UL 5128 18 AWG Mica Wrapped Wire — 450°C · 300 Vac · Mica Tape with Treated Glass Braid
This page covers UL AWM Style 5128 in 18 AWG: a conductor wrapped in non-extruded mica tape (or mica composite) and covered with a glass braid treated with silicone varnish or TFE finish. The Style is rated 450°C, 300 Vac, horizontal flame, under UL Subject 758, Section 5. At 18 AWG the wire falls in the 24–12 AWG group, which requires 15 mils minimum average of total mica tape layers and 7 mils minimum average of treated glass braid.
UL Style 5128 is for internal wiring of high-temperature equipment where the wire is not subjected to repeated flexing and is protected from mechanical abuse; the acceptability, including current-carrying capacity, has been determined by UL. The wire carries power inside the equipment. It is not a heating element.
UL 5128 18 AWG Specifications
| Parameter | Value |
|---|---|
| UL AWM Style | 5128 (Subject 758, Section 5) |
| Conductor Size | 18 AWG, solid or stranded (Style range 24–4 AWG) |
| Temperature Rating | 450°C |
| Voltage Rating | 300 Vac |
| Insulation | Non-extruded mica tape or mica composite, 15 mils (0.38 mm) min. average total tape layers |
| Braid | Glass braid treated with silicone varnish or TFE finish, 7 mils (0.18 mm) min. average |
| Shield (optional) | Stainless steel alloy 304, applied as a braid over the treated glass braid |
| Flame | Horizontal flame; VW-1 / FT-1 constructions available |
| Marking | General |
| Use | Internal wiring of high-temperature equipment where not subjected to repeated flexing and protected from mechanical abuse; acceptability, including current-carrying capacity, determined by UL |
| RoHS / REACH | Documentation available on request |
18 AWG Mica Wire: Wall Thickness by UL Style
Several UL mica Styles cover 18 AWG. They differ in voltage rating and in how much mica and braid the Style requires at this size:
| Style | Rating | Mica at 18 AWG (min. avg.) | Braid at 18 AWG (min. avg.) |
|---|---|---|---|
| UL 5360 | 200 or 450°C, 300 Vac | 12 mils | 7 mils |
| UL 5128 | 450°C, 300 Vac | 15 mils | 7 mils |
| UL 5334 | 450°C, 300 Vac | 17 mils (composite mica glass) | 5 mils |
| UL 5359 | 200 or 450°C, 600 Vac | 16 mils | 7 mils |
| UL 5476 | 450°C, 600 Vac | 17 mils | 7 mils |
| UL 5335 | 450°C, 600 Vac | 23 mils | 5 mils |
| UL 5107 | 200 or 450°C, 600 Vac | 25 mils | 7 mils |
For 300 Vac equipment at 450°C, UL 5128 is the mica tape Style with a 15 mil wall at 18 AWG. Where 600 Vac is required, a 600 V Style such as UL 5359 or UL 5107 applies.
Construction Options
- Conductor: solid or stranded. Conductor material and plating are not fixed by the Style and are confirmed with the order; 450°C constructions commonly use nickel-clad copper or nickel.
- Mica tape or mica composite: either is permitted under the glass braid.
- Braid finish: silicone varnish or TFE.
- SS304 braid: optional stainless steel braid over the treated glass braid for added abrasion protection.
- Multi-conductor: two or more conductors may be cabled, max O.D. 1.500 in, with optional mica glass binder, fiberglass fillers and overall treated glass braid. See UL 5128 multi-core mica glass braid cable.
Installation Limits
Mica and glass braid withstand 450°C, but not repeated movement. Route 18 AWG UL 5128 wire in fixed positions, secure it against vibration, and keep it away from sharp edges and abrasion. It should not be used where the wire flexes in service.
FAQ — UL 5128 18 AWG Wire
What is 18 AWG mica wrapped wire?
An 18 AWG conductor insulated with wrapped mica tape and covered with a treated glass braid. Under UL Style 5128 it is rated 450°C and 300 Vac.
What wall thickness does UL 5128 require at 18 AWG?
15 mils minimum average of total mica tape layers and 7 mils minimum average of treated glass braid.
Is this wire used as a heating element?
No. UL 5128 is internal wiring of high-temperature equipment. It connects heaters and other components inside the equipment; it is not resistance heating wire.
What is the difference between UL 5128 and UL 5359 at 18 AWG?
UL 5128 is rated 450°C / 300 Vac with 15 mils of mica; UL 5359 is rated 200 or 450°C / 600 Vac with 16 mils of mica.
Request a Quote
Please include: quantity in metres or feet, solid or stranded, conductor material, braid finish (silicone varnish or TFE), colour, whether an SS304 braid is required, and the equipment the wire will be installed in.
For other gauges in this Style, see UL 5128 mica wire, or compare all mica wire Styles.
