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
Specifying MTW
Order by gauge (18 AWG through 500 MCM), color (panel shops standardize color codes for AC, DC, neutral, and foreign-voltage circuits), and stranding class. We stock machine tool wire alongside a full hook-up wire range, cut to length with same-day quotes. For part numbers, constructions, and dimensional data, download our MTW / UL 1015 spec sheet (PDF).
