Yes, there is a potential problem with that setup. Here's a breakdown: Overcurrent Protection and Conductor Ampacity

The #8 AWG conductors are typically rated for 40A in most common wiring methods. So, the wire is technically protected by the 40A breaker.

Generator Breaker as Primary Protection

You correctly point out that the generator has its own 30A breaker. This is the primary overcurrent protection for the generator. If the generator tries to supply more than 30A, its breaker should trip before the 40A breaker in the panel.

Potential Issue - Sustained Overload BETWEEN 30A and 40A

This is the crucial point. The 40A breaker would not trip if the generator delivered a sustained load between 30A and 40A. The generator's 30A breaker could trip, but not necessarily.

NEC 445.13

Per the NEC, generator conductors must be protected in accordance with their ampacity. #8 AWG copper wire has an ampacity of 40 amps. As such, this is compliant with the NEC.

The Problem

While the wiring isn't immediately unsafe in the same way as running a #14 wire on a 20A breaker, there's a risk of operating the generator above its rated output, possibly damaging the generator or causing premature wear and tear. You would have to monitor the load coming off of the generator to ensure that it is not overloading it, as the 40A breaker in your panel will not do that.

Considerations and Best Practices


Ideal Scenario

The ideal setup is to match the breaker in the panel to the generator's breaker (30A in this case). This ensures that the breaker in the panel will trip before the generator can be overloaded.2.

Load Management

If you MUST use the 40A breaker, you need to be extremely careful about load management. Do not assume that you can load the generator up to 40 amps. Keep the total load WELL below 30A. Use an amp meter to monitor the load.3.

Voltage Drop

With #8 wire, long runs can result in voltage drop under load, which can be detrimental to sensitive electronics. Be mindful of the distance from the inlet to the panel.4.

Proper Installation

Make sure the generator inlet, interlock, and wiring are all installed by a qualified electrician and meet all applicable local and national codes.

Recommendation:

While the 40A breaker is technically acceptable because of the 40 amp ampacity of the #8 wire, the 30A breaker in the generator provides overcurrent protection, but I would consider replacing the 40A breaker with a 30A breaker. This provides much better overall protection of the generator and connected equipment. The cost of a 30A breaker is minimal. Flag for review