Open any industrial control cabinet and most of the wire you see is MTW, short for Machine Tool Wire. It's the default conductor for machine wiring in North America. Here's what it is and when to use it.
MTW at a Glance
- Standard: UL 1063 (Machine Tool Wires and Cables)
- Voltage: 600V
- Temperature: 90°C dry / 60°C in the presence of oil (higher for some constructions)
- Insulation: Flexible PVC, oil- and moisture-resistant
- Conductor: Stranded copper, often fine-strand (Class K) for panel work
- Flame rating: VW-1
Why Machines Get Their Own Wire Type
NFPA 79 (Electrical Standard for Industrial Machinery) governs the wiring on machine tools, packaging lines, robots, and other factory equipment. Machines vibrate, leak cutting fluid, and get rewired constantly, so NFPA 79 favors a conductor that checks three boxes:
- Flexible. Fine stranding routes cleanly through wireways and survives vibration without work-hardening.
- Oil-resistant. Cutting oils and coolants destroy ordinary insulation.
- Easy to terminate. It strips cleanly and crimps reliably in ferrules.
MTW is built around exactly those needs. THHN, by contrast, is optimized for pulling through building conduit. Its stiffer stranding and nylon jacket are assets in a raceway and liabilities inside a dense panel.
MTW vs THHN vs SIS
| MTW | THHN | SIS | |
|---|---|---|---|
| Home turf | Machine panels (NFPA 79) | Building raceways (NEC) | Switchboards/switchgear (UL 891) |
| Stranding | Flexible / fine | Standard (Class B/C) | Stranded, often tinned |
| Insulation | PVC | PVC + nylon | XLPE thermoset |
| Oil resistance | Yes, a core requirement | Limited | Good |
Many wires are dual- or triple-rated (MTW/THHN/THWN-2, or SIS/MTW combinations like UL 3173) so one spool can satisfy multiple specifications. For switchboard work specifically, see our SIS wire guide.
Typical Applications
- Control panel wiring: relays, PLCs, terminal blocks, drives
- Motor branch wiring inside machine enclosures
- Wireway and gutter runs on industrial machinery
- Appliance and equipment internal wiring where oil exposure exists
Sizing MTW
Inside a UL 508A panel, MTW is sized to the terminal temperature rating, not to its own 90°C or 105°C insulation rating: 14 AWG carries 15 A, 12 AWG 20 A, 10 AWG 30 A, and so on up the table. Our MTW wire ampacity chart lays out UL 508A Table 28.1 and the NFPA 79 small-gauge values from 24 AWG to 4/0, with the 60°C vs 75°C column rule.
Specifying MTW
Order by gauge (24 AWG through 4/0 in stock), color (panel shops standardize color codes for AC, DC, neutral, and foreign-voltage circuits), and stranding class. We stock MTW / UL 1015 machine tool wire alongside a full hook-up wire range, cut to length with same-day quotes. Per-size part numbers, stranding, diameters, and weights are on the product page, or download our MTW / UL 1015 spec sheet (PDF).