HVAC crew set a new 4-ton condenser.

No, the electrician is wrong and this is a code violation.

Per NEC 440.22(A), branch-circuit conductors and overcurrent protection for hermetic refrigerating equipment must have an ampacity of at least 125% of the motor-compressor rated-load current (RLA). Here:

• Compressor RLA = 18.6A
• 18.6 × 1.25 = 23.25A minimum required

The nameplate specifies Minimum Circuit Ampacity (MCA) = 25A, which already accounts for the 125% rule and includes the fan load. The existing #10 NM cable is rated for 30A (90°C), but the 30A breaker does not satisfy the MCA requirement — it's below the 25A minimum.

Additionally, NEC 440.22(B) requires the overcurrent device to be sized no greater than the manufacturer’s maximum rating. The nameplate allows up to a 40A max breaker/fuse, so the 30A breaker is acceptable on that end — but the cable and MCA still fail.

Also, NEC 440.14 requires a fused disconnect within sight of the condenser unless the breaker serves as the disconnect. The old non-fused pull-out doesn’t meet this requirement.

Correct fix:

• Replace the 30A breaker with a 40A 2-pole (per nameplate max).
• Verify #10 NM is acceptable (it is, at 30A) — but ideally upgrade to #8 for safety margin.
• Install a fused disconnect or use the new breaker as the sole disconnect.

This setup is unsafe and violates multiple code sections. A licensed electrician should correct it.

No, the electrician is wrong and creating a code violation. Here is the breakdown:

1. Conductor Ampacity (NEC 210.19(A)(1), 310.16, 240.4(D))

• MCA = 25A. Conductors must be sized at 125% of RLA + Fan FLA (which equals the MCA).
• #10 NM-B (Romex) is rated 30A at 60°C (NEC 334.80), but NEC 240.4(D)(5) limits #10 copper to a 30A OCPD maximum.
• While #10 can carry 30A, the MCA is 25A. You have zero margin for voltage drop or derating (attic heat, bundling). #8 CU (40A/55A) is the professional standard for a 4-ton unit.

2. Overcurrent Protection (NEC 440.22, Nameplate)

• Nameplate MOP (Max Fuse/Breaker) = 40A.
• NEC 440.22 allows the breaker up to the MOP (40A) to handle compressor inrush without nuisance tripping.
• A 30A breaker is undersized per the manufacturer's specs. It will nuisance trip on hot days during locked-rotor startup.

3. The Disconnect (NEC 440.14, 110.3(B))

• The old non-fused pull-out must be rated for the new circuit ampacity (40A).
• If it is a standard 30A disconnect, it is undersized and unlisted for this load. It must be replaced with a 60A non-fused pull-out (standard for 40A circuits).

4. "It only draws 20 amps"

• Irrelevant. Code sizes circuits for MCA (25A) and protects per MOP (40A), not running amps. The compressor draws 100A+ on startup.

Required Fix:

1. Replace breaker with 40A 2-pole.
2. Replace #10 NM with #8 CU (THHN in conduit or NM-B if protected per 334.15).
3. Replace disconnect with 60A non-fused pull-out (or 30A fused if using fuses, but 60A non-fused is standard).

Bottom line: The electrician is exposing you to liability, failed inspection, and compressor damage. Do not sign off. This requires a licensed electrician to correct.