Raychem nvent MI Series Manual
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Raychem nvent MI Series Manual

Raychem nvent MI Series Manual

Mineral insulated cable
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Mineral Insulated Cable
Heating Cable Repair Guide

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Summary of Contents for Raychem nvent MI Series

  • Page 1 Mineral Insulated Cable Heating Cable Repair Guide...
  • Page 2 Important Safeguards WARNING: Fire and shock hazard. nVent RAYCHEM heating cables must be installed correctly to ensure proper operation and to prevent electrical shock and fire. Read these important warnings and carefully follow all the installation instructions. • To minimize the danger of fire from sustained...

  • Page 3: Table Of Contents

    Table of Contents General Information 1.1 Introduction 1.2 Safety Guidelines 1.3 Electrical Codes 1.4 Heating Cable Configurations 1.5 Heating Cable Identification Pre-Repair Information 2.1 General 2.2 Safety Precautions 2.3 Changes to the Heating Cable Length 2.4 Tools and Materials Required 2.5 Repair Kit Components 2.6 Cross-section of Completed Joints and End Cap Heating Cable Repair...
  • Page 4 Appendix E: Flame Size for Oxy-acetylene Torch Appendix F: Heat Shrink Tubing Installation for Polymer Jacketed Cables 9.1 Cables using a 1/2 in (13 mm) joint 9.2 Installation for end cap Appendix G: Stripping the Cable Sheath Appendix H: Typical Repair Jig...

  • Page 5: General Information

    Introduction The purpose of these instructions is to provide a procedure for the repair or modification of RAYCHEM Copper and Alloy 825 sheath mineral insulated (MI) heating cables manufactured by nVent. They must be carefully followed to ensure that the MI cable performs safely and as intended.

  • Page 6: Safety Guidelines

    General Information Safety Guidelines The safety and reliability of any heat tracing system depends on both the quality of the products selected and the manner in which they are installed and maintained. Incorrect design, handling, installation, or maintenance of any of the system components can cause damage to the heating cable system, and may result in system failure, electric shock, or fire.

  • Page 7: Heating Cable Identification

    General Information spliced into larger bus wires. A final transition at the end of the cold lead section provides an environmental seal and tails for the electrical connection. At the opposite end of the cable, the conductors of Design D cables are joined and hermetically sealed within an end cap.

  • Page 8: Pre-Repair Information

    Pre-Repair Information General Both single conductor and dual conductor copper sheath and Alloy 825 sheath cables can be field repaired or modified. The field repair kits can be used to complete the following: • To repair or replace a joint in the heated section (hot-hot joint) •...

  • Page 9: Changes To The Heating Cable Length

    Pre-Repair Information Changes to the Heating Cable Length A new tag is not required for repaired or modified heating cables provided the total length of the heated section of the cable is not changed by more than 3%. Where the heated section of the cable set is changed by more than 3%, to facilitate the repair or where the cable is modified, then a new MI cable tag must be ordered.

  • Page 10: Tools And Materials Required

    Pre-Repair Information Tools and Materials Required TAbLe 2: TOOLS AND MATeRIALS 500 Vdc Megohmmeter Small hammer Ohmmeter (multimeter) Needle nose pliers Drill press and bits (see Appendix C) Steel rule Vernier caliper (or Micrometer) Flat file (3/16 in thick) Small tube cutter Round file Diagonal (side) cutters Hacksaw...

  • Page 11: Repair Kit Components

    Pre-Repair Information Repair Kit Components TAbLe 3: FIeLD RePAIR KIT FOR COPPeR SHeATH CAbLeS Item Description 1 ea 3/4 in (19 mm) brass joint (grooved) 1 ea 1/2 in (13 mm) brass joint (grooved) 1 ea 7/16 in (11 mm) brass end cap (grooved) 1 ea Brass end cap plug...
  • Page 12 Pre-Repair Information TAbLe 4: FIeLD RePAIR KIT FOR ALLOY 825 SHeATH CAbLeS Item Qty Description 1 ea 3/4 in (19 mm) stainless steel joint (grooved) 1 ea 1/2 in (13 mm) stainless steel joint (grooved) 1 ea 7/16 in (11 mm) stainless steel end cap (grooved) 1 ea stainless steel end cap plug 10 in A-56T flux coated silver solder (orange color)

  • Page 13: 2.6: Cross-Section Of Completed Joints And End Cap

    Pre-Repair Information 2.6: Cross-section of completed joints and end cap 6-32 Brass Silver screw solder Silver solder Heating Joint Groove Heating cable cable Magnesium oxide Figure 5: Completed heated-section to heated- section joint for single conductor cable 6-32 brass screw Silver solder Silver solder...
  • Page 14 Pre-Repair Information 6-32 brass screw Silver Silver solder solder Cold lead Joint Groove Heating cable cable Magnesium oxide Cross section view Filler hole Filler hole perpendicular Conductors to plane of conductors Figure 8: Completed heated-section to cold- section joint for two conductor cable Silver Silver Endcap...

  • Page 15: Heating Cable Repair

    Heating Cable Repair General • For field modifications, heating cable resistance should be checked with an ohmmeter to ensure that it is within ± 10% of the cable’s calculated resistance. Calculated resistance = heated length (ft) x Ω/foot; (heated length (m) x Ω/meter) Note: Ω/foot (Ω/meter) of heating cable may be obtained from the product data sheets, H56870 for Alloy 825 sheath heating cables and H56990...

  • Page 16: Selecting The Correct Size Of Joint And/Or End Cap

    Heating Cable Repair Selecting the Correct Size of Joint and/or End Cap Use a vernier caliper or micrometer to measure the outside diameter of the heated section and/or the cold lead section. Select the 1/2 in (13 mm) or 3/4 in (19 mm) stainless steel or brass joint from Table 5 or Table 6.
  • Page 17 Heating Cable Repair TABLE 6: SELECTING JOINT SIZE FOR DESIGN B, D, OR E COPPER SHEATH HEATING CABLE 1/2 in (13 mm) brass joint For heated-section to For heated-section to cold lead section heated-section joint joint Max. diameter Max. diameter Max.

  • Page 18: Joining Design B, D, And E Cables

    Heating Cable Repair Joining Design B, D, and E Cables The instructions following apply to both heated section-heated section (hot-hot) joints and heated section-cold lead section (hot-cold) joints. Read these instructions completely before attempting to complete the repair or modification and refer to the Appendices for additional information where indicated.
  • Page 19 Heating Cable Repair Note: Do not remove more than 3% of length of heated section. If more than 3% must be removed to facilitate the repair or modification, a new MI cable tag must be ordered (see Section 2.3). If the bell-mouth is not re-used, care must be taken not to bend the cable at the joint as this will break the cable at the new braze.
  • Page 20 Heating Cable Repair Figure 12: Check insulation resistance Verify continuity of conductors using a multimeter or ohmmeter. Using a vernier caliper (or micrometer), measure the outside diameter of the heated section and/or cold lead section (not including polymer jacket) and select the 1/2 in (13 mm) or 3/4 in (19 mm) joint from Table 5 or Table 6.
  • Page 21 Heating Cable Repair Hot-hot joint: From the table in Appendix C, select the correct drill bit size for the cable diameter measured above (the drill bit should be 4/1000 in (0.1 mm) to 10/1000 in (0.25 mm) larger than the cable diameter).
  • Page 22 Heating Cable Repair Hot-hot joint: Ensure the end of each heated section is straight for approximately 12 in (30 cm). Hot-cold joint: Ensure the ends of the heated section and cold lead section are straight for approximately 12 in (30 cm). File the face of the cold lead section square using a flat file, filing in the forward direction only (end of conductor(s) should be clean).
  • Page 23 Heating Cable Repair If heated section and/or cold lead section is polymer jacketed, place 6.9 in (18 cm) lengths of heat shrinkable tubing onto the end of each cable and move clear of ends (heat will cause the heat shrinkable tubing to recover); place a 6.9 in (18 cm) length of larger diameter heat shrinkable tubing on one of the cable ends.
  • Page 24 Heating Cable Repair Hot-hot joint: Using the tube cutter, lightly score the sheath on each end of the heated section cables approximately 3/16 in (5 mm) from the end of each cable. With the diagonal cutters, remove the sheath up to the score mark. See note below. Hot-cold joint: Using the tube cutter, score the sheath of the cold lead section approximately 1/4 in (6 mm) from the end of the cable.
  • Page 25 Heating Cable Repair Emery cloth Figure 21: Clean conductors Note: Do not clean the magnesium oxide powder from the conductors of the cold lead section as silver solder is applied only to the face of the conductor. With pliers, break away 1/2 in (13 mm) of flux from end of flux coated brazing rod.
  • Page 26 Heating Cable Repair Continue heating conductor with the oxy-acetylene torch (this does not take much heat) and at the same time touch brazing rod to the end of the conductor and apply enough silver solder to tin the end of the conductor. Repeat for remaining conductors on both cables to be joined.
  • Page 27 Heating Cable Repair Hot-hot joint: Align the two cables so that the conductor tips butt together and touch the tip of the flame to the tinned conductors. The solder on both ends will melt and draw together. Do not add any more silver solder.
  • Page 28 Heating Cable Repair Hot-hot joint: Ensure that the brazed junction is the same diameter as the heating cable conductor. If not, the brazed junction may be a cold joint and it will be necessary to remake it. Hot-cold joint: Ensure that the brazed junction has formed a cone from the large to small diameter conductor.
  • Page 29 Heating Cable Repair Use a pick to remove any flux or carbon which may have contaminated the magnesium oxide powder at the ends of each cable. Figure 28: Clean face of cable Hot-hot joint: For two conductor cable, ensure that the conductors are the same distance from each other as they are in the cable.
  • Page 30 Heating Cable Repair Using a large sizzling flame (see Appendix E), heat out the moisture from the cable beginning 12 in (30 cm) back from the joint (begin 4 in (10 cm) back for polymer jacketed cables), stopping 1/2 in (13 mm) from the joint.
  • Page 31 Heating Cable Repair Heat the joint and heated section cable using a large flame. When the area to be brazed is up to temperature, deposit a large bead of silver solder on the top part of the area to be joined. Apply heat to both the joint and the cable and move the flame slowly around the circumference of the joint.
  • Page 32 Heating Cable Repair While joint is still hot, use syringe to fill the joint with magnesium oxide powder. Use an engraving tool or other vibration method to pack the powder. If using an engraving tool, reverse the engraving bit so that the blunt end is visible and place the bit against the joint.
  • Page 33 Heating Cable Repair Insert the brass screw approximately 2 full turns into the fill hole, ensuring that the screw does not protrude into the joint and touch the conductors. Brass screw - 2 turns Figure 35: Insert brass screw Saw off the screw flush with the joint. Using the edge of a flat file, groove a recessed area over and around the screw, filing in one direction only.
  • Page 34 Heating Cable Repair Check the insulation resistance (IR) again. A value greater than 20 MΩ should be attained. If the IR is lower, remove the moisture from the cable by follow- ing the drying out procedure in Appendix D and then repeat IR test.
  • Page 35 Heating Cable Repair Use a flat file and then emery cloth to clean flux from all brazed areas and visually inspect to ensure that there are no pinholes or gaps which could allow moisture to enter. Emery cloth Figure 39: Clean joint If necessary, touch up pinholes by cleaning the area and applying more silver solder.
  • Page 36 Heating Cable Repair Again, test the insulation resistance with a 500 volt Megohmmeter. Minimum IR should be 20 MΩ. Quench with a rag soaked in water by wrapping it tightly around the joint. Leave on for 4 to 5 minutes. If there are any remaining pinholes, moisture will be absorbed into the joint as it cools and the reading on the Megohmmeter will drop.
  • Page 37 Heating Cable Repair Check resistance of heating cable using an ohmmeter – it should be within 10% of specifications. If open circuit, cut off joint and repeat procedure. The finished joint is shown below. Figure 42: Completed joint If repairing a hot-cold joint and reusing 1/2 in (13 mm) or 3/4 in (19 mm) bell-mouth, place a few drops of a suitable retaining compound (such as Loctite...

  • Page 38: End Cap Procedure

    Heating Cable Repair End Cap Procedure Note: Shield work area from environmental factors such as wind as it will cool the joint temperature making brazing difficult and disconnect power from the heating cable before attempting any repairs or modifications to the heating cable.
  • Page 39 Heating Cable Repair 6 in. Figure 44: Remove polymer jacket Check the insulation resistance (IR) of the cable at this point using a 500 volt Megohmmeter (see Appendix B for details on testing). This test checks for the presence of moisture in the magnesium oxide insulation. A value greater than 20 MΩ...
  • Page 40 Heating Cable Repair Figure 46: Check cable diameter From the table in Appendix C, select the correct drill bit size for the cable diameter measured above (the drill bit should be 4/1000 in (0.1 mm) to 10/1000 in (0.25 mm) larger than the cable diameter). Drill a hole straight through the end cap using the pilot hole (smaller hole) as a guide and check it for burrs.
  • Page 41 Heating Cable Repair If heated section is polymer jacketed, place a 6.9 in (18 cm) length of small diameter and a 6.9 in (18 cm) length of larger diameter heat shrinkable tubing onto the end of the cable and move clear of end;...
  • Page 42 Heating Cable Repair Score Figure 51: Strip cable sheath Clean magnesium oxide powder from the conductors with emery cloth or use side cutters to lightly scrape conductor surface. Conductor surface must be free of powder for silver solder to bond. Emery cloth Figure 52: Clean conductors...
  • Page 43 Heating Cable Repair Using oxy-acetylene torch, apply heat to the tip of the twisted conductors with a small flame (see Appendix E) and touch or wipe brazing rod onto the tip by turning the rod between the fingers. This will ensure that the flux melts off the rod and onto the conductors evenly.
  • Page 44 Heating Cable Repair Slide the end cap as far forward as possible (the flare on the cable sheath will stop it), then move it back 3/16 in (5 mm) to ensure proper placement of the heating cable in the end cap (see cross section). 3/16 in (5 mm) End cap...
  • Page 45 Heating Cable Repair Reduce sizzling flame to a large flame (see Appendix E). Using flux coated brazing rod and with a touching or wiping motion of rod, apply flux around end where the end cap will be brazed to the cable sheath.
  • Page 46 Heating Cable Repair While the end cap is still hot, fill end cap to approximately 3/16 in (5 mm) below the opening at the top of the end cap. Use an engraving tool or other vibration method to pack the powder. If using an engraving tool, reverse the engraving bit so that the blunt end is visible and place the bit against the end cap.
  • Page 47 Heating Cable Repair Check the insulation resistance (IR) again. A value greater than 20 MΩ should be attained. If the IR is lower, remove the moisture from the cable by following the drying out procedure in Appendix D. Repeat IR test. Figure 61: Check insulation resistance Using oxy-acetylene torch with a large flame, apply heat to the end cap sweeping the flame from...
  • Page 48 Heating Cable Repair Note: While brazing, it is important to avoid using excess heat on the portion to be brazed. Direct flame contact can oxidize the metal surface, preventing the silver solder from adhering to the metal. Care must also be taken not to overheat the end cap, which can cause the conductor joint (junction) to melt.
  • Page 49 Heating Cable Repair Water soaked rag Figure 65: Wrap end cap with water soaked rag Note: If the Megohmmeter reading declines, remove wet rag and visually inspect end cap for pinholes. If pinholes exist, dry out cable according to procedure in Appendix D, being careful not to trap any moisture.

  • Page 50: Field Modification Approval Request Form

    Appendix A: Field Modification Approval Request Form MI Heating Cable Field Modification Approval Request Form For field modifications, where the heating cable length is changed by more than three percent (3%), the change must be reviewed by nVent and a new cable identification tag must be ordered. Please fill in this form and fax to 1-800-272-7808.
  • Page 51 Appendix A: Field Modification Approval Request Form must be ordered. Please fill in this form and fax to 1-800-272-7808. nVent will review the change and advise if the modification is appropriate. Company: Telephone: Fax: Email: New Tag Information For Internal Use Only ...

  • Page 52: Appendix B: Heating Cable Testing

    Appendix B: Heating Cable Testing Testing: A 500 volt insulation tester (Megohmmeter) is used to check insulation resistance. A minimum value of 20 meg- ohms should be obtained when testing the insulation resis- tance between the conductors/tails and the cable sheath, and between conductors (2-conductor cable only).

  • Page 53: Continuity (Resistance) Test - Test

    Appendix B: Heating Cable Testing Continuity (Resistance) Test – Test 2 Continuity testing is conducted using a standard Digital Multimeter (DMM) and measures the resistance between the cold lead tails or between conductors. Test Criteria Measure the resistance of the MI heating cable with the DMM.
  • Page 54 Appendix B: Heating Cable Testing 12. Using the multimeter, check the continuity (resistance) of the heating cable between the two tails or between the conductors (conductors at far end may have to be shorted). Note the resistance value and compare to the calculated value.

  • Page 55: Cable Size Vs Drill Bit Selection Chart

    Appendix C: Cable Size vs Drill Bit Selection Chart Drill bit selection chart Drill Drill Cable Diameter (in) Identifier Cable Diameter (in) Identifier 0.124 – 0.131 0.262 – 0.263 0.132 – 0.135 0.264 – 0.267 6.8mm 0.136 – 0.139 0.268 – 0.272 0.140 –...

  • Page 56: Appendix D: Drying Out Procedure

    Appendix D: Drying Out Procedure IMPORTANT: Wear full face shield when drying out MI cable. Damage to the cable sheath or a damaged or missing joint or end cap will cause the magnesium oxide insulation (white powder) to absorb moisture, resulting in low IR readings.
  • Page 57 Appendix D: Drying Out Procedure Gradually move the flame toward the joint, while maintaining the short sweeping motion of the torch. When initially checking insulation resistance after the damaged joint or end cap has been removed, continue the sweeping motion of the torch past the end of the cable. When heating out the cable prior to brazing the joint or end cap to the cable sheath, stop the sweeping motion of the torch 1/2 in (13 mm) from the joint or end cap (Figure D2).
  • Page 58 Appendix E: Flame Size for Oxy-acetylene Torch Use the small (oxidizing) flame when soldering the conductors together. 3/16 in. (5 mm) Figure 70: Small (oxidizing) flame Use a large (neutral) flame when soldering the joint or end cap to the sheath of the cable. 3/16 in.
  • Page 59 Appendix F: Heat Shrink Tubing Installation for Polymer Jacketed Cables Cables using a 1/2 in (13 mm) joint: Hot-hot joint: 2 pieces 3/8 in (9 mm) dia. x 6.9 in (18 cm) long heat shrinkable tubing for heating cable 1 piece 3/4 in (19 mm) dia.
  • Page 60 Appendix F: Heat Shrink Tubing Installation for Polymer Jacketed Cables Hot-cold joint: Move 3/8 in (9 mm) dia. x 6.9 in (18 cm) long piece of heat shrinkable tubing (previously installed) for- ward to completely cover bare heating cable sheath. Cover the bare cold lead with the 1/2 in (13 mm) tubing (previously installed).
  • Page 61 Appendix F: Heat Shrink Tubing Installation for Polymer Jacketed Cables Installation for end cap 1 piece 3/8 in (9 mm) dia. x 6.9 in (18 cm) long heat shrink tube 1 piece 1/2 in (13 mm) dia. x 6.9 in (18 cm) long heat shrink tube Heat shrink is installed over completed end cap as follows:...
  • Page 62 Appendix G: Stripping the Cable Sheath Use a tube cutter to score around the cable sheath the required length from the end. This will cause the sheath to peel away at the score providing a smooth end when the cable sheath is stripped. The correct depth of score one third the thickness of the sheath.
  • Page 63 Appendix G: Stripping the Cable Sheath Continue this motion in a series of short ‘rips’, keeping the sidecutters at about 45° to the line of the cable, removing sheath spirally. Score Figure 79: Strip cable sheath Continue removing the sheath to the score mark. When about to break into the score, bring sidecutters to right angle with cable.
  • Page 64 Appendix G: Stripping the Cable Sheath The cable sheath is correctly stripped, with the sheath flared slightly outwards, as shown in (a). In (b) the sheath is neither flared outwards nor beveled inwards, but is acceptable. Ensure that the sheath is not curved or beveled inward as shown in (c).
  • Page 65 Appendix H: Typical Repair Jig Repair jig is made from angle iron welded to form shape as shown in Figures H1 and H2. Each cable is clamped to the 4 in (10 cm) upper surface and meet in the middle. If working on a pipe, middle section may be clamped to the pipe.
  • Page 66 ©2018 nVent. All nVent marks and logos are owned or licensed by nVent Services GmbH or its affiliates. All other trademarks are the property of their respective owners. nVent reserves the right to change specifications without notice. Raychem-IM-H57640-EN-1810...

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