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Quarterly News for California Building Departments

Issue #53, Jan - Mar 2017

Photovoltaic Systems

The How and Why of Derating Electric Conductors in Conduit on Rooftops

rooftop conduit

Rooftop conduit photo by Willdan

By Dan Chudy, Ph.D., CBO, LEED AP, CASp
Principal Project Manager – Willdan Engineering

With the popularity of solar photovoltaic systems on rooftops, there has been a proliferation of electrical conduit on rooftops. One of the basic principles of electricity is that heat has a negative effect on the current carrying capacity of wire conductors. The NEC has two requirements for derating the ampacity of wire conductors based on heat; (1) ambient temperature of the environment around the wire, and (2) the number of wires inside the conduit.

The requirement to derate conductors installed in conduit on rooftops was originally introduced in the 2008 edition of the National Electrical Code in Section 310.15(B)(2)(c). At that time, the wire manufacturing industry had done extensive testing to determine the temperature increases inside conduits placed on various roof types and placed at various heights above the roof. Their findings were that the rooftop temperature increases were substantial and that conduits on lighter roofs actually developed hotter temperatures inside the conduit. This is because light-colored roofs (i.e., Cool Roofs) reflect more heat away from the building, and as a result, into the rooftop conduits above. 

The purpose of this article is to explain how to derate conductors in conduit on rooftops.  

DERATING FOR AMBIENT TEMPERATURE

The 2016 California Electrical Code Table 310-15(B)(16) uses 30°C (86°F) as the baseline ambient temperature to determine the baseline ampacity of specific conductors. At the bottom of this table, the single asterisk footnote (*) refers you to 310.15(B)(2) which, in turn refers you to Table 310.15(B)(2)(a) (see California Electrical Code page 70-158). This table gives you the ampacity correction factor where the ambient temperature is other than 30°C (86°F).

So where do you find what the ambient temperatureis for your specific city or county? The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) deals with outdoor temperatures in order to design heating and air conditioning systems. ASHRAE has developed a weather data base, including outdoor design temperatures, for 753 locations in the United States, and 4,422 worldwide. If you have the ASHRAE documents, or a paid subscription to the on-line versions, you can simply look up the required data. If you don’t, you can access some of that ambient temperature data (free of charge) from a document created by the Copper Development Association.

As an example: What is the ampacity of a #10 AWG, copper, type THHW-90°C conductor in Riverside, California? 

The Copper Development Association document identified the ambient temperature in Riverside as 99°F. Therefore, the answer is found by taking the ampacity from Table 310-15(B)(16) and multiplying it by the appropriate correction factor for 99°F (which is found in Table 310.15(B)(2)(a).  

40 amps X 0.91 derating factor = 36.4 amperes. 

But wait!  This is not the only derating factor that you need to apply when the conductors are in a conduit on a rooftop.  You also need to apply an additional temperature adjustment factor.

ADDITIONAL TEMPERATURE ADJUSTMENT FOR ROOFTOP CONDUITS EXPOSED TO SUNLIGHT

The 2016 California Electrical Code Table 310-15(B)(3)(c) (see NEC page 70-160) applies an additional temperature adjustment (called the “Temperature Adder”) for rooftop conduit exposed to direct sunlight.  Depending on the distance the conduit is above the roof (between 0” to 36”) the additional temperature which is added to the ambient temperature can be between 60°F to 25°F.

As an example: What would be the adjusted ambient temperature used for the conductor derating calculation if the ambient temperature was 99°F and the rooftop conduit was 2” above the roof and exposed to direct sunlight? 

The adjusted ambient temperature would be 99°F Ambient Temperature + 40°F Temperature Adder = 139°F. 

Therefore the derating calculation for this example would be:

40 amps X 0.71 derating factor from Table 310.15(B)(2)(a) for 139°F = 28.4 amperes

DERATING FOR NUMBER OF CONDUCTORS

2016 California Electrical Code Section 310.15(B)(3) contains the requirement for derating ampacity because of adjacent current-carrying conductors.  The reason is that adjacent load-carrying conductors not only generate heat due to current flow, but the presence of multiple conductors within a single conduit impedes heat dissipation from the conductor itself.  This section states that when the number of conductors in a conduit exceeds 3, the ampacities are to be reduced by the appropriate percentage identified in Table 310.15(B)(3)(a) (see California Electrical Code page 70-160).

As an example: What is the adjusted ampacity of (6) current carrying #10 AWG, copper, type THHW-90°C conductors installed in one conduit?

From Table 310-15(B)(16) the baseline ampacity is 40 amperes. From Table 310.15(B)(3)(a), the derating factor for (6) current carrying conductors is 80 percent (or a factor of 0.8). Therefore:

40 amps X 0.8 derating factor from Table 310.15(B)(3)(a) = 32 amperes per conductor

DERATING FOR ALL FACTORS - AMBIENT TEMPERATURE, ROOFTOP TEMPERATURE ADDER, AND NUMBER OF CONDUCTORS

When derating for all three conditions is necessary, then all calculations must be made. For simplification purposes, let’s assume the same conditions as above: Wire size and number of conductors is (6) #10 AWG conductors on a rooftop conduit in Riverside, California where the ambient temperature is 99°F and the conduit is 2” above the roof and exposed to direct sunlight (with a Temperature adder of 40°F).  Below is the derating calculation:

40 amps X 0.71 derating factor from Table 310.15(B)(2)(a) for 139°F X 0.8 derating factor from Table 310.15(B)(3)(a) = 22.72 amps

CSUMB Chapman
CSU Monterey Bay Dorms
CSU Sacto Parking
CSU Sacto Hall
UC Irvine Housing
UC Irvine dorms

Pictured: A few buildings plan-checked or inspected by Willdan

Can You Help Me Find it in the Code?

I’ve been reviewing the 2016 California Codes and often I have difficulty finding a particular code reference that I thought was there. I suppose that’s what happens to a lot of us “Old Guys”. As the codes continue to change with new provisions being added and old ones being dropped (or moved), it is important that we keep our knowledge current. With as many code professionals that read the Willdan Letter, there is bound to be someone out there who has the answer to every question.  That’s why this portion of the Willdan Newsletter has been created: To solicit your help in answering some code-related questions.

QUESTION: If electrical receptacle outlets are installed in a non-habitable Patio Enclosure (fully weatherproof), are the receptacle outlets required to be GFCI protected? If so, what code section would you cite?

If you have an answer to the question posed in this section, please send it to: dchudy@willdan.com, and we will publish it in the next issue.

Focus on the Codes

A New Tool for Your Tool Box (Part 4 of a 4-part Series)

code books

By Dan Chudy, Ph.D., CBO, LEED AP, CASp
Principal Project Manager – Willdan Engineering

architectural house drawing

After a full 360 days of retirement, I decided to get back to work. I had spent 24 years as a Building Official and 6 years as a Building Inspector/Plans Examiner and came to the realization that I needed some brushing-up on the codes if I was going to get back into the inspection business. As a Building Inspector, back in the 1980’s, I had learned the value of having a certain inspection routine and the challenges of trying to memorize all of the codes. Those same challenges are experienced by Plans Examiners as they thumb through hundreds of pages of code to find that certain code section which is applicable to the scenario drawn on the plans. After dusting off my code books and beginning to study, I realized that there was a more logical way (at least for me) to organize and consolidate the most common residential code requirements by segregating them according to which room in the house they applied. The result was an abbreviated listing of hundreds of code provisions grouped according to the room or area in a dwelling to which they related.

The complete list is much too large to publish in a single newsletter article; therefore, this article will be continued in subsequent newsletters as we move through a typical home, from A (Attic) to U (Utility Room). The "Focus on the Codes" page presents a compilation of the published provisions.

Please understand that this effort is a work in progress and I make no claim that the list is all inclusive nor that it is without error. If any errors or omissions are found, please email me at so that the list can be improved.

Postscript: The code section references in this article are based on the 2013 California Codes.  In a future edition of this Newsletter, we anticipate publishing an updated version with code references based on the 2016 California Codes.

CODE PROVISIONS SEGREGATED ALPHABETICALLY BY SPECIFIC ROOMS IN DWELLINGS, continued from part 3

Click the + next to each title to view its description, or click the "Show All" button.

LAUNDRY AREA

  1. CRC R105.1 – Clothes dryers are exempt from permits
  2. CRC R306.4 – Hot and cold water required to washing machine outlets
  3. CRC R312.2.1 – When fall from window would be more that 72” to surface below, window sill to be 24” min. above floor OR, if less than 24” above floor, window opening shall not allow the passage of a 4” diameter sphere.
  1. NEC 210.11 (C) – At least (1) 20 amp branch circuit required for laundry receptacle outlet – no other outlets allowed on this circuit.
  2. NEC – 210.12 – Arc-fault circuit interrupter required for outlets in all rooms of house that are not protected by GFCI (Laundry room NOT specifically mentioned in code but could be considered to be covered under “and similar areas”).
  3. NEC 210.52(A) – General convenience receptacle outlet requirements (12’ spacing) NOT applicable in bathrooms (UNLESS you consider the “or similar room or area” to apply).
  4. CEC 210.52(F) - Provide at least one accessible receptacle outlet for the laundry room area.
  5. NEC 210.70 (A) – at least (1) wall switched light outlet required in every habitable room and bathroom and hallway, stairway, garage, exterior side of outdoor grade level entrances (garage vehicle doors are exempt)
  6. NEC 406.12 – Tamper resistant receptacle outlets for all non-locking 120V/15 & 20 amp outlets unless for dedicated appliance or luminaries or over 5.5’ above floor.
  1. CPC 507.4 – Drainage pan under water heater if: in attic, on floor/ceiling, floor/subfloor where damage results from leakage.  ¾” minimum drainage line from pan to approved location
  2. CPC 507.5 – Temperature & Pressure relief valve prohibited from discharging into drainage pan.
  3. CPC 804.1 – Clothes washer stand pipe limited to between 18” – 30” above trap.  Trap to be between 6” – 18” above floor.
  1. CMC 504.2 - Domestic kitchen downdraft grill-range ventilation ducts installed under a concrete slab floor may be of approved Schedule 40 PVC when certain conditions are met.
  2. CMC 504.3 – Clothes dryer ducts shall NOT be connected with screws
  3. CMC 504.3 – Clothes dryer ducts shall NOT extend through plenums or ducts
  4. CMC 504.3.1 - Ducts for dryer vents shall be a minimum of 4” in diameter.  The exhaust duct shall not exceed a total combined horizontal and vertical length of 14 feet, including two 90 degree elbows.  Two feet shall be deducted for each 90 degree elbow in excess of two.
  5. CMC Section 504.3.1 - Where a closet is designed for the installation of a clothes dryer, an opening of not less than 100 square inches for makeup air shall be provided in the door or by other approved means. 
  6. CMC 701.4.1 – Indoor combustion air for a clothes dryer in confined space is to be at least 50 cubic feet of area for every 1000 BTU/h of the name plate rating of the dryer OR combustion air must be provided to the space from other areas.
  7. CMC 902.2 – Fuel burning appliances shall not be installed in bedroom or bathroom unless room size is at least 50 cubic feet of area for every 1000 BTU/h of the name plate rating of the dryer OR combustion air must be provided to the space from other areas.
  8. CMC 905.3 – Clothes dryer to be provided with make-up air in accordance with manufacturer’s specifications.
  1. CEC Lighting Mandatory Measures (150.0(k)) – Garage, Laundry, and Utility Rooms to have high-efficacy light fixtures AND controlled by a vacancy sensor
  2. CEC Pipe Insulation Mandatory Measure (150.0(j)2)) – R4 (1”) pipe insulation required on all water pipes (hot and cold) ¾” or larger to point of use and all pipes (regardless of size) to kitchen faucet
  3. CEC 150.0(a) & 150.2(a) – ASHRAE 62.2 – Laundry rooms must be built with a duct to the outdoors, to be connected to the clothes dryer.  Warm moist air from clothes dryer is prohibited from being used in the home for heating purposes (some cold climates like this warm/moist air to be used in the home – but it is prohibited by the ASHRAE standards because of the dust in the exhaust air)

LIVING ROOM (see FRONT ROOM)

MUD ROOM (aka: UTILITY ROOM, MECHANICAL CLOSET)

  1. CRC R313.3.1.1 Exception 4 – Fire sprinklers not required in unheated mud rooms adjacent to an exterior door.
  2. CRC R305.1 – minimum ceiling height 7’-0”
  3. CRC R306.4 – hot and cold water required to washing machine outlets
  4. CRC R312.2.1 – When fall from window would be more that 72” to surface below, window sill to be 24” min. above floor OR, if less than 24” above floor, window opening shall not allow the passage of a 4” diameter sphere.
  1. NEC – 210.12 – Arc-fault circuit interrupter required for outlets in all rooms of house that are not protected by GFCI (with a few exceptions for dedicated circuits)
  2. NEC 210.70 (A) – at least (1) wall switched light outlet required in every habitable room and bathroom and hallway, stairway, garage, exterior side of outdoor grade level entrances (garage vehicle doors are exempt)
  3. NEC 406.12 – Tamper resistant receptacle outlets for all non-locking 120V/15 & 20 amp outlets unless for dedicated appliance or luminaries or over 5.5’ above floor.

Mechanical and Plumbing: See FAU and Water heater requirements

  1. CEC Lighting Mandatory Measures (150.0(k)) – Garage, Laundry, and Utility Rooms to have high-efficacy light fixtures AND controlled by a vacancy sensor

PATIO, PATIO ENCLOSURE, SUNROOM, PORCH

  1. CRC R303.1 Ex #3 – Natural ventilation from patio can be used in adjoining rooms (see R303.2 for limits).
  2. CRC R303.2 Exception – Opening for Light and ventilation from patio to be 20 Sq. Ft. min (openable) or 10% (openable) of floor area of room.
  3. CRC R303.8 Ex #1 – Required windows may open onto porch as long as ceiling is at least 7’ tall and longer side of porch is 65% open.
  4. CRC R303.8.1 - Required windows may open onto patio or sunroom as long as ceiling is at least 7’ tall and 40% min. of sunroom walls are open (or insect screening).
  5. CRC R312.2.1 – When fall from window would be more that 72” to surface below, window sill to be 24” min. above floor OR, if less than 24” above floor, window opening shall not allow the passage of a 4” diameter sphere.
  6. CRC R313.3.1.1 Exception 4 – Fire Sprinklers not required in open attached porches
  7. CRC R327.7.6 - The exposed underside of exterior porch ceilings in designated Fire Hazard Severity Zones shall be protected by specified noncombustible or ignition resistant materials. 
  8. CRC Appendix H – Patio Enclosures - AH103.1 – Longer wall plus one additional wall to be 65% open or glazed below 6’-8” (Glass, insect screen, translucent plastic are OK)
  9. CRC Appendix H – Patio Enclosures - AH103.2 – Bedroom windows – Patio covers over bedroom egress windows to be unenclosed.
  10. CRC Appendix H (AH103.1)– Patio enclosure glass (in enclosure walls) to be tempered per CRC R308
  1. NEC 210.8 – GFCI outlets required outdoors (some jurisdictions consider a Patio Enclosure to be similar to a Patio Cover and thereby require GFCI protected outlets in Patio Enclosures)
  2. NEC – 210.12 – Arc-fault circuit interrupter required for outlets in all rooms of house that are not protected by GFCI (with a few exceptions for dedicated circuits)
  3. NEC 210.52(E)(1) – at least (1) receptacle outlet required at front and (1) at rear of house
  4. NEC 210.52 (E)(3) – Balconies, decks and porches to have at least one receptacle outlet
  5. NEC 210.70 (A) – at least (1) wall switched light outlet required in every habitable room and bathroom and hallway, stairway, garage, exterior side of outdoor grade level entrances (garage vehicle doors are exempt)
  6. NEC 406.9 (A) & (B) – Outdoor receptacle outlets to be weatherproof covered with the chord/plug in if in wet location (w/o plug in if in damp location).  Damp location is protected from rain by roof (i.e. under patio cover)
  7. NEC 406.12 – Tamper resistant receptacle outlets for all non-locking 120V/15 & 20 Amp outlets unless for dedicated appliance or luminaries or over 5.5’ above floor.
  8. 406.12 – Tamper resistant receptacle outlets for all non-locking 120V/15 & 20 amp outlets unless for dedicated appliance or luminaries or over 5.5’ above floor.
  1. CPC 507.4 – Drainage pan under water heater if: in attic, on floor/ceiling, floor/subfloor where damage results from leakage.  ¾” minimum drainage line from pan to approved location
  2. CPC 507.5 – Temperature & Pressure relief valve prohibited from discharging into drainage pan.
  3. CPC 804.1 – Clothes washer stand pipe limited to between 18” – 30” above trap.  Trap to be between 6” – 18” above floor.
  1. CEC Lighting Mandatory Measures (150.0(k)) – All other rooms (excluding kitchen, laundry, garage, utility, bathroom) to have either high-efficacy light fixtures OR controlled by a dimmer or vacancy sensor
  2. CEC Lighting Mandatory Measures (150.0(k)) – Outdoor lighting must be high-efficacy OR have motion sensor plus photocontrol or astronomical time clock AND a manual On/Off switch that does not override the automatic controls.

UTILITY ROOM (see MUD ROOM)

LEGISLATIVE REVIEW

For a list of legislative actions which may have an impact on local building departments, visit the CALBO Legislative Watch page.

LEGISLATIVE REVIEW

For a list of legislative actions which may have an impact on local building departments, visit the CALBO Legislative Watch page.

New law on “Granny flats” (aka: Accessory Dwelling Units)

Granny flat sketchup example, calebclark.org CC BY-NC-SA 2.0

On September 27, 2016, Governor Jerry Brown signed Senate Bill 1069 into law.  The new law took effect on January 1, 2017.  The new state law is intended to significantly increase the number of accessory dwelling units built in backyards.  As Senate Bill 1069 moved through the Legislature last year, numerous municipalities voiced concerns that the law would erode local control and negatively impact the character of the neighborhood.

Among other things, the law prohibits cities from denying accessory dwelling units based on a lack of available parking and also states that these accessory dwelling units do not need to be provided with independent utility hook-ups (they can share the utility hook-up from the primary dwelling on the property). The law was intended to alleviate California’s affordable housing problem by encouraging homeowners to build rentable secondary units behind their homes.

UPCOMING CALBO Events

ANNUAL BUSINESS MEETING

CALBO will host its 55th Annual Business Meeting in Newport Beach at the Hyatt Regency Newport Beach, March 19-23, 2017. www.CALBO.ORG/ABM

Meeting highlights include:

  • Training opportunities for attendees
  • Network with other code professionals and old friends
  • Learn about new legislation affecting Building Departments
  • Talk to vendors showcasing their products

JOB FAIR

CALBO's Job Fair and Career Development Day will be held on the last day of the Annual Business Meeting (Thursday, March 23, 2017) from 8:30am - 12:00pm).

  • Explore a Career in Building Departments
  • Over 30 companies and local cities
  • Resumé advice
  • Job opportunities and Internships

Questions about CALBO events?

Contact CALBO at 916-457-1103 or info@calbo.org.