Source for Temperature Information

czars

Czars
Location
West Melbourne, FL
Occupation
Florida Certified Electrical Contractor
Does anyone know where we can obtain official ambient and attic temperature information which can be used to compute the derating of NM and SE cables in attics with insulation?
 

mgookin

Senior Member
Location
Fort Myers, FL
Does anyone know where we can obtain official ambient and attic temperature information which can be used to compute the derating of NM and SE cables in attics with insulation?
The ambient is easy but every attic is going to have different readings. Just the angle of the orientation of the building will change it. Now change the roof covering, underlayment, color, insulation, geography, etc.

Do you just want to know if you're over 65C? Or 90C?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
The ambient is easy but every attic is going to have different readings. Just the angle of the orientation of the building will change it. Now change the roof covering, underlayment, color, insulation, geography, etc.

Do you just want to know if you're over 65C? Or 90C?
Please explain how ambient temp. is easy. Ambient is not average
 

mgookin

Senior Member
Location
Fort Myers, FL
Please explain how ambient temp. is easy. Ambient is not average
Ambient temperature? The national weather service and pretty much every tv station have datalogging sensors (thermometers) all over the place. There's pretty much unlimited data out there.

OP speaks of temperature of "attics" in the plural implying he's looking for a formula or similar; at least that's how I interpret the request. Maybe I'm reading it wrong.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
That is rooftop and raceways with direct sunlight

Ambient temperature? The national weather service and pretty much every tv station have datalogging sensors (thermometers) all over the place. There's pretty much unlimited data out there.

OP speaks of temperature of "attics" in the plural implying he's looking for a formula or similar; at least that's how I interpret the request. Maybe I'm reading it wrong.
There is no way you can have data on ambient temp except at the moment you take the temp. Ambient temp is the temp at any moment so how do you calculate the derating-- the temp upon install, the highest temp (then it should say highest ambient temp), etc.

The wording IMO need help to clarify what the intent may be. I have never seen nm in an attic that had issues because of ambient temp. It get 130? in the attic around here at times
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It also depends where in the attic the insulation is installed in relation to the cable. Under the insulation there would be no need for any ambient temperature adjustment.
 

Smart $

Esteemed Member
Location
Ohio
It also depends where in the attic the insulation is installed in relation to the cable. Under the insulation there would be no need for any ambient temperature adjustment.
However, where two NM cables are not spaced and in contact with the insulation, derating for number of ccc's under 310.15(B)(3)(a) applies. [334.80]
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It also depends where in the attic the insulation is installed in relation to the cable. Under the insulation there would be no need for any ambient temperature adjustment.

However, where two NM cables are not spaced and in contact with the insulation, derating for number of ccc's under 310.15(B)(3)(a) applies. [334.80]
True, but the OP made no mention about multiple cables, also that would apply to walls and floors with insulation not only attics.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
The ACCA Manual J has a table of "design temperatures" to use for heating and cooling outside temperatures. Seems like a decent low ambient and high ambient to use, but in reality the actual conditions will be worse on some days.
 

Smart $

Esteemed Member
Location
Ohio
The ACCA Manual J has a table of "design temperatures" to use for heating and cooling outside temperatures. Seems like a decent low ambient and high ambient to use, but in reality the actual conditions will be worse on some days.
Generally speaking, confined space temperatures, such as in an attic, are assumed to typically exceed outside ambient temperatures on warm days. However, several ventilation techniques can drastically affect the validity of that assumption. :happyyes:
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
The wording IMO need help to clarify what the intent may be. I have never seen nm in an attic that had issues because of ambient temp. It get 130? in the attic around here at times
The wording needs to be thrown out. It is entirely stupid. How many wires are out there that were run prior to all these temp adjustments being required? I drive around my town a lot and take at least one road trip a year; don't see many attics or roof tops with smouldering conductors.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Generally speaking, confined space temperatures, such as in an attic, are assumed to typically exceed outside ambient temperatures on warm days. However, several ventilation techniques can drastically affect the validity of that assumption. :happyyes:
I agree, that's why I only listed ambient. I don't have a solution for attics or rooftops, as they can be all over the map and can even change when someone puts on a new roof.
 

iwire

Moderator
Staff member
Location
Massachusetts
The wording needs to be thrown out. It is entirely stupid. How many wires are out there that were run prior to all these temp adjustments being required? I drive around my town a lot and take at least one road trip a year; don't see many attics or roof tops with smouldering conductors.
And I think electricians should learn to deal with change and make money doing so.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
Generally speaking, confined space temperatures, such as in an attic, are assumed to typically exceed outside ambient temperatures on warm days. However, several ventilation techniques can drastically affect the validity of that assumption. :happyyes:
Well said, and more understandable than many code sections.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
..my opinion on the temp correction factors. They are stooooooopid.
Drive past a major amusement park during a sustained ambient over 95?F, and look up to see all the stranded people in the sky, waiting for the circuit breakers to cool, or the Fire Department to extract them.

The NEC derating section never reminds the reader that power factors, with higher current for inductive motor loads, are a separate adjustment.

The NEC motor-load calculations never remind the reader that ambients or conductor bundling will be a separate adjustment if needed.

The failure of licensed builders to get both of these adjustments right is demonstrated every summer.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Drive past a major amusement park during a sustained ambient over 95?F, and look up to see all the stranded people in the sky, waiting for the circuit breakers to cool, or the Fire Department to extract them.

The NEC derating section never reminds the reader that power factors, with higher current for inductive motor loads, are a separate adjustment.

The NEC motor-load calculations never remind the reader that ambients or conductor bundling will be a separate adjustment if needed.

The failure of licensed builders to get both of these adjustments right is demonstrated every summer.
I don't work in amusement parks. I work on buildings. I think the NEC did a fine job of sizing everything quite well up to '05. Then they went a blew up art. 310.

If there are people constantly stranded on rides during the summer I would think ticket sales would go down and business would get involved, or complaints would go up and city or county government would get involved. I would also hope that someone involved on the design end would have enough pride and ability to get the job done right.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
..the design end
You would think city Permits for such structures with large-motor loads would require electrical engineering, and that any changes would be supervised under engineering supervision. Therefore engineers could be blamed for overheated conductors.

I believe its more likely changes during the building process escalate difficulty with engineers, who lose credibility with owners, resulting in the builders defaulting to their best application of NEC-ampacity tables, historically miss applied where motors must be added to derating schemes.

I also believe, unless you are an eye witness, or helped remodel electrically-driven equipment that resulted in death, non-disclosure clauses --used for years in injury & casualty settlements-- minimize informing the public domain, who blissfully engage in further risk.
 
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