful consideration should be given to corrosion concerns when selecting tray types. Tray selection may vary depending on the area of a facility. In areas that have a corrosive atmosphere (such as caustic sprayings, salt water intake structures, etc.), trays shall be selected with suitability for the atmosphere. For these areas, fiberglass trays or metal PVC coated trays shall be considered.

If the trays are intended to maintain their installed position during a fire, consideration should be given to the combustibility and structural integrity of the tray. Steel trays are suitable for this application.

4.2 Cable Tray Type

Cable trays shall be ladder-type with rung spacing of 9 in. to allow exiting the tray from the bottom. Cable tray types include ladder, solid bottom, ventilated channel with or without covers. Solid bottom trays should not be used for power cables unless an analysis of the required cable derating is conducted.




4.3 Cable Tray Fill

Cable trays for random fill power cables shall only be filled based on 40% of a usable 3 in. depth siderail regardless of a greater actual siderail depth. Four-inch usable depth tray shall be considered only when structural integrity demands the added rail strength. Cable trays for control cables may take advantage of the 4 in. usable depth siderail by loading to 50% of the usable area.

Vendor requirements shall be reviewed for instrument and control cable installation in trays where only steel trays with solid bottoms and covers may be required.

4.4 Cable Tray Arrangement

Cable tray arrangement shall be designed so that the higher voltage cable tray is above the lower voltage cable tray.

The minimum vertical distance between stacked trays (i.e., bottom to bottom of tray) shall be 16 in. and the bottom of tray to the ceiling above shall be minimum 16 in.

Trays shall not be located close to heat sources, unless cables are derated for the expected temperature.

When the tray system is run parallel to a wall with wall sleeves, the design shall offset the ducts and trays so that the cables drop out of the ducts and to the trays, and tray is no more than 12 inches from the wall sleeve.

Some specific areas of concern include the following:

1) Care should be exercised to avoid excessive temperatures on cable, raceway, raceway brackets, and supports due to electrical or ambient/convection heat sources.

2) Hysteresis and eddy current losses in the steel brackets and supports and currents induced in the tray sides circulating through the bracket and support connection can result in temperatures sufficiently high to damage cable jackets. This type of heating usually occurs in high current applications such as station service leads and generator leads consisting of two or more conductors per phase and not arranged to reduce effects. Specific instructions showing the required conductor spacing and arrangements shall be shown on the design drawings and / or installation specifications. The correct installation requires that each set of sub-phase conductors A,B,C be installed as a group and not all A phase, all B phase, all C phase as a group.

3) The use of aluminum brackets will eliminate high temperatures which might occur in steel hangers and brackets caused by hysteresis and/or eddy currents,

4) When a single sub-phase conductor is installed in a tray and where the hanger system is necessarily arranged so that induced circulating currents can flow in the system and result in




heating, it may be necessary to isolate the trays from the supports with insulating material to break up the circulating current paths and also to shorten the continuous run of tray to reduce the induced voltage to a safe value. Where trays are insulated from their supports, a single ground bonded to a tray near the midpoint of each unbroken run is mandatory. In addition, a field check should be made on such insulated tray sections, after energizing of the circuits, to assure that the tray to ground potential does not exceed 15 V at any point. If so, additional grounding may be required.

4.5 Cable Tray Supports

Tray sections shall be supported near section extremities and at fittings such as tees, crosses, and elbows.

These fittings should be located under existing structural steel in order to provide support near the splice points.

Cable tray supports shall be of the trapeze, cantilever, or propped cantilever types. Tray systems utilizing trapeze type supports shall be used unless space limitations or method of attachment precludes their use. Trapeze supports shall utilize threaded rods and strut type material.

Cable tray supports shall be designed based on sustaining an allowable working load capacity of 50 lb per linear foot (including tray and cable weight) and a concentrated load of 200 lb at mid-span. The 50 lb per linear foot is designated by the symbol A in NEMA VE 1. The longitudinal distance between cable tray supports in general shall be 8 ft. The support span shall not exceed the recommended span for the NEMA class, i.e. for a NEMA Class 8 the support span is 8 ft per NEMA VE 1, this is a Load/Span Class designation of 8A. The 200 lb mid span load must be added to this. Vendor recommendation for support location should be followed.

Cable loading in trays is usually less than 35 lb/ft.

The effects of ice, wind and snow loading on the trays shall be reviewed for tray loading adequacy with the Structural Engineer.

The effects of seismic loading on the trays shall be reviewed with the Structural Engineer.

4.6 Cable Tray Fittings

The cable tray system design shall make use of appropriate tray fittings, such as elbows, tees, crosses, reducers, covers, barrier strips, etc, and accessories.




Splice plates complete with bolts, nuts, locking devices, and bonding jumpers shall be used for the joints between tray sections. When required, expansion splice plates shall be used, complete with bonding jumpers to assure ground continuity across the expansion joint.

The inside radius of the tray fittings shall be suitable for the bending radius of the cables. Typically the bending radius concern is with medium voltage cables. Uniformity in tray width sizes should be considered especially for support installations and to minimize fitting types.

Dropout fittings shall be provided when the minimum cable bend radius cannot be maintained.

Horizontal trays exposed to falling objects or accumulation of debris shall have covers of the same material as that of the tray to be covered.

Vertical tray risers at floor levels and other locations where possible physical damage to cables could occur, shall have covers on all sides.

Use of tray covers for indoor applications is generally a client decision or to provide barrier separation or to protect cable from debris.

Tray covers are required for all outdoor installations to protect the cables from the effects of the sunlight, even when purchasing sunlight resistant cables. It should be noted that applying covers to trays may also require cable ampacity derating. Use of trays, with side ventilated tray covers or trays with raised covers, normally does not require conductor ampacity derating; however, solid covers will require derating of power cables.

Power tray covers, when used, shall be solid top, side ventilated. I/C cable covers may be solid. Tray covers shall be vendor’s standard galvanizing process, whether galvanized before or after fabrication.

4.7 Tray Grounding

The cable tray system shall be bonded to ensure continuity, and grounded to the grounding system or building in accordance with the Electrical Design Criteria for Grounding and Lightning Protection and the National Electrical Code.

Equipment grounding methods and requirements should also be factored into tray selection. If the tray system is used for equipment grounding, consideration should be given to the tray cross sectional area, the continuity of the tray including splice plates, bonding jumpers, and also to installing a continuous copper cable in the tray. See 39BCC-06, “Grounding and Lightning Protection Design Criteria”, (Ref. 8.1).




4.8 Tray Barriers

The use of cable tray barriers is permitted where necessary to eliminate a separate tray system on an isolated run or where there is insufficient number of cables to justify a separate tray. This barrier may be used if 5 kV power cable and control cables are installed in the same tray. Each side of the barrier should be assigned a different raceway number for identification.

4.9 Cable Tray Clearance to Isolated Phase Bus

Note: User select as appropriate:

1) Isolated phase bus with welded enclosures (miniflux design) confines the magnetic field to the bus enclosures and has minimal effect on adjacent building steel or cable trays. A minimum of 6-inch (152 mm) clearance is required between the isolated phase bus and building steel and tray with the use of the miniflux design.

2) Isolated phase bus with gasketed or insulated enclosures produces an external magnetic field that causes inductive heating in adjacent structural steel and cable trays. Isolated phase bus with gasketed or insulated enclosures is no longer specified but may be found in generating stations built before 1975. Table 2 may be used as a guide in determining minimum clearances of cable trays from gasketed or insulated type isolated phase generator leads. Cable ampacity of power cable installed to the clearances presented in Table 2, must be derated by 25% to account for the additional 20°C rise above ambient temperature.

Notes and Conditions for Table 2:

1) Except as obvious in the illustrations, d is the distance from the bus housing to bottom or cover of tray.

2) Clearances given are conservative and will assure a temperature rise not exceeding 20°C.

3) Clearances may be reduced if necessary by use of short circuiting bands, shields, or amortisseur grids.

4) Clearances are based on the following:

a) Round high conductivity bus enclosures not welded

b) Basket or ladder type trays

c) Phase spacing of bus 50 inch (1270 mm) or less

d) Trays running parallel to bus have a return conducting path. (This is unavoidable unless special steps are taken to insulate the tray from supporting members)




Table 2

Clearance Between Tray and

Gasketed or Insulated Type Isolated Phase Generator Leads

Clearances - d- inches (mm)

Bus

Amp

Steel Alum.

Steel Alum.

Steel Alum.

Steel Alum.

5,000 7(178) 6(152) 6(152) 6(152) 6(152) 6(152) 6(152) 6(152)

6,000 11(279) 6(152) 6(152) 6(152) 7(178) 7(178) 6(152) 6(152)

7,000 15(381) 6(152) 9(229) 6(152) 11(279) 10(254) 6(152) 6(152)

8,000 18(457) 8(203) 12(305) 6(152) 14(356) 13(330) 8(203) 8(203)

9,000 20(508) 10(254) 14(356) 8(203) 17(432) 16(406) 11(279) 10(254)

10,000 23(584) 12(305) 17(432) 10(254) 19(483) 18(457) 13(330) 12(305)

15,000 32(813) 18(457) 25(635) 15(381) 28(711) 26(660) 21(533) 19(483)

20,000 38(965) 24(610) 30(762) 20(508) 35(889) 32(813) 27(686) 25(635)

d

d

d d

d

d




5.0 CONDUIT SYSTEM DESIGN CRITERIA

The conduit system provides mechanical protection to the cables. It shall be designed to allow cables to be installed without exceeding permissible pull tensions and sidewall pressures to prevent damage to the cable.

The maximum allowable conduit bends are three equivalent 90 degrees. Note: This can be increased to four 90 degree bends, in accordance with the NEC, for short runs of less than 20 ft.

Conduit system design shall use junction boxes, pull boxes, condulets, etc., where necessary to facilitate easy installation of cables.

Pull boxes shall be sized to ensure the cable permanent bend radius limits are not exceeded. Extra large boxes are typically necessary for medium voltage power cables.

Conduit systems shall be designed so that the maximum percent of cross-section area of cable shown in Table 3 is not exceeded. This table is applicable to cables pulled into empty conduits.

Table 3 Maximum Percent of Cross Section

of Conduit and Tubing for Cable Number of Cables Cable Type

1 2 3 4 Over 4 All, except Lead

Covered 53 31 40 40 40

Lead Covered 55 30 40 38 35

If the final design layout of the conduit between pull points can not conform to the guidelines of IEEE –1185, a cable pulling calculation shall be performed. In addition, conduits containing three single conductor power cables shall be sized to avoid critical jamming ratio diameters. See 39BCC-08 "Wire and Cable Design Criteria" (Ref. 8.2) and 39BDC-05 "Cable Pulling Calculations"(Ref. 8.3).

Note: Cable jamming can occur when three equal size single conductor power cables are pulled into the same conduit/duct and the sum of their cable diameters (d) equals the inner diameter of the conduit/duct (D). If the jam ratio (D/d) is between 2.8 and 3.1, either the conduit size shall be changed or the cable dimensions changed (add jacket thickness or use a larger conductor size). In this case a larger size conduit shall be selected.

Conduit runs shall slope to the end points (e.g., pull or junction boxes) for drainage. Where raceways and boxes may be subject to moisture accumulation, drain holes should be provided at appropriate locations. Conduits entering equipment enclosures from above or sides should be located so that water will not drip on or into equipment. Suitable steps, such as sealing the open




end of the conduit, drains, etc., shall be taken to prevent water from entering and/or accumulating within the conduits or enclosures. Conduit hubs shall be used for outdoor installation.

The entire metallic conduit system, whether exposed or concealed, shall be electrically continuous and grounded in accordance with the NEC and Electrical Design Criteria for Grounding and Lightning Protection.

Spare conduit should be capped to prevent the entrance of moisture.

Note: Single-phase power cables shall not be run individually in a magnetic conduit or be routed through a single hole in magnetic boxes unless a slot is cut between holes in the box. This can occur when multiple conductors per phase are required to equipment. Example, do not run A,A in one conduit; B,B in one conduit; and C,C in another conduit to the equipment terminals. The correct method is to run A,B,C in one conduit and A,B,C in another. The phases can then be spread in a connection box.

Conduit shall comply with ANSI C80.1, C80.3, C80.5, C80.6, NEMA RN 1, TC 2 and TC 13 as applicable.

5.1 Conduit Type and Material Selection

Table 4 lists the available conduit types and the applicable NEC article governing its permitted use and other restrictions.

Table 4 Available Conduit Type and Applicable NEC Article

Conduit Types Available Materials

NEC Article

Electrical Nonmetallic Tubing

362

Intermediate Metal Conduit (IMC)

342

Rigid Metal Conduit Steel, Aluminum 344 Rigid Nonmetallic Conduit PVC, PE, Fiber 352 Electrical Metallic Tubing

(EMT) 358

Flexible Metallic Tubing 360 Flexible Metal Conduit 348

Liquidtight Flexible Conduit 350




5.1.1 Rigid Metal Conduit

Rigid aluminum or galvanized steel conduit may be used for all exposed indoor and outdoor runs of power, instrumentation, and control cables. Galvanized steel is the preferred type but aluminum is easier to install in larger sizes (3” and up). In areas that have a corrosive atmosphere, it will be necessary to select the conduit based on its suitability for the atmosphere.

Typically, metallic conduit installed in corrosive soil or atmosphere may require coating with an asphaltum or bituminous compound, or a plastic or PVC coating.

Rigid galvanized steel conduit may be used for applications that require concrete encasement, including use in duct banks. Aluminum conduit shall not be encased in concrete, masonry walls and floors, or buried in earth. Rigid steel conduit may be directly buried in earth.

Minimum conduit size shall be ¾ in. If devices have a ½ inch opening, a reducer to ½ inch conduit shall be used to accommodate the device.

Where exposed conduit crosses a vibration joint or where conduit expansion provision is required, a short length of flexible conduit shall be provided. Where conduit crosses a vibration joint in a slab, an 18 in. length of flexible steel conduit, wrapped with 1/2 in. of oakum and three thicknesses of burlap and thoroughly painted with asphaltum, shall be used or equal protection provided.

All conduit, boxes and fittings located in screenwells, underground tunnels, and on masonry or concrete walls where exposed to moisture, shall be mounted so there is an. air space between the conduit and the supporting structure. The minimum air space shall be ¼ inch.

The positive and negative polarity conductors connecting the 125V DC station battery to the Dc power distribution equipment shall be run in separate conduits. However, this should never be done with single-phase ac current in rigid steel conduit.

5.1.2 Electrical Metallic Tubing

Electrical metallic tubing (EMT) may be used in non-hazardous and dry indoor locations, in areas not subject to severe mechanical damage or excessive vibration, for lighting, miscellaneous low voltage power and communication circuits.




5.1.3 Liquidtight Flexible Metal Conduit

Liquidtight flexible metal conduit consisting of an inner flexible metal core with an outer liquidtight, nonmetallic, sunlight resistant PVC jacket, shall be used between rigid metal conduit and equipment conduit boxes on all motors, connections to thermocouples, pressure and level switches, or in any situation where vibration is anticipated or frequent maintenance or adjustment, may be required.

Flexible conduit length shall not exceed 6 ft; if it must exceed 6 ft. or the overcurrent protection for the circuit exceeds 20A, refer to NEC Article 350.10 and Article 250.118 for specific requirements.

Flexible conduit shall permit free movement of vibratory equipment. Electrical continuity between conduit and equipment shall be provided by suitable connectors or jumpers. Refer to the design criteria 39BCC-06 for “Grounding and Lightning Protection” (Ref. 8.1) for methods of installing jumpers.

Flexible conduit shall be grounded in accordance with NEC Article 350.60.

5.1.4 Conduit Fittings

Conduit fittings for rigid metal conduit and intermediate metal conduit (IMC) are interchangeable.

Conduit fittings for EMT are threadless, such as compression, indentation, set screw or push on type couplings and connectors. Compression fittings only should be used.

Conduit design shall utilize shop fabricated elbows for large conduits (3 in. and greater) thereby limiting the need for field design and minimizing field bending of large conduit.

Boxes or fittings shall be provided in vertical runs to permit installation of conductor supports when the length is long enough to require additional support.

Junction and pull boxes providing access points for pulling and feeding conductors into the conduit system may be galvanized sheet steel or aluminum.

Where practicable, pull boxes and conduits shall be arranged to provide a straight cable pull-through capability.

Conduits entering galvanized sheet steel or aluminum boxes from the top or side, that are exposed to water or rain, shall be terminated with a sealing hub type fitting or sealing lock nut.

Conduits entering boxes and fittings indoors, shall be terminated with insulating bushings, unless the box or fitting provides equivalent protection, and with locknuts. Where bushings fabricated




entirely of insulating material are used, two locknuts shall be installed, one outside and one inside the box, to assure proper rigid connection and electrical grounding continuity between the box and conduit.

Boxes and fittings shall comply with NEMA 250, FB 1, OS 1, and OS 2 as applicable.

5.1.5 Conduit Supports

Rigid metal conduit, IMC and EMT shall be supported by means of conduit hangers, such as O-Z/Gedney Type H-WBS, or equivalent.

Maximum spacing between supports for rigid metal conduit and EMT shall be in accordance with NEC Section 344.30. Maximum distance between IMC conduit supports shall be in accordance with Section 342.30 which requires a maximum of ten ft between supports, unless special exceptions are taken. Maximum distance between nonmetallic conduit supports shall be in accordance with NEC Section 352.30. In addition, all above conduits shall be supported within 3 ft of each box, cabinet or other conduit terminations, unless NEC special exceptions are taken.




6.0 RACEWAY PENETRATIONS DESIGN CRITERIA

Blockouts or slots are preferred over sleeves for passage of cable through building floors or walls.

Floor and wall openings shall be designed for addition of cables at a later date without sacrificing structural integrity of the floor or wall.

In areas where multiple sleeves are required in a group, consideration should be given to the configuration and number of sleeves to allow access to each sleeve for sealing purposes or for future use.

Spare sleeves or openings shall be capped or enclosed for future use.

Whenever a raceway penetrates a fire-rated wall, floor, etc, the raceway cable interstices shall be sealed so that the fire resistant barrier is not diminished. Seals shall also be considered between areas with different environments such as dust, pressurized, etc. Design shall be in accordance with the following Cable Raceway Fire Stop design considerations. Note: This requirement shall be specified in the applicable project electrical installation specification and on the raceway drawings.

6.1 Design Considerations for Electrical Fire Stop Penetrations

The performance of an electrical firestop varies with the firestop material, design features of the penetration opening, and the cable/raceway materials. The following guidelines will ensure the use of cost-effective fire stop material from a variety of suppliers.

6.2 Penetrations for Cables in Trays

Figure 1 illustrates the preferred method of penetrating fire resistive-rated barriers for cable tray. The dimensions shown are necessary so that adequate reinforcing can be installed and to facilitate cable installation.

In this design, the cable tray does not pass through the fire-resistive-rated barrier. A grounding wire shall be installed through the firestop and bonded to the tray side rails on each side of the barrier.




Figure 1 - Fire Stop Penetration For Cables in Trays




6.3 Penetrations for Cables in Conduit

Figure 2 illustrates a fire stop design for conduits which penetrate fire-resistive-rated barriers. Conduits 5 inch and larger shall be sealed at the barrier. Conduits 4 inch and smaller that extend a minimum of 5 ft on each side of the barrier may be sealed at the end of the conduit.

Figure 2 - Fire Stop Penetration for Cables in Conduit




7.0 UNDERGROUND DUCT SYSTEM DESIGN CRITERIA

The underground duct system shall consist of rigid nonmetallic or metal conduit resistant to moisture and corrosive agents suitable for concrete or earth encasement.

Duct runs shall be as straight as practicable, avoiding major interference with foundations, pipes, etc. The straight line route between pull points should be selected without regard for being parallel or perpendicular to building steel or underground piping. Anticipated use of excavations common to other underground work will, however, influence routing, particularly on long runs. The careful selection of manhole locations and orientation will help eliminate bends.

7.1 Underground Ductbanks

Ducts in duct banks encased in concrete or in concrete slabs shall be PVC schedule 40. Direct buried ducts shall be PVC Schedule 80. Rigid galvanized steel conduit may also be used if PVC Schedule 80 is not available.

Where buried ducts are run below a concrete slab, it may be possible to use PVC Schedule 40. The Responsible Engineer must evaluate this use.

Individual ducts shall not be encircled by ferrous materials (e.g. rebar or iron mesh) to avoid heating damage from circulating currents.

Duct sizes shall be based on 53 percent fill for one cable, 31 percent two cables, and 40 percent for three or more cables, and are limited to 2 in and larger.

The number of cables in the same duct shall be limited to the allowable fill. It is desirable when scheduling cables in ducts that cables pulled simultaneously have generally the same origin and destination.

The type of sweep required is dependent on the allowable cable bend radius. Where special long radius sweeps are required, they shall be specified on the drawings.

Where ducts turn up for terminating at building walls, equipment foundations, or elsewhere, transition from plastic to metal conduit shall made by the use of approved watertight threaded adapters.

Ducts shall be spaced according to duct configurations to provide adequate heat transfer. Design of duct bank must be coordinated with the cable sizing calculations.




Concrete-encased duct banks shall be adequately reinforced under roads, railroad tracks, and in areas where heavy equipment may be moved over the duct bank. The Electrical Engineer shall obtain approval from the Structural Engineer for the duct bank design in these areas.

Prefabricated manholes and handholes shall be used wherever practical. Manhole vendor design shall used. When this is not practical then the Manhole details shall be as shown on Electrical Design Standard Details in 39BKH (egd-32A, B and egd-41A, B) should be used.

Manhole openings shall be sized for the cable-bending radius and shall be a minimum of 3 ft-0 in. in diameter. All cable pulling points shall have covers large enough to permit exit and reentry of cable without compromising the minimum bending radius of the largest cable to be pulled. Manholes shall include a sump pit to allow for the use of portable sump pumps.

The duct bank shall be designed so that the maximum pulling tension, including sidewall pressure, does not exceed the cable manufacturer's recommend value. This is accomplished by adhering to the following duct layout guidelines or by performing cable pulling calculations. In general, cable pulling calculations should be considered for ducts runs exceeding 1500 ft or where more than two manholes are required in a single duct run. If cable pulling calculations are performed, then the duct bank drawings shall clearly indicate which direction cable pulling can be made.

The length of duct between pulling points shall not exceed:

• Straight run (with up to 30 degrees in bends) - 550 ft

• Up to 90 degrees in bends - 350 ft

• Up to 180 degrees in bends - 150 ft

Ducts shall slope 3 in. per 100 ft toward the manhole, handhole, or other point suitable for drainage.

The most desirable cable installation is that which permits pulling from termination-to-termination without splices. This is not always possible, especially with long runs, heavy cables, or excessive bends. In the interest of avoiding splices, each installation shall be reviewed to determine direction of pull, location of "pull-through" manholes, and facilities for exit and reentry. Where splicing is necessary, the locations shall be predetermined and cable lengths specified.

Duct banks shall have a minimum earth cover of 2 ft. 6 in. wherever possible. In those cases where depth of duct banks is critical to avoid interference and heavy vehicle loading is not a factor, a minimum earth cover of 18 may be used. If the duct bank requires a minimum earth cover greater than 2 ft 6 in, derating of the cables may be required as outlined in the cable criteria.

If a lesser earth depth is desired, the Structural Engineer should be consulted.




Where more than 12 power cable ducts are required, separate duct banks should be considered.

7.2 Cable Trench System

Cable trenches shall be installed in the earth with covers flush with, or extending above the surrounding finished grade.

Cable trenches shall be with precast concrete walls and floor. Covers shall be pre-cast concrete, fabricated galvanized steel or aluminum.

Where vehicles cross cable trenches, trenches and covers shall be designed to carry the anticipated load. The Electrical Engineer shall obtain the truck load-rating of trenches from the Structural Engineer. The rating designation must be clearly shown on the drawings.

Ample drainage shall be provided for the bottom of cable trenches to avoid constant immersion of cables in water.




8.0 REFERENCES

8.1 39BCC-06 "Grounding and Lightning Protection Design Criteria."

8.2 39BCC-08 "Wire and Cable Design Criteria"

8.3 39BDC-05 "Cable Pulling Calculation"

8.4 IEEE 422-86 Guide for the Design and Installation of Cable Systems in Power Generating Stations

8.5 IEEE 1185-94 Guide for Installation Methods in Generating Station Cables




9.0 CODES AND STANDARDS

CABLE TRAY STANDARDS NEMA VE 1-91 Metal Cable Tray Systems NEMA FG 1-93 Fiberglass Cable Tray Systems

RACEWAY AND BOXES STANDARDS ANSI C80.1-1990 Rigid Steel Conduit, Zinc-Coated ANSI C80.3-1995 Electrical Metallic Tubing, Zinc-Coated ANSI C80.5-1990 Rigid Aluminum Conduit ANSI C80.6-1986 Intermediate Metal Conduit (IMC) NEMA 250-91 Enclosures for Electrical Equipment (1000 Volts Maximum) NEMA FB 1-93 Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit and

Cable Assemblies NEMA OS 1-89 Sheet-Steel Outlet Boxes, Device Boxes, Covers, and Box

Supports NEMA OS 2-86 (R91) Nonmetallic Outlet Boxes, Device Boxes, Covers, and Box

Supports NEMA RN 1-89 Polyvinyl-Chloride (PVC) Externally Coated Galvanized Rigid

Steel Conduit and Intermediate Metal Conduit NEMA TC 2-90 Electrical Plastic Tubing (EPT) and Conduit (EPC-40 and EPC-80)NEMA TC 13-93 Electrical Nonmetallic Tubing (ENT) NFPA 70-2002 National Electrical Code

raceway

Documents

cable tray type

cable tray arrangement

cable tray fittings

tray grounding

tray barriers

cable tray material

raceway design criteria

raceway identification