Where is LFNc not permitted?

1. Where flexibility is required for installation, operation, or maintenance.
2. Where protection of the contained conductors is required from vapors, machine oils, liquids, or solids.
3. For outdoor locations where listed and marked as suitable for the purpose.
4. For direct burial where listed and marked for the purpose.
5. Type LFNC shall be permitted to be installed in lengths longer than 1.8 m (6 ft) where secured in accordance with 356.30.
6. Type LFNC-B as a listed manufactured prewired assembly, metric designator 16 through 27 (trade size 1/2 through 1) conduit.
7. For encasement in concrete where listed for direct burial and installed in compliance with 356.42.
8. Conductors or cables rated at a temperature rating of LFNC conduit shall be permitted to be installed in LFNC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFNC.

Informational Note: Extreme cold can cause some types of nonmetallic conduits to become brittle and therefore more susceptible to damage from physical contact.

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LFNC shall be permitted to be used in exposed or concealed locations for the following purposes:

All questions and answers are based on the NEC.

Q. What uses are not permitted by the NEC for liquidtight flexible nonmetallic conduit?

A. Liquidtight flexible nonmetallic conduit cannot be used if:

(1) subject to physical damage [Sec. 356.12].

(2) the ambient temperature and/or conductor temperature is in excess of its listing.

(3) longer than 6 ft, except if approved by the authority having jurisdiction (AHJ) as essential for a required degree of flexibility.

(4) in any hazardous location, except as permitted by Sec. 501.10(B), Sec. 502.10(A) and (B), and Sec. 504.20.

Liquidtight flexible nonmetallic conduit is more or less a flexible version of PVC and is actually made from a more pliable type of PVC.

Q. Which alternating current systems are required to be grounded by the NEC?

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A. Systems operating below 50V aren&#;t required to be grounded or bonded in accordance with Sec. 250.30 unless the transformer&#;s primary supply is from [Sec. 250.20(A)]:

(1) A 277V or 480V system.

(2) An ungrounded system.

The following 50V to 1,000V systems must be grounded (connected to the earth) [Sec. 250.20(B)]:

(1) Single-phase systems where the neutral conductor is used as a circuit conductor.

(2) 3-phase, wye-connected systems where the neutral conductor is used as a circuit conductor.

(3) 3-phase, high-leg delta-connected systems where the neutral conductor is used as a circuit conductor.

Q. The neutral of a grounded electric utility service must be installed and terminated at what location in accordance with the NEC?

A. A service neutral conductor must be run from the electric utility power supply with the ungrounded conductors and terminate to the service disconnect neutral terminal [Sec. 250.24(C)]. A main bonding jumper [Sec. 250.24(B)] must be installed between the service neutral terminal and the service disconnect enclosure [Sec. 250.28].

The service neutral conductor provides the effective ground-fault current path to the power supply to ensure that dangerous voltage from a ground fault will be quickly removed by opening the overcurrent protection device [Sec. 250.4(A)(3) and Sec. 250.4(A)(5)].

Even if the service equipment is only supplying loads with no neutral conductor, such as a 3-phase motor, a service neutral conductor between the electric utility and service is part of the effective ground-fault current path needed in case there is a ground fault condition (Figure).

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