The only place with grounds…

[MAD]

You did say the 1930's house wire had a ground but that cable does not have a ground.

Here is the catalog page again cropped to make the image part larger and easier to read, and the grounding wire notes underlined and circled.

 

[SlappyWhite]

My house (Canada FWIW) was K&T (1941 build) before my rewire. The bathroom vanity light boxes had an individual ground wire going back to the closest metal plumbing pipe. Power came via the K&T. I assume this was original to the house as the bathrooms that had it were pretty much all original (any past minor renos did not include opening the walls).

 

[35Ford]

It allows the installation of knob and tube?

Not ****** likely. A ground is mandatory.

It does, in some limited cases. See NEC sec 394.

 

[grounded-b]

Knob and Tube is still allowed by the NEC as extensions to existing installations in limited cases. ( NEC art. 394 )

It can not be covered by insulation. It can only feed lighting outlets and GFCI receptacles. ( which do not need a ground to operate properly, BTW ) Installation of 2 prong, ungrounded outlets are not allowed by the NEC.

Not saying that I would EVER do it, just that it is still allowed to be done.

 

[Norcal]

It allows the installation of knob and tube?

Not ****** likely. A ground is mandatory.

In the 1971 NEC, article 324 is concealed knob & tube wiring, in the 2023 edition it is article 394, it is permitted 1) For extension of existing installations, 2) Elsewhere by special permission.

 

[sparky 1971]

It allows the installation of knob and tube?

Not ****** likely. A ground is mandatory.

I can't think of any instance where it would be used, even as an extension of an existing circuit, but it's permissible.


394.1 Scope
This article covers the use, installation, and construction specifications of concealed knob-and-tube wiring.
394.10 Uses Permitted
Concealed knob-and-tube wiring shall be permitted to be installed in the hollow spaces of walls and ceilings, or in unfinished attics and roof spaces as provided by 394.23, only as follows:

1. For extensions of existing installations
2. Elsewhere by special permission

394.12 Uses Not Permitted
Concealed knob-and-tube wiring shall not be used in the following:

1. Commercial garages
2. Theaters and similar locations
3. Motion picture studios
4. Hazardous (classified) locations
5. Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors

394.17 Through or Parallel to Framing Members
Conductors shall comply with 398.17 where passing through holes in structural members. Where passing through wood cross members in plastered partitions, conductors shall be protected by noncombustible, nonabsorbent, insulating tubes extending not less than 75 mm (3 in.) beyond the wood member.

394.19 Clearances
(A) General
A clearance of not less than 75 mm (3 in.) shall be maintained between conductors and a clearance of not less than 25 mm (1 in.) between the conductor and the surface over which it passes.
(B) Limited Conductor Space
Where space is too limited to provide these minimum clearances, such as at meters, panelboards, outlets, and switch points, the individual conductors shall be enclosed in flexible nonmetallic tubing, which shall be continuous in length between the last support and the enclosure or terminal point.
(C) Clearance From Piping, Exposed Conductors, and So Forth
Conductors shall comply with 398.19 for clearances from other exposed conductors, piping, and so forth.

394.23 In Accessible Attics
Conductors in unfinished attics and roof spaces shall comply with 394.23(A) or (B).
Informational Note: See 310.14(A)(3) for temperature limitation of conductors.
(A) Accessible by Stairway or Permanent Ladder
Conductors shall be installed along the side of or through bored holes in floor joists, studs, or rafters. Where run through bored holes, conductors in the joists and in studs or rafters to a height of not less than 2.1 m (7 ft) above the floor or floor joists shall be protected by substantial running boards extending not less than 25 mm (1 in.) on each side of the conductors. Running boards shall be securely fastened in place. Running boards and guard strips shall not be required where conductors are installed along the sides of joists, studs, or rafters.
(B) Not Accessible by Stairway or Permanent Ladder
Conductors shall be installed along the sides of or through bored holes in floor joists, studs, or rafters.
Exception: In buildings completed before the wiring is installed, attic and roof spaces that are not accessible by stairway or permanent ladder and have headroom at all points less than 900 mm (3 ft), the wiring shall be permitted to be installed on the edges of rafters or joists facing the attic or roof space.

394.30 Securing and Supporting
(A) Supporting
Conductors shall be rigidly supported on noncombustible, nonabsorbent insulating materials and shall not contact any other objects. Supports shall be installed as follows:

1. Within 150 mm (6 in.) of each side of each tap or splice, and
2. At intervals not exceeding 1.4 m (41/2 ft).

Where it is impracticable to provide supports, conductors shall be permitted to be fished through hollow spaces in dry locations, provided each conductor is individually enclosed in flexible nonmetallic tubing that is in continuous lengths between supports, between boxes, or between a support and a box.
(B) Securing
Where solid knobs are used, conductors shall be securely tied thereto by tie wires having insulation equivalent to that of the conductor.
394.42 Devices
Switches shall comply with 404.4 and 404.10(B).
394.56 Splices and Taps
Splices shall be soldered unless approved splicing devices are used. In-line or strain splices shall not be used.
394.104 Conductors
Conductors shall be of a type identified in Table 310.4(1).

 

[cgrutt]

Interesting. Even though it was no longer actually being used or in service, where I saw it was actually in a concealed space above bathroom ceiling. There was another floor above the bathroom so it was within floor joist of the floor above bathroom. I don't recall specifically how deep the floor joists were but they were much deeper and thicker than anything used today probably 12" or more. There was blown in insulation in ceiling which I believe was added much later, probably within past 50 years would be my guess, and the knob and tube wiring was probably disabled before the insulation was added. Between the water damage, insulation, plaster and residual from over 100 years of critters the demo on that particular project was probably the worst I ever experienced lol.

 

[35Ford]

I have extended existing knob and tube wiring as allowed. It's a lot different than traditional wiring methods.

 

[JunkBonds]

I have extended existing knob and tube wiring as allowed. It's a lot different than traditional wiring methods.