CEC Conduit Fill Calculator
Size your raceway right the first time. Built on CEC Rule 12-910, Tables 6-9—no overfilled conduits, no re-pulls.
Switch to NECHow We Calculate Conduit Fill (CEC)
This calculator uses conductor areas from CEC Tables 6A-6K and conduit internal areas from Table 9A. Fill percentages come from Table 8.
The calculation is straightforward:
- Sum conductor areas — Look up each wire size/type in Tables 6A-6K, multiply by quantity
- Determine fill percentage — Based on total conductor count (Table 8)
- Find minimum conduit — Select smallest conduit where conductor area ≤ allowable fill area
CEC vs NEC: Key Differences
Metric Units
CEC uses metric trade sizes (16, 21, 27, 35 mm, etc.) and areas in mm². This calculator handles the conversions automatically—no need to convert between imperial and metric.
Wire Type Designations
Canadian wire types have different designations: RW90 (similar to THHN), TWN75 (similar to THWN), TW, and others. The CEC Tables 6A-6K specify exact areas for each type.
Same Fill Percentages
The fill percentages (53%, 31%, 40%, 60%) are identical between CEC and NEC. The underlying physics of conductor jamming and heat dissipation don't change at the border.
CEC Conduit Fill: What Canadian Electricians Should Know
Which CEC tables does this calculator use?
This calculator uses data from CSA C22.1:21 (2021 Canadian Electrical Code):
- Tables 6A-6K: Conductor areas for various wire types (RW90, TWN75, TW, etc.)
- Table 8: Maximum fill percentages
- Table 9A: Internal areas of conduits and tubing
What's the most common wire type for CEC calculations?
RW90 (also called R90XLPE or RW90XLPE) is the most common building wire in Canada. It's rated for 90°C wet or dry locations and is equivalent to THHN/THWN-2 in the NEC.
For typical commercial and residential work, RW90 is your default choice unless specifications require otherwise.
How do I convert between metric and imperial conduit sizes?
Here are the common equivalents between metric trade sizes and imperial:
- 16 mm ≈ 1/2"
- 21 mm ≈ 3/4"
- 27 mm ≈ 1"
- 35 mm ≈ 1-1/4"
- 41 mm ≈ 1-1/2"
- 53 mm ≈ 2"
- 63 mm ≈ 2-1/2"
- 78 mm ≈ 3"
What's the nipple length in metric?
Under CEC, a nipple is a conduit length less than 600 mm (which is approximately 24 inches). The 60% fill allowance applies the same as in NEC—useful for short runs between panels or junction boxes.
Do equipment grounding conductors count toward fill?
Yes. Per CEC Rule 10-814, equipment bonding conductors are included in conduit fill calculations. Use the bare conductor area for bare grounds, or the insulated area if you're running insulated bonding conductors.