Lower branch wires in main raceway

[Jerry Simon]

What is the rationale for not allowing lower branch circuit wiring to run back through the main service entrance cable raceway (what are the risks)?

[Chad Fabry]

Induced current.

[Marc]

The main panel feeders are protected only by the downstream device.  The super-lag utility fuse situated upstream is too big to protect it.  If you consider a branch circuit conductor in the same conduit as those feeders, a failure in the respective branch circuit breaker could cascade into a feeder failure with violent and catastrophic results.

Edited May 18, 2017 by Marc