Cables and raceways
What you’ll learn
- The difference between a cable and a raceway.
- The common cables: non-metallic sheathed, armoured, and jacketed industrial cable — by their Canadian and US names.
- The common raceways: EMT, rigid metal, rigid PVC, ENT and flexible conduit.
- How to count lengths and couplings for a conduit run.
A wiring method is how the conductors get from the panel to the load and stay protected on the way: either inside a cable that arrives ready-made, or pulled into a raceway you installed first. Each method is built for a set of conditions — dry or wet, hidden or exposed, likely to be hit or not. This lesson is a tour of the ones you will meet most, with both their Canadian and US names. Where each is allowed, and the details of installing it, belong to your code book.
Cables
| Cable | What it is | Where you usually see it |
|---|---|---|
| NMD90 (CA) · NM-B (US) | Insulated conductors and a bare bonding conductor in a plastic jacket. | Houses and small buildings, inside walls and ceilings. |
| AC90 (CA) · AC, MC (US) | Insulated conductors under a spiral interlocked metal armour. | Commercial interiors, fished runs, exposed drops to fixtures. |
| TECK90 (CA) · jacketed MC (US) | Armoured cable with an overall PVC jacket. | Industrial plants, cable tray, wet or corrosive places. |
| NMWU (CA) · UF (US) | Non-metallic cable built for wet locations and, where the code allows, burial. | Outbuildings, outdoor runs. |
Raceways
| Raceway | What it is | Why you would pick it |
|---|---|---|
| EMT | Thin-wall steel tubing, unthreaded, set-screw or compression fittings. | Light, bendable on site, the everyday commercial raceway. |
| Rigid metal (RMC) · IMC (US) | Heavy-wall threaded steel or aluminium pipe. | Maximum protection: services, exposed industrial work. |
| Rigid PVC | Plastic pipe, solvent-welded joints. | Underground and corrosive places; needs a separate bonding conductor and expansion fittings on long exposed runs. |
| ENT | Flexible corrugated plastic tubing. | Concealed in walls and in poured concrete where permitted. |
| Flexible metal · liquidtight flex | Spiral metal hose, with a plastic jacket in the liquidtight kind. | Short final connections to motors and vibrating equipment. |
Conductors pulled into raceways are single insulated wires, usually T90 Nylon or RW90 in Canada and THHN/THWN-2 or XHHW-2 in the US. The letters describe the insulation and where it may be used — wet, dry, hot. In the Canadian names the number is the temperature rating in °C (T90, RW90 = 90 °C); in the US names a “-2” suffix marks a 90 °C wet-and-dry rating. How many fit in a given raceway is a fill calculation that uses your code book’s tables.
Ask four things: Is it wet or dry? Is it hidden or exposed? Could it be hit or crushed? Will anyone want to change the wiring later? The answers usually narrow it to one or two methods — then the code book and the spec have the final word.
Worked example
Counting EMT for a straight run
- A straight run of 87 ft (26.5 m) along a ceiling. EMT comes in 10 ft (3.05 m) lengths.
- 87 ÷ 10 = 8.7, so 9 lengths (26.5 ÷ 3.05 = 8.7 in metric — the same answer). The last one is cut to 7 ft (about 2.1 m).
- Joining 9 lengths end to end takes 9 − 1 = 8 couplings, plus a connector at each box: 2 connectors.
- Straps: count them from the support spacing in your code book, and add one near each box.
Try one: a 42 ft (12.8 m) run
42 ÷ 10 = 4.2 → 5 lengths, 4 couplings, 2 connectors. (12.8 ÷ 3.05 = 4.2 → the same.)
En la obra
Tips from the job
- Ask what the spec calls for before you pick a method. On commercial work the drawings or spec usually decide; on residential work it is often NM-type cable unless something says otherwise.
- Read the print on the jacket or the conduit: type, temperature rating, size and listing are all there. It answers most “can I use this here?” questions in combination with your code book.
- Ream every cut end of metal conduit. The burr left by a saw or cutter strips insulation during the pull.
- Keep offcuts sorted. Short lengths of EMT make good nipples and offsets; see conduit bending basics.
Common mistakes
- Using a wiring method outside what it is rated for — wet, damp, exposed, buried, or subject to damage. The jacket print and your code book decide.
- Forgetting the anti-short bushing on armoured cable, so the cut armour chews the conductor insulation.
- Pulling conductors through unreamed conduit or too many bends; the code book limits the bends between pull points.
- Treating the maximum fill or support spacing as something to remember. Look it up every time — it varies by method, size and code edition.
- Mixing up EMT set-screw and compression fittings where the location needs the wet-rated kind.
Check yourself
6 questions. Tap an answer — it is marked straight away and the reason opens under it. Get 80% or better and the lesson is ticked off on the year page.
Not started yet.
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What is the main difference between a cable and a raceway?
Answer and why
B. Cable = conductors and jacket in one assembly. Raceway = the empty pipe or channel you install, then pull individual conductors into.
-
NMD90 in Canada and NM-B in the US are…
Answer and why
C. Both are non-metallic sheathed cable — insulated conductors and a bare bonding conductor in a plastic jacket — the everyday residential wiring method.
-
Why might you choose EMT over cable in a commercial ceiling?
Answer and why
B. A raceway gives mechanical protection and makes the system changeable: add or replace conductors without opening walls. Metal raceways can also serve as a bonding path when installed as the code allows.
-
EMT comes in 10 ft (3.05 m) lengths. How many lengths for a straight 87 ft run?
Answer and why
B. 87 ÷ 10 = 8.7, so you need 9 lengths (and you will cut the last one). Joining 9 lengths end to end takes 8 couplings.
-
Liquidtight flexible conduit is typically used to…
Answer and why
B. Flexible conduit takes vibration and movement and makes alignment easy; the liquidtight jacket keeps water and oil out. Its length and where it may be used are code questions.
-
Rigid PVC conduit expands and contracts with temperature. What do you use to deal with that on a long, exposed run?
Answer and why
B. PVC changes length noticeably with temperature. Expansion fittings let the run grow and shrink without pulling apart or bowing. The maker’s data and your code book say when and how many.
Preguntas frecuentes
What is the difference between AC90 and TECK90?
Both are armoured cables used in Canada. AC90 has an interlocking aluminium armour with no jacket over it, used in dry building interiors. TECK90 has an armour with an overall PVC jacket (and usually an inner jacket too), so it is used in industrial and wet or corrosive locations. In the US the nearest equivalents are AC or MC cable, and MC with a PVC jacket.
Is EMT the same as rigid conduit?
No. EMT (electrical metallic tubing) is thin-walled, unthreaded, and joined with set-screw or compression fittings. Rigid metal conduit is heavy-walled and threaded, and it gives much more protection against damage. There is also IMC in the US, in between the two.
Ver también
- Lo básico del doblado de conduit
- Fittings index — the connectors, couplings and bodies that go with each method.
- Lo básico de baja tensión y datos
- Conductors and insulation — what goes inside the cable or raceway.
- Voltage drop — the next lesson.
- All second year lessons
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