8 Feb 2017

flexible-metal-conduitFlexible conduit for electrical wiring installation continues to gain market acceptance.

We attribute this to the ease of installation compared to traditional methods because they require less physical labor to install. Many of these installations are standard commercial and industrial applications. As a result of newer technologies and advancements in materials, applications where flexible conduit is desired have increased.

Contractors often call on manufacturers as well as the National Electrical Manufacturers Association (NEMA) for guidance on installation challenges or questions. After many inquiries regarding the use of flexible conduit for structural joints, NEMA issued Bulletin No. 108. This outlined instructions on how to determine the type, length, and bend radius of flexible conduit products used for structural joints intended for expansion, contraction, or deflection, that are used in buildings, bridges, parking garages or other structures.

Contractors have begun to use flexible metal conduit (FMC) more frequently in applications such as bridges, parking garages or buildings that might frequently expand and contract from changes in temperature and other environmental conditions. In these instances, knowing what length of rigid conduit to install to offset movement can be difficult to calculate. That leads us to the question of how to more easily account for this with flexible metal conduit.

How much flexible conduit should be used for structural joints that might expand or contract?

The first step is to determine which type of flexible conduit should be installed: standard FMC or liquid-tight LFMC. Next, crucial to the length calculation, finalize the trade size of the product for installation. Once these items are finalized, refer to NEMA Bulletin 108: Application for Flexible Conduit for Structural Joints Intended for Expansion, Contraction, or Deflection. NEMA outlines the calculations to follow based on different factors.

Take a moment to listen to AFC’s manager of codes and standards, George Strainero, talk about these calculations on a recent NEMA podcast.