240-volt and dedicated circuits: breaker size, wire gauge and permit

Match the breaker, the wire and the plug

A circuit is safe when three parts agree. The breaker trips at a set current. The wire can carry at least that much. The outlet is rated at or above the breaker. Break any link and the weakest part overheats. Section 210.21 says a single receptacle must be rated at least as high as its breaker.

For copper wire in a house, the 60-degree column of NEC Table 310.16 usually applies to equipment rated 100 amps or less. These are the values:

Wire (copper)	Table ampacity	Common breaker	Typical use
12 AWG	20 A	20 A	Dedicated 120 V line, bathroom, small appliance
10 AWG	30 A	30 A	Electric dryer, water heater
8 AWG	40 A	40 A	Some ranges, small EV charger on a short run
6 AWG	55 A	50 A	Range, EV charger, subpanel feeder

Small wire also has a hard cap under 240.4(D): 15 amps for 14 AWG, 20 for 12 AWG and 30 for 10 AWG, whatever the table says. A long run may need a heavier wire because of voltage drop, and aluminum wire is sized differently.

Common 240-volt jobs

Dryer. A 30-amp, two-pole breaker with 10-gauge wire and a 14-30 receptacle is the usual choice. Check the dryer’s label.

Range. Most electric ranges use a 50-amp circuit on 6-gauge wire, but the label rules. A cooktop and wall oven may be separate, each with its own circuit.

EV charger. Charging counts as a continuous load, so the breaker is at least 125 percent of the charger rating. A 40-amp charger means a 50-amp breaker. Each charging outlet gets its own branch circuit with no other outlets. For brand and load details see EV chargers, the Tesla Wall Connector page, and load calculation explained.

Mini-split or heat pump. The outdoor unit label states the minimum circuit ampacity and the maximum breaker. The wire and breaker follow it, with a disconnect in sight. See heat pump electrical requirements.

Four wires or three

New range and dryer circuits use four wires: two hots, a neutral and a separate ground. The old three-wire setup connects the case to the neutral. The code allows that only on an existing circuit that has no ground wire, so a replacement appliance on an old circuit may stay three-wire. When a new cable is run, it is four-wire, and the dryer’s bonding strap comes off. Match the cord: a 14-30 plug is four-prong, and an old 10-30 plug is three-prong.

Is there room in the panel

A 240-volt breaker takes two slots, and each load adds to the total the service must carry. The electrician checks the number of free slots first. For bigger additions, such as a charger plus a heat pump, a load calculation shows whether the service can take it. The result may be a subpanel, a load manager or a panel upgrade. A full panel is the usual reason a $459 to $1,388 circuit becomes a bigger job.

Permit and cost

A new 240-volt circuit needs an electrical permit, and the city inspects the wire, breaker and receptacle before you use it. See the permit guide.

Cost depends on distance, wall finish and panel space. As of October 2026 no neutral guide prices a full dedicated 20-amp circuit (Fixr lists $100 to $150 for a 20-amp outlet), and a Level 2 charger circuit runs $1,000 to $2,000 on the EV charger cost page. The heat pump circuit page gives $1,500 to $6,000 as a desk estimate that swings with panel capacity. No sourced price range exists yet for a dryer or range circuit alone, so ask for a written quote.

Long runs, aluminum and old panels

Three things change a 240-volt quote more than people expect.

• Distance. A charger at the far end of a long garage or a detached building may need a heavier wire to keep voltage drop low. The table above gives the minimum for current, not the best choice for distance.
• Aluminum. Aluminum cable is sized differently from copper and needs terminals made for it. Homes with older aluminum branch wiring are a separate issue, covered under aluminum wiring.
• Old panels. A panel that is full, rusted or a brand with a poor record may need replacing before a new circuit goes in. See Zinsco and Federal Pacific panels.

Ask the electrician to write down the breaker size, the wire gauge, the receptacle and the route. That four-line list is the quickest way to compare two quotes.

For a first conversation, bring the appliance model number or the charger spec sheet, a photo of the panel and a rough distance from the panel to the spot. That is enough for an electrician to name a breaker size and a likely price range before a visit. See how to prepare for the visit.