brother
Senior Member
As a practice we usually put knob and tube #12 on 15 amp protection. In your area do they allow you to put # 12 knob and tube on 20 amp protection?
Knob and tube OCP
- Thread starter brother
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Was there ever an NEC requirement to limit #12 knob and tube to 15 amps?
- Location
- Illinois
- Occupation
- retired electrician
Original K&T was protected in accordance with Table 310.17 as the conductors are separated and in open air....20 amp protection of 15 amp K&T was legal before the small conductor rule was added to the code a few decades ago.
ptonsparky
Tom
- Occupation
- EC - retired
In real life most K&T had 30s. Sometimes a penny, but I have seen a dime.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Did they leave .09 change?
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Are the current ratings different between an all copper penny and one of the post 1982 zinc/copper-clad ones? (Probably)
No need to waste all that money, just score the copper fuse collar on either side of the fuse and bend one side down across the point of the fuse, screw it back in,, and,,,,,
keep the change.
Jap
I don't think the 'free air' tables were used for concealed knob and tube (as opposed to open wiring).
The NEC for along time had a type of branch circuit called a 'lighting circuit'.
Up thru the 1920 NEC the maximum fuse allowed on a lighting circuit was 10 amp. At that time the calculated load for any 10Amp branch circuit could not exceed 660 watts or 16 lamp ‘sockets’.
'outlets' were not yet counted.
The 1923 NEC added permission to use fuses of 15 amperes capacity instead of 10 amperes for the protection of 14 AWG lighting and other branch circuits.
Before rural electrification in the 1930's many voltages were locally generated.
Since voltages were all over the place, a rural house wired with knob and tube could have first been served by a Delco DC generator at 32 volts.
With a lower voltage DC system early electricians would have 'plumbed' the wiring, by starting out with #12 ( or even #10) and dropping to 14 later.
So without tracing the entire knob and tube system, I'd put a #12 at the panel on a 15A breaker.
Or now 100 years later that were back to having 10A lighting circuits you could even use a 10A breaker and protect it as it was intended.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
I would be very hesitant to use a 20-amp breaker without being very confident that it was 12-gauge from beginning to end. (if that level of confidence is even possible) I have seen lighting circuits in older houses wired with 16-gauge wire.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
If they're being used in an Edison-base fusebox, I don't think the difference is significant.
That's a little disturbing. Oh, well, it's on the Internet now. (and on a credible site, at that)
Comparing the current carrying capabilities of a copper penny vs. a 1982 zinc/copper penny is disturbing also if you're serious about it.
My post was simply a response to those of us old enough to witness code violations of penny's, dimes, etc,, that were installed behind screw in fuses to bypass the overcurrent protection.
And,
Examples of code violations are posted here on a daily basis.
JAP>
rc/retired
Senior Member
- Location
- Bellvue, Colorado
- Occupation
- Master Electrician/Inspector retired
My 2 cents on this matter is, if you are involved in a remodel with knob and tube, be sure to grab some of the tubes as they are great for sharpening knives.
Oh yeah, I don't have a problem with #12 terminated on a 20 amp breaker.
Ron
Oh yeah, I don't have a problem with #12 terminated on a 20 amp breaker.
Ron
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Of all things to worry about with K&T, ampacity doesn't make my list. Putting 12awg K&T on regular 15A breakers strikes me as a 'false sense of security' kind of thing.
ptonsparky
Tom
- Occupation
- EC - retired
I generally didn't worry about K&T other than tell the owners it was there. Once AFCI came about the guys would manage to get them on one. For this area, there were usually only two circuits and those were mostly lighting nowadays.
There is allot of it around here.
One time I went to a service call for some non working lights.
Older bungalow house probably late teens early 1920's, the customer was a very chatty lady, and was telling me every last detail while my apprentice somehow went in the tiny attic.
After a while he was making muffled yet loud noises, and I finally here him say 'I found it'.
I poked my head up there to see a bright orange glowing splice, like a old car cigarette lighter.
There was blackened blow in insulation all around it.
The attic had just been insulated by a weatherization grant.
And it was obvious whomever did the work stepped all over the K&T, straining the brittle 90 YO splices.
Yeah probably the best use of an AFCI / GFCI breaker is K&T.
One time I went to a service call for some non working lights.
Older bungalow house probably late teens early 1920's, the customer was a very chatty lady, and was telling me every last detail while my apprentice somehow went in the tiny attic.
After a while he was making muffled yet loud noises, and I finally here him say 'I found it'.
I poked my head up there to see a bright orange glowing splice, like a old car cigarette lighter.
There was blackened blow in insulation all around it.
The attic had just been insulated by a weatherization grant.
And it was obvious whomever did the work stepped all over the K&T, straining the brittle 90 YO splices.
letgomywago
Senior Member
- Location
- Washington state and Oregon coast
- Occupation
- residential electrician
If you rewire all of the outlets what would the lighting load even be in these old houses with led bulbs. Put it all on a dual function and the load is what 4 amps max on that circuit. I don't mind taking the work but I feel bad when the homeowner has such a hard time paying just to replace a 3 way switch for a single bulb stair light.
letgomywago
Senior Member
- Location
- Washington state and Oregon coast
- Occupation
- residential electrician
When a full removal is out of the question for costs I have been hired to just remove all the exposed in the attic runs and basement/crawl.
rambojoe
Senior Member
- Location
- phoenix az
- Occupation
- Wireman
Went on a service call one time where there were 2 copper 1/2" pipes run the length of the attic. 1 served as hot the other as neutral fed from a 2p 60 with #6's soldered to the ends. The 2w #12 romex drops down the walls to the outlets were soldered to the 2 pipes In the attic as needed.
Jap>
Jap>
- Status