Minimum size by temperature column
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| Copper | 250 kcmil215 A | 3/0 AWG200 A | 3/0 AWG225 A |
| Aluminum | 350 kcmil210 A | 250 kcmil205 A | 4/0 AWG205 A |
Equipment grounding conductor
A circuit protected at 200 A takes a 6 AWG copper or 4 AWG aluminum equipment grounding conductor, from the 200 A row of NEC Table 250.122. Raise the ground with the ungrounded conductors when you increase them for voltage drop or any reason other than 310.15(B) or (C) derating, because 250.122(B) requires the same proportion. The ground is never required to be larger than the circuit conductors.
Longest run at 3% voltage drop
| Conductor | 240 V single phase | 240 V three phase |
|---|---|---|
| 3/0 AWG copper | 230 ft | 270 ft |
| 250 kcmil aluminum | 210 ft | 245 ft |
NEC 210.19(A)(1) Informational Note 4 recommends keeping branch-circuit drop at or below 3%. These lengths come from the Table 8 resistance at 75°C for a stranded conductor at unity power factor, rounded to the nearest 5 ft. Reactance is not included, so a large conductor in a steel raceway falls short of the figure. A balanced three-phase run reaches about 15% farther than the single-phase figure.
Dwelling service allowance under 310.15(B)(7)
A 120/240 V single-phase dwelling service or feeder rated 100 A through 400 A may use conductors with an ampacity of 83% of the rating. For 200 A that is 166 A, which the 75°C column meets with 2/0 AWG copper or 4/0 AWG aluminum.
The allowance covers service and feeder conductors only. Branch-circuit conductors, the equipment grounding conductor, and any local amendment are unaffected, and the neutral may be reduced separately under 220.61.
What a 200 A circuit feeds
- A standard residential service entrance
- Whole-house and workshop feeders
Two hundred amps is the standard residential service. 3/0 copper or 250 kcmil aluminum reaches it at 75°C, which is the basis for a service built with modern terminations. The 60°C column would need 250 kcmil copper or 350 kcmil aluminum, two sizes up.
The service equipment is normally a meter socket with a 200 A panel, and the conductors are often SER or SEU cable rather than conduit. Continuous loads top out at 160 A, and the 310.15(B)(7) allowance is why most dwelling services at this rating use one size smaller than the Table 310.16 answer.
Aluminum is common at this size because it costs less than copper and the terminations are identified for it. The riser is conduit sized for the service conductors by the fill rules in Chapter 9, and the grounding electrode system is usually two ground rods or a concrete-encased electrode at the footing. Where the service feeds a detached building, Article 225 governs the feeder and its disconnect there.
200 A wire size questions
- What size wire do I need for a 200 amp circuit?
- 3/0 AWG copper or 250 kcmil aluminum at the 75°C column, which 110.14(C)(1)(b) requires for equipment rated over 100 A. On the 60°C column the same circuit would need 250 kcmil copper or 350 kcmil aluminum.
- What size ground wire for a 200 amp circuit?
- 6 AWG copper or 4 AWG aluminum, taken from the 200 A row of NEC Table 250.122.
- What size aluminum wire for 200 amps?
- 250 kcmil aluminum at the 75°C column carries 205 A. Terminations on aluminum conductors must be identified for the material.
- Can I use 2/0 AWG copper for 200 A?
- Table 310.16 lists 2/0 AWG copper at 145 A at 60°C, 175 A at 75°C, and 195 A at 90°C. It falls short at 75°C, the column this circuit uses.