I want to run one 12-3 to the kitchen and split it into two 20A countertop circuits sharing the neutral.

Yes — this is a Multi-Wire Branch Circuit (MWBC) and requires specific handling at the panel per NEC 2020 210.4.

Key requirements:

1. Common trip or handle tie: The two 20A breakers must be mechanically tied (handle tie) or use a 2-pole common-trip breaker. This ensures both circuits disconnect simultaneously (NEC 210.4(B)).

1. Opposite hot legs: The two hot wires must land on different phases (A and B) in the panel. This prevents the neutral from carrying double current. With a standard 120/240V panel, using a double-pole breaker or adjacent breakers with a handle tie ensures this.

1. Neutral and ground: The neutral must be insulated and continuous — never switched. Ground wires must be properly bonded.

1. GFCI protection: GFCI breakers or receptacles are required for kitchen countertop outlets (NEC 210.8(A)(6)). Note: GFCI protection on MWBCs can be tricky — GFCI breakers are preferred over GFCI receptacles to avoid nuisance tripping from shared neutral current.

At the panel:

• Install a 2-pole 20A breaker or two single-pole 20A breakers with a factory handle tie (e.g., Siemens EXFT, Eaton CL-2K).
• Connect the white (neutral) to the neutral bus.
• Connect grounds to the ground bus.

Warning: If you're unsure about phase orientation or proper breaker selection, consult a licensed electrician — incorrect MWBC installation can cause fires or equipment damage.

Yes. This is a multi-wire branch circuit (MWBC) per NEC 210.4. Critical panel requirements:

1. Handle-tied 2-pole breaker (or two single-pole breakers with an identified handle tie listed for that purpose). NEC 210.4(B). This ensures simultaneous disconnect and forces opposite legs (120/240V), preventing neutral overload.
2. Opposite phases (legs). The two hots must land on different bus stabs (A/B phase). If on same leg, neutral carries sum of currents (up to 40A on #12) → fire hazard.
3. Neutral pigtail required at first device box (NEC 300.13(B)). Do not rely on device terminals to carry the shared neutral downstream. If a receptacle is removed, neutral continuity for the other circuit is lost → 240V across 120V loads.
4. AFCI protection required for kitchen countertop receptacles (NEC 210.12(A)). Use a 2-pole AFCI breaker (handles tied internally) or a listed handle-tied combination of two 1-pole AFCIs. Standard handle tie on non-AFCI breakers won't meet AFCI requirement.
5. GFCI protection also required (210.8(A)(6)). Easiest: 2-pole Dual Function (AFCI/GFCI) breaker. If using receptacle GFCIs, the first device on each leg must be a GFCI receptacle (fed via pigtail), protecting downstream.

Panel summary: Install a 2-pole Dual Function (AFCI/GFCI) breaker. Land red on one pole, black on the other, white on neutral bar, ground on ground bar. Done.

Warning: If you cannot verify opposite phases or install the correct breaker, stop. Hire an electrician. MWBC errors are dangerous.