90c insulation
- Thread starter kimrichi
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- Logan, Utah
Are you talking about from a code perspective or a physics perspective?
Chris
Chris
For purpose of your discussion, my suggestion is to look at the conductor (CU or AL) and the insulation separately. A #12 copper conductor with a 20 amp load will pretty much run the same temperature no matter the insulation type. Keep this in mind for purposes of terminating.
You don't want to exceed the 60? ampacity if you are terminating on a 60? rated device as you don't want the actual conductor temperature to radiate excessive heat to the device.
Beyond termination concerns, you need to take into account that excessive temperature causes insulation breakdown. A wire with a higher rated insulation can withstand a higher heat whether that come from the core conductor carrying current or from outside sources such as number of conductors in a raceway or ambient.
From a practical standpoint, you select a conductor that can handle the environment such as a THHN ao you will not have an insulation failure, then you make sure your actual current does not exceed the termination rating so as not to damage the device.
You don't want to exceed the 60? ampacity if you are terminating on a 60? rated device as you don't want the actual conductor temperature to radiate excessive heat to the device.
Beyond termination concerns, you need to take into account that excessive temperature causes insulation breakdown. A wire with a higher rated insulation can withstand a higher heat whether that come from the core conductor carrying current or from outside sources such as number of conductors in a raceway or ambient.
From a practical standpoint, you select a conductor that can handle the environment such as a THHN ao you will not have an insulation failure, then you make sure your actual current does not exceed the termination rating so as not to damage the device.
This point is often ignored and the same with 75degC terminations. When testing breakers and control often times the device relies upon the being a heat sink taking heat away from the device. The only devices that I'm aware of that requires the use of 90degC rated wire are 100% rated breakers. In order to achieve their 100% rating the breaker must be installed in a suitable enclosure as directed by the instructions. The 90degC rated wire must be used but the wire's ampacity is applied at 75degC. I doubt if the terminals have as 90degC rating as those terminals are no different than standard breakers.
liquidtite
Senior Member
- Location
- Ny
So when terminating a conductor with insulation in the (90)degree column thhn, to a bracket that is rated at 65 degrees . Do you have to take that conductor at 65 degrees instead of 90
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Yep
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Sort of, the limiting factor of a 60C or 75C termination on the bracket requires the circuit to be rated for that ampacity.
In short, the weakest link/lowest rated piece of equipment in a circuit determines the final ampacity.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
See if this Data Bulletin by Schneider Electric helps explain.
http://static.schneider-electric.us/docs/Power Management/0110DB9901.pdf
http://static.schneider-electric.us/docs/Power Management/0110DB9901.pdf
kwired
Electron manager
- Location
- NE Nebraska
There are two things that need considered when determining conductor ampacity, termination temperature rating and insulation temperature rating.
For the most part you will seldom if ever run into 90 degree terminations, so even if using conductor with 90 degree insulation you still must use minimum conductor size from the 60 or 75 degree columns in the ampacity table.
Now lets say you are running a circuit through a high ambient temperature area and/or have more than three current carrying conductors in a raceway. It is adjustments for these kinds of factors that allow you to derate from the 90 degree values in the ampacity tables.
To come up with final conductor selection size, use the larger of the conductors determined needed for termination temp or for insulation temp.
An example - we have a circuit requiring an ampacity of 52 amps, 8 AWG 90 degree copper conductor has an ampacity of 55 amps, but we also have to consider terminals on our equipment are likely 75 degree, that means the minimum size conductor needs to be at least 6 AWG, because that is smallest conductor in the 75 degree column that is 52 or more.
Now lets assume same conductor requiring minimum ampacity of 52 and put it in a raceway with 10 current carrying conductors. We are allowed to start ampacity adjustments at 90 degree ampacity levels because it is the insulation and not the termination that needs adjustment. So we still must have at least 6 AWG minimum for termination rating but with 10 current carrying conductors we have a 50% ampacity adjustment factor - which results in 6 AWG having a derated 90 deg ampacity of (75 x .50 =) 37.5 amps. That is less than the needed 52 so we must select a larger conductor. (6 AWG is acceptable for the termination temp but not the insulation temp in this case) A 4 AWG 90 deg conductor also results in less than 52 after adjustment, but a 3 AWG is (115 x .50 =) 57.5 which is equal or greater than the needed 52 for our application.
It is possible and often happens where the ampacity based on insulation temp will result in a smaller conductor being allowed, but you can never go smaller than the size determined by termination temperature.
For the most part you will seldom if ever run into 90 degree terminations, so even if using conductor with 90 degree insulation you still must use minimum conductor size from the 60 or 75 degree columns in the ampacity table.
Now lets say you are running a circuit through a high ambient temperature area and/or have more than three current carrying conductors in a raceway. It is adjustments for these kinds of factors that allow you to derate from the 90 degree values in the ampacity tables.
To come up with final conductor selection size, use the larger of the conductors determined needed for termination temp or for insulation temp.
An example - we have a circuit requiring an ampacity of 52 amps, 8 AWG 90 degree copper conductor has an ampacity of 55 amps, but we also have to consider terminals on our equipment are likely 75 degree, that means the minimum size conductor needs to be at least 6 AWG, because that is smallest conductor in the 75 degree column that is 52 or more.
Now lets assume same conductor requiring minimum ampacity of 52 and put it in a raceway with 10 current carrying conductors. We are allowed to start ampacity adjustments at 90 degree ampacity levels because it is the insulation and not the termination that needs adjustment. So we still must have at least 6 AWG minimum for termination rating but with 10 current carrying conductors we have a 50% ampacity adjustment factor - which results in 6 AWG having a derated 90 deg ampacity of (75 x .50 =) 37.5 amps. That is less than the needed 52 so we must select a larger conductor. (6 AWG is acceptable for the termination temp but not the insulation temp in this case) A 4 AWG 90 deg conductor also results in less than 52 after adjustment, but a 3 AWG is (115 x .50 =) 57.5 which is equal or greater than the needed 52 for our application.
It is possible and often happens where the ampacity based on insulation temp will result in a smaller conductor being allowed, but you can never go smaller than the size determined by termination temperature.
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