Replaced standard Siemens 15 amp light circuit breaker with new Siemens 15 amp dual function. Standard was fine but new dual trips immediately

Question

Code changes require all living areas to be arc and ground fault protected. Finishing basement and initially used standard breakers with no issues. When I learned of code changes, replaced all breakers with dual function breakers. One of the light circuits immediately trips when energized. Tried another new dual function and got same result. Tried standard breaker again and it worked fine. Pulled all switches to ensure connections were right/tight. Looking for troubleshooting ideas.

Answer 1

The first thing to do is to check the manual and find out how to distinguish between arc fault, ground fault and overcurrent types of breaker trips.

Since a regular breaker works fine, that should rule out overcurrent problems. Since this is new wiring, that should rule out arc faults. Not an absolute guarantee, but the typical arc fault problems are thinks likely faulty insulation, nails through wires, loose connections, etc. all of which should not be happening on a reasonably well done new installation.

That leaves ground faults, provided the troubleshooting in the instructions agrees. That can easily happen if you have:

• Neutrals shared between circuits
• Neutrals crossed between circuits
• Neutrals connected to the neutral bar instead of to the breaker (an ordinary breaker doesn't have a neutral connection, AFCI/GFCI breakers do)
• Neutral and ground combined anywhere in the circuit. For example, a neutral screw touching a metal box will not cause a problem for a regular circuit breaker but will result in some current going through ground, resulting in an immediate GFCI trip.