NMD90 vs NMWU Wire — Indoor vs Outdoor Wiring in Canada
Share
NMD90 vs NMWU Wire — Indoor vs Outdoor Wiring in Canada
Using the right wire type in the right location is fundamental to electrical safety and code compliance. In Canada, the two most common residential wire types are NMD90 and NMWU — and using the wrong one in the wrong place is a code violation.
Quick Comparison
| Feature | NMD90 | NMWU |
|---|---|---|
| Full name | Non-Metallic Dry 90°C | Non-Metallic Wet Underground |
| Use | Indoor, dry locations | Outdoor, wet, underground |
| Jacket | PVC (not moisture-resistant) | Moisture-resistant PVC |
| Conductor insulation | PVC, 90°C | Cross-linked polyethylene (XLPE) |
| Direct burial | ❌ No | ✅ Yes |
| Exposed to weather | ❌ No | ✅ Yes |
| In conduit outdoors | ❌ No | ✅ Yes |
| Price (14/2, 75M) | ~$70 | ~$120 |
NMD90 — Indoor Building Wire
NMD90 is the standard cable for interior residential wiring in Canada. The "D" stands for "Dry" — it's rated for dry locations only.
Where to use NMD90:
- All interior wall and ceiling wiring
- Between floors and in attics
- In dry basements (above grade)
- Behind finished walls
- Through interior studs and joists
Where NOT to use NMD90:
- Outdoors (any exposure to weather)
- Underground (even in conduit)
- In wet or damp locations
- In concrete (direct pour)
- Exposed on exterior walls
Our NMD90 14/2 - 75M and NMD90 12/2 - 75M are ETL or UL certified copper building wire for interior residential circuits.
NMWU — Outdoor and Underground Wire
NMWU is designed for wet locations and direct burial. Its moisture-resistant jacket and XLPE insulation protect conductors from water, soil chemicals, and temperature cycling.
Where to use NMWU:
- Underground runs (direct burial or in conduit)
- Outdoor receptacle and light circuits
- Garage to house connections (underground)
- Supply to detached sheds, garages, and pools
- Any outdoor exposed location
Burial depth requirements (CEC Rule 12-012):
| Method | Minimum Depth |
|---|---|
| Direct burial (no conduit) | 600mm (24") |
| In rigid PVC conduit | 450mm (18") |
| Under driveways / parking | 600mm (24") in conduit |
What About TECK Cable?
TECK90 is armoured cable used in commercial and industrial settings:
| Feature | TECK90 |
|---|---|
| Armour | Interlocked aluminum |
| Use | Commercial, industrial, exposed runs |
| Can be exposed | Yes |
| In wet locations | Yes |
| Direct burial | Yes (with proper fittings) |
Our TECK90 12/3 - 30M is available for commercial wiring projects.
Common Scenarios
Running Power to a Detached Garage
- Inside the house: NMD90 from panel to exterior wall
- Underground to garage: NMWU (direct burial at 600mm or in conduit at 450mm)
- Inside the garage: NMD90 for interior circuits
Adding an Outdoor Receptacle
- Interior wiring to exterior wall: NMD90
- Through the wall and outdoors: Transition to NMWU where it exits the building
- Alternative: Run NMD90 to a junction box at the wall, then NMWU outdoors
Hot Tub Installation
- NMD90 from panel to exterior wall
- NMWU from exterior to hot tub disconnect (underground or exposed outdoor run)
- GFCI protection required per CEC for hot tub circuits
Landscape Lighting
- Low-voltage landscape lighting (12V/24V): Use landscape-rated direct burial cable, not NMD90 or NMWU
- Line-voltage outdoor lighting (120V): NMWU underground to each fixture
Code Summary
CEC Rule 12-102 specifies cable types by location:
| Location | Permitted Cable Types |
|---|---|
| Dry interior | NMD90, TECK90, AC90 |
| Wet interior | NMWU, TECK90 |
| Outdoor exposed | NMWU, TECK90 |
| Underground | NMWU, TECK90 (direct burial rated) |
| In conduit (indoor) | NMD90, THHN, RW90 |
| In conduit (outdoor) | NMWU, RW90 |
What to Buy
| Product | Application | Price |
|---|---|---|
| NMD90 14/2 - 75M | Indoor 15A circuits | $69.99 |
| NMD90 12/2 - 75M | Indoor 20A circuits | $99.99 |
| TECK90 12/3 - 30M | Commercial / exposed | $149.99 |
For NMWU cable and specialty wire, visit our Brampton showroom or call for pricing.
Need outdoor or underground wiring? Safer Electric (ESA Licence #7008996) handles outdoor circuits, hot tub installations, and underground runs across the GTA. ESA permit included. Call (647) 383-9500.
FAQ
Can I run NMD90 through outdoor conduit? No. Even in conduit, NMD90 is not rated for outdoor use. Moisture can enter the conduit through condensation and compromise the cable. Use NMWU or individual conductors rated for wet locations.
What if I find NMD90 used outdoors in my home? This is a code violation. It should be replaced with the appropriate cable type. A licensed electrician can assess the situation and bring it up to code.
Is NMWU more expensive than NMD90? Yes, typically 40-60% more due to the moisture-resistant materials. But it's the only correct choice for outdoor and underground applications.
Can I use NMWU indoors? Yes. NMWU is rated for wet AND dry locations. However, it costs more, so there's no practical reason to use it indoors where NMD90 is appropriate.