I am splicing some lamp cables. The cable is SPT-2 18-2 lamp wire. First I will be using some vinyl insulated butt splices rated for 22-18 AWG and 600v to make the connection. Then, I want to cover the splices with heat shrink tubing. I'm having a hard time finding definitive results on what size tubing to use, though I am inferring from various sources that it's probably 3/4" polyolefin tubing that I need. Can anyone confirm or deny this, or otherwise make a suggestion?


You should not be splicing lamp wires outside the fixture or lamp. If you need to splice in the middle of a run you should replace the cord.

Inside a fixture or lamp no heat shrink is required or needed.

Heat shrink tubing just needs to fit over the area to be covered before shrinking.

Article 400 Flexible Cords and Cables

400.9 Splices

Flexible cord shall be used only in continuous lengths without splice or tap where initially installed in applications permitted by 400.7(A). The repair of hard-service cord and junior hard-service cord (see Trade Name column in Table 400.4) 14 AWG and larger shall be permitted if conductors are spliced in accordance with 110.14(B) and the completed splice retains the insulation, outer sheath properties, and usage characteristics of the cord being spliced.

  • Why do you say I shouldn't splice outside the lamp? Let me give you a bit more detail. I am interconnecting strip lights which came with short (~2 feet) connector cables. I need them a bit longer, and I have a roll of the same cable type the connector is made from. There's no way to put the splice inside the fixture, and I can't find longer cables with the same connector at the end. My plan was to splice with the butts, then heat shrink, and, if necessary, place the spliced area inside a box or conduit. Is this not enough to be safe?
    – bubbleking
    Apr 2 '16 at 21:21
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    If its line voltage (120/240v) then splices need to be in a box, fixture or enclosure. Splices should not be in conduit. If this is a setup with factory wiring that comes pre-wired you should not be splicing it at all Apr 3 '16 at 20:55
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    i'm sorry if you don't like it, but for NEC (which applies to 120v household wiring) Speedy is right. NEC forbids splicing line cords for appliances outside an electrical box or listed splice device (which don't exist for line cords). The rules on diy.se is that we give code legal answers, we do not advise infringement simply because it is popular. Apr 3 '16 at 21:30
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    I must take the above back! I checked with Gardner-Bender. They do claim their common automotive-grade crimp terminals are UL listed for code electrical work, citing this: database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/… Apr 10 '16 at 22:17
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    How does one splice something in accordance with 110.14(B) ? This answer is useful, but fails to mention what type of shrink tube, "retains the insulation, outer sheath properties, and usage characteristics of the cord being spliced."
    – Mazura
    Apr 13 '16 at 1:38

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