What Size Wire for a 450 Amp Breaker?
Verified against NEC 2023, checked against the 2026 edition · Last checked August 18, 2026
A 450 amp breaker takes 2 × 4/0 AWG copper or 2 × 300 kcmil aluminum with 75°C terminations, sized from NEC Table 310.16. This assumes THHN-class conductors in conduit, no more than three current-carrying conductors, 86°F ambient and a non-continuous load.
Common on this rating: commercial services.
| Conductor | Size | Usable | Basis |
|---|---|---|---|
| Copper · 75°C terminals | 2 × 4/0 AWG | 460 A | Table 310.16 · 75°C column |
| Aluminum · 75°C terminals | 2 × 300 kcmil | 460 A | Table 310.16 · 75°C column |
| Ground wire (EGC) | 2 AWG Cu or 1/0 AWG Al | Table 250.122 |
EGC from Table 250.122. If conductors are upsized for voltage drop, the EGC upsizes in proportion · 250.122(B).
What changes this answer
Parallel sets · 310.10(G)
A size written 2 × means two conductors per phase in parallel, minimum 1/0 AWG each. Each raceway carries a full-size EGC · 250.122(F).
Continuous load · 210.19(A)
A load running 3 hours or more needs conductors sized at 125% of that current. Sizes above assume a non-continuous load.
More than 3 conductors · 310.15(C)(1)
Four or more current-carrying conductors in one raceway derate ampacity by 20% or more. Run the calculator with your count.
Hot locations · 310.15(B)(1)
Ambient above 86°F cuts ampacity. Attics and rooftop conduit routinely trigger this correction.
Long runs and voltage drop
Distance does not change the NEC minimum, but past roughly 100 feet voltage drop usually forces a larger conductor.
Round-up rule · 240.4(B)
Where a conductor ampacity is not a standard breaker rating, the next higher standard breaker is sometimes permitted. The table above never relies on it, so its sizes never depend on that permission.
Size it on the job site, offline.
The JobVolt app runs this same verified math with no signal, keeps every calculation in History, and turns it into an inspector-ready PDF submittal on your letterhead.
Common questions
- What size wire do I need for a 450 amp breaker?
- 2 × 4/0 AWG copper or 2 × 300 kcmil aluminum with 75°C terminations, per NEC Table 310.16.
- Can I use aluminum wire on a 450 amp breaker?
- Yes. 2 × 300 kcmil aluminum at 75°C terminations carries 460 A, which covers a 450 A breaker · Table 310.16. Modern aluminum conductors are AA-8000 alloy, not the old 1960s wire.
- Does distance change the wire size for 450 amps?
- Not in Table 310.16, but long runs lose voltage. Size the run with JobVolt's free voltage drop calculator so the equipment still sees full voltage.