Determine Ambient Air Temperature

Status
Not open for further replies.
L

Leo1

Member
Location
Los Alamos, NM
1. What is a reliable, creditable source for determining ambient air temperature for a project. When I Google average temperatures for a give city dozens of sources come up? Is one more acceptable than the other?

2. If raceways are located in a facility that is temperature controlled between 68-72 degrees F, then can that average temperature be used for conductor selection or must the average outside ambient air temperature be used?

Thank you.
 
The idea of ampacity adjustment for ambient temp is to prevent the conductor insulation from being overheated - so the temp where the conductor is located is important and if indoors in a ambient controlled environment you shouldn't care about what is outside.

When there is a big change in temp whether daily, seasonally or whatever, you should be considering highest ambient possible. That may be a little tricky when it comes to determining what is the highest ambient temp outdoors. Highest temp ever encountered in a location is likely not the thing to go by, but neither is average temp. Maybe average high temps during the summer season is a better place to start. I don't think the NEC addresses how to determine such ambient temp but your local AHJ may have a method they use.
 
mwm1752 said:
I posted this awhile back but the replys were mixed

A useful link http://www.copper.org/applications/e...df/rooftop.pdf
Click to expand...

An example of where the actual temperature in the conductor location is more important then the measured temp at some other point even though both points are outdoors and in same geographical area. It can be 145 degrees on the roof and at the same time on same building it may only be 90 -95 degrees on a wall on the shaded side of the building. An underground conductor associated with same building may only be in a 65 degree ambient.
 
kwired said:
An example of where the actual temperature in the conductor location is more important then the measured temp at some other point even though both points are outdoors and in same geographical area. It can be 145 degrees on the roof and at the same time on same building it may only be 90 -95 degrees on a wall on the shaded side of the building. An underground conductor associated with same building may only be in a 65 degree ambient.
Click to expand...

There has to be a starting point in order to make proper adjustments -- Ambient temps ave are estimated in a ave. zone area. Certainly inches above the sidewalk compared to 4' above have different readings try to add wind to the formula and we be discussing all day long. Maybe an add of a chart of ambient temps per location to the NEC would be helpful when they require adjustment as such. There is no perfect answer.
 
mwm1752 said:
There has to be a starting point in order to make proper adjustments -- Ambient temps ave are estimated in a ave. zone area. Certainly inches above the sidewalk compared to 4' above have different readings try to add wind to the formula and we be discussing all day long. Maybe an add of a chart of ambient temps per location to the NEC would be helpful when they require adjustment as such. There is no perfect answer.
Click to expand...

Don't give any ideas to the CMP's or this will add 20+ pages of charts to the NEC.

I remember when chapter 9 was simple, one raceway fill chart for all raceways - how did we ever get by with that concept then in about 1996 they add a separate chart for each and every raceway type as well as the unnecessary Annex C and made a significant change in number of pages just with those two items alone.
 
Leo1 said:
1. What is a reliable, creditable source for determining ambient air temperature for a project. When I Google average temperatures for a give city dozens of sources come up? Is one more acceptable than the other?

2. If raceways are located in a facility that is temperature controlled between 68-72 degrees F, then can that average temperature be used for conductor selection or must the average outside ambient air temperature be used?

Thank you.
Click to expand...
If you are under '14 you can use XHHW-2 and ignore the whole silly, stupid temperature thing.
 
Last edited by a moderator:
kwired said:
Don't give any ideas to the CMP's or this will add 20+ pages of charts to the NEC.

I remember when chapter 9 was simple, one raceway fill chart for all raceways - how did we ever get by with that concept then in about 1996 they add a separate chart for each and every raceway type as well as the unnecessary Annex C and made a significant change in number of pages just with those two items alone.
Click to expand...
You didn't see those NASA pics of buildings bursting into flames like the Hindenburg...... good thing someone got them in front of the CMP's and was able to explain how bad things were getting.

I pulled my kids out of school since I knew the the RTU's had not been updated since the '90's at least.
 
Status
Not open for further replies.
Top