200 Amp Main Service Entrance Wire Size
A 200 A service lateral where ampacity, not voltage drop, usually governs.
Formula SSC-2026.1
K method · SSC-2026.1
Minimum size
250 kcmil · 127.0 mm²
Single conductor set
Voltage drop
1.36 V
0.57% · end 238.6 V
Power loss
271 W
I²R at the operating current
Required ampacity
200.0 A
Each conductor 205 A
Material estimate
$938.80
3 conductors + RMC
Conductor weight
33.7 lb
15.3 kg · approximate insulated weight
Circle diameters track circular mils. The drawing is a schematic, not a conduit-fill layout.
| Item | Net | Waste | Order | Unit price | Line total |
|---|---|---|---|---|---|
| aluminum 250 kcmil · 127.0 mm² | 40 ft one way | cuts excluded | 3 conductors | USD | $748.80 |
| RMC conduit | 40 ft | — | 40 ft | USD | $190.00 |
| Material | Minimum size | mm² | Drop | End voltage | Loss |
|---|---|---|---|---|---|
| aluminum | 250 kcmil · 127.0 mm² | 127.0 | 0.57% | 238.6 V | 271 W |
| copper | 3/0 AWG · 85.0 mm² | 85.0 | 0.51% | 238.8 V | 246 W |
| Distance | Minimum size | Drop | Percent | End voltage |
|---|---|---|---|---|
| 40 ft | 250 kcmil · 127.0 mm² | 1.36 V | 0.57% | 238.6 V |
Show the deterministic formula
Single phase: Vdrop = 2 × K × I × D / cmil. Three phase: Vdrop = 1.732 × K × I × D / cmil. K is 12.9 for copper and 21.2 for aluminum. D is one-way feet.
Percent drop = Vdrop ÷ source voltage × 100. Green is 3% or less, amber is 3 to 5%, and red is over 5%. Power loss is I²R on the current-carrying conductors.
The smallest conductor that meets both the ampacity (125% when continuous) and the drop limit is selected. Ampacity does not include bundling or temperature correction.
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Project: 200 Amp Main Service Entrance Wire Size
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
The preset is aluminum, 200 A, 240 V, 40 ft, in rigid metal conduit, with a 3 percent limit and the continuous box off. At this short distance the voltage drop is small, so the size is the smallest aluminum conductor at or above 200 A in the 75°C column. Dwelling services may use the NEC 310.12 sizing rule in editions that allow it, which can permit a smaller service conductor than the general table. The utility and the inspector control the service. Do not order lateral conductors from this page alone.
Code reference
NEC Table 310.16 75°C ampacity, the dwelling service provisions of 310.12 where adopted, and the serving utility's lateral specification. This estimate does not apply those exceptions automatically.
Field questions
- Why is aluminum the default for 200 amps?
- Service laterals are commonly aluminum because of weight and cost. Switch the conductor control to copper to see the smaller copper alternative and its price.
- Will voltage drop change a 40 foot service?
- Usually no. Read the drop percent. If it stays well under 3 percent, ampacity chose the size.
- Does this include the ground rods or the mast?
- No. The bill is conductor length plus conduit material. Bonding, the mast, and the meter socket are outside the calculation.