Conduits Exposed to Sun Light
- Thread starter faresos
- Start date
Deltaforce
Senior Member
- Location
- India
- Occupation
- Electrical Engineer
Derate 3 conductors more than in conduit
brycenesbitt
Senior Member
- Location
- United States
Yes, but derate to what temperature? Metal in direct sunlight can get hot enough to fry eggs. What's the appropriate temperature?
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Which seemingly no one understands.
This is another poorly written code section. Can't we just get a table that states what the derating is based on temperature at a given location?
ptonsparky
Tom
- Occupation
- EC - retired
So when it's cooler we can allow more current.
35 degrees in the morning but conduit is in 95 degree sunshine by 2 PM.
35 degrees in the morning but conduit is in 95 degree sunshine by 2 PM.
does painting the conduit with solar reflective white paint helps a lot with reducing the heat inside the conduits? Other option might be the use of cable tray with cover on a pipe rack (20ft above ground), might be an option as well. Is there specific recommended cable tray to be used with this option? it's about 50ft run
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I don't think that code actually specifies the temperature you need to consider for the situation you describe. Code says you are required to derate for ambient temperature, but doesn't really tell you what temperature to use.
The conduit will be in pretty unobstructed air flow so that will help, but sun can heat stuff up quite a bit. You might consider a simple sunshade spaced a couple of inches above the conduit.
The conduit will be in pretty unobstructed air flow so that will help, but sun can heat stuff up quite a bit. You might consider a simple sunshade spaced a couple of inches above the conduit.
TwistLock
Senior Member
- Location
- California
- Occupation
- Electrician
Table 310.16 is based on 3 current-carrying conductors in a 78°F to 86°F ambient temperature.
| Ambient Temperature 69 to 770F | Ambient Temperature 78 to 860F (30°C) | Ambient Temperature 87 to 95°F |
| 90°C Table Ampacity Correction Factor = 104% (1.04) | 90°C Table Ampacity Correction Factor = 100% (1.00) | 90°C Table Ampacity Correction Factor = 96% (0.96) |
brycenesbitt
Senior Member
- Location
- United States
Shade works really really well. A little sun hat made of sheet metal works awesome.
Conduit being galvanized is hard to paint in a way that will work reliably over the long term.... and you can be sure even if you paint it, nobody else ever will.
- Occupation
- Licensed Electrician
Not one of the things I worry about. There must be a million miles of conduit installed on rooftops pre-temp derating and it's standing the test of time.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
I don't think i have ever derated for temperature. "We" have this unspoken agreement that i wont increase the ampacity of my underground conductors dur to cool temps, and i wont decrease for high temps like in attics and such.
From 310.15(B)(2)
Informational Note:
The ASHRAE Handbook — Fundamentals is one source for the ambient temperatures in various locations.
ETA: The ASHRAE site is hard to navigate and find the information, at least for me it is.
However, Copper Development has the same info. Although it mentions roof top, but it does give you an idea what the average highest temperature is to use for your cals.
copper.org
Informational Note:
The ASHRAE Handbook — Fundamentals is one source for the ambient temperatures in various locations.
ETA: The ASHRAE site is hard to navigate and find the information, at least for me it is.
However, Copper Development has the same info. Although it mentions roof top, but it does give you an idea what the average highest temperature is to use for your cals.
Building Wire - Outdoor and Rooftop Temperatures for Selected U.S and Canadian Locations
The National Electrical Code Section 310.15(A)(3), and good design practice, requires adjustment of ampacity of wires and cables installed in ambient temperature conditions that are higher than those upon which the listed ampacities of Table 310.15(B)(16) are based.
copper.org
- Occupation
- Licensed Electrician
It was the copper development gang that got this garbage in the code. Imagine that. A code rule that requires larger copper conductors.
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
When I was a kid we use to etch galvanized with vinager before we painted. The household stuff helped but if you wanted it to last you needed something high concentration like this
There are also self etching primers , but the whole thing is a lot more work, and yeah it's never going to be done again