Author archives: Mark

The purpose of this application note is to provide a safe and reliable method to pull additional cable slack where needed. When pulling cable through conduit or cable tray systems in most cases the cable puller (tugger) is positioned where enough slack can be pulled to make the final connection. However, there are instances where additional slack is needed after the cable end has reached the tugger. Another instance where a mare’s tail is needed is when an assist puller is used.

Methods For slack needed in low tension pulls (below hundred pounds) rope, soft or flat straps can be applied to the cable using several half-hitch knots. It is important to only use this method on low tension pulls or else the rope or straps can leave indents or tear the jacket. For higher tension pulls (above 500 pounds) or assist pulling, a mare’s tail is recommended. A mare’s tail is a rope eye with 4-6 flat long straps that are wrapped around the cable to form a basket. The straps will not dig into the cable jacket since they lay flat on the cable surface and are made from aramid fiber which has low stretch, high strength properties. Mare’s tails are a recognized practice in IEEE 1185 Recommended Practice for Cable Instal- lations in Chapter 5.

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General
Tray cable, Type TC is an approved wiring method in the NEC found in article 336. It is an efficient method of installing feeders, branch circuits and control cable because multiple runs of tray cable can be installed in one cable support system (i.e. cable tray) rather than multiple conduit runs, which adds to labor and material cost.
Description
Tray cable is a factory assembly of two or more insulated conductors with or without an associated equipment ground conductor under a non-metallic jacket. For feeder and branch circuits, tray cable can be manufactured with any of the insulation types found in NEC 310.4 (A) or (B). Depending on the insulation used, tray cable will have either 600, 1000 or 2000 volt rating. Metallic shields are allowed over groups of conductors or under the outer jacket or both. Metallic sheaths or armor is not allowed under or over the non-metallic jacket, doing so would make the cable type MC cable.
Use/Locations
Type TC cable can be used for a variety of applications such as, power, lighting, control, signal circuits, class 1 circuits and non-power limited fire alarm circuits. Tray cable cannot be installed where it is subject to physical damage and must be installed in a cable tray with exceptions. Sections of the tray can have up to one foot breaks or separations without the need of adding protection to the cable in these areas.

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Background:
Color codes are used to identify conductors for point-to-point wiring and for circuit diagrams. The Insulated Cable Engineers Association outlines the color code in Standard S-73-532 in Annex E. The Standard breaks down the color code into methods of circuit identification. The most common methods used are Method 1, 3, and 4. After the Method is selected then the assembly of conductors must follow a color sequence from the tables with Table 1 and 2 being the most common.
National Electrical Code (NEC)
The NEC specifies that conductor colored white be used only as grounded conductors and that conductors colored green or green/yellow be used only as grounding conductors and that neither white nor green be used in any manner on ungrounded conductors. Tables 2 provide color sequences that do not include white or green conductors. If grounded or grounding conductors, or both, are used in the cable, they shall be colored white or green respectively, and inserted as the second or third, or both, designated conductor in the first sequence of circuit identification only. Where these conductors are required, they shall be specified.
Methods of Circuit Identification:
Method 1 - Colored Compounds
This method uses base color of insulation and uses tracers when needed, in accordance with Table 1 or 2. Base colors may be obtained by suitable color coatings applied to the insulation or jacket surface or by colored insulation or jacket compound. Tracers shall be colored stripes or bands marked on the surface of the insulation or jacket in such a manner as to afford distinctive circuit coding throughout the length of each wire. Tracers may be continuous or broken lines, such as a series of dots or dashes, and shall be applied longitudinally, annularly, spirally, or in other distinctive patterns.

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Purpose: Withstand testing can be performed on either new or aged cables. The test should only be done if there is concern that cable damage has occurred possibly during installation or the insulation has been compromised due to heat, water or chemicals. General Testing Information • The test can be conducted with AC or DC voltages. • AC Withstand Test for field acceptance is 80% of factory test voltage. See table below. • DC Withstand Test for field acceptance is three times greater than the AC Withstand Test. See table below.

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The objective of this procedure is to provide a means of repairing gouges, tears or indents on cables that occasionally happen in the field. Thisprocedurecoversbothmediumvoltageandlowvoltage power cables and will restore the cable back to its original integrity. The purpose of the outer jacket on medium voltage cables and low voltage multi-conducor cables is to protect the underlying components from physical and environmental damage and serves no dielectric purpose. On low voltage single conductor cables, generally, the outer layer is the cables primary insulating layer. For medium voltage cables with damage beyond the outer jacket such as the copper tape shield is torn or on low voltage cables where the conductor is damaged, contact your Southwire Represen- tative. Cable jacket repairs should only be performed by qualified personnel.

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Purpose: Insulation resistance testing is a non-destructive test procedure. The test measures the insulation resistance between the phases and/or between phase and ground. It is commonly used in the industry for acceptance testing prior to energizing the cable and for maintenance testing programs. General Testing Information • For single conductor non-shielded cable on a reel, insulation resistance testing cannot be performed due to the fact that low voltage single conductors do not have a grounding conductor, shield or ground plane. • For other cable on a reel, insulation resistance testing can be performed provided the sealing caps are removed. The procedure to test these cables is outlined below. • NOTE: It is important to remove sealing caps from both ends of the cable to be tested. Residue inside the sealing cap can be conductive and lead to false readings.

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DC Hi-Pot Testing is used for proof testing shielded cables (5kV to 46kV) in the field. The test can be done at various times such as acceptance of new cable installation, maintenance testing to track insulation degradation and as a pre and post test for splicing existing cables to new ones. The test will expose gross imperfections that are caused by improper handling, installation techniques or termination workmanship. A DC Hi-Pot test is not capable of locating the point of failure, rather it gives you an assessment of the whole system.

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