Conduit Fill Guide for Red Seal Exam (Updated to CEC 2024!)
Red Seal Exam Question Guides
Conduit fill is like packing a suitcase. You’ve got to fit your clothes (wires) into your suitcase (conduit), but you can’t overstuff it — or the trip (a.k.a. your wiring job) won’t go smoothly.
The Canadian Electrical Code (CEC) says:
Only 40% of the conduit’s inside area can be filled by conductors (unless special rules apply).
To check if everything fits, you’ll use:
Table 6: Area of the conductors
Table 8: Max fill percentage (usually 40%)
Table 9: Conduit types and their total space
Sometimes Table D5
Table 6
Pay attention to the VOLTAGE and whether or not the conductor is jacketed or unjacketed!
Assume stranded conductor unless the question says otherwise
SOLID conductors is at the bottom of the table!
Table 8
Most conductors are NOT lead-sheathed, but that pesky C of Q wants to trip you up. So if you see a cable you do not recognize, head over to Table D1 to see what the conductor is made out of.
“Don’t assume 40% fill,” ALWAYS double-check!
Table 9
Make sure you pick the right table based on the fill percentage!
Same-Size Conductors
Let’s say you’re stuffing 3 identical wires into a rigid metal conduit:
Example:
3 × #6 AWG RW90XLPE unjacketed
Table 6A: each #6 = 38 mm²
Total: 3 × 38 = 114 mm²
Table 8 (max fill): 40%
Table 9G: Find a conduit with at least 114 mm² capacity at 40% fill
Result: Choose 21 Trade Size (TS) rigid metal conduit
Now Try Eight Big Wires
8 × #3 AWG TW in EMT
Table 6J: each #3 = 73 mm²
Total: 8 × 73 = 584 mm²
40% fill = Table 9G → 53 Trade Size
That's one chunky conduit!
Mixed-Size Conductors
When you mix wire sizes, just add up their individual areas.
Example 1: EMT with Two Sizes
Six #12 AWG RW90XLPE unjacketed = 69.5 mm²
Four #8 AWG T90 nylon = 94.7 mm²
Total: 69.5 + 94.7 = 164.2 mm²
Then go to Table 9G, check what size EMT conduit allows 164.2 mm² at 40% fill
Example 2: PVC with 3 Sizes
Four #10 AWG TW75 solid = 53.1 mm²
Three #6 AWG T90 nylon = 98.1 mm²
Two #2 AWG RW90 jacketed = 148 mm²
Total = 299.2 mm²
Head to Table 9G, look for Rigid PVC conduit that allows at least 299.2 mm² at 40% fill. Boom. You’ve cracked it.
Fun Fact!
💡 The C of Q Exam will often mix up the Trade Size, Metric, and Imperial designators on purpose!
There is a table in the beginning of the CEC (even before the Table of Contents), which shows you Trade Size to inch conversion. You will absolutely need to know about that!
⚠️ Also, just to be tricky, if the question doesn’t mention a specific TYPE of cable…Go to Table D5!
Want to pass your Red Seal exam on the first try?
Download now to access 2,500+ practice questions and master the Canadian Electrical Code!
