Should I use MCA or the breaker size?

Ampacity follows the minimum circuit ampacity. The breaker follows the maximum overcurrent device on the nameplate. This page asks for the load current you want checked.

Why mark a heat pump continuous?

HVAC compressors can run for hours. The 125 percent factor keeps the conductor ahead of that duty. Turn it off only if a qualified person tells you the load is noncontinuous.

What end voltage should I expect?

End voltage is source voltage minus the drop. On 240 V, a 3 percent limit means you still have at least 232.8 V at the unit.

240 V Mini-Split Heat Pump Wire Gauge

A 25 A heat pump on 240 V, 60 ft from the panel, with the 125 percent ampacity check on.

Formula SSC-2026.1

K method · SSC-2026.1

Minimum size

8 AWG · 8.37 mm²

Single conductor set

Voltage drop

2.34 V

0.98% · end 237.7 V

Power loss

59 W

I²R at the operating current

Required ampacity

31.3 A

Each conductor 50 A

Material estimate

$352.80

3 conductors + EMT

Conductor weight

11.5 lb

5.2 kg · approximate insulated weight

Single-line and conductor gaugeLive scaled blueprint

Circle diameters track circular mils. The drawing is a schematic, not a conduit-fill layout.

Bill of materials and shopping list
Item	Net	Waste	Order	Unit price	Line total
copper 8 AWG · 8.37 mm²	60 ft one way	cuts excluded	3 conductors	USD	$241.80
EMT conduit	60 ft	—	60 ft	USD	$111.00

Copper versus aluminum at this run
Material	Minimum size	mm²	Drop	End voltage	Loss
copper	8 AWG · 8.37 mm²	8.4	0.98%	237.7 V	59 W
aluminum	8 AWG · 8.37 mm²	8.4	1.61%	236.1 V	96 W

Same load at other one-way distances
Distance	Minimum size	Drop	Percent	End voltage
25 ft	8 AWG · 8.37 mm²	0.98 V	0.41%	239.0 V
40 ft	8 AWG · 8.37 mm²	1.56 V	0.65%	238.4 V
60 ft	8 AWG · 8.37 mm²	2.34 V	0.98%	237.7 V
80 ft	8 AWG · 8.37 mm²	3.13 V	1.30%	236.9 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: 240 V Mini-Split Heat Pump Wire Gauge

Prepared by

Date

Verified by (PE / electrician / inspector)

License number

Signature

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 operating current is 25 A and the continuous box is on, so the conductor must carry 31.25 A before voltage drop is considered. The run is 60 ft of copper in EMT at 3 percent. Use the MCA from the nameplate when you have it. The 25 A figure is a planning value for a small single-zone heat pump, not a substitute for the unit label. The disconnect and the whip are not in the conduit length.

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

Should I use MCA or the breaker size?: Ampacity follows the minimum circuit ampacity. The breaker follows the maximum overcurrent device on the nameplate. This page asks for the load current you want checked.
Why mark a heat pump continuous?: HVAC compressors can run for hours. The 125 percent factor keeps the conductor ahead of that duty. Turn it off only if a qualified person tells you the load is noncontinuous.
What end voltage should I expect?: End voltage is source voltage minus the drop. On 240 V, a 3 percent limit means you still have at least 232.8 V at the unit.