Choose heat shrink tubing that passes over the largest splice feature, recovers below the smallest landing diameter and preserves the required coverage after shrinking. Cut and preload it before closing the connection, accept the electrical joint, position the sleeve, recover it with the specified heating process, then cool, inspect and complete the required assembly tests.
This procedure covers a specified straight inline splice. Heat shrink tubing provides the specified insulation or protection; it does not make the electrical connection. Shielded, multicore and medium- or high-voltage joints need their own assembly instructions. A tightly recovered sleeve is not evidence that a joint is electrically acceptable or environmentally sealed.
1. Confirm the work instructions and isolation
Before cutting cable or applying heat, obtain the splice drawing, joining instructions, exact tubing data, application process and acceptance requirements. Work on an isolated circuit verified de-energized under the equipment and site procedure. In U.S. workplaces, OSHA 1910.333(b) sets out lockout/tagout and verification by a qualified person.
Use a job record to connect the measurements to the eventual acceptance decision:
| Record before starting | Decision it controls |
|---|---|
| Cable/jacket, splice and sleeve identification | Material compatibility and applicable instructions |
| Largest feature on the sleeve’s insertion path | Required supplied inside diameter |
| Left and right landing outside diameters | Required recovery on both sides |
| Joint span and specified overlap on each side | Minimum finished coverage |
| Electrical duty, environment and available space | Construction, wall and assembly suitability |
| Heating, cooling and acceptance instructions | Process limits and release checks |
Have suitable measuring tools, a cutter, the specified joining tools and a permitted controlled heat source available. Hold the job if a required instruction or acceptance criterion is missing.
2. Select the construction and check both diameters
Choose construction for the specified task. YOCL’s heat shrink tubing range includes HTS single-wall tubing and HS3X/HS4X adhesive-lined tubing. An unlined sleeve can serve an insulation/protection requirement; an adhesive-lined sleeve needs a compatible jacket interface and a verified application process when sealing is required. Use the single-wall versus dual-wall guide if this decision remains unresolved.
Measure the complete insertion path, including any connector shoulder the sleeve must cross. Record both landing diameters separately; conductor cross-sectional area is not a jacket diameter. Check the supplied minimum inside diameter against the largest pass-over feature and the recovered maximum inside diameter against the smallest landing.
The larger-before/smaller-after principle appears in KSC-E-165 Revision F, §3.8.1.1.1(a), a specification for KSC ground-support control and monitoring equipment. It supports this dimensional screen, not a universal installation margin.
For example, assume a 7.4 mm largest pass-over feature and a 4.0 mm smallest landing. The current YOCL HS3X table gives:
| HS3X nominal size | Supplied ID | Recovered ID | Preliminary result |
|---|---|---|---|
| 6.4 mm | ≥6.4 mm | ≤2.2 mm | Guaranteed supplied minimum does not clear 7.4 mm |
| 9.5 mm | ≥9.5 mm | ≤3.2 mm | Clears both basic diameter checks |
The 9.5 mm row is a dimensional candidate, not an approved sealed splice. Confirm the required insertion allowance, tolerances, wall/space, duty and jacket compatibility. Consult the size chart for other rows; use the shrink-ratio comparison when passage and landing geometry demand another ratio.
3. Determine cut length and preload the sleeve
Finished coverage must include the joint span and the specified overlap on each side. Allow for longitudinal change using the applicable process data. Do not substitute an arbitrary extra-length percentage or a laboratory axial-change value for an established installation allowance.
Where the instructions establish a maximum shortening fraction s, a planning calculation is:
Minimum cut length = (joint span + left overlap + right overlap) ÷ (1 − s)
Use the specified overlap and validated s for that application, round up to the permitted cut length, and verify actual coverage after cooling. If those inputs are unknown, the calculation cannot release the sleeve for cutting.
YOCL’s HTS installation notes direct cutting to the required length and sliding tubing on before completing the connection when necessary. Preload the selected sleeve while access remains. Park it clear of the connection-making area under the joining instructions.
If access has been closed without preloading, stop for an approved correction; slitting a standard closed tube does not make it an approved wraparound sleeve.
4. Complete and accept the connection before covering it
Make the splice using its specified connector, conductor combination and joining procedure. Complete the required connection inspection before the sleeve conceals the joint. A failed or undocumented connection remains on hold even if the tubing fits.
Prepare the landing surfaces according to the selected jacket, sleeve and adhesive instructions. If they require cleaning, priming or drying, follow those material-specific directions. Do not improvise a solvent or abrasion method. For an adhesive-lined sealing job, unresolved surface compatibility or preparation means the sleeve is not ready for application.
5. Position the sleeve to the drawing
Move the sleeve into its specified position and check coverage at both ends.
Expected result: the joint and both required landing overlaps lie within the intended finished coverage. Reposition before heating if one end lacks coverage; extra material on the other end does not satisfy that requirement.
6. Recover with the specified heating process
HTS requires uniform recovery with controlled, even heat; other models need their applicable process.
Use the heat source, heating sequence, exposure limits and completion criteria established for the actual assembly. A catalogue shrink temperature is not a heat-gun dial setting, nozzle distance or dwell time. If these process requirements are unresolved, obtain the applicable instructions before heating.
NASA-STD-8739.4A Change 4, §9.9, in its NASA mission-hardware scope, ties heat and exposure to tubing size/type and requires protection of the covered item and nearby heat-sensitive parts. These are useful workmanship boundaries; they do not establish settings for a YOCL splice.
Hold the assembly if the specified recovery cannot be completed within its thermal limits or visible heat damage develops.
7. Cool and inspect the application
Let HTS cool before handling; follow the selected assembly’s cooling and inspection instructions. Check:
- Position and actual finished coverage against the drawing.
- Uniform recovery and grip where required.
- Cracks, punctures, blisters or burned areas, plus damage to the cable jacket.
- Any model-specific adhesive and interface acceptance criteria.
NASA-STD-8739.4A §§9.10–9.11 provide scoped examples of positioning, recovery/grip and visible defect checks. Appearance alone does not establish electrical performance or a complete hidden adhesive bond. An adhesive bead can be a specified local process cue; by itself it does not prove an environmental seal.
Route defects or unresolved sealing to the applicable rework process. The split-or-fail-to-seal guide explains the separate diagnosis task; do not keep reheating without authorized rework instructions.
8. Complete the release record before restoration
Record three separate decisions: connection accepted, sleeve workmanship accepted, and required assembly tests passed. Enter the cable/splice and sleeve identification, measured coverage, process reference and test results. A missing seal-verification requirement cannot be replaced with “looks tight.”
Complete the specified electrical and, where required, environmental acceptance tests using the assembly procedure. Hold failed or incomplete results. Restore service only through the equipment/site authorization process; OSHA 1910.333(b)(2)(v) sets out restoration checks for its U.S. workplace scope.
For YOCL model selection, provide the pass-over dimension, both landing diameters, required coverage, jacket material and duty when requesting the applicable tubing and process documentation. That information turns a catalogue size candidate into a reviewable application choice.
References
- OSHA — 29 CFR 1910.333, electrical work practices, verification and restoration.
- YOCL — Heat Shrink Tubing, current product families.
- NASA KSC — KSC-E-165 Revision F, §3.8.1.1.1(a), dimensional selection.
- YOCL — HS3X 3:1 Dual-Wall Tubing, supplied/recovered size table.
- YOCL — HTS 2:1 Single-Wall Tubing, Installation Notes.
- NASA — NASA-STD-8739.4A Change 4, §§9.9–9.11, heating and workmanship.