Service Conductors Above Roofs

[zcanyonboltz]

230.24 (A) Ex 2 says if the roof has a slope of 4" in 12" or greater a reduction from the 8' clearance requirement to 3' shall be permitted.
My question is what is greater than 4" in 12"?, is 5" in 12" would this be greater?, what would a flat roof be greater or less than 4" in 12"? I understand the pitch of the roof the wording greater is what is getting me. Thanks

Also can anyone explain 230.24 (A) Ex 3 this says if the conductors clearance can be reduced to 18" if going thru a through the roof raceway and not more 6' of conductors pass above the roof and 4 feet horizontally. What does horizontally refer to? Thanks

 

[iwire]

5" in 12" is greater pitch than 4" in 12"

0" in 12" would be flat.

 

[zcanyonboltz]

5" in 12" is greater pitch than 4" in 12"

0" in 12" would be flat.

Thanks a lot so a flat roof is less than 4" in 12" so 8' clearance is required.

 

[Dennis Alwon]

Thanks a lot so a flat roof is less than 4" in 12" so 8' clearance is required.

correct.

 

[Dennis Alwon]

just for reference a 12/12 pitch is 45 degrees

 

[iwire]

just for reference a 12/12 pitch is 45 degrees

:thumbsup:

Easy way to visualize it.

 

[ActionDave]

just for reference a 12/12 pitch is 45 degrees

Old timers call that a full pitch.

 

[kwired]

230.24 (A) Ex 2 says if the roof has a slope of 4" in 12" or greater a reduction from the 8' clearance requirement to 3' shall be permitted.
My question is what is greater than 4" in 12"?, is 5" in 12" would this be greater?, what would a flat roof be greater or less than 4" in 12"? I understand the pitch of the roof the wording greater is what is getting me. Thanks

Also can anyone explain 230.24 (A) Ex 3 this says if the conductors clearance can be reduced to 18" if going thru a through the roof raceway and not more 6' of conductors pass above the roof and 4 feet horizontally. What does horizontally refer to? Thanks

Greater pitch will result in a steeper angle from "horizontal" or "level". A 4" in 12" pitch gives you about an 18 degree angle from "horizontal" roof surface.

The second question in your OP: In many thru the roof applications you usually are only passing over a limited amount of roof because the portion below the roof is usually still on exterior of the building. They are saying you can not reduce the clearance to 18 inches permitted by that exception if the roof "overhang" is more then 4 feet, or because of the angle of the overhead conductors in relation to the roof you exceed more then 4 feet over the roof. (over head drop doesn't need to be exactly perpendicular to the roof, but needs to still head away from the structure and not parallel to the roof)

The 6 foot mentioned allows you to have six feet of conductor over the roof - but you are still limited to 4 foot horizontal dimension.

Note the 4/6 foot part only applies where it is permitted to reduce clearance to 18 inches above the roof.

 

[Dennis Alwon]

To add to kwired post-- the pitch is a function of the Tangent of an angle. Thus a 45° can be written as 12/12 = 1. The tan of 45° = 1

4/12= .33 so using the tangent table Tan(18°) =~ .33
6/12= .5 Tan(27°) =~ .5

Here is a Tangent Table
https://www.grc.nasa.gov/www/k-12/airplane/tabltan.html

 

[david luchini]

To add to kwired post-- the pitch is a function of the Tangent of an angle. Thus a 45° can be written as 12/12 = 1. The tan of 45° = 1

4/12= .33 so using the tangent table Tan(18°) =~ .33
6/12= .5 Tan(27°) =~ .5

Here is a Tangent Table
https://www.grc.nasa.gov/www/k-12/airplane/tabltan.html

I was told there would be no math :lol:

 

[mgookin]

I was told there would be no math :lol:

Then try this on for size.

All roofs are flat roofs regardless of slope (domes excepted). Those roofs which appear to be horizontal are low slope roofs usually 1/4" per foot.

Slope in roofing is expressed as rise/ run.
You go up, then over.
The run is always expressed as 12 because we use a 12 based counting system in construction in America.
Increase the top number and you rise more per the same amount of run.

 

[zcanyonboltz]

Thanks for the replies I appreciate the info and time!