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Appendix G: Stripping the

Cable Sheath

60 | nVent.com

nVent.com | PB

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). This will occur if the score made with the tube

cutter is too deep. In this case, remove a further 1/4 in

(6 mm) of sheath.

Figure 81: Correct end preparation

Unacceptable

Acceptable

Preferred

(c)

(b)

(a)

Summary of Contents for nvent MI Series

Page 1: ...Mineral Insulated Cable Heating Cable Repair Guide ...

Page 2: ... the requirements of nVent agency certifications and national electrical codes ground fault equipment protection must be used on each heating cable branch circuit Arcing may not be stopped by conventional circuit protection Damaged heating cable can cause electrical arcing or fire Repair or replace damaged heating cable or terminations Contact factory for assistance To prevent shock or personal in...

Page 3: ...ir Kit Components 7 2 6 Cross section of Completed Joints and End Cap 9 3 Heating Cable Repair 11 3 1 General 11 3 2 Selecting the Correct Size of Joint and or End Cap 12 3 3 Joining Design B D and E Cables 14 3 4 End Cap Procedure 34 4 Appendix A Field Modification Approval Request Form 46 5 Appendix B Heating Cable Testing 48 5 1 Testing 48 5 2 Insulation Resistance Megohmmeter Test Test 1 48 5 ...

Page 4: ...ne Torch 54 9 Appendix F Heat Shrink Tubing Installation for Polymer Jacketed Cables 55 9 1 Cables using a 1 2 in 13 mm joint 55 9 2 Installation for end cap 57 10 Appendix G Stripping the Cable Sheath 58 11 Appendix H Typical Repair Jig 61 ...

Page 5: ... is therefore the only feasible alternative The successful repair or modification of these cables is a specialized procedure and as such only qualified personnel at industrial establishments with the necessary competency are permitted to repair or modify MI heating cable sets Where the work involves a change to the existing design participation in the redesign is required by the manufacturer or al...

Page 6: ... CEC regarding the field repair or modification of MI electrical heat tracing cables The repair of MI heat tracing cables must comply with all national and local codes 1 4 Heating Cable Configurations The Field Repair Kit includes two joints and an end cap to allow for field repair or modification of the heating cable configurations shown in Table 1 TABLE 1 MI HEATING CABLE CONFIGURATION MI cable ...

Page 7: ...er provides information regarding the heating cable length power output and operating voltage Also printed on the tag are the designer s circuit identification number optional the cable current rating serial number and maximum cable sheath temperature If the cable has been designed for a hazardous location the area classification is printed in the Haz Locations section of the tag CAT NO NO DE CAT ...

Page 8: ... heating cables with an Alloy 825 sheath heated section and Alloy 825 sheath cold lead section and are suitable for exposure temperatures up to 1022 F 550 C They are also used to repair or modify heating cables with an Alloy 825 sheath heated section and copper sheath cold lead section for exposure temperatures up to 482 F 250 C Note If the attempted repair cannot be done successfully please conta...

Page 9: ...r or modification and a permanent record of the modification must be retained Caution Shortening the length of the heated section will decrease the resistance resulting in increased current draw and wattage Similarly increasing the length of the heated section will increase the resistance resulting in decreased current draw and wattage Pay special attention to the over current protective device to...

Page 10: ...file 3 16 in thick Small tube cutter Round file Diagonal side cutters Hacksaw An oxy acetylene torch with No 0 welding tip or equivalent Flat nose pliers Knife to strip jacketed copper cable Scribe or pick Vise grip pliers or Handvise tool Cotton cloth or rag Small screwdriver with flat blade Bottle of water Steel repair jig or equivalent and two C clamps to hold cable firm when welding see Append...

Page 11: ...1 ea Brass end cap plug E 10 in A 56T flux coated silver solder orange color F 1 ea 3 8 in heat shrink tubing 13 7 in 35 cm long G 1 ea 3 4 in heat shrink tubing 6 9 in 18 cm long H 1 ea 1 2 in heat shrink tubing 6 9 in 18 cm long I 3 ea 6 32 brass machine screw J 24 in Fine grit emery cloth 180 grit K 1 ea Syringe assembly with MgO and steel needle vacuum sealed L 1 ea Joint packing rod A I J L K...

Page 12: ... steel joint grooved C 1 ea 7 16 in 11 mm stainless steel end cap grooved D 1 ea stainless steel end cap plug E 10 in A 56T flux coated silver solder orange color F 24 in Medium grit emery cloth 80 grit G 3 ea 6 32 brass machine screw H 1 ea Syringe assembly with MgO and steel needle vacuum sealed I 1 ea Joint packing rod A G I H B C D E F Figure 4 Kit contents for Alloy 825 sheath cables ...

Page 13: ... cable Groove Magnesium oxide Heating cable Heating cable Joint Silver solder 6 32 brass screw Silver solder Filler hole perpendicular to plane of conductors Cross section view Filler hole Conductors Figure 6 Completed heated section to heated section joint for two conductor cable Groove Magnesium oxide Heating cable Cold lead cable Joint Silver solder Silver solder 6 32 Brass screw Figure 7 Compl...

Page 14: ...der 6 32 brass screw Heating cable Filler hole perpendicular to plane of conductors Cross section view Filler hole Conductors Figure 8 Completed heated section to cold section joint for two conductor cable Groove Silver solder Endcap Magnesium oxide Plug Heating cable Silver solder Figure 9 Completed end cap ...

Page 15: ...er faults may exist in the cable For two conductor heating cable conductors or tails on far end of cable may have to be shorted together For single conductor heating cable the conductor or tail on far end can be shorted to the sheath and continuity checked between the conductor and sheath on opposite end Follow appropriate repair procedure to make a joint Section 3 3 or end cap Section 3 4 When br...

Page 16: ...OR E ALLOY 825 SHEATH HEATING CABLES 1 2 in 13 mm stainless steel joint For heated section to heated section joint For heated section to cold lead section joint Max diameter heated section cable Max diameter heated section cable Max diameter cold lead section cable 0 325 in 0 292 in 0 325 in 3 4 in 19 mm stainless steel joint For heated section to heated section joint For heated section to cold le...

Page 17: ...ion to cold lead section joint Max diameter heated section cable Max diameter heated section cable Max diameter cold lead section cable 0 543 in 0 480 in 0 543 in The end cap supplied with the kit is suitable to repair the majority of MI heating cables Select the appropriate end cap and plug from Table 7 In those instances where the heating cable diameter exceeds 0 300 in contact nVent technical s...

Page 18: ...tors 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 Ensure that the portion of the cable being worked on can be moved away from the surface at least 6 in 15 cm to allow access when brazing see repair jig in Appendix H Expose heated section and or cold lead se...

Page 19: ...ing and strip back 6 in 15 cm of the jacket from each end taking care not to nick or damage the copper sheath 6 in Figure 11 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 should be attaine...

Page 20: ...e 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 Figure 13 Check cable diameter Note If replacing the hot cold joint the diameters of both the heated section and cold lead section must be considered when choosing the correct size joint from Table 5 or Table 6 ...

Page 21: ...Cross section of hot hot joint Hot cold joint From the table in Appendix C select the correct drill bit sizes for the cable diameters 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 Using the pilot hole as a guide drill a hole straight through the joint with the smaller diameter drill Using the larger drill drill one end of the joint abo...

Page 22: ... 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 It is not necessary to file the face of heated section square Cold lead File in forward direction only Figure 16 File face of cold lead Sand about 2 in 5 cm of each end of the cable sheath with emery cloth The surface must be clean for brazing Figure 17 ...

Page 23: ...igure 18 Place heat shrink on cable Hot hot joint Slide the joint over either end of the heated section cables Ensure that the joint will easily slide over both ends Use a flat file or emery cloth to touch up the ends of the cables if necessary Hot cold joint Slide the joint over the heated section cable smaller diameter cable ensuring the larger hole faces the cold lead section Make sure joint wi...

Page 24: ...the sheath up to the score mark Using diagonal cutters strip back the sheath of the heated section without the aid of the tube cutter approximately 1 4 in 6 mm Note Do not cut too deeply with the tube cutter as this will cause the sheath to be pushed inwards towards the conductors possibly resulting in cable failure See Appendix G for detailed instructions on stripping cable sheath Score Figure 20...

Page 25: ...m oxide powder There should be enough flux left on the brazing rod to allow proper brazing Hot hot joint Using oxy acetylene torch heat conductor with a small flame see Appendix E and touch or wipe brazing rod onto the tip of the conductor by turning the rod between the fingers This will ensure that the flux melts off the rod and onto the conductor evenly Take care not to get any flux near the end...

Page 26: ... off the rod and onto the conductor evenly Take care not to get any flux near the end of the cable where it might contaminate the magnesium oxide powder Continue heating cold lead conductor with the oxy acetylene torch this does not take much heat and at the same time touch brazing rod to the face of the conductor and apply enough silver solder to form a small bead on the conductor face If repairi...

Page 27: ...zing a hot hot joint Hot cold joint Apply some flux to the conductors of the heated section Align the two cables so that the conductor tips butt together and heat the larger cold lead conductors one at a time so that the solder on the tip melts then push the smaller heated section conductors into the solder Do not add any more silver solder Remove the heat and hold for two seconds until the solder...

Page 28: ...t the brazed junction may be a cold joint and it will be necessary to remake it Note If insufficient heat is applied to the conductors the brazed junction may be surrounded by the ball of silver solder but not actually bonded and an open circuit failure will occur Figure 26 Hot cold junction Remove all trace of flux from the conductors with the emery cloth Straighten the conductors with needle nos...

Page 29: ... cold joint For two conductor cable conductors from the heating cable to the cold lead should be formed in a Y shape as shown in the previous step This will prevent the conductors in the heating cable from shorting to the sheath Slide the joint over the exposed conductors ensuring that the fill hole faces up and is centered over the conductor junction Fill hole Figure 29 Center joint over conducto...

Page 30: ...ils on heating out drying out the cable may be found in Appendix D If making a hot cold joint solder the heated section side smaller cable of the joint first 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 joint will be brazed to the cable sheath Turning the rod between the fingers will ...

Page 31: ...s needed Ensure that the solder flows to the bottom of the joint to ensure a continuous braze around the entire joint Figure 32 Braze joint to cable Repeat procedure for other side of joint 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 als...

Page 32: ...thod will evenly distribute the powder and ensure that it is well packed Figure 33 Fill joint with powder CAUTION Joint will be hot Do not touch joint or cable with bare hands Remove syringe and use 1 1 2 in 3 8 cm long packing rod supplied with kit to pack powder tak ing care not to push in more than 1 8 in 3 mm so as not to bend the conductors inside the joint If required add more powder to fill...

Page 33: ...t 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 The recess should be about 1 4 6 mm square File in one direction only Figure 36 File groove ...

Page 34: ...n resistance This step must be done with great care as excess heat will cause the air within the joint to expand and cause a pinhole in the silver solder Using oxy acetylene torch with a small flame heat joint and apply a small amount of flux over the screw using flux coated brazing rod Continue heating until the silver solder flows freely when touched to the joint completely filling recessed area...

Page 35: ...pect 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 Ensure that all flux is removed from all brazed areas CAUTION Joint will be hot Do not touch joint or cable with bare hands ...

Page 36: ... on the Megohmmeter will drop Joint must be cool to get a proper IR reading Figure 40 Check insulation resistance Water soaked rag Figure 41 Wrap joint with water soaked rag Note If the Megohmmeter reading declines file off all solder from over brass screw and drive out the moisture from the cable as described in Appendix D the Megohmmeter reading will increase when the cable is dry Once the moist...

Page 37: ...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 648 on the inside of the bell mouth Slide bellmouth onto the new joint and let set If heat shrink tubing was used above copper sheath cables only follow instructions in Appendix F to complete heat shrink installat...

Page 38: ...le Remove old end cap by cutting through cable with a hacksaw as close as possible to the solder on the end cap 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 Note Ensure that the portion of the cable being worked on can be moved away from the surface at least 6 in...

Page 39: ...in Appendix D Repeat IR test Verify continuity of conductors using a multimeter or ohmmeter Note If the insulation resistance IR for a polymer jacketed cable is still low after drying out the cable see Appendix D it will be necessary to remove a a longer length of the polymer jacket and begin drying out the cable further back from the end Figure 45 Check insulation resistance Using a vernier calip...

Page 40: ...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 Plug End cap Groove Figure 47 Cross section of end cap Sand about 2 in 5 cm of the end of the cable sheath with emery cloth The surface must be clean for soldering Emery cloth 2 in 50 mm Figure 48 Sand cable sheath ...

Page 41: ... detailed instructions 6 9 in 18 cm 6 9 in 18 cm Figure 49 Place heat shrink on cable Check inside of end cap for burrs and if present remove with round file Slide the end cap onto the cable making sure the plug end larger end faces outwards Figure 50 Place end cap on cable Using side cutters strip the sheath back about 3 8 1 2 in 9 13 mm taking care to flare the sheath of the cable slightly outwa...

Page 42: ...ree of powder for silver solder to bond Emery cloth Figure 52 Clean conductors Using pliers twist conductors together through approximately two full 360 turns Figure 53 Twist conductors With pliers break away 1 2 in 13 mm of flux from end of flux coated brazing rod This will help prevent excess flux from contaminating the magnesium oxide powder There should be enough flux left on the brazing rod t...

Page 43: ... and at the same time touch brazing rod to the end of the twisted conductors and apply enough silver solder to form a small bead Slightly fan torch back and forth several times to draw the silver solder backwards about 1 4 in 6 mm along the twisted conductors Remove heat Brazing rod Figure 54 Join conductors Care must be taken to avoid over heating the conductors and to avoid depositing an excessi...

Page 44: ...nt of cable in end cap You are now ready to braze the end cap to the cable sheath Using a large sizzling flame see Appendix E heat out the moisture from the cable beginning 12 in 30 cm back from the end cap begin 4 in 10 cm back for polymer jacketed cable stopping 1 2 in 13 mm from the end cap Immediately proceed to next step Note Details on heating out drying out the cable may be found in Appendi...

Page 45: ...circumference of the end cap This will cause the solder to wick its way around the joining area and also draw the solder inside the end cap making a stronger braze Add more silver solder as needed Ensure that the solder flows to the bottom of the end cap to ensure a continuous braze around the end cap Large flame Figure 58 Braze end cap to cable Note While brazing it is important to avoid using ex...

Page 46: ...graving tool reverse the engraving bit so that the blunt end is visible and place the bit against the end cap Using an engraving tool or other vibration method will ensure that the powder is well packed CAUTION End cap will be hot Do not touch end cap or cable with bare hands 3 16 in Engraving tool Figure 59 Fill end cap with powder Insert the plug and firmly and gently tap it down to further comp...

Page 47: ...end cap 4 to 5 times This will aid in removing any moisture trapped in the powder Heat the top of the plug and apply flux around area where the plug will be brazed to the end cap using flux coated brazing rod Ensure that the flux is applied around the entire junction and braze the plug to the end cap Do not apply excess heat at this time as excess heat will cause the air within the end cap to expa...

Page 48: ...nt junction to melt Magnesim oxide powder Plug Figure 63 Cross section of completed end cap Test the insulation resistance with a 500 volt Megohmmeter Minimum IR should be 20 MΩ Clean end cap to remove all flux With Megohmmeter still connected 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 a...

Page 49: ...hole Once the moisture is removed touch up the solder as necessary and retest If still low or if no pinholes are visible replace end cap CAUTION Endcap will be hot Do not touch endcap or cable with bare hands Check resistance of heating cable using an ohmmeter it should be within 10 of specifications If open circuit cut off end cap and repeat procedure The finished end cap is shown below Figure 66...

Page 50: ...Cable Modification CABLE INFORMATION AND DESCRIPTION OF CHANGE All Fields MUST be Completed Original Tag Information may be found on the metal identification tag attached to the cold lead Do NOT fill in this area Original Tag information Serial No Amps Max Surface Temp C Cable Design Cable Reference Cable Length Ft Meter Watts Volts Cold Lead Length Ft Meter Cold Lead Code or AWG Joint Type Connec...

Page 51: ...quest Form m y nt Company Telephone Fax Email New Tag Information For Internal Use Only Ft Meter ONS Signature Date 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 ...

Page 52: ...tical a rag soaked in water should be wrapped around the joint while it is still hot this procedure is used in the installation instructions for both the joint and end cap A decrease in insulation resistance indicates the presence of pin holes that must be fixed before proceeding A final careful visual inspection of the joint should be made to ensure the work conforms to the high quality required ...

Page 53: ...s Insulation Resistance and Continuity Test 1 De energize the circuit 2 Disconnect the temperature controller or thermostat if installed 3 Disconnect the heating cable from supply wires or ter minal block if installed 4 Set Megohmmeter test voltage at 0 Vdc or off 5 Connect the positive lead to the heating cable sheath 6 Connect the negative lead to one of the heating cable tails or bare conductor...

Page 54: ...ce value and compare to the calculated value 13 Disconnect the multimeter 14 Reconnect heating cable and temperature controller or thermostat once repairs are completed WARNING Fire hazard in hazardous locations Megohmmeter tests can produce sparks Be sure there are no flammable vapors in the area before performing this test Figure 67 Insulation resistance and continuity test Tails Test 1 Insulati...

Page 55: ...34 Q 0 176 0 177 15 0 335 0 339 R 0 178 0 180 14 0 340 11 32 0 181 0 182 13 0 341 0 343 8 5mm 0 183 0 184 3 16 0 344 0 349 S 0 185 0 186 12 0 350 0 353 9 0mm 0 187 0 188 11 0 354 T 0 189 0 191 10 0 355 0 359 23 64 0 192 0 194 9 0 360 0 363 9 25mm 0 195 0 196 8 0 364 0 370 U 0 197 0 198 7 0 371 0 372 3 8 0 199 13 64 0 373 0 377 V 0 200 6 0 378 0 381 9 7mm 0 201 0 204 5 0 382 0 385 W 0 205 0 208 4 0...

Page 56: ... 12 in 30 cm back from the joint or end cap heat cold lead first if making a hot cold joint If repairing polymer jacketed heating cable and or cold leads begin 4 in 10 cm back from the joint or end cap to avoid melting the polymer jacket Alloy 825 sheath cable should be heated to a dull red color and copper sheath cables should be heated to a bluish gray color Use a short sweeping motion of the to...

Page 57: ...stop the sweeping motion of the torch 1 2 in 13 mm from the joint or end cap Figure D2 If you heat toward the end of the cable too quickly you may skip over the moisture and drive it further back into the cable Figure 69 Sweep flame to end of cable On completion check IR with a 500V insulation tester Megohmmeter Test between the tails conductors and the sheath and between the tails conductors for ...

Page 58: ...ductors 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 5 mm Figure 71 Large neutral flame Use a sizzling reducing carbonizing flame to dry out the cable 1 5 in 38 mm Figure 72 Sizzling reducing carbonizing flame ...

Page 59: ...ce of the 1 2 13 mm tubing It will be necessary to locally source a 1 in 25 mm diameter heat shrinkable tub ing adhesive lined to cover the joint Follow proce dure below to complete joint Heat shrink is installed over completed 1 2 in 13 mm joint as follows Hot hot joint Move 3 8 in 9 mm dia x 6 9 in 18 cm long pieces of heat shrinkable tubing previously installed for ward to completely cover bare...

Page 60: ... mm dia x 6 9 in 18 cm long piece of heat shrink forward and center over joint heat shrink should overlap both ends of joint equally Using heat gun shrink the tubing over the joint by applying heat from the center then outwards to the ends Figure F2 shows the completed joint Figure 73 Heat shrink over exposed copper cable and 1 2 in joint Figure 74 Completed joint with heat shrink seal 3 4 in 19 m...

Page 61: ...ompletely cover bare cop per sheath cable Figure F3 Using heat gun shrink the tubing over the exposed copper 2 Slide 1 2 in 13 mm dia x 6 9 in 18 cm long piece of heat shrink forward and center over end cap heat shrink should equally overlap both ends of end cap Using heat gun shrink the tubing over the end cap Use needle nose pliers to crimp section of tubing past end cap to form a seal as shown ...

Page 62: ...s stripped The correct depth of score one third the thickness of the sheath Note Do not cut too deeply with the tube cutter as this will cause the sheath to be pushed inwards towards the conductors possibly resulting in cable failure Figure 77 Score cable sheath Grip the edge of the sheath between the jaws of the sidecutters and twist clockwise then take a new grip and rotate through a small angle...

Page 63: ...gure 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 Finish off with point of sidecutters held parallel to the cable The sheath will peel away leaving a clean cut when the score mark is reached Ensure that the sheath is not flared inward Figure 80 Sidecutter angle for final stripping Score ...

Page 64: ...n 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 This will occur if the score made with the tube cutter is too deep In this case remove a further 1 4 in 6 mm of sheath Figure 81 Correct end preparation Unacceptable Acceptable Preferred c b a ...

Page 65: ... 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 4 in 10 cm 6 in 15 cm 12 in 30 cm 4 in 10 cm Figure 82 Front of repair jig Figure 83 Back of repair jig ...

Page 66: ...t to change specifications without notice Raychem IM H57640 EN 1810 North America Tel 1 800 545 6258 Fax 1 800 527 5703 thermal info nvent com Asia Pacific Tel 86 21 2412 1688 Fax 86 21 5426 3167 cn thermal info nvent com Europe Middle East Africa Tel 32 16 213 511 Fax 32 16 213 604 thermal info nvent com Latin America Tel 1 713 868 4800 Fax 1 713 868 2333 thermal info nvent com nVent com ...

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