[ \textMin conduit area = \frac0.26190.40 = 0.65475 \text sq in ]
“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.” how to calculate conduit size for cables
Mike grinned. “Why not 3/4 inch? It’s cheaper.” [ \textMin conduit area = \frac0
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 | Don’t guess