What is the smallest bonding jumper you can run inside a flexible metal conduit between a transformer and a 300-A panel board?

To determine the smallest bonding jumper that can be run inside a flexible metal conduit between a transformer and a 300-A panel board, it’s important to refer to the National Electrical Code (NEC) guidelines. The bonding jumper must be adequately sized to ensure safety and effectiveness in fault conditions.

The NEC specifies the minimum size of a bonding jumper based on the rating of the circuit conductors, and it includes considerations for copper and aluminum wiring. For a 300-A panel board, the minimum size bonding jumper typically needs to be sized according to the ampacity of the overcurrent protection devices and the requirements of the system.

In this scenario, a bonding jumper size of 2 AWG is appropriate as it can sufficiently handle the possible fault current and ensure a good electrical connection necessary for grounding practices. This size ensures that the bonding system maintains integrity and effectiveness throughout its life, providing necessary safety features in case of a fault, such as equipment grounding and fault clearing.

Other sizes, like 4 AWG or smaller, may not provide adequate protection and might not meet NEC requirements for such a circuit configuration, which is why they aren’t suitable choices in this context. Meanwhile, larger sizes, such as 1/0 or 3/0 AWG