Customer says his kitchen breaker kept tripping when he ran the microwave and toaster together, so his brother-in-law swapped the 15A breaker for a 20A and it hasn't tripped since.

No, he should not be happy with this "fix." This is a dangerous code violation.

The Problem: NEC 240.4(D)(4) requires 14 AWG copper wire to be protected by a maximum 15 amp overcurrent device. By installing a 20A breaker on 14-2 wiring, the brother-in-law created a fire hazard. The wire can overheat and potentially ignite before the breaker trips.

Why It "Works": The microwave and toaster together likely draw 12-16 amps, which is within the 20A breaker's capacity but exceeds the 15A breaker's rating. However, the 14 AWG wire may not safely handle sustained loads above 15 amps.

Proper Solutions:

1. Revert to 15A breaker and use appliances one at a time
2. Upgrade to 12-2 wiring and install a 20A breaker (NEC 210.19(A)(1))
3. Install a dedicated 20A circuit for the microwave (NEC 210.11(C)(1) requires kitchen small appliance branch circuits)

Immediate Action Required: Replace the 20A breaker with a 15A breaker immediately. This is not a permanent solution but prevents potential wire overheating.

Bottom Line: This setup violates electrical code and poses a serious fire risk. A licensed electrician should properly upgrade the circuit wiring to handle the load safely.

No, he should not be happy. This is a serious fire hazard.

The Violation: NEC 240.4(D)(3) limits 14 AWG copper conductors to 15 amperes maximum overcurrent protection. A 20A breaker on 14-2 cable is a code violation.

The Danger: The breaker protects the wire, not the appliances. 14 AWG wire is rated for 15A continuous. At 20A, the insulation degrades, connections overheat inside boxes, and the wire can ignite surrounding wood/framing before the 20A breaker trips.

Why it "works": The microwave (~10–12A) + toaster (~8–10A) = 18–22A load. The 15A breaker did its job: it tripped to save the wire. The 20A breaker allows the overload to continue, heating the 14-gauge wire dangerously.

Correct Fixes (pick one):

1. Dedicated 20A circuit for microwave (12-2 wire, 20A breaker, 20A receptacle) — Best practice, NEC 210.52(B).
2. Dedicated 20A circuit for toaster (same as above).
3. Run new 12-2 cable for the existing circuit and keep 20A breaker.
4. Reinstall 15A breaker and tell the customer: "Don't run both at once."

Action: Tell the customer the brother-in-law created a hidden fire risk. Replace the breaker with a 15A today. Quote the dedicated circuit properly.