effect of rooftop exposure (in direct sunlight) on conduit ambient temperatures connected home...

Effect of Rooftop ExposureEffect of Rooftop Exposure(in Direct Sunlight)(in Direct Sunlight)

On Conduit Ambient On Conduit Ambient TemperaturesTemperatures

Connected Home CouncilConnected Home Council

October 27, 2011October 27, 2011

Presented byPresented by

David BrenderDavid Brender

Copper Development Association Inc.Copper Development Association Inc.

© 2011 CDA Inc.

Effect of Rooftop Exposure On Conduit Ambient Temperatures

Correct application of ambient temperature correction in NEC

Conductors in insulation

Original goal: How does sunlight affect electrical conductors in conduits exposed to direct sunlight?

© 2011 CDA Inc.

When electrical conductors operate in high ambient temperature environments…

Copper Development Association’sCopper Development Association’sAmbient Temperature Research ProgramAmbient Temperature Research Program

Why Las Vegas?

In Summer, Las Vegas has similar solar radiation to other Southwestern and Western states.

In Spring and Fall, Las Vegas solar radiation matches Summer solar intensities in most of the U.S.

Las Vegas has high number of ‘clear days’ to conduct research

Solar Radiation

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SUNDAY JULY 16, 2006

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NEC Covers Ambient Temperature Correction

NEC 310.10

Temperature Limitation of Conductors. No conductor shall be used in such a manner that its operating temperature exceeds that designated for the type of insulated conductor involved.

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© 2011 CDA Inc.

Table 310.16

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Temperature correction is required,but usually ignored

Data did not exist to allow:

Engineers and contractors to choose an appropriate temperature for correction.

Inspectors to effectively enforce 310.10 .

© 2011 CDA Inc.

Experiments to determine the extent of heating in copper wires in areas exposed to solar radiation…

ElevatedAmbientTemperatureStudy

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Residential and Commercial Buildings

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Rooftops and exterior walls

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May 20, 2003

8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00

AM Time of Day PM

70 F

90 F

110 F

130 F

150 F

170 F

Tem

pera

ture

Temperatures of 12 AWG Wires in EMTCompared to Outdoor Temperature

Tarred to roof

On Surface

On Struts

Outdoor Temp.

Rooftop temps considerably higher than outdoor temps…

© 2011 CDA Inc.

Types of Conduit/Cable

EMT, RNC, MC

Distance above roof On roof5/8 inch1-1/2 inch3.5 inch6 inch12 inch36 inch

Roof Colors Black mineral rolled roof surface White mineral rolled roof surface White elastomeric paint roof surface

UnloadedRange of:

Outdoor temperatures Solar radiation intensities

Solar Research

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Black mineral rolled Black mineral rolled roof surfaceroof surface

White mineral rolled White mineral rolled roof surfaceroof surface

White elastomeric White elastomeric paint roof surfacepaint roof surface

20042004

© 2011 CDA Inc.

On Roof

Strut (5/8”)

3.5 inch12-inch 1.5 inch6-inch36-inch

2004

(85 Conduits/Cables)© 2011 CDA Inc.

Effect of Rooftop Exposure On Conduit Ambient Temperatures

Research Findings

© 2011 CDA Inc.

119.3 F119.3 F

160.5 F160.5 F

125.7 F125.7 F

Roof Temperature 9/28/04 13:15Roof Temperature 9/28/04 13:15

Outdoor Temp = 92 F© 2011 CDA Inc.

Temperature Differential vs. Outside Ambient (92F)

On DeckOn Deck38 F38 F

3.5” above3.5” above19.4 F19.4 F

6” above6” above16.6 F16.6 F

36” above36” above12.7 F12.7 F

RoofRoof68 F68 F

© 2011 CDA Inc.

Recommended Ambient Temperature Adjustments

June, July and August averagedWhite and dark roofs averagedASHRAE 2% design temperatures

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Distance Above RoofºC ºF

On roof, up to and including 1.6 cm. above roof 33 60Above ½ inch, up to and including 9 cm. above roof 22 40Above 3-½ inches, up to and including 30 cm. above roof 17 30

Above 12 inches, up to and including 91 cm. above roof 14 25

Temperature

Table 6. Recommended Adjustments (Additions) to Outdoor Temperatures to Determine Ambient Temperatures Inside Conduits

Table 310.15(B)(2)(c)

Mandatory in 2008 and 2011 NEC

© 2011 CDA Inc.

UL – MC cable

Studied all types of raceway and cables allowed on rooftop

Type MC cable was chosen to represent metal clad and metal sheathed cables and conduits (e.g. Type MC, MI, LFMC, etc.)

Sizes 12 AWG, 1/0 AWG, and 500 kcmil were chosen to represent cables of the smaller, medium, and larger sizes

© 2011 CDA Inc.

UL - Cables

Type SE and TC cable was also chosen in the 1/0 AWG size to represent jacketed cables (e.g. Type SE,TC, MV, UF, etc.)

© 2011 CDA Inc.

All conduit types

Type RMC and EMT were chosen to represent circular metal raceways in ½, 1 ½, 4” RMC,

¾, 1 ½, 4” EMTType PVC was chosen to represent nonmetallic

conduits and raceways in ¾, 1 ½, 4” sizesMetal raceway was chosen in the 4x4 inch and 8x8

inch sizes to represent smaller and larger raceways in general

© 2011 CDA Inc.

UL Fact Finding August 2011

© 2011 CDA Inc.

UL Fact Finding August 2011

© 2011 CDA Inc.

Solar Irradiance

Procedure

For each test sample, the rise above outdoor ambient temperature for the three thermocouple

temperatures were averaged for each five-minute increment to record the temperature rise above outdoor ambient

For analysis of results purposes, 10 days were chosen during this time period where solar irradiance exceeded 1000 W/m2 for a prolonged period of time

3 thermocouple readings were averaged

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Procedure

For each of the ten chosen days, the maximum, minimum, 90th, 75th, and 50th percentile temperatures were calculated for each test sample at each elevation for the period of time that day when the solar irradiance was greater than or equal to 1000 W/m2.

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Results

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Results

© 2011 CDA Inc.

Results

“For all wiring systems mounted directly on the roof, the maximum temperature rise above outdoor ambient with a 95% confidence interval would statistically be 62.2° F. For all wiring systems mounted at a distance above the roof (1/2 inch and greater) the maximum temperature rise above outdoor ambient with a 95% confidence interval would statistically be 51.4° F.”

© 2011 CDA Inc.

Remember:

Temperature derating is a “CORRECTION FACTOR”Correction factors AND adjustment factors BOTH apply

More than 3 current-carrying conductors in a conduit requires further multiplier

Section 110.14 (c) still applies

© 2008 CDA Inc.© 2011 CDA Inc.

Tools

Web: http://www.copper.org

© 2011 CDA Inc.

Contact Info:

dbrender@cda.copper.org

© 2008 CDA Inc.© 2011 CDA Inc.