Technical Answers & Applications Technical Tip
NEC Code Changes That Affect Liquidtight & Flexible Metal Conduit
Important:
A simple word change in seven Articles of the 1996 National Electrical Code may significantly impact the future use of unlisted flexible metal conduit, liquidtight and several other electrical products.
The word "Listed" has replaced "Approved" in the applicable sections of the following NEC Articles:
Article
Title
339
Underground Feeder and Branch-Circuit Cable
343
Nonmetallic Underground Conduit
345
Intermediate Metal Conduit
346
Rigid Metal Conduit
348
Electrical Metallic Tubing
350
Flexible Metal Conduit
351
Liquidtight Flexible Metal Conduit and
Liquidtight Flexible Non Metallic Conduit
By definition, "Listed" pertains to equipment and materials evaluated by an organization (testing laboratory) acceptable to the inspector. When making the revision, Code Making Panels 7 & 8 concluded the use of Listed products will more effectively provide consistent quality, and agreed the word "Approved" appropriately applied to the work performed by testing laboratories, not to the inspection service provided by the local AHJ.
The effect of the world change has already been noted in many parts of the country, as knowledgeable inspectors enforce the '96 NEC and insist on seeing evidence of product listing through tags, labels or print legends.
Conduit Fill Revised
The number of conductors permitted in 3/8" Flexible Metal Conduit has been revised. In general, the allowable fill for the 3/8" flex with a fitting inside the conduit has increased and decreased with fittings applied to the outside of the conduit. For example:
Maximum Number of Insulated Conductors in a 3/8" Flexible Metal Conduit
Conductor Size AWG
THHN, TFN A*
THHN, TFN B*
XHHW A*
XHHW B*
18
5(4)
8(8)
3(3)
5(7)
16
4(3)
6(7)
3(2)
4(4)
14
3(3)
4(7)
2(0)
3(4)
12
2(0)
3(4)
1(0)
2(3)
10
1(0)
1(2)
1(0)
1(0)
*A= With fitting inside conduit
*B= With fitting outside conduit
( ) = '93 NEC
The table footnote has also changed and now permits an additional covered or bare equipment grounding conductor. The '93 NEC only permitted a bare equipment ground of the same conductor size.
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