Code Q&A: Flexible Metal Conduit

Your most pressing National Electrical Code (NEC) questions answered

 

Q. What uses does the NEC permit and forbid for flexible metal conduit?

A. According to 348.10 of the 2011 NEC, flexible metal conduit (FMC) is permitted in exposed or concealed locations. On the other hand, the locations where FMC is not permitted are much more specific. As noted in 348.12, FMC shall not be used:

  •     In wet locations.
  •     In hoistways, other than as permitted in 620.21(A)(1).
  •     In storage battery rooms.
  •     In any hazardous location, except as permitted by 501.10(B).
  •     Exposed to material having a deteriorating effect on the installed conductors.
  •     Underground or embedded in poured concrete.
  •     If subject to physical damage.

Discuss this Article 2

ken c (not verified)
on Feb 13, 2013

Is the first panel after a transformer treated like a panel to the service? with ground and neutral bonded and ground rod. Or like a sub panel with ground and neutral independent from each other?

Sam Alexander (not verified)
on Feb 27, 2013

The neutral-to-ground bond (system bonding jumper) at the first panel after the facility transformer is equivalent to the neutral-to-ground bond (main bonding jumper) at the main distribution panel fed from the utility transformer. This is because they both establish a new grounding zone. If, however, the system bonding jumper is made at the facility transformer instead of at the first panel downstream of this transformer, then the first panel would be identical to a sub-panel with an isolated neutral. The NEC does allow a neutral-to-ground bond at both the facility transformer and at the first panel downstream of this transformer. However, the supply-side bonding jumper connecting these two neutral buses must be omitted to prevent objectionable neutral current.

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