What is NMD90 wire and why does my electrician keep mentioning it?

NMD90 is the standard residential electrical cable used in Ontario homes, and your electrician mentions it because it's the wire going into your walls for virtually every circuit in a modern Canadian home. The name stands for Non-Metallic Dry 90°C — meaning it has a non-metallic (plastic) outer sheath, is rated for dry locations, and the conductor insulation can handle temperatures up to 90 degrees Celsius.

Inside that plastic outer jacket, NMD90 contains two or three insulated copper conductors plus a bare copper ground wire. The most common sizes you'll encounter in residential work are 14/2 (two 14-gauge conductors plus ground, used for standard 15A lighting and outlet circuits), 12/2 (two 12-gauge conductors plus ground, used for 20A kitchen and bathroom circuits), 10/3 (three 10-gauge conductors plus ground, used for dryers and air conditioners), 8/3 (used for ranges and cooktops), and 6/3 (used for EV chargers and sub-panel feeds). The first number is the wire gauge — lower numbers mean thicker wire that can carry more current safely. The second number tells you how many insulated conductors are inside, not counting the ground.

If you're comparing NMD90 to what you might see referenced in American home improvement content, it's essentially Canada's equivalent of Romex — but they're not identical. NMD90 is manufactured to CSA (Canadian Standards Association) specifications, and only CSA-approved cable can be used in Ontario. Your electrician can't install American-spec Romex in your home even if it looks the same.

The alternative to NMD90 that you might encounter is AC90 (also called BX or armoured cable), which has a metal jacket wrapped around the conductors instead of plastic sheathing. AC90 is required in exposed locations where the cable could be physically damaged — running along the surface of a basement wall, through a garage, or in commercial applications. It's also what you'll find in many Toronto homes built in the 1950s through 1970s. AC90 costs roughly two to three times more than NMD90 per foot, so it's only used where code requires the extra mechanical protection.

For a typical GTA rewiring project, NMD90 cable costs approximately $0.50 to $3.00 per foot depending on gauge. A full home rewire uses hundreds of metres of cable, so the material cost adds up — but labour is the dominant expense in any rewiring project. Your electrician buys NMD90 in large spools (typically 75-metre or 150-metre rolls) from electrical supply houses, and pricing fluctuates with copper commodity prices.

When your electrician discusses the wiring plan for your project, they're selecting the appropriate NMD90 size for each circuit based on the amperage rating and the load it needs to carry. Using undersized wire is a code violation and a fire hazard — it's one of the things the ESA inspector specifically checks during inspection. If you're getting quotes for electrical work and want to understand what's being proposed, knowing that NMD90 is simply the standard copper cable going in your walls helps you follow the conversation.