knob & tube ampacity

[dana1028]

I'm looking at some old K&T ...initially thinking the 14 AWG is over fused with a 20A fuse.

However, looking at Table 2, Chap. 10, 1953 NEC [house built in 1955] the ampacity for #14 is 20A...and note 3 to the table reads:
'For...concealed K&T work, the allowable current-carrying capacities of Table 2 shall be used.'

I can't find a code section similar to our current 240.4(D) for small conductors.

So? It's OK to use a 20A fuse with the old K&T 14 AWG wire?

 

[jwjrw]

I dont know if its legal but I do see it that way here. That dont make it right but.....you know.

 

[skeshesh]

Hopefully Augie will answer this one and we'll finally see first hand if he's journeyman test did in fact include K&T :grin:

 

[jwjrw]

Hopefully Augie will answer this one and we'll finally see first hand if he's journeyman test did in fact include K&T :grin:

Thats tooo funny.

 

[480sparky]

..............However, looking at Table 2, Chap. 10, 1953 NEC..........I can't find a code section similar to our current 240.4(D) for small conductors..........................

Because the 'small conductor rule' wasn't introduced until 1956.

 

[al hildenbrand]

I'm looking at some old K&T ...initially thinking the 14 AWG is over fused with a 20A fuse.

However, looking at Table 2, Chap. 10, 1953 NEC [house built in 1955] the ampacity for #14 is 20A...and note 3 to the table reads:
'For...concealed K&T work, the allowable current-carrying capacities of Table 2 shall be used.'

I can't find a code section similar to our current 240.4(D) for small conductors.

So? It's OK to use a 20A fuse with the old K&T 14 AWG wire?

Take a look at 1953 NEC Article 210 Section 2127 - Table Of Requirements. The minimum conductor size for a 20 Amp rated circuit is #12 wire.

 

[dana1028]

Because the 'small conductor rule' wasn't introduced until 1956.

Introduced until when???

 

[480sparky]

Introduced until when???

1956. What part didn't you understand?

 

[dana1028]

1956. What part didn't you understand?

The part about 1956.

Could you please provide a code section? Not that I don't trust your expertise...just I like to be able to reference a code section for this particular application.

 

[dana1028]

Take a look at 1953 NEC Article 210 Section 2127 - Table Of Requirements. The minimum conductor size for a 20 Amp rated circuit is #12 wire.

Thank you!

Don't you just luv it when these guys have these old code books around to help us out.

 

[480sparky]

The part about 1956.

Could you please provide a code section? Not that I don't trust your expertise...just I like to be able to reference a code section for this particular application.

The notes to Tables 1 and 2 in Chapter 10.

Take a look at 1953 NEC Article 210 Section 2127 - Table Of Requirements. The minimum conductor size for a 20 Amp rated circuit is #12 wire.

That isn't the same as the 'small conductor rule'. It simply states minimum size for the ampacity of the circuit, not the ampacity (which is a maximum) of a conductor.

 

[augie47]

o.k. you need an old timers Code...........
The National Board of Fire Underwriters in the 1895 edition,#14 B&S Wire, 12 amps concealed, 16 amps open.
The American Electricians Hnadbook 1921 edition, #14 B&S safe carrying akpo capacity in conduit 15 amps, 3 wires allowed in Milkd Steel Conduit.

The more things change, the more they stay the same

 

[al hildenbrand]

That isn't the same as the 'small conductor rule'. It simply states minimum size for the ampacity of the circuit, not the ampacity (which is a maximum) of a conductor.

The OP is not "Where is 240.4(D) in the 1953 NEC?"

Rather, it is whether it's normal for K&T #14 gauge copper branch circuits to be given over current protection of 20 Amps.

And, if 1953 2127 says the min gauge on a 20 A OCP is #12, how is that saying that the smaller #14 can be given a 20 A OCP?

 

[dana1028]

The notes to Tables 1 and 2 in Chapter 10.




That isn't the same as the 'small conductor rule'. It simply states minimum size for the ampacity of the circuit, not the ampacity (which is a maximum) of a conductor.

Notes 1 & 2, Chap. 10 deal with alum. and bare conductors...no mention of 'small' conductors.

 

[480sparky]

Notes 1 & 2, Chap. 10 deal with alum. and bare conductors...no mention of 'small' conductors.

The notes at the bottom of Tables 1 & 2, not Notes 1 & 2. It does not mention 'small conductors', but the language eventually becomes the 'small conductor rule'.

 

[480sparky]

The OP is not "Where is 240.4(D) in the 1953 NEC?"

Rather, it is whether it's normal for K&T #14 gauge copper branch circuits to be given over current protection of 20 Amps.

And, if 1953 2127 says the min gauge on a 20 A OCP is #12, how is that saying that the smaller #14 can be given a 20 A OCP?

Because 2127 deals with branch circuits with more than one outlet. If there's only one outlet, 2127 does not apply.

 

[al hildenbrand]

Because 2127 deals with branch circuits with more than one outlet. If there's only one outlet, 2127 does not apply.

And just how many single outlet K&T circuits exist in a common dwelling built in 1955? I submit it was highly unusual.

The question to dana1028 is, "Are you asking about a K&T #14 gauge branch circuit with more than one outlet?"

 

[dana1028]

Because 2127 deals with branch circuits with more than one outlet. If there's only one outlet, 2127 does not apply.

OK thanx -

It appears the actual 'small conductor rule' did not appear until 1999.

Yes, there were limits under certain conditions in T310.16 limiting #14 to 15A, but you could still install #14 on knob & tube [310.17] at 20A until 1999. [...as long as you did not violate 1956 section 2127... so this section would seem to be applicable to limiting #14 to 15A in 'normal' residential wiring].

Thanx Al

 

[480sparky]

..............It appears the actual 'small conductor rule' did not appear until 1999.
..............

240.4(D) today is simply the language relocated from the note at the bottom of 310-16 prior to 1999. That language goes back to T310-15 of the 1975, T310-12 of the 1965, and the bottom of tables 1&2 in Chapter 10 of the 1956.

 

[dana1028]

240.4(D) today is simply the language relocated from the note at the bottom of 310-16 prior to 1999. That language goes back to T310-15 of the 1975, T310-12 of the 1965, and the bottom of tables 1&2 in Chapter 10 of the 1956.

Yes it does...however it really doesn't mean exactly the same thing as does the small conductor rule.

Until the small conductor rule, 310.17 would allow you to run a circuit with #14 on a 20A breaker/fuse.

Now that you have all gone to this trouble to help me out I'd like to explain why I needed this information.

I'm in CA where amendments to 394.12 create an exception to the 'no insulation' rule. The exception basically says, if an electrician can certify that no violations to the code have taken place on K&T wiring, and the wiring is in good condition, then CA will allow the home to be insulated.

As Al has indicated, as of 1956 the rules in section 2127 of the 1956 NEC prohibit a breaker larger than 15A on a multi-outlet branch circuit. I was inspecting a house built in 1955 [1953 NEC] that was protected with a 20A OCPD; it would appear they are not in violation of over fusing the 14 AWG circuit wiring.