NEC Changes For #14 Ampacity

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FionaZuppa

FionaZuppa

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Part Time Electrician (semi retired, old) - EE retired.
hi all. was wondering where the reference material may be (evidence) that caused NEC to change the #14 ampacity #'s, from say NEC2002 to NEC2008.

2002 it was 20/20/25
2008 it was 15/20/25

but even with those ampacities NEC has restricted (less the exceptions) #14 to 15A OCD.
 
I thought that it was in 2011 and the changes were made to bring the NEC and CEC (Canadian Electric Code) ampacity tables closer to the same values. # 12 and a few others were changed also.

You can look at the ROP at the NFPA website for the info.
 
jumper said:
I thought that it was in 2011 and the changes were made to bring the NEC and CEC (Canadian Electric Code) ampacity tables closer to the same values. # 12 and a few others were changed also.

You can look at the ROP at the NFPA website for the info.
Click to expand...

I here that often, but the interesting thing is that ampacities actually went up in the 2012 CEC, and a special lax was made regarding electric heat where #14 could be loaded to 20amps and the breaker sized by 125% without the wire. Very peculiar.


EDIT: The two CEC tables side by side:
 
the 2012 CEC went back to the 2002 NEC table.
 
jumper said:
I thought that it was in 2011 and the changes were made to bring the NEC and CEC (Canadian Electric Code) ampacity tables closer to the same values. # 12 and a few others were changed also.

You can look at the ROP at the NFPA website for the info.
Click to expand...

thats just the ampacity #, if Romex NM-B wire is rated 90C then why does NEC restrict that type of wire back down to the 60C column, and hence 15A(max) OCD? this 90C wire usually hooks to terminations that are rated 75C. from the wire ratings and such it doesnt make sense to me. are there no known big reasons why #14 is restricted to 15A OCD (less the exceptions). the defined exceptions suggests to me no fire hazard with #14 on a 20A OCD.
 
FionaZuppa said:
.... if Romex NM-B wire is rated 90C then why does NEC restrict that type of wire back down to the 60C column, and hence 15A(max) OCD? ......
Click to expand...


The 'small conductor rule' dates back to the 1956 NEC 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 RHH at 15, 20 and 30 amps respectively.

I have yet to find anything that says why. None of my handbooks from that era say one peep about it. Most likely, anyone involved in the NEC back then is gone, and perhaps the real reason will forever be lost to the ages.
 
FionaZuppa said:
thats just the ampacity #, if Romex NM-B wire is rated 90C then why does NEC restrict that type of wire back down to the 60C column, and hence 15A(max) OCD? this 90C wire usually hooks to terminations that are rated 75C. from the wire ratings and such it doesnt make sense to me. are there no known big reasons why #14 is restricted to 15A OCD (less the exceptions). the defined exceptions suggests to me no fire hazard with #14 on a 20A OCD.
Click to expand...

To be honest there is absolutely no hazard in typical building installations when #14 NM-B is subjected to 20amps (as is NEC ampacity tables are highly conservative), the fact the CEC lets you go that route would be actual real world proof.

Some possible theories behind 240.4 (D) are that small conductors are frequently found on multi outlet circuits where overload is likely. Most breaker trip curves start at around 125%, and under UL standards a typical residential breaker is not even required to trip at that threshold. Thus, it is theoretically possible to load #14 to 25 amps continuously without tripping a breaker where as 125% of 15 is 18.75 amps. Small conductors are also the most likely to be mis-used by unqualified personnel, ie over filled conduit or bundling without appropriate de-rating. Other possibilities are hold overs from rubber insulated wire days where insulation was nowhere near as good as it is today.

Another motive for 240.4(D) might be voltage drop. While code does not enforce voltage being merely a FPN, it could be another motive to seal the deal so to speak. Picture a 100 foot home run to a kitchen. At 120 volts, 20amps, unity power factor, ambient at 86*F, the voltage drop is about 6.2%. Same scenario with #14 is 10.4%. An extra 4.2%.
 
480sparky said:
The 'small conductor rule' dates back to the 1956 NEC 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 RHH at 15, 20 and 30 amps respectively.

I have yet to find anything that says why. None of my handbooks from that era say one peep about it. Most likely, anyone involved in the NEC back then is gone, and perhaps the real reason will forever be lost to the ages.
Click to expand...

Do you have the ampacity tables to those old codes? What was #14 rated back then? The 1965 NEC that I have has #14 listed at 15 amps across all 3 columns, ditto for #12 and 10.
 
the 2002 NEC listed #14 as 20/20/25.

125% of 20A ocd for #12 would exceed the 60C ampacity, so i dont understand the 125% ocd argument.
 
FionaZuppa said:
the 2002 NEC listed #14 as 20/20/25.

125% of 20A ocd for #12 would exceed the 60C ampacity, so i dont understand the 125% ocd argument.
Click to expand...



125% of 20amps is 25amps, what #12 is rated for at the 75*C column. However if I used a multi outlet circuit (which would be illegal for basic 120 volt 15/20 amp circuits but just for the conversation) 125% of 25 amps 31.25 amps placing current for #12 over the 90*C column.
 
mbrooke said:
To be honest there is absolutely no hazard in typical building installations when #14 NM-B is subjected to 20amps (as is NEC ampacity tables are highly conservative), the fact the CEC lets you go that route would be actual real world proof.

Some possible theories behind 240.4 (D) are that small conductors are frequently found on multi outlet circuits where overload is likely. Most breaker trip curves start at around 125%, and under UL standards a typical residential breaker is not even required to trip at that threshold. Thus, it is theoretically possible to load #14 to 25 amps continuously without tripping a breaker where as 125% of 15 is 18.75 amps. Small conductors are also the most likely to be mis-used by unqualified personnel, ie over filled conduit or bundling without appropriate de-rating. Other possibilities are hold overs from rubber insulated wire days where insulation was nowhere near as good as it is today.

Another motive for 240.4(D) might be voltage drop. While code does not enforce voltage being merely a FPN, it could be another motive to seal the deal so to speak. Picture a 100 foot home run to a kitchen. At 120 volts, 20amps, unity power factor, ambient at 86*F, the voltage drop is about 6.2%. Same scenario with #14 is 10.4%. An extra 4.2%.
Click to expand...

Have you ever held a 14/2 NM cable with a steady 12 to 15 amp load on it? I have and it gets pretty warm. While not an overt hazard, that kind of heating for an extended period of time will degrade the insulation.
 
peter d said:
...that kind of heating for an extended period of time will degrade the insulation.
Click to expand...

Only if it exceeds the temperature rating of the cable. If you can hold it in your hand for any reasonable length of time it is unlikely you have even gotten to 60C (140F) much less 90C.
 
peter d said:
Have you ever held a 14/2 NM cable with a steady 12 to 15 amp load on it? I have and it gets pretty warm. While not an overt hazard, that kind of heating for an extended period of time will degrade the insulation.
Click to expand...

Warm might be 100-110*F. The wire insulation is good for a minimum of 194*F. Anyone who has seen #14 loaded to 20amp knows it doesnt get anywhere near that temperature.
 
peter d said:
So you're both saying it's acceptable to load #14 wire to 20 amps or more?
Click to expand...

Technically it is, otherwise Canada wouldn't be doing it.


FWIW 1.5mm2 wire (thinner then our 2.08mm2 14 gauge) is allowed to carry 15amps inside a wall at 70*C.
 
mbrooke said:
Warm might be 100-110*F. The wire insulation is good for a minimum of 194*F. Anyone who has seen #14 loaded to 20amp knows it doesnt get anywhere near that temperature.
Click to expand...

And your point is? I2R losses are real and that's what you discount when you want to reduce ampacity to the bare minimum.
 
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