Question

If you have a motor that must remain adaptable to several sizes of belts, what is the maximum length of flexible metal conduit you can use before the conduit requires fastening?

Answer 1

I assume that you are asking about requirements of the US National Electrical Code. The 2005 edition of the code states in article 348.30 that, where flexibility is required, flexible metal conduit type FMC can be run 3 feet before being fastened for sizes 1/2 to 1-1/4", 4 feet for sizes 1-1/2 to 2" and 5 feet for sizes 2" and larger. All sizes of liquidtight flexible metal conduit type LFMC can be run 3 feet before being fastened if flexibility is required.

Added Note:

The requirements in the 2008 NEC for Type FMC are the same as the requirements in the 2005 NEC. The 2008 NEC requirements for Type LFMC are the same as the requirements for Type FMC.

Hope that help!