Bare neutral

[mbrooke]

Under the NEC, can the neutral of a system over 1kv, buried underground, be bare?

 

[John120/240]

I do not know. I imagine pulling XXHW or THHN or RHW or some other suitable insulated wire for the phase conductors & the neutral. The only time I recall bare neutral is in service cable.

 

[kwired]

Without looking in NEC my first guess is service conductors - yes

non service conductors - no.

I base this more on the need to separate grounded/equipment grounding conductors beyond the service then I do on the voltage involved.

 

[meternerd]

Not sure about NEC, but utilities used to use open concentric medium voltage direct burial cable all the time. The neutral is unsheathed bare copper wires wrapped around the insulated center phase conductor. Most use a jacketed "unishield" design now, which uses copper foil instead of wire. Less prone to damage, and can be pulled through conduit.

 

[ptonsparky]

I hit the wire surrounding a buried primary once with my shovel. Thought it was tree root until I wiped away the surronding dirt with my fingers. Didn't take long to get out of the ditch.

 

[mbrooke]

Not sure about NEC, but utilities used to use open concentric medium voltage direct burial cable all the time. The neutral is unsheathed bare copper wires wrapped around the insulated center phase conductor. Most use a jacketed "unishield" design now, which uses copper foil instead of wire. Less prone to damage, and can be pulled through conduit.

This is the cable in question. I know the NESC allows for it, but not sure if the NEC does.

 

[Dennis Alwon]

This is for systems and circuits over 1000 volts

250.184 Solidly Grounded Neutral Systems. Solidly
grounded neutral systems shall be permitted to be either
single point grounded or multigrounded neutral.
(A) Neutral Conductor.
(1) Insulation Level. The minimum insulation level for neutral
conductors of solidly grounded systems shall be 600 volts.
Exception No. 1: Bare copper conductors shall be permitted
to be used for the neutral conductor of the following:
(1) Service-entrance conductors
(2) Service laterals or underground service conductors
(3) Direct-buried portions of feeders
Exception No. 2: Bare conductors shall be permitted for the
neutral conductor of overhead portions installed outdoors.
Exception No. 3: The grounded neutral conductor shall be
permitted to be a bare conductor if isolated from phase
conductors and protected from physical damage.

 

[jeepx]

Even though the NEC may allow a buried neutral allow for service I would check with the inspector I do know that in my area it is no longer allowed if im not mistaken knob and tube wiring is still in the code but again no longer allowed at least in my area

 

[kwired]

Even though the NEC may allow a buried neutral allow for service I would check with the inspector I do know that in my area it is no longer allowed if im not mistaken knob and tube wiring is still in the code but again no longer allowed at least in my area

The reason K&T is still in the code is to tell us how to deal with existing K&T. It doesn't exactly tell us directly we can't use it for new installations. Key wording in 394.10 Uses Permitted is the two conditions listed where permitted:

(1) For extensions of existing installations
(2) Elsewhere by special permission

so we are limited to dealing with existing installations and it is pretty unlikely to get special permission elsewhere unless some really bizzare condition comes up.

 

[MasterTheNEC]

This is for systems and circuits over 1000 volts

Most important part of that statement is the fact it was for "over 1000 Volts"