Effect of Rooftop Exposure (in Direct Sunlight) On Conduit Ambient Temperatures Connected Home Council October 27, 2011 Presented by David Brender 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’s Ambient 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 © 2011 CDA Inc.

SUNDAY JULY 16, 2006 © 2011 CDA Inc.

NEC Covers Ambient Temperature Correction NEC 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. © 2011 CDA Inc.

Table © 2011 CDA Inc.

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 © 2011 CDA Inc.

In 2002, CDA Launched: Experiments to determine the extent of heating in copper wires in areas exposed to solar radiation… E levated A mbient T emperature S tudy © 2011 CDA Inc.

Residential and Commercial Buildings © 2011 CDA Inc.

Rooftops and exterior walls © 2011 CDA Inc.

May 20, :009:0010:0011:0012:00 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 Temperature Temperatures of 12 AWG Wires in EMT Compared 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 roof 5/8 inch 1-1/2 inch 3.5 inch 6 inch 12 inch 36 inch Roof Colors Black mineral rolled roof surface White mineral rolled roof surface White elastomeric paint roof surface Unloaded Range of: Outdoor temperatures Solar radiation intensities Solar Research © 2011 CDA Inc.

Black mineral rolled roof surface White mineral rolled roof surface White elastomeric paint roof surface 2004 © 2011 CDA Inc.

On Roof Strut (5/8”) 3.5 inch12-inch1.5 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 F F F Roof Temperature 9/28/04 13:15 Outdoor Temp = 92 F © 2011 CDA Inc.

Temperature Differential vs. Outside Ambient (92F) On Deck 38 F 3.5” above 19.4 F 6” above 16.6 F 36” above 12.7 F Roof 68 F © 2011 CDA Inc.

Recommended Ambient Temperature Adjustments June, July and August averaged White and dark roofs averaged ASHRAE 2% design temperatures © 2011 CDA Inc.

Distance Above Roof ºCºF On roof, up to and including 1.6 cm. above roof3360 Above ½ inch, up to and including 9 cm. above roof2240 Above 3-½ inches, up to and including 30 cm. above roof1730 Above 12 inches, up to and including 91 cm. above roof 1425 Temperature Table 6. Recommended Adjustments (Additions) to Outdoor Temperatures to Determine Ambient Temperatures Inside Conduits Table (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” EMT Type PVC was chosen to represent nonmetallic conduits and raceways in ¾, 1 ½, 4” sizes Metal 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 © 2011 CDA Inc.

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. © 2011 CDA Inc.

Results © 2011 CDA Inc.

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 (c) still applies © 2008 CDA Inc. © 2011 CDA Inc.

Tools Web: © 2011 CDA Inc.

Contact Info: © 2008 CDA Inc. © 2011 CDA Inc.