This article is about installation, splicing, and termination requirements for power and control wire and cable in conduit and cable tray. Main keywords for this article are Installing Cable in Conduit, Conduit Sizing, Selecting Conduit Raceway, Conduit Size Calculations, Conductor jamming, Conductor Area, Installing Cable in Cable Tray, Cable Grouping Requiring Segregation by Separators, Slicing and Terminating Cable 600 Volt and Below, Splice and Termination Kits, Splicing And Terminating Cable Above 600 Volts.
Wires and Cables Installation, Splicing, and Termination Requirements
References
National Fire Protection Association (NFPA)
70 National Electrical Code (NEC)
American National Standards Association /International Electrical Testing Association (ANSI/NETA)
ATS- Acceptance Testing Specifications for Electric Power Distribution Equipment and Systems
Installing Cable in Conduit
Conduit Sizing
Preventing Overstress of Conductor.
Correct conduit sizing is necessary to prevent overstressing of the conductor due to excessive tension and/or damage to the conductor insulation during the pulling operation.
Selecting Conduit Raceway
Before a specific conduit raceway size can be selected, the number of conductors to be installed and the total area (in square inches) to be occupied by the conductors must be established.
- Percent of Available Area
The total cross-sectional area of the conductors shall not exceed 40% of the cross-sectional area of the conduit they are installed in. - How to Obtain Conductor Area
The conductor area for insulated conductors manufactured to American Standards may be obtained directly from NEC Chapter 9, Table 5. The conductor area for cables manufactured to European (IEC) Standards must be obtained from the manufacturer’s data as actual conductor size will var y from the nominal cross-sectional area (mm2). - Multi-Conductor Cables
Multi-conductor cables are treated as single conductors when calculating conduit fill. I.E., the cross-sectional area of a multi-conductor cable is equal to the total of the individual conductors in the cable
Conduit Size Calculations
- American type conductors of the same size and insulation type
Refer to NEC Appendix C for conduit size calculations when all conductors to be installed in a specific raceway system are manufactured to American Standards and are of the same size and insulation type. NEC Appendix C provides very accurate calculations generated from NEC Tables 1, 4, 5, and 5A without having to perform the calculations according to NEC Chapter 9, Table 1.
To select the correct trade-size conduit or tubing from NEC Appendix C, the following steps should be used:
a. Select the desired raceway system from Tables C1 through C12.
b. Select the desired conductor type (i.e., general-wiring conductors, fixture wires, or compact conductors).
c. Select the desired insulation type.
d. Select the correct trade-size conduit or tubing for the given quantity and size of conductors required.
Calculate conduit size for IEC conductors using the cross-sectional area of the cables/conductors such that the total does not exceed 40% of the conduit cross-sectional area. - Conduit Internal Area Determination
NEC Chapter 9, Table 4 provides accurate dimensional data on conduit internal diameter and allowable usage area, in square inches, for 12 types of conduit raceway systems. It is important to note that different types of conduits of the same trade size may have different diameters and areas. Therefore, the particular section in Table 4 for the specific type of raceway system selected must be used in the calculation.
Limitations
The calculations for selecting the correct conduit size shall be adjusted if any of the limitations described in Sections 5.4.1 to 5.4.3 are experienced.
- Bend and Distance
Calculations and data presented or referenced in this document are based on conditions of proper cabling and alignment of conductors in conduit or tubing systems containing no intermediate pull boxes or fittings. In addition, the length of the conductor pull and the number of bends in the conduit or tubing system must be within the following limits:
a. A 15.2 m (50-ft) run with no more than three 90-degree or equivalent bends
b. A 30.4 m (100-ft) run with no more than two 90-degree or equivalent bends
c. A 45.6 m (150-ft) run with no more than one 90-degree or equivalent bend
d. A 60.8 m (200-ft) straight run with no bends
Where the above limits cannot be met, pull boxes and/or fittings should be introduced into the run at selected points to ensure compliance. If the addition of pull boxes or fittings is not practical, the conduit or tubing sizes should be increased to the next standard size. - Conductor size – Where conductors exceed one inch in diameter, the stated conductor area should be increased by 30 percent for the purpose of calculating conduit fill area.
Conductor jamming
When conduits are bent in the field, the conduit will take an oval shape through the bend, increasing the inside diameter (I.D.) at that point. Factory manufactured elbows do not normally experience this expansion.
However, in elbows that are not factory-manufactured, ovality will occur to some degree in either conduits or tubing during the bending process due to uncontrolled sidewall expansion. The type and condition of the bender used will affect expansion. Ovality occurs particularly in Electro-metallic tubing (EMT).
Where three (no more, no less) conductors or cables of the same size are being installed in a conduit, jamming can occur even when 40 percent fill allowances are observed. At a bend, the increased diameter (ovality) in the bend area permits the third conductor to be pulled between the other two conductors. As the conductors exit the bend, and the raceway I.D. returns to normal, the conductors may jam. Jamming can also occur in straight runs where the ratio of the raceway’s I.D. and the conductor’s outside diameter (O.D.) approaches 3. Jamming is more likely when conductors are pushed into the conduit or a combination of pushing and pulling is used during installation of the conductors.
To prevent jamming when pulling three conductors or cables into a conduit, use the next larger size raceway if the ratio of the raceway’s I.D. to the conductor’s O.D. is between 2.8 and 3.2.
Conductor Area
- Dimensional data for insulated conductors and fixture wires can be found in NEC, Chapter 9, Table 5.
- When insulated grounding conductors are included in the raceway system, they must be included in the calculations for determining conduit fill.
Installing Cable in Cable Tray
This section describes cable grouping permitted to be on the same cable tray system without segregation, or with segregation by means of separators or dividers.
Voltage Considerations
- The insulation voltage rating of the cables, their type of outer jacket or sheath, and the circuit service, are determining factors regarding cable groupings permitted to be installed in the same tray. Generally, cables supplying services to a production line, or to a unitized operation, preferably should be installed on individual cable trays or be segregated by separators when installed on the same cable trays with cables to other equipment. Also, consideration should be given to installing medium-voltage (over 600 volts) cables on separate cable trays from cables operating on circuit voltages of 600 volts, or less, and to further segregation of cables for different services. In some cases, desired segregation on separate cable trays is not practical economically due to the increased number of tray systems which would be required. Permissible cable groupings, with and without segregation by separators or dividers, are discussed below.
- In general, the NEC does not allow low-energy, low-voltage circuits to be mixed with power and lighting circuits-regardless of the insulation level of the cables involved in the low-level circuits. Installations of these type cables shall meet the requirements of NEC Articles 725, 760, 800, 810, and 820.
- Cables rated over 600 volts shall not be installed in the same cable tray with cables rated 600 volts or less unless the groups are separated by solid noncombustible fixed barriers or the over 600-volt cables are Type MC (NEC 318).
Cable Permitted to be Grouped in Cable Tray Without Segregation
- It is permissible to install the following combined cable groupings or services supported in the same tray assembly without providing for segregation between the different cable groupings:
a. Unarmored or metallic-sheathed medium-voltage feeder cables (over 600 volts) and cables for medium-voltage motor leads of the same insulation voltage rating.
b. Medium-voltage feeder cables having different insulated voltage ratings providing all cables are metal clad (Type MC).
c. Power and lighting cables used on systems of 600 volts, or less, without regard as to whether the individual circuits are ac or dc, providing all the cables have insulation voltage ratings suitable for the maximum voltage of that of any cable in the group (NEC 300).
d. Cables for 600V motor control may be installed in the same cable tray with the associated motor’s power cable.
Cable Grouping Requiring Segregation by Separators
- Generally, it is permissible to install the following combined cable groupings or services in the same tray providing the groupings are separated from each other by grounded fixed metal barriers:
a. Medium-voltage cables of the unarmored or metallic-sheathed type having different insulation voltage ratings.
b. Medium-voltage cables of the unarmored or nonmetallic-sheathed type and low-voltage cables of either the unarmored, armored, or metallic sheathed type. c. Medium-voltage cables of the armored or metallic-sheathed type of one group and low-voltage cables of the non-armored or nonmetallic sheathed type of another group (NEC 318). d. Medium-voltage cables of the nonmetallic-sheathed type of one group and low-voltage cables of the armored or metallic-sheathed type of another group (NEC 318). - Cable tray barriers shall be fabricated of the same material as all the other cable tray fittings and should include necessary splice clips, and mounting bolts, nuts, and washers. All exposed edges must be smooth and free of any projections that might injure cable sheath and jackets. Where necessary to cross cables over separator or divider strips, the cables should be supported free of the top edge of the strips, or the strips should be provided with cable protectors where cables cross over.
- Where required, separators or dividers of the same general type as those illustrated for straight tray sections should be furnished for the cable tray fittings. Where formed separators or dividers are desired for use with fittings in the horizontal plane, the radius (which determines tray division) must be furnished.
- Cable segregation outlined in this section shall be maintained when any changes in routing of existing cables, or new cable additions, are made in any continuous rigid cable tray assembly.
Slicing and Terminating Cable 600 Volt and Below
All conductor and cable termination kits, splice kits, and associated hardware shall be approved by the manufacturer, for the cable construction and conductor material (copper) on which they are installed.
- Conductors shall be spliced or joined with splicing devices suitable for the use or by brazing, welding, or soldering. Soldered splices shall first be so spliced or joined as to be mechanically and electrically secure without solder before they are soldered. Where necessary, all splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device certified by the manufacturer for the purpose (NEC Article 110).
- Connection of conductors to terminal parts shall ensure a good mechanical and electrical connection without damaging the conductors. It shall be made by means of pressure connectors (including set screw type), welded lugs, or splices to flexible leads. However, connection by means of wire terminal screws or studs and nuts having upturned or hook-type lugs shall be permitted for 6mm2 (No. 10 AWG) or smaller conductors (NEC 110). Terminals that accommodate more than one conductor shall be identified as suitable for the purpose.
- Types of Conductor Connections and Connectors
- Acceptable methods of connecting and terminating circuit wiring utilize:
a. Crimp- or compression-type (solderless) connectors
b. Mechanical-type (bolted) connectors
c. Soldered connections
d. Welded (thermal-weld ) connections
A comparison of the various types of conductor connections is given in Table 2. - Crimp- or compression-type connectors are superior to most mechanical connectors. Once installed, they cannot be removed without damaging or destroying the connectors and affected portions of the conductors. Special installation tools are required.
a. Only circumferential, elliptical, hexagonal, quadruple, or triangular indent-type compression connectors are recommended for 25mm2 (No. 4 AWG) and larger conductors. These types can be compressed almost completely around the circumference of the connector barrel or body when used with the proper tool and precision die.
b. On conductors 16 mm2 (No. 6 AWG) and larger, connectors of one manufacturer shall not be compressed on conductors with tools and dies of another manufacturer unless the connector manufacturer so approves. The tool and die number specified by the connector manufacturer for a specific size and type of connector must be used; otherwise, excessive or inadequate compression can occur and cause failure of the connection. Installation instructions shall be strictly followed and the compression action must not be stopped until the dies are fully closed, or closed the amount specified in the instructions. - Mechanical connectors are used for joining and terminating conductors where later removal may be a requirement. With this type of connector, conductors are placed in the barrels or bodies of the connector and a screw or saddle is forced down on the conductors. The high-pressure wedge effect of the screw or saddle on the conductors provides a positive interstrand contact. They are reliable when properly selected and installed.
- Solder connections may be used for small conductors.
- For buried ground connections, thermal-weld connections shall be used. For above ground connections, mechanical connections shall be used.
- Acceptable methods of connecting and terminating circuit wiring utilize:
Splice and Termination Kits
- For splicing single 600 Volt conductors the following kits or approved equal shall be used.
a. Manufacturer: Raychem
b. Multiconductor Splice Kit: Type LV-MSK - For splicing 600 Volt multiconductor cables the following kits or approved equal shall be used.
a. Manufacturer: Raychem
b. Multiconductor Splice Kit: Type LV-MSK - For terminating 600 Volt conductors and cables on motor leads the following kits or approved equal shall be used.
a. Manufacturer: Raychem
b. Motor Connection Kit: Type MCK
Splicing And Terminating Cable Above 600 Volts
Terminations and splices represent only a small fraction of the total cable system installation, yet general industry statistics show that they have a much higher failure rate than the cable insulation itself. The reason for this is the skill and precision required to install them in a manner such that they perform reliably over the life of the cable. The majority of these failures can be attributed to poor workmanship, incorrect procedures, improper material or environmental effects. All cable termination, splicing kits and hardware shall be installed in accordance with the manufacturer’s instructions.
https://www.youtube.com/watch?v=ZIm_9Ll0ed0
Splicing Personnel Qualification Requirements
- All workmen who install terminations or splices greater than 600 volts shall be certified by the Contractor.
- Bending Radius – When cables are terminated it is important that they not be bent or formed in any manner or at any time that causes the minimum bending radius to be exceeded. In general this minimum radius is 12 times the outside diameter of the cable.
- Support – All cables shall be supported so that there is no stress on the terminations.
- Grounding – The grounding jumpers for terminations and splices shall be maintained separate from grounds that are used for surge arrestors. This will prevent the cable shielding system from being raised to an abnormally high voltage during surge conditions.
- Splice and Termination Kits
- For splicing MV (5kV through 35 kV) cable the following kits or approved equal shall be used.
a. Manufacturer: Raychem
b. Non-Armored Type HVS
c. Armored Type HVSA - For terminating medium voltage cables and conductors on motor leads the following kits or approved equal shall be used.
a. 5KV
(i) Manufacturer: Raychem (ii) Conductor Motor Conn. Kit: Type MCK
(iii) Modification Kit for 3/C cable Type MOD
b. 15KV
(i) Manufacturer: Raychem
(ii) Conductor Motor Conn. Kit: Type HTV
(iii) Modification Kit for 3/C cable Type MOD - For cable termination in medium voltage motor controllers or switchgear (5kV –35kV) the following kits or approved equal shall be used.
a. Manufacturer: Raychem
b. Type HTV
c. Modification Kit for 3/C cable Type MOD
- For splicing MV (5kV through 35 kV) cable the following kits or approved equal shall be used.