Tap conductor on 12AWG branch circuit

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peter i think the point that jim was trying to make is that it is not uncommon for a 20A circuit breaker to not trip at levels continuously over 20A. i've measured up to 23A continuous load on 15A breakers before w/ #14. The point i believe was that you could see a current draw of say, 26A or so on this circuit w/o tripping the breaker; now what if that load was coming only from what was connected to the #14? i'm not trying to argue w/ you, but just trying to help clear up the point; i think. ;)
 
brantmacga said:
peter i think the point that jim was trying to make is that it is not uncommon for a 20A circuit breaker to not trip at levels continuously over 20A. i've measured up to 23A continuous load on 15A breakers before w/ #14. The point i believe was that you could see a current draw of say, 26A or so on this circuit w/o tripping the breaker; now what if that load was coming only from what was connected to the #14? i'm not trying to argue w/ you, but just trying to help clear up the point; i think. ;)
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And that may be exactly why the NEC put the "fudge factor" in there. :)
 
This is not a tricky situation, it's just a situation where the NEC says two different things about the same piece of wire but does not provide any reason why.
 
peter d said:
Not OK by the NEC, even though T310.16 lists the ampacity of #14 as 20 amps.
I have no idea why this is the case.



Yes.
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imsho, because of the way the code is written regarding allowable ckts where 14awg can be used with 20A ocpd's, I would have to believe that somewhere down the line homeowners were burning down their houses. In that respect, I think a more appropriate statement would be that "table 310.16 lists the ampacity of #14 conditionally at 20amps, depending on its use"
 
peter d said:
This is not a tricky situation, it's just a situation where the NEC says two different things about the same piece of wire but does not provide any reason why.
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You could say the same thing about most of the tables in Art. 310.
 
brantmacga said:
peter i think the point that jim was trying to make is that it is not uncommon for a 20A circuit breaker to not trip at levels continuously over 20A. i've measured up to 23A continuous load on 15A breakers before w/ #14. The point i believe was that you could see a current draw of say, 26A or so on this circuit w/o tripping the breaker; now what if that load was coming only from what was connected to the #14? i'm not trying to argue w/ you, but just trying to help clear up the point; i think. ;)
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All very interesting and for what it's worth a breaker most breakers will carry 120% of the rated current forever.

However if that is the reason for 240.4(D) why is it I can protect 14 AWG @ for many types of circuits? Motors, HVAC units, welders etc.

I agree with all Pete has said here and I don't understand why he is getting a bunch of grief for stating that 14 AWG is rated 20 amps when that is the actual rating of 14 AWG @ 60 C.

Not once did he say to ignore 210.4(D). :)
 
peter d said:
You're wrong, the ampacity of #14 is 20 amps and if the current went "far above" 20 amps it would trip the breaker rather quickly. If it's a short circuit, the current would be in the thousands of amps and last time I checked there is no wire on the market with a rating that high.
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The UL standard permits the breaker to take up to 1 hour to trip at 135% of rated current and does not require the breaker to ever trip at 134% of rated current.
 
peter d said:
The point is that while this is a code violation, it is not a hazardous one.
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I don't believe that you can support this statement.

It is absolutely clear that the ampacity of a 14ga conductor is 20. This simply means that a 20A continuous current will not damage the conductor in the operating conditions assumed by table 310.16. I _totally_ agree with you that there is no hazard from continuous operation at 20A.

But this does not mean that an OCPD device with a 20A _rating_ will sufficiently protect a conductor with 20A ampacity. Without knowing the history of 240.4(D) we cannot say if it eliminates a real hazard, or if it is an artifact required by older equipment or wiring practice (eliminating a real hazard that is no longer applicable), or if it was one CMPs way of telling another that they were wrong, etc.

Possibly the hazard is that given the normal and accepted tolerances of OCPD manufacture, that an OCPD with a 20A trip rating cannot be expected to protect a conductor with 20A ampacity, unless there are other aspects of the circuit providing protection.

Or possibly the hazard was to the pockets of the CDA :)

Does anyone here know the history of the 'Small Conductors' rule?

-Jon
 
winnie said:
IDoes anyone here know the history of the 'Small Conductors' rule?

-Jon
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The current Table 310-16 was a rather 'mobile' history, whose lineage is as follows:

In my 1911 NEC it was called Rule 18 and was titled "Allowable Carrying Capacities of Conductors." 14, 12 and 10 had ampacities of 12, 17 and 24 for rubber insulation, 16,23, and 32 for other insulations (those were you only two choices then!).

In my 1930 NEC, it was relocated as Table 1 of Rule 618.

In 1937, it was moved to the back of the book and became Table 1, Chapter 9.

In 1940 Table 1 was moved further back to Chapter 10.

In 1956, the following was added to the bottom of the table:
"The current-carrying capacities for Type RHH conductors for sizes 14, 12 and 10 shall be the same as designated for Type RH conductors in this Table." This put 14, 12 and 10 at 15, 25 and 40 amps respectively.

In '59 it was relocated again and became Table 310-12. The ampacites were also changed for Type RH conductors, so this put 14, 12 and 10 at 15, 20 and 30 amps we know today.

In '65, the Table was renumbered 310-15.

In 1978, the 14AWG/15a, 12AWG/20a and 10AWG/30a were obelisk (†) notes at the bottom of (again renumbered) T310-16.

In 1999, the obelisk note was changed to refer you to 240.3.

In 2002, the reference was changed to 240.4(D).
 
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480 Nice piece of research, thanks. But we still don't know why the limitations. It seems that the manufacturers think the wire can take it but the NEC panels don't believe it - or don't have the stones to change the rule.

I woundn't be surprised if there was also a history of code change proposals to remove the limitations. I would be interested to see the panel's reasoning in rejecting those proposals.
 
bkludecke said:
480 Nice piece of research, thanks. But we still don't know why the limitations. It seems that the manufacturers think the wire can take it but the NEC panels don't believe it - or don't have the stones to change the rule.

I woundn't be surprised if there was also a history of code change proposals to remove the limitations. I would be interested to see the panel's reasoning in rejecting those proposals.
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The history I gave here is not garnered from some source, other than opening up my old Codebook collection and going through the various issues.

There probably is a paper trail somewhere about the changes, but I don't know where it would be outside of possibly the NFPA. ROPs and ROCs are common today, but I don't know when that formal process began.

1965 is the first NEC I have that lists CMPs in it. It also has in the back a section titled "Rules of Procedure for the NFPA Electrical Section and the National Electricl Code Committee". Not sure if that when CMPs were started or if they existed before then, or in what capacity they served.

If you're truly interested in seeing why it is rejected, make a proposal for the '11 and see what happens.
 
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winnie said:
It is absolutely clear that the ampacity of a 14ga conductor is 20. This simply means that a 20A continuous current will not damage the conductor in the operating conditions assumed by table 310.16. I _totally_ agree with you that there is no hazard from continuous operation at 20A.

But this does not mean that an OCPD device with a 20A _rating_ will sufficiently protect a conductor with 20A ampacity.
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Jon, there are many times where the NEC does allow 14 AWG to be protected with a 20 amp OCPD.
 
don_resqcapt19 said:
The UL standard permits the breaker to take up to 1 hour to trip at 135% of rated current and does not require the breaker to ever trip at 134% of rated current.
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Good to know. :)

But as for short circuits, does the wire size really matter?
 
iwire said:
Jon, there are many times where the NEC does allow 14 AWG to be protected with a 20 amp OCPD.
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Yes, that would be the 'other aspects of the circuit providing protection' :)

Not necessarily other overcurrent devices, but other features of the circuit which along with the OCPD permit a rating above 15 (for 14 AWG) to be trusted.

-Jon
 
iwire said:
All very interesting and for what it's worth a breaker most breakers will carry 120% of the rated current forever.

However if that is the reason for 240.4(D) why is it I can protect 14 AWG @ for many types of circuits? Motors, HVAC units, welders etc.

I agree with all Pete has said here and I don't understand why he is getting a bunch of grief for stating that 14 AWG is rated 20 amps when that is the actual rating of 14 AWG @ 60 C.

Not once did he say to ignore 210.4(D). :)
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Bob, why you tryin' to call me out?

I wasn't condemning peter for anything, just trying to make it more clear what the opposing argument was.
 
I understand Peter's view when it comes to "TAP" conductors. I'm not saying it's right, and neither did he, but I do understand his logic. The "Small conductor rule" is code plain and simple. #14 @75C is 20I but, your not sizing conductors for motors. 480 Sparky great job on the history of conductor ampacity and the NEC. I really enjoyed that. Can you tell the class "WHY" wires were "Coated" when using rubber insulation?:grin:
 
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