Thread: NM Liquid Tight

NM liquid tight is not allowed to be underground, right?

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Originally Posted by brianmiller

NM liquid tight is not allowed to be underground, right?

ADM has posted an incorrect siting. This is not about type NM cable.

Article 356.10(4) allows liquidtight Flexible Nonmetallic Conduit for use in direct burial where it is listed and marked for the purpose.

There is however a prohibition against use where subject to physical damage.

NM is still NOT PERMITTED to be used in direct burial even in liquid tight conduit

This is not about NM-B. LNMC is covered by Article 358 entitled Liquidtight Nonmetallic Conduit, commonly called Sealtite. The NM is to differentiate it from Liquidtight Metallic Conduit or LFMC.

Originally Posted by Jim Port

This is not about type NM cable.

Originally Posted by Jim Port

This is not about NM-B.

The NM is to differentiate it from Liquidtight Metallic Conduit or LFMC.

Jim is correct on that.

However, has shown in the photo that is not allowed as that falls under conductors emerging from grade, which require protection from physical damage, which would be rigid, IMC, or Sch 80 PVC to a depth of 18" below ground to a height of the first enclosure or 8 feet above ground, which ever is less (in this case the first enclosure is less).

Originally Posted by Jim Port

ADM has posted an incorrect siting. This is not about type NM cable.

Article 356.10(4) allows liquidtight Flexible Nonmetallic Conduit for use in direct burial where it is listed and marked for the purpose.

There is however a prohibition against use where subject to physical damage.

It's not likely to survive landscapers, just chiming in to agree w/ Jim.

Oops yes misread in same way. (however NM cable still can't be in the raceway outside or burried).

Yes if marked for DB for the direct burrial portion, but as others have said this is not protected from damage at riser. Listed Sch. 80 (pvc) would protect from damage at riser and be Nonmetallic.

So let me get this right:

The NM liquid tight IS rated for burial, however, the NM conductors inside the conduit needs to be protected from physical damage coming out of the ground? Could you provide the code section please.

Br

Originally Posted by brianmiller

So let me get this right:

The NM liquid tight IS rated for burial, however, the NM conductors inside the conduit needs to be protected from physical damage coming out of the ground? Could you provide the code section please.

Br

Not quite, the conduit requires protection.

As was said above, you cannot install Type NM cables in the conduit that is outside.

THanks, Jim,

Could you provide the code that says the NM liquid tight requires protection?

b

Originally Posted by brianmiller

THanks, Jim,

Could you provide the code that says the NM liquid tight requires protection?

b

Not Jim, but ...

- 356.10 Uses Permitted.
- - LFNC shall be permitted to be used in exposed or concealed locations for the following purposes:
- - - FPN: Extreme cold may cause some types of nonmetallic conduits to become brittle and therefore more susceptible to damage from physical contact.
- - - (1) Where flexibility is required for installation, operation, or maintenance.
- - - (2) Where protection of the contained conductors is required from vapors, 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-B 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 ½ through 1) conduit.
- - - (7) For encasement in concrete where listed for direct burial and installed in compliance with 356.42.
- 356.12 Uses Not Permitted.
- - LFNC shall not be used as follows:
- - - (1) Where subject to physical damage
- - - (2) Where any combination of ambient and conductor temperatures is in excess of that for which the LFNC is approved
- - - (3) In lengths longer than 1.8 m (6 ft), except as permitted by 356.10(5) or where a longer length is approved as essential for a required degree of flexibility
- - - (4) Where the operating voltage of the contained conductors is in excess of 600 volts, nominal, except as permitted in 600.32(A)
- - - (5) In any hazardous (classified) location, except as permitted by other articles in this Code

Originally Posted by brianmiller

So let me get this right:

The NM liquid tight IS rated for burial, however, the NM conductors inside the conduit needs to be protected from physical damage coming out of the ground? Could you provide the code section please.

Br

Yes, LFNC (Liquidtight Flexible Nonmetallic Conduit) IS rated for direct burial (when so identified on itself), but, because it is not rated for protection from physical damage it must be protected in the range where physical damage needs protection. Basically that is (for conductor emerging from grade as shown in the original post's photo) from 18" below grade to 8' above grade or to the first enclosure, whichever is lower - the only things rated for protection from physical damage in that area are: a) rigid metal conduit; b) intermediate metal conduit; c) Schedule 80 PVC rigid nonmetallic conduit.

Is that Outlet GFI protected?

[quote=Jerry Peck;173094]Yes, LFNC (Liquidtight Flexible Nonmetallic Conduit) IS rated for direct burial (when so identified on itself), but, because it is not rated for protection from physical damage it must be protected in the range where physical damage needs protection.Basically that is (for conductor emerging from grade as shown in the original post's photo) from 18" below grade to 8' above grade or to the first enclosure, whichever is lower - the only things rated for protection from physical damage in that area are: a) rigid metal conduit; b) intermediate metal conduit; c) Schedule 80 PVC rigid nonmetallic conduit.[/quote]


Jerry, could you post the code section for the bolded ? thanks!

Brian

Brian,

First, the NEC does a very poor job on defining protection from physical damage other than to say that something may not be used where subject to physical damage nor does the NEC define what is included in the range of physical damage areas.

I believe we all would agree that the insulation of conductors and cables for direct burial will be (for lack of a better phrase) 'physically more robust' even though the electrical dielectric properties may be the same for most of the direct burial conductors and cable.

As such, it is safe to say that conductors with regular insulation and sheaths (i.e., those which are not "direct burial" rated) are 'less physically robust' and as such would require 'the same protection' or 'greater protection' from physical damage as specified for direct burial conductors and cables - agreed?

As the NEC does not give any guidance on what would constitute 'greater protection' we must fall back to 'the same protection' for non-direct burial conductors and cables as is required for direct burial conductors and cables. Without additional guidance in the NEC, that would be a reasonable minimum to apply.

Okay, so now for the part you were asking about:
- 300.5 Underground Installations.
- - (D) Protection from Damage. Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).
- - - (1) Emerging from Grade. Direct-buried conductors and cables emerging from grade and specified in columns 1 and 4 of Table 300.5 shall be protected by enclosures or raceways extending from the minimum cover distance below grade required by 300.5(A) to a point at least 2.5 m (8 ft) above finished grade. In no case shall the protection be required to exceed 450 mm (18 in.) below finished grade.
- - - (2) Conductors Entering Buildings. Conductors entering a building shall be protected to the point of entrance.
- - - (3) Service Conductors. Underground service conductors that are not encased in concrete and that are buried 450 mm (18 in.) or more below grade shall have their location identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the underground installation.
- - - (4) Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, or equivalent.

If the conductors or cables in that location are subject to physical damage and are to be protected by enclosures or raceways, see (1) above, then those enclosures or raceways will also be subject to the same physical damage and would need to meet (4) above.

So no EMT? That's surprising to me. Learned something new today.

Originally Posted by Jim Robinson

So no EMT? That's surprising to me. Learned something new today.

There is EMT that is listed for direct burial but it is so rare I've only experienced it a few times. Using lfnc as shown is really a poor choice IMO. Sch. 80 above grade then convert on a pvc sweep 90 as you transition to horizontal. You could run your typical emt down to just above grade then convert to pvc but that is sorta goofy in my experience.