Wire loom (also called split loom tubing or wire conduit) protects wire harnesses from abrasion, heat, moisture, and mechanical damage. It's a standard component in automotive wiring, marine installations, and industrial cable management.
This guide covers the main types of wire loom, how to size them, and installation best practices.
What Is Wire Loom?
Wire loom is a flexible conduit that bundles and protects multiple wires. The most common type is split loom — a corrugated tube with a lengthwise slit that allows wires to be inserted without threading them through the end.
Wire loom serves several purposes:
- Abrasion protection: Prevents wires from chafing against metal edges, brackets, or other wires
- Heat protection: Shields wires from exhaust heat, engine heat, or other heat sources
- Moisture protection: Keeps water and contaminants away from wire insulation
- Organization: Bundles multiple wires into a neat, manageable harness
- UV protection: Protects wires from UV degradation in outdoor applications
Types of Wire Loom
Split Loom Tubing (Corrugated)
The most common type. A corrugated plastic tube with a lengthwise slit for easy wire insertion.
Material options:
- Polyethylene (PE): Standard, flexible, good chemical resistance. Temperature range: -40°C to +90°C
- Polypropylene (PP): Stiffer, better heat resistance. Temperature range: -20°C to +120°C
- Nylon (PA): Best heat and chemical resistance. Temperature range: -40°C to +150°C
- Halogen-free: For applications requiring low smoke/toxicity
Best for: General automotive wiring, under-hood applications, general wire bundling.
Braided Sleeving
Expandable braided sleeve made from polyester, nylon, or PET fibers. Expands to accommodate varying bundle diameters.
Advantages:
- Flexible and expandable — accommodates branches and connectors
- Neat appearance
- Good abrasion resistance
Disadvantages:
- Not split — wires must be threaded through or ends must be open
- Less protection than solid conduit
Best for: Visible wiring, audio/video installations, custom builds where appearance matters.
Corrugated Conduit (Closed)
Similar to split loom but without the slit. Wires must be threaded through. Provides better protection than split loom.
Best for: Permanent installations where maximum protection is needed.
Heat-Resistant Loom
Fiberglass or silicone-coated loom for high-temperature applications near exhaust systems or engines.
- Fiberglass sleeving: Up to 550°C continuous
- Silicone fiberglass: Up to 200°C, flexible
- Reflective sleeving: Aluminum-coated, reflects radiant heat
Best for: Exhaust heat shields, turbo applications, engine bay wiring near heat sources.
Wire Loom Sizes
Split loom is sized by the inner diameter (ID), which should match the outer diameter of the wire bundle.
| Loom ID | Typical Wire Bundle | Common Applications |
|---|---|---|
| 3/16" (5 mm) | 1–3 small wires | Sensor wires, small harnesses |
| 1/4" (6 mm) | 2–4 wires (18–22 AWG) | Automotive sensors, lighting |
| 3/8" (10 mm) | 4–8 wires | General automotive harnesses |
| 1/2" (13 mm) | 8–12 wires | Main harness sections |
| 3/4" (19 mm) | 12–20 wires | Large harness bundles |
| 1" (25 mm) | 20+ wires | Main power harnesses |
Sizing tip: The loom ID should be approximately equal to the bundle diameter. Split loom can accommodate bundles slightly larger than its nominal ID due to the slit.
How to Install Split Loom
Tools needed:
- Split loom tubing (correct size)
- Loom installation tool (optional but helpful)
- Electrical tape or loom clips
- Scissors or loom cutter
Steps:
-
Measure and cut: Cut the loom to the required length. A loom cutter or sharp scissors gives a clean cut.
-
Open the slit: Use your fingers or a loom installation tool to open the slit along the length of the loom.
-
Insert the wires: Feed the wire bundle into the loom through the slit. Work along the length, pressing wires in section by section.
-
Secure the ends: Wrap the ends with electrical tape or use loom end caps to prevent the loom from sliding and to keep the slit closed.
-
Secure along the run: Use loom clips, cable ties, or adhesive mounts to secure the loom to the chassis or frame at regular intervals (every 12–18 inches).
Securing Wire Loom
| Method | Best For |
|---|---|
| Electrical tape | Quick, temporary, or low-vibration applications |
| Loom clips (P-clips) | Permanent mounting to chassis or brackets |
| Cable ties | Bundling and securing to existing harnesses |
| Adhesive cable mounts | Mounting to flat surfaces without drilling |
| Loom end caps | Sealing loom ends against moisture and debris |
Automotive Wire Loom Applications
Engine bay:
- Use nylon or PP loom for heat resistance
- Route away from exhaust manifolds and hot surfaces
- Use heat-resistant loom within 6 inches of exhaust components
Under-dash:
- PE split loom is sufficient
- Use loom clips to secure to body panels
- Leave service loops at connectors for future access
Under-vehicle:
- Use UV-resistant loom
- Secure every 12 inches to prevent road debris damage
- Use grommets where loom passes through body panels
Summary
Wire loom is an essential component for protecting and organizing wire harnesses. Key selection criteria:
- Split loom: Best for most automotive and general applications — easy installation
- Braided sleeving: Best for visible, custom installations
- Heat-resistant loom: Required near exhaust or high-heat sources
- Size: Match loom ID to bundle diameter
Secure loom at regular intervals and seal ends to prevent moisture ingress and loom migration.
CZT supplies automotive connectors, wire harness components, and cable management accessories. Browse our automotive connector range for compatible wire protection products.
