Response from RFI concerning current carrying conductors. Am I crazy

[Dsg319]

Question that was sent

All of these conduits contain over three current-carrying conductors. According to NEC Table 310.15(c)(1), derating must be applied, which affects the ampacities of the conductors. As a result, the conductors may not be adequately protected by their corrected ampacities.

For example, Conduit AC-MCC contains 18 current-carrying conductors. This results in a derated ampacity of only 15 amperes for #12 AWG conductors, due to a 50% correction factor. Consequently, these conductors cannot be protected by a 20-amp OCPD.


Reply below

The calculated load for each of the heat trace circuits was a 15A continuous load. The conductors are sized correctly to carry the anticipated H/T load, even with the 310.15(C)(1) derating factor taken into account. Although the conductors have a calculated ampacity of 15A, a 20A OCPD is permitted. Section 240.4(B) permits the use of the next higher standard rating of OCPD. This also checks out based on 210.20(A) given that a 15A continuous load would require a 20A OCPD.

 

[petersonra]

Did you have a question?

 

[Dsg319]

Did you have a question?

I believe the response is incorrect regarding the number of CCC still protected by a 20amp breaker.

 

[petersonra]

I believe the response is incorrect regarding the number of CCC still protected by a 20amp breaker.

I don't believe there is any limit on the number of ccc that can be protected by a 20 amp breaker.

I don't recall offhand what the exact wording is of the provision allowing the use of the next rated ocpd though.

Also, I don't recall if heat trace is considered a continuous load requiring 125 % ampacity.

 

[infinity]

The calculated load for each of the heat trace circuits was a 15A continuous load. The conductors are sized correctly to carry the anticipated H/T load, even with the 310.15(C)(1) derating factor taken into account. Although the conductors have a calculated ampacity of 15A, a 20A OCPD is permitted. Section 240.4(B) permits the use of the next higher standard rating of OCPD. This also checks out based on 210.20(A) given that a 15A continuous load would require a 20A OCPD.

Whoever wrote that needs a little re-education. The next size up rule would only be allowed if 15 amps wasn't a standard size.

 

[roger]

As Rob says, the person that answered the RFI needs to read to 240.6

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard
ampere ratings for fuses and inverse time circuit
breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50,
60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300,
350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000,
2500, 3000, 4000, 5000, and 6000 amperes. Additional
standard ampere ratings for fuses shall be 1, 3, 6, 10, and
601. The use of fuses and inverse time circuit breakers with
nonstandard ampere ratings shall be permitted.

 

[augie47]

I don't believe there is any limit on the number of ccc that can be protected by a 20 amp breaker.

I don't recall offhand what the exact wording is of the provision allowing the use of the next rated ocpd though.

Also, I don't recall if heat trace is considered a continuous load requiring 125 % ampacity.

For branch circuit rating I believe it would be considered continuous such as noted in 427.7

 

[infinity]

For branch circuit rating I believe it would be considered continuous such as noted in 427.7

Hard to decipher but it sounds like each heat trace load is 15 amps and would need a minimum conductor sized at 15*125%=18.75 amps. Not only are the derated conductors too small they also cannot be protected at 20 amps.

 

[Dsg319]

I don't believe there is any limit on the number of ccc that can be protected by a 20 amp breaker.

I don't recall offhand what the exact wording is of the provision allowing the use of the next rated ocpd though.

Also, I don't recall if heat trace is considered a continuous load requiring 125 % ampacity.

Yes they may not be a limit of CCC allowed per raceway but you have to upsize the conductors due to the ampacity adjustments.

No way can you have over 9CCC that are #12AWG still protected by a 20amp breaker.

And yes we always factor HT as a continuous use load.

 

[petersonra]

Yes they may not be a limit of CCC allowed per raceway but you have to upsize the conductors due to the ampacity adjustments.

The code is clear on this point. Having 18 CCC makes the ampacity of the #12 wires 15 Amps, assuming normal wires, etc.

No way can you have over 9CCC that are #12AWG still protected by a 20amp breaker.

What if they are motors?

And yes we always factor HT as a continuous use load.

Just because you do that does not mean it is a code requirement. Off hand I don't know if it is or not.

 

[don_resqcapt19]

Question that was sent

All of these conduits contain over three current-carrying conductors. According to NEC Table 310.15(c)(1), derating must be applied, which affects the ampacities of the conductors. As a result, the conductors may not be adequately protected by their corrected ampacities.

For example, Conduit AC-MCC contains 18 current-carrying conductors. This results in a derated ampacity of only 15 amperes for #12 AWG conductors, due to a 50% correction factor. Consequently, these conductors cannot be protected by a 20-amp OCPD.


Reply below

The calculated load for each of the heat trace circuits was a 15A continuous load. The conductors are sized correctly to carry the anticipated H/T load, even with the 310.15(C)(1) derating factor taken into account. Although the conductors have a calculated ampacity of 15A, a 20A OCPD is permitted. Section 240.4(B) permits the use of the next higher standard rating of OCPD. This also checks out based on 210.20(A) given that a 15A continuous load would require a 20A OCPD.

That only applies where the conductor ampacity does not match with a standard size OCPD. In this case the adjusted ampacity is 15 amps and 15 is a standard size OCPD. The maximum permitted OCPD for this circuit is 15 amps.

240.4(B) Overcurrent Devices Rated 800 Amperes or Less.
The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

• (1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
• (2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
• (3) The next higher standard rating selected does not exceed 800 amperes.

 

[jaggedben]

Did you have a question?

Yeah the problem with his RFI is that it wasn't an RFI. He forgot to include "Who is going to pay for this when it doesn't pass inspection? (Because it's not going to be me.)"

 

[Dsg319]

The code is clear on this point. Having 18 CCC makes the ampacity of the #12 wires 15 Amps, assuming normal wires, etc.


What if they are motors?


Just because you do that does not mean it is a code requirement. Off hand I don't know if it is or not.

Sure if the motors do not operate simultaneously. Same concept with traveler wires in 3 or 4 way switch set up IMO.

 

[hornetd]

Same concept with traveler wires in 3 or 4 way switch set up IMO.

I had an inspector try to turn me down on the basis of travelers being 2 current carrying conductors. I had a 3 way, 2 point switch circuit in every room that had 2 ways to enter and exit. The 4th wire was the required neutral in the switch boxes. So in switch boxes that had no neutral current flowing and an actual lighting load of ~10 amperes they wanted 12 AWG to carry the output of a 15 ampere breaker. I said "No offense but I'm going to have to talk to the Chief Electrical Inspector about that. The circuit is wired so that the only energized conductors in the box are the 3 wire switch leg. There is no constant hot in that box and the code does not require one." They called me back before the end of the day saying I could tear up the correction order. They thought I was being an a-hole when I insisted I wanted a signed withdrawal of the order. I couldn't afford to have that weird idea pop up after the walls were buttered. They did come by and gave me a signed withdrawal of the numbered correction order but I could see that they didn't like it one bit.

Tom Horne

 

[Tainted]

what's the total heat trace load? they are saying each heat trace is 15 amps, but how many of the heat traces are 15 amps?

 

[Dsg319]

what's the total heat trace load? they are saying each heat trace is 15 amps, but how many of the heat traces are 15 amps?

We’re not included in any of these engineered load calculations so I couldn’t tell you.

 

[Tainted]

We’re not included in any of these engineered load calculations so I couldn’t tell you.

Does each heat trace have their own dedicated breaker? or is he feeding multiple heat traces on 1 single 20 amp breaker?

 

[Dsg319]

Each has its own dedicated GFEP breaker.

 

[letgomywago]

I had an inspector try to turn me down on the basis of travelers being 2 current carrying conductors. I had a 3 way, 2 point switch circuit in every room that had 2 ways to enter and exit. The 4th wire was the required neutral in the switch boxes. So in switch boxes that had no neutral current flowing and an actual lighting load of ~10 amperes they wanted 12 AWG to carry the output of a 15 ampere breaker. I said "No offense but I'm going to have to talk to the Chief Electrical Inspector about that. The circuit is wired so that the only energized conductors in the box are the 3 wire switch leg. There is no constant hot in that box and the code does not require one." They called me back before the end of the day saying I could tear up the correction order. They thought I was being an a-hole when I insisted I wanted a signed withdrawal of the order. I couldn't afford to have that weird idea pop up after the walls were buttered. They did come by and gave me a signed withdrawal of the numbered correction order but I could see that they didn't like it one bit.

Tom Horne

Had that happen in eastern WA also.

 

[Tainted]

I understand why a 20 amp wire can't be used because of derating of course, but why can't a 20 amp breaker be used for each heat trace? Maybe I'm missing something