Conduit Size For Cables ((top)) — How To Calculate

“Six THHN wires: three #8 AWG and three #6 AWG. Need them in a single conduit, underground from the panel to the new HVAC unit. Tell me the smallest size EMT you can use. Don’t guess. Calculate it.”

Mike nodded. “Welcome to the trade. Never guess—calculate.” | Step | Action | Example (Elena’s job) | |------|--------|------------------------| | 1 | Count wires & find fill % | 6 wires → 40% | | 2 | Get each wire’s area (NEC Table 5) | #8: 0.0366 sq in, #6: 0.0507 sq in | | 3 | Total wire area | 0.2619 sq in | | 4 | Divide by fill % (0.40) | 0.65475 sq in minimum conduit area | | 5 | Check NEC Table 4 for conduit type | 1" EMT = 0.864 sq in → ✅ | | 6 | Verify jamming rule (optional but smart) | 1" ID vs wire OD → safe | how to calculate conduit size for cables

She replied, “Total wire area is 0.2619 sq in. 40% of 3/4" EMT is only 0.2316 sq in—that’s not enough. 1" gives us 0.864 sq in, which is well within code and allows for future pulls.” “Six THHN wires: three #8 AWG and three #6 AWG