80A Garage Feeder, Aluminum, 120 Feet
An 80 A aluminum feeder at 120 ft is a detached-garage planning run. Conduit fill and burial depth are not calculated.
Formula SSC-2026.1
K method · SSC-2026.1
Minimum size
2 AWG · 33.6 mm²
Single conductor set
Voltage drop
6.13 V
2.56% · end 233.9 V
Power loss
491 W
I²R at the operating current
Required ampacity
80.0 A
Each conductor 90 A
Material estimate
$908.40
3 conductors + EMT
Conductor weight
27.9 lb
12.7 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 2 AWG · 33.6 mm² | 120 ft one way | cuts excluded | 3 conductors | USD | $686.40 |
| EMT conduit | 120 ft | — | 120 ft | USD | $222.00 |
| Material | Minimum size | mm² | Drop | End voltage | Loss |
|---|---|---|---|---|---|
| aluminum | 2 AWG · 33.6 mm² | 33.6 | 2.56% | 233.9 V | 491 W |
| copper | 4 AWG · 21.2 mm² | 21.2 | 2.47% | 234.1 V | 475 W |
| Distance | Minimum size | Drop | Percent | End voltage |
|---|---|---|---|---|
| 95 ft | 2 AWG · 33.6 mm² | 4.86 V | 2.02% | 235.1 V |
| 120 ft | 2 AWG · 33.6 mm² | 6.13 V | 2.56% | 233.9 V |
| 145 ft | 1 AWG · 42.4 mm² | 5.88 V | 2.45% | 234.1 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.
Contractor sign-off
Project: 80A Garage Feeder, Aluminum, 120 Feet
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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
An 80 A aluminum feeder at 120 ft is a detached-garage planning run. Conduit fill and burial depth are not calculated. The run is 120 ft one way at 80 A on 1ph-240. K is 12.9 for copper and 21.2 for aluminum. Ambient temperature, bundling, and rooftop adders are not applied.
Code reference
NEC 210.19(A) and 215.2(A) informational notes recommend 3 percent on a branch circuit and 5 percent total with the feeder. Ampacity follows the 75°C column of Table 310.16 plus the small-conductor limits. Confirm the adopted edition.
Field questions
- What current is used for the 80 A voltage drop?
- Both the drop and the ampacity check use the entered amps, because this preset is not marked continuous.
- Does this replace the equipment installation manual?
- No. The nameplate, the breaker, and the adopted NEC edition still control. This page is the K-method size and the percent drop.
- Can I switch copper and aluminum?
- Yes. The conductor control and the comparison table both recompute size, drop, and the planning cost.
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