RHH Wire Fill Chart
RHH, RHW, and RHW-2 rubber-insulated maximum conductors across every conduit type — NEC 2023. Notably fewer conductors per conduit than THHN due to thicker insulation.
RHH / RHW / RHW-2 conductors have significantly larger cross-sectional area than THHN at the same AWG — nearly double for 12 AWG (0.0260 in² vs 0.0133 in²). This drops the conductor count per conduit dramatically. For details, see what is RHH wire.
- 1/2" EMT4 wires
- 3/4" EMT8 wires
- 1" EMT13 wires
- 1-1/4" EMT23 wires
- 1-1/2" EMT31 wires
- 2" EMT51 wires
- 2-1/2" EMT90 wires
- 3" EMT136 wires
- 3-1/2" EMT177 wires
- 4" EMT227 wires
| TRADE → WIRE ↓ | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 6 | 10 | 16 | 28 | 39 | 64 | 112 | 169 | 221 | 282 |
| 12 AWG | 4 | 8 | 13 | 23 | 31 | 51 | 90 | 136 | 177 | 227 |
| 10 AWG | 3 | 6 | 10 | 18 | 24 | 40 | 70 | 106 | 138 | 177 |
| 8 AWG | — | 4 | 6 | 10 | 14 | 24 | 42 | 63 | 83 | 106 |
| 6 AWG | — | 3 | 4 | 8 | 11 | 18 | 32 | 48 | 63 | 81 |
| 4 AWG | 1 | — | 3 | 6 | 8 | 13 | 24 | 36 | 47 | 60 |
| 3 AWG | 1 | — | 3 | 5 | 7 | 12 | 20 | 31 | 40 | 52 |
| 2 AWG | 1 | — | 2 | 4 | 6 | 10 | 17 | 26 | 34 | 44 |
| 1 AWG | 1 | 1 | — | 3 | 4 | 7 | 12 | 18 | 24 | 31 |
| 1/0 | — | 1 | — | 2 | 3 | 6 | 10 | 16 | 20 | 26 |
| 2/0 | — | 1 | 1 | — | 3 | 5 | 9 | 13 | 17 | 22 |
| 3/0 | — | 1 | 1 | — | 2 | 4 | 7 | 11 | 15 | 19 |
| 4/0 | — | — | 1 | — | — | 3 | 6 | 9 | 12 | 16 |
| 250 | — | — | 1 | 1 | — | 3 | 5 | 7 | 10 | 13 |
| 300 | — | — | 1 | 1 | — | 2 | 4 | 6 | 8 | 11 |
| 350 | — | — | — | 1 | — | — | 4 | 6 | 7 | 10 |
| 400 | — | — | — | 1 | 1 | — | 3 | 5 | 7 | 9 |
| 500 | — | — | — | 1 | 1 | — | 3 | 4 | 6 | 7 |
| 600 | — | — | — | 1 | 1 | — | 2 | 3 | 4 | 6 |
| 700 | — | — | — | — | 1 | 1 | — | 3 | 4 | 5 |
| 750 | — | — | — | — | 1 | 1 | — | 3 | 4 | 5 |
| 800 | — | — | — | — | 1 | 1 | — | 3 | 3 | 5 |
| 900 | — | — | — | — | — | 1 | — | 2 | 3 | 4 |
| 1000 | — | — | — | — | — | 1 | — | 2 | 3 | 4 |
EMT — Electrical Metallic Tubing × RHH (90°C dry) · NEC 2023 Ch.9 Tables 4 & 5 · 40% (3+), 31% (2), 53% (1)
NOTES & CONTEXT
RHH vs RHW vs RHW-2
- RHH: Rubber, Heat-resistant, 90°C dry only
- RHW: Rubber, Heat & Water-resistant, 75°C wet / 90°C dry
- RHW-2: Rubber, 90°C wet AND dry
Why RHH/RHW takes more space
The rubber insulation used in RHH-family conductors is thicker than the thermoplastic PVC + nylon used in THHN. NEC Table 5 lists 12 AWG RHH at 0.0260 in² vs 12 AWG THHN at 0.0133 in² — a 96% increase. The fill % math is unforgiving: half as many RHH conductors fit in the same conduit at 40% fill.
Where RHH is still used
In modern US installations, RHH/RHW has largely been displaced by THHN/THWN-2 for cost and conduit-fill reasons. Surviving applications:
- Legacy installations being modified — match existing insulation type
- Specifications calling out rubber insulation for chemical resistance
- Equipment manufacturers' internal wiring (rare)
Practical implication
When a panel was originally installed with RHW and you're replacing or adding circuits, verify whether you must continue with RHW or can transition to THHN/THWN-2. Most AHJs permit modernization, but check.