10AWG and 40Amps

[chrisreisinger79]

When is 10AWG able to be used up to the 40amp rating from table 310.15? The application in question is a heater with an FLA of 38.9 amps, max fuse of 40amps, THHN conductors with terminals and wire rated at 90 degrees Celcius. My question then is can 10AWG be used or does the max OCP of 30amps for 10AWG apply here?

 

[norcal]

When is 10AWG able to be used up to the 40amp rating from table 310.15? The application in question is a heater with an FLA of 38.9 amps, max fuse of 40amps, THHN conductors with terminals and wire rated at 90 degrees Celcius. My question then is can 10AWG be used or does the max OCP of 30amps for 10AWG apply here?

The 90 degree rating is not normally used, but even if the 75 degree values in Table 310.15(B)(16) are used the 35A rating is still not adequate.

 

[dkidd]

When is 10AWG able to be used up to the 40amp rating from table 310.15? The application in question is a heater with an FLA of 38.9 amps, max fuse of 40amps, THHN conductors with terminals and wire rated at 90 degrees Celcius. My question then is can 10AWG be used or does the max OCP of 30amps for 10AWG apply here?

I doubt that the terminals are rated 90. What does the heater say that the MCA is?

 

[Strathead]

When is 10AWG able to be used up to the 40amp rating from table 310.15? The application in question is a heater with an FLA of 38.9 amps, max fuse of 40amps, THHN conductors with terminals and wire rated at 90 degrees Celcius. My question then is can 10AWG be used or does the max OCP of 30amps for 10AWG apply here?

Remember that the terminals at the breaker have to be rated at 90º also.

 

[chrisreisinger79]

You are correct about the terminals only being rated for 75 degrees. So at this point, despite THHN being rated for 90, the terminals throw us into the 75 degree chart for wire ampacity? Do you ever use the 90 degree chart for THHN when figuring for ampacity since that's where THHN is classified?

 

[jumper]

You are correct about the terminals only being rated for 75 degrees. So at this point, despite THHN being rated for 90, the terminals throw us into the 75 degree chart for wire ampacity?

See 110.14(C).

 

[kwired]

You are correct about the terminals only being rated for 75 degrees. So at this point, despite THHN being rated for 90, the terminals throw us into the 75 degree chart for wire ampacity? Do you ever use the 90 degree chart for THHN when figuring for ampacity since that's where THHN is classified?

You can use 90 C table values as a starting point when making ambient temp adjustments and number of conductors in raceway adjustments. You must still have a minimum conductor size based on termination temp rating though.

Motors and air conditioning is a common place where you can have 10 AWG on more then 30 amp overcurrent device, but MCA or FLA (x 1.25) is still within 75 C conductor ampacity rating in those cases.

 

[chrisreisinger79]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

 

[kwired]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

Can't speak for all exam administrators, but today's reality is that 75C is pretty much the standard termination rating for under 600 volts devices, if you have older equipment or are using NM cable then 60C must be used.

 

[infinity]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

IMO you would 60 degree C or 75 degree C based on 110.14(C)(1).

 

[Carultch]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

If you are given an example where it is used in a circuit, you have to follow the default assumptions of 110.14(C), unless it is specified in the problem, or there is a master statement at the front of the exam specifying otherwise. Even if you know 75C is the industry norm for every practical problem you will solve, when taking an exam, you still have to follow the academic rule and go by the 110.14(C) defaults.

By contrast, if you are just asked for the ampacity of the conductor, you choose from the largest column that wire type appears within. Be aware that there could be a wet location/dry location distinction, where one ampacity applies in wet locations and the other applies in dry locations.

 

[texie]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

Infinity is right on-use 110.14(C)(1) as your guide. These types of questions, with no temperature rating of the terminations given, are very common on licensing exams. They want to see if you understand temperature limitation requirements. It is also common to have questions where it is not specified CU or AL. If not specified always assume CU.
But as kwire mentioned, in the real world today, most equipment is rated 75 degree.

 

[tom baker]

Thanks for all the help guys. One last question then. When it comes to a code test related question where you are asked the ampacity rating of a conductor without any other information regarding terminal ratings or ambient temperature ratings...which is the default chart to use, especially if the conductor type is found on both the 75 and 90 chart? I had a question like this on a code test for XHHW Aluminum. Based on the thread here...do you assume the lower temperature rating?

The ampacity of 12 AWG THHN is 30 amps (Art 310)
The over current protection is normally 20 amps, some times 25. (Art 240)
Two different articles...

 

[augie47]

If the question only concerns the ampacity of the wire then you rely on the appropriate value in 310.15(B)(16) with any required adjustment from 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c). If the question concerns the allowable circuit size (overcurrent protection and termination taken into account) size the you take 110.14 and 240.4 into account.

 

[Sparky1999]

jumper

jumper

Jumper is absolutely correct. 110.14(C) is the key to all the tricky questions when you have no other info. I had about 5 of those questions on my Oregon and Washington Super and Master tests.