feeder size

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sleepy

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i have a question table 310.16
being a designer i have always size the wire by using the first column 60 degree
from18 awg to #1 and then went to 75 degree from 1/0 down.
i remember this way of sizing was mentioned in the code.
moved to a different company they do only the 75 degree column
was i just dreaming about using the 60 degree column. is there somewhere
in the code that still mentions this
thanks as always if you could help
 
sleepy said:
i have a question table 310.16
being a designer i have always size the wire by using the first column 60 degree
from18 awg to #1 and then went to 75 degree from 1/0 down.
i remember this way of sizing was mentioned in the code.
moved to a different company they do only the 75 degree column
was i just dreaming about using the 60 degree column. is there somewhere
in the code that still mentions this
thanks as always if you could help
Click to expand...

75 if thhn 60 for any romex and 90 to do derating from
 
I believe that you are thinking of 110.14(C)(1) for temperature limitations of terminals. If the terminals for wires smaller than #1 are marked at 75 degrees C then you are permitted to use the 75 degree column provided that the wire is also rated at least 75 degrees.

Chris
 
raider1 said:
I believe that you are thinking of 110.14(C)(1) for temperature limitations of terminals. If the terminals for wires smaller than #1 are marked at 75 degrees C then you are permitted to use the 75 degree column provided that the wire is also rated at least 75 degrees.

Chris
Click to expand...

Let me ask you this. 110.14(C)(1)(a)(3) basically says for 100 amps and under if all terminals are rated 90 degree than you can use 90 degree wire at 90 degree ampacity. But I noticed that the section for over 100 amps it does not specify this.

If all your terminations are 90 degree are you still stick using the 75 degree column for over 100 amps?
 
Twoskinsoneman said:
Let me ask you this. 110.14(C)(1)(a)(3) basically says for 100 amps and under if all terminals are rated 90 degree than you can use 90 degree wire at 90 degree ampacity. But I noticed that the section for over 100 amps it does not specify this.

If all your terminations are 90 degree are you still stick using the 75 degree column for over 100 amps?
Click to expand...

You can use the 90 degree column IF all the terminations and equipment are rated for 90 degrees. Take a look at the last part of 110.14(C)(1)(b)(2)

Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors
Click to expand...

Chris
 
feeders

feeders

so i guess i could say if you know what the temperature of the breakers you could
use the 75 or 90 degree columns, but what if you are designing the job, do you use the 60 degree column up to #1, and the 75 degree column from 1/0 on up, to be safe?
thanks
 
but what if you are designing the job, do you use the 60 degree column up to #1, and the 75 degree column from 1/0 on up, to be safe?
Click to expand...

You sure could. But most, if not all the breakers made today are rated at 75 degrees as well as most devices.

As far as 90 degrees goes, I am not aware of any breakers that are listed for use at that temperature.

Chris
 
raider1 said:
You sure could. But most, if not all the breakers made today are rated at 75 degrees as well as most devices.

As far as 90 degrees goes, I am not aware of any breakers that are listed for use at that temperature.

Chris
Click to expand...

I agree..

also keep in mind you can use the 90? column for derating as long as you don't exceed the 110.14 rating.
For example using #2 THHN with 3 ccc in a conduit in a 104? F ambient
would derate to 118.3 (130 X .91) BUT 110.14 would still limit you to 115 amps.
 
feeder

feeder

thank you, but then why would an inspector say we need #2's for 100 amps
looking at table 310 16, 100 amps -#3
there is no voltage drop here
any help
thanks
 
augie47 said:
I agree..

also keep in mind you can use the 90? column for derating as long as you don't exceed the 110.14 rating.
For example using #2 THHN with 3 ccc in a conduit in a 104? F ambient
would derate to 118.3 (130 X .91) BUT 110.14 would still limit you to 115 amps.
Click to expand...

Correct.

Chris
 
raider1 said:
As far as 90 degrees goes, I am not aware of any breakers that are listed for use at that temperature.
Click to expand...

There is no UL listed equipment (other than some drawout power switchgear) that is rated for conductors sized using the 90?C column.
 
sleepy said:
thank you, but then why would an inspector say we need #2's for 100 amps
looking at table 310 16, 100 amps -#3
there is no voltage drop here
any help
thanks
Click to expand...

If the terminals for the installation are all rated at 75 degrees then the inspector is wrong. Again it all hinges on the temperature rating of the terminals.

Chris
 
sleepy said:
thank you, but then why would an inspector say we need #2's for 100 amps
looking at table 310 16, 100 amps -#3
there is no voltage drop here
any help
thanks
Click to expand...

more than 3 cc conductors in a raceway ?? high ambient (over 123? F) ??
 
Must be Identified also.

Must be Identified also.

We just had this discussion in our office and it was agreed to use the 60 and 75* columns as described in 110.14.
Remember that per 110.14C.1.a.3 states "if the equipment is listed and identified for use with such conductors.
Not all devices are identified as such, e.g. wiring devices, smaller motors.
Most/all devices are listed, but most are not identified. Exhibit 110.6 in the NEC is a good example of the approbiate listing and identification required.

It would be great if the devices were identified, but unfortunately they are not.
 
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