Wire Size ↔ Allowable Current (IV & VVF)
This chart lists ampacity for 600 V IV wire and VVF cable under Japanese electrical practice at the stated 30°C condition. Select the correct wire construction and size, then apply the listed derating factor when multiple conductors share a conduit.
Working current = base allowable current × reduction factor (by conductor count) × temperature correction if ambient ≠ 30°C.
Solid wire (単線) — by diameter| Diameter (mm) | Allowable current (A) |
|---|
| 1.2 | 19 |
| 1.6 | 27 |
| 2.0 | 35 |
| 2.6 | 48 |
| 3.2 | 62 |
| 4.0 | 81 |
| 5.0 | 107 |
Stranded wire (より線) — by cross-section| Cross-section (mm²) | Allowable current (A) |
|---|
| 2 | 27 |
| 3.5 | 37 |
| 5.5 | 49 |
| 8 | 61 |
| 14 | 88 |
| 22 | 115 |
| 38 | 162 |
| 60 | 217 |
| 100 | 298 |
Reduction factor — several conductors in one conduit| Current-carrying conductors | Factor |
|---|
| 3 or fewer | 0.70 |
| 4 | 0.63 |
| 5–6 | 0.56 |
| 7–15 | 0.49 |
VVF cable (JIS C 3342) — by loaded cores| Diameter (mm) | 2-core (A) | 3-core (A) |
|---|
| 1.6 | 18 | 15 |
| 2.0 | 23 | 20 |
| 2.6 | 32 | 27 |
IV: values follow the interpretation of the Electricity Facility Technical Standards, Article 146, and the Interior Wiring Regulations (JEAC 8001); reference condition a single wire in air at 30°C, construction per JIS C 3307. Several conductors in one conduit must be MULTIPLIED by the reduction factor; a hotter ambient needs a further temperature correction. VVF (60°C PVC sheathed cable, JIS C 3342): values follow the Interior Wiring Regulations / JCS 0168 and already account for the number of loaded cores, so they are lower than bare IV and do NOT take the reduction factor above. This is a guidance table — actual design must follow the installation method, cable type and the project's applicable standard.
Frequently asked questions
Can wire size be selected from load current alone?
No. Load current must remain below the adjusted ampacity after wire type, installation, temperature and derating are considered. Use the matching chart section, then also check voltage drop and protection.
Which columns apply to solid and stranded IV wire?
Solid wire is listed by conductor diameter, while stranded wire is listed by nominal cross-section in mm² (sq). Use the corresponding subsection and read its ampacity row.
Should the grouped-wire derating factor be applied again to the VVF values?
Not in the way this chart is arranged. VVF values are already listed by core count; use the correct two- or three-core row and verify the actual installation conditions.
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