Average Ambient Temp

[schole]

Where can I find a reference to average ambient air temperature for New Hampshire. Need to calculate roof top conductors in GRC.
Need to apply 310.15 (B) factor

 

[infinity]

Should be here: www.ashrae.org

 

[iwire]

Where can I find a reference to average ambient air temperature for New Hampshire.

Where does the NEC say to use the average temp?

My personal feeling is you must use the highest temp the conductors will operate in.


Don't forget that under the 2008 NEC there is also a required 'adder' to the ambient temp for conduits on roofs.

 

[infinity]

Look here:

Table 310.15(B)(2)(c) Ambient Temperature Adjustment for Conduits Exposed to Sunlight On or Above Rooftops
Temperature Adder
Distance Above Roof to Bottom of Conduit ?C ?F
0 ? 13 mm (? in.) 33 60
Above 13 mm (? in.) ? 90 mm (3? in.) 22 40
Above 90 mm (3? in.) ? 300 mm (12 in.) 17 30
Above 300 mm (12 in.) ? 900 mm (36 in.) 14 25
FPN to Table 310.15(B)(2)(c): The temperature adders in Table 310.15(B)(2)(c) are based on the results of averaging the ambient temperatures.

 

[iwire]

Rob, IMO that FPN has nothing to do with picking the temp to use with Table 310.16. That FPN is only telling us how they arrived at the temps in 310.15(B)(2)(c).

The average ambient temp in New Hampshire is likely 40 to 50 F so I guess we can 'uprate' the conductors.

This site shows the average, averaged July temp in NH as 66F. The 'averaged' high temp in July as 80F


http://www.nhliving.com/weather/temperatures.shtml


So if the NEC allows the use of an 'average temp' what average temp do we use? Average yearly daytime temp? Average yearly temp overall? The high average for July?

See what I am getting at, it is not so simple to pick the average temp and it will not tell us much anyway.

 

[infinity]

Here's the NEC FPN which sends you to the link that I posted:

(c) Conduits Exposed to Sunlight on Rooftops.Where conductors or cables are installed in conduits exposed to direct sunlight on or above rooftops, the adjustments shown in Table 310.15(B)(2)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.16 and Table 310.18.
FPN: One source for the average ambient temperatures in various locations is the ASHRAE Handbook ? Fundamentals.

 

[iwire]

Here's the NEC FPN which sends you to the link that I posted:

OK, I still ask Which average temp?


Not trying to be a PITA here but I see nothing in the actual code or FPNs that specifies which average temp we can use. :-?

If I can use the year long average temp I can save a ton of money.

 

[Pierre C Belarge]

The first question I would ask is:
What is "Ambient Temperature?"

Ambient temperature is not the air temperature, as we would see on the news or websites.


2008 NEC, 310.15(B)(2)(c)

"...shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 310.15"


It is difficult to take the average state temperature, as the differences of temperature in one state from north to south of the state may be considerable.
(I am guessing the average is state wide)

Since this Section of the NEC is new, I believe we will see some modifications to the wording.

P.S.
The temperature outside may be 90F, but the rooftop could be 130F.

 

[iwire]

Pierre I am missing your point

 

[M. D.]

This definition is from NFPA 79

3.5 ambient temperature: The temperature of the air or other
medium where the equipment is to be used. [IEV 826-01-04]
NOTE?Ambient air temperature as applied to an enclosure or
housing is the average temperature of the surrounding air that
comes in contact with the enclosure or housing. Ambient air
temperature as applied to a component or device within the
enclosure is the average temperature of the surrounding air that
comes in contact with the component.

Does the NEC perscribe the use of the highest ambient tempature,...

poorly written .

 

[Dennis Alwon]

Pierre I am missing your point

I think Pierre is saying there is no way to determine ambient temp based on a state wide temp. The ambient temp in an attic is very different then the outside temp and as you know is very different in the Berkshires then it is at the beach. Thus if I am in Boston what temp do I use?

I don't know of anyone who deals with ambient temp in attics for residential work. It never has been a problem here. I would guess if the wire was in 135 degrees year round then perhaps there would be an issue but as Bob said this has not been defined.

 

[M. D.]

......results of averaging the ambient temperatures.

What ambient temps??? are they talking about

....adjustments shown in Table 310.15(B)(2)(c) shall be added to the outdoor temperature ...

So is outdoor temperature now the same as the ambient temp where the raceways are ?? If I install this raceway in the fall and the outdoor temp is 45 degrees ,.. now what.

 

[markstg]

You guys are killing me.......Are ya'll arguing over what is what is ambiant temperature. Ambient temperature is what is reported on the nightly weather report. What the code is recognizing is that in certain locations such as roofs, the temperature gets Hotter than the ambiant. And the temperature at the time at which you install the cables is not the ambiant temperature to correct cables too. It is the highest temperature the installation will see over a typical year. At my site in South Louisiana, we correct to the 95 degree F factor.

 

[iwire]

And the temperature at the time at which you install the cables is not the ambient temperature to correct cables too. It is the highest temperature the installation will see over a typical year.

I agree with your thoughts here and I think it is the prudent way to go, but there is nothing in the NEC that makes it that clear.

For what it's worth I am willing to bet your area has days hotter then 95F so you are not even following your own advice. :grin:

 

[markstg]

I agree with your thoughts here and I think it is the prudent way to go, but there is nothing in the NEC that makes it that clear.

For what it's worth I am willing to bet your area has days hotter then 95F so you are not even following your own advice. :grin:

Sorry, the 95 deg F is the average high termperature for the region.

 

[Dennis Alwon]

Ambient means encircling or surrounding. Surrounding temp is not average nor is it the high temp. If the high temp in a region is 106 degrees but only gets that hot once or twice a year for a few hours then do we use that temp. I don't have the answer but I do believe someone needs to define it better.

 

[M. D.]

ambient : existing or present on all sides.

 

[Twoskinsoneman]

My personal feeling is you must use the highest temp the conductors will operate in..

I disagree and think this is silly. Your basically saying you have to take the record high ever (adding 10 degrees for global warming of course :grin and apply that temp....

You basically have to assume that the conductor will be loaded to it's limit at the same time it is exposed to a record high...

Code doesn't say either way but I believe you use the average....

 

[Smart $]

Where can I find a reference to average ambient air temperature for New Hampshire. Need to calculate roof top conductors in GRC.
Need to apply 310.15 (B) factor

Try this website: http://www.worldclimate.com/

You can probably hone in on your county, city, or vicinity in metropolitan areas. It even has the year average of 24-hour temperatures, which seems to be what the code is saying to use.

...and it is FREE

 

[iwire]

I disagree and think this is silly. Your basically saying you have to take the record high ever

If your sizing a conductor supplying a load that 363 days a year draws 30 amps but 1 day a year will draw 50 amps do you get to ignore that 50 because it is just one day a year?

Either way it is all about the heat the insulation is subjected to.