K & T Question

[Fred B]

I have yet to see ANY K&T that hasn't been "disturbed", altered, modified, or just plainly slaughtered over the years. Only positive I can say regarding K&T is I never seen rodents chewed K&T wire, even with significant evendence of their presence (nut shells in ceiling attic space).

Currently working on a "modified" system that I have been replacing that has multiple points of modifying that created mutliple reversal of L/N down the line and even someone "making" a fused neutral in the original fuse box used as a "sub panel" from the "newer" service with breaker panel. Also Live K&T Just cut off and left dangling with no wirenut covering at the bare end buried in attic insulation. Light fixtures with no neutrals, or a switched neutrals. Open up receptical or light fixture and it looks like I've got rag wire but it was fed by K&T with a flying splice. Broked Tubes or knobs throughout as well.

Alot of the time will have situation by just shuting down the K&T circuit that it will "kill" half the house, "hit and miss" throughout the house depending on what was modified and when. A what I call "here is a wire let's use that" syndrome.

Had investigated one K&T system sooo bad that I could stand in middle of living room and my ticker would ring off as if I was tracing on a live wire.

So would I EVER tell a customer that it's OK to leave the K&T active? NOOO.

 

[ptonsparky]

I've seen some K&T that looked as good as the day it was installed, not counting the 30 amp fuses.
Fused neutrals were common enough. Maybe leftover from the DC systems?

 

[don_resqcapt19]

I've seen some K&T that looked as good as the day it was installed, not counting the 30 amp fuses.
Fused neutrals were common enough. Maybe leftover from the DC systems?

I believe originally K&T was treated as free air so 14 could have 20 amp fuses and 12 could have 30 amp fuses.

 

[tortuga]

I believe originally K&T was treated as free air so 14 could have 20 amp fuses and 12 could have 30 amp fuses.

The NEC never permitted that, its a myth that leads to over fusing and one we should dispel on this forum, like the over built porcelain tubes and knobs the early NEC was more conservative, see Rule 23 1920 NEC.
The maximum fuse the 1920 NEC allowed on 14awg (and a edision socket) for was 10 amp.
The calculated load for any 10Amp branch circuit was limited 660 watts and 16 lamp ‘sockets’, outlets were not yet counted.
20A lighting circuits were not allowed till later.

Motors and heating appliances that required more than 660 watts were to be on dedicated circuits.(Rule 25.a)

The 660 watt rating of Edision base lamp-holders exists to this day.

1922 is when romex was patented by the 1930's I'd imagine EC's would be using it extensively.

 

[don_resqcapt19]

The NEC never permitted that, its a myth that leads to over fusing and one we should dispel on this forum, like the over built porcelain tubes and knobs the early NEC was more conservative, see Rule 23 1920 NEC.
The maximum fuse the 1920 NEC allowed on 14awg (and a edision socket) for was 10 amp.
The calculated load for any 10Amp branch circuit was limited 660 watts and 16 lamp ‘sockets’, outlets were not yet counted.
20A lighting circuits were not allowed till later.

Motors and heating appliances that required more than 660 watts were to be on dedicated circuits.(Rule 25.a)

The 660 watt rating of Edision base lamp-holders exists to this day.

1922 is when romex was patented by the 1930's I'd imagine EC's would be using it extensively.

Thanks...I wonder why that was?....20 amps on 14 installed in free air like K&T, would have less heat build up on each conductor then where you have 15 amps on on 14-2 NM.

 

[tortuga]

Thanks...I wonder why that was?....20 amps on 14 installed in free air like K&T, would have less heat build up on each conductor then where you have 15 amps on on 14-2 NM.

I have wondered this also, Back then (pre 1930's) you had all kinds of mishaps, exploding bulbs, poorly manufactured fixtures, failing rubber insulation over non-tinned copper, telegraph wire used instead of 'code' rubber wire.
There was not standardized voltage or frequency (southern CA was on 50hz). AC vs DC was not even settled (NYC was on 110/220 DC for a time). Probably more often accidental contact with secondary and primary lines.
Appliances and stuff mostly used standard Edison 'medium' screw base as a receptacle.
Lots of Non-soldered western union splices,.
I think a lot of the 10 amp & later 15 amp limit has to do with the Edison screw base itself and the pull chain or 'key' switches in them, as the first medium base permitted on a 20A or 'heavy duty' circuit were the 'key-less' type (1935 I think).

There were code interpretations that came out in the 1942 supplement that clarified mogul base bi-pin fluorescent fixtures could be on a 20A lighting circuit.
The first reference I can find to standard 'medium base' and standard fluorescent lighting being generally permitted, like today, on a general purpose 20A circuit in a dwelling is in the 1951 NEC.

 

[don_resqcapt19]

I have wondered this also, Back then (pre 1930's) you had all kinds of mishaps, exploding bulbs, poorly manufactured fixtures, failing rubber insulation over non-tinned copper, telegraph wire used instead of 'code' rubber wire.
There was not standardized voltage or frequency (southern CA was on 50hz). AC vs DC was not even settled (NYC was on 110/220 DC for a time). Probably more often accidental contact with secondary and primary lines.
Appliances and stuff mostly used standard Edison 'medium' screw base as a receptacle.
Lots of Non-soldered western union splices,.
I think a lot of the 10 amp & later 15 amp limit has to do with the Edison screw base itself and the pull chain or 'key' switches in them, as the first medium base permitted on a 20A or 'heavy duty' circuit were the 'key-less' type (1935 I think).

There were code interpretations that came out in the 1942 supplement that clarified mogul base bi-pin fluorescent fixtures could be on a 20A lighting circuit.
The first reference I can find to standard 'medium base' and standard fluorescent lighting being generally permitted, like today, on a general purpose 20A circuit in a dwelling is in the 1951 NEC.

Was the 10 amp limited to 14AWG used for K&T installations, or did it apply in general to all 14 AWG conductors?

 

[LarryFine]

Remember, too, that in the beginning, most homes were wired just for ceiling lighting. The loads were relatively known and fixed. Then adapters like these started popping up, the pull-chain allowing turning off the light while keeping the sockets hot:

 

[tortuga]

Was the 10 amp limited to 14AWG used for K&T installations, or did it apply in general to all 14 AWG conductors?

It applied to what we think of as a general purpose lighting and receptacle branch circuit, the kind of k&t lighting circuit that is probably difficult and expensive to replace thus still in found in historic dwellings over 100 years later like what the OP is asking about.
There were different rules for dedicated circuits for motors, heating, large chandeliers etc.
A 12A load (1320W @ 110V) was allowed by special permission with keyless fixtures "where the location of sockets and receptacles is such as to render unlikely the attachment of flexible cords thereto".

type R was a 60C wire, 14 was rated 15 amps, and 'R' was the required type for k&t.

23 Automatic Cut-outs ( Fuses and Circuit-breakers ).
(d)
Must be placed so that no set of small motors, small heating devices or incandescent lamps, whether grouped or on one fixture or several fixtures or pendants (nor more than 16 medium size or 25 candelabra size sockets or lamp receptacles) requiring more than 660 watts will be dependent on one cut-out.

Where a single socket or receptacle is used on a circuit the limitation of watts permissible on the final cut-out shall be the maximum capacity for which such socket or receptacle is approved.

The fuses in the branch cut-outs protecting circuits of 660 watts or less shall not have a rated capacity greater than given in the following table;

125 Volts or less ………………..10 amperes

126 to 250 volts ………………...6 amperes

A scan (not mine) of the 1920 NEC can be found here if your interested in some old code.
rule 23 is around page 54 of the scan.
The ampacity table (18) is interesting:

 

[PaulMmn]

My brother worked for an agency that had enough fires after blowing in insulation around K&T, that they would not do it. Yes, most likely it was in poor repair. Does not matter. It happened.

Would also depend on what the insulating material was. Chopped, insect-proofed newspaper or fiberglass tufts?

 

[ptonsparky]

Would also depend on what the insulating material was. Chopped, insect-proofed newspaper or fiberglass tufts?

Newspaper of course! He describes fiberglass as a big air filter. I tend to agree. Two foot of blown fiberglass and I can still feel the air exchange at ceiling boxes.

 

[brycenesbitt]

I have yet to see ANY K&T that hasn't been "disturbed", altered, modified, or just plainly slaughtered over the years. Only positive I can say regarding K&T is I never seen rodents chewed K&T wire, even with significant evendence of their presence (nut shells in ceiling attic space).

In what area are you working? In the San Francisco Bay Area "unmodified" K&T is mostly what I see. There are scattered modifications, but the nightmare ones are rare. Plenty of three prong outlets on old circuits though. The workmanship on the old K&T is something I admire: really heads and shoulders above much of the modern spaghetti that may be layered on top or in place of.
---
If the insulation crew did it right there was a City form to fill out, and the crawl spaces will have a two sided sign - one side listing the rules & name of the electrician that inspected, the other with a warning:

WARNING: Knob and Tube Wiring Use Caution When Entering Attic
AVISO: Cables de Perilla y Tubo Tenga Precaución al Entrar al Ático

 

[rc/retired]

If the insulation crew did it right there was a City form to fill out, and the crawl spaces will have a two sided sign - one side listing the rules & name of the electrician that inspected, the other with a warning:

WARNING: Knob and Tube Wiring Use Caution When Entering Attic
AVISO: Cables de Perilla y Tubo Tenga Precaución al Entrar al Ático

Is that required?

Ron

 

[brycenesbitt]

Is that required?
Ron

In my local area, yes, required.

https://berkeleyca.gov/sites/default/files/2022-02/146%20Knob%20and%20Tube%20Wiring%20Safety%20Report.pdf

 

[GoldDigger]

The house is 97 years old. The home inspector that cited the K & T never mentioned the attic space. He observed some K & T in the basement box sill that had some fiberglass insulation bats in contact with the K & T that was visible. Based on that, he mentioned that the wiring in the house be evaluated by a licensed electrician. So basically, he kicked the can down the road. That was the extent of his comments regarding K & T. I went into the attic to follow my suspicion that there probably was K & T up there as well. There was, hence my reason for starting this thread. It's very obvious that the insulation in the attic has been there for many decades based on the material used.

The California amendments appear to specifically prohibit use of foil-backed batt insulation in K&T areas. (Most likely to be an issue in outside walls.)

 

[letgomywago]

There is a similar exception in Oregon. When I do k&t surveys for these weatherization upgrades I always require the following:

• k&t needs to meet article 394 (funny how hard this can be).
• Must have 15A AFCI/GFCI protection, if fuses are involved they have to be type s.
• Exposed splices or connections shall be protected from insulation by installing flame resistant, non-conducting, open top enclosures which provide three inches, but not more than four inches side clearances, and a vertical clearance of at least four inches above the final level of the insulation.
• Insulation shall have a flame spread rating not to exceed 25 and a smoke density not to exceed 450 when tested in accordance with ASTM E84-91A. Foamed in place insulation shall not be used with knob-and-tube wiring.
• No more than 400 SQFT of residence per k&t circuit (10A load @ 3VA per sqft)
• No more than 10% voltage drop @ 12A load (tested a farthest point with a Ideal 'sure test').
• No BX (or other metallic wiring methods) cable tapped off k&t.
• Short single wire repairs are done with single conductor UF.
• Hard wired smoke detectors required to current code.

WA has some requirements for when doing this not as extensive as your personal requirements but there is a requirement to put all KnT on 15a gfi protection.