Know the Code: PV and NEC

Size: px

Start display at page:

Download "Know the Code: PV and NEC"

Dominic Stewart Harper
5 years ago
Views:

1 Know the Code: PV and NEC September 2014 PV Installer's Course ---NEC Article 690 Highlights 1

2 First National Electrical Code 1881 September 2014 PV Installer's Course ---NEC Article 690 Highlights 2

3 The National Electrical Code was invented to reduce the risk of FIRE And ELECTROCUTION September 2014 PV Installer's Course ---NEC Article 690 Highlights 3

4 Electrical Safety Get the NEC Handbook: Order it on-line At Read John Wiles book about article 690 (which applies to PV) Photovoltaic Power Systems and the National Electrical Code: Suggested Practices This is on-line at Photovoltaics/Codes-Stds/PVnecSugPract.html September 2014 PV Installer's Course ---NEC Article 690 Highlights 4

5 National Electrical Code Chapter 1 General Chapter 2 Wiring and Protection Chapter 3 Wiring Methods and Materials Chapter 4 Equipment for General Use Chapter 5 Special Occupancies Chapter 6 Special Equipment Chapter 7 Special Conditions Chapter 8 Communications Systems Chapter 9 Tables September 2014 PV Installer's Course ---NEC Article 690 Highlights 5

6 Each Chapter has many sections Chapter 6 Special Equipment 600 Electric Signs and Outline Lighting 604 Manufactured Wiring Systems 605 Office Furnishings (Consisting of Lighting Accessories and Wired Partitions). 610 Cranes and Hoists 620 Elevators, Dumbwaiters, Escalators, Moving Walks, Wheelchair Lifts, and Stairway Chair Lifts 625 Electric Vehicle Charging System 626 Electrified Truck Parking Spaces 630 Electric Welders 640 Audio Signal Processing, Amplification,and Reproduction Equipment 645 Information Technology Equipment 647 Sensitive Electronic Equipment 650 Pipe Organs 660 X-Ray Equipment 665 Induction and Dielectric Heating Equipment 668 Electrolytic Cells 669 Electroplating 670 Industrial Machinery 675 Electrically Driven or Controlled Irrigation Machines 680 Swimming Pools, Fountains, and Similar Installations 685 Integrated Electrical Systems. 690 Solar Photovoltaic Systems Fuel Cell Systems 694 Wind energy systems 695 Fire Pumps. September 2014 PV Installer's Course ---NEC Article 690 Highlights 6

7 Then there sub-headings and sub-sub-headings 690 Solar Photovoltaic Systems (this is the page number) I. General Scope Definitions II. Circuit Requirements III. Disconnecting Means IV. Wiring Methods V. Grounding VI. Marking VII. Connection to Other Sources VIII. Storage Batteries IX. Systems Over 1000 Volts X. Electric Vehicle Charging September 2014 PV Installer's Course ---NEC Article 690 Highlights 7

8 Who Makes the Code? NATIONAL ELECTRICAL CODE COMMITTEE CODE-MAKING PANEL NO. 4 Articles 225,230, 690, 692,694,705 Ronald J. Toomer Chair, Toomer Electrical Company LA [IM] Rep. International Association of Electrical Inspectors 7 members plus alternates Our Go-to guys are Ward I. Bower, Solar Energy Industries Association and William F. Brooks, Brooks Engineering September 2014 PV Installer's Course ---NEC Article 690 Highlights 8

9 There are several other articles referenced in 690 Solar Photovoltaic Systems n n n Chapter 1 General u Article 100 Definitions u Article 110 Installation Requirements Chapter 2 Wiring and Protection u Article 200 Grounded Conductor u Article 210 Branch Circuits u Article Services u Article 240 Overcurrent Protection u Article Grounding Chapter 3 Wiring Methods u Article 310 Conductors u Article 314 J-Boxes sizing u Article 338 Service Entrance cables Chapter 4 Equipment for General Use u Article 445 Generators u Article 450 Transformers u Article 480 Storage Batteries Chapter 6 Special Equipment u Article 690 Photovoltaic Systems u Article 692 Fuel Cell Systems Chapter 7 Special Conditions u Article 705 Interconnected Power Sources u Article 720 Circuits less then 50 volts September 2014 PV Installer's Course ---NEC Article 690 Highlights 9

10 NEC Figure 690.1(A) September 2014 PV Installer's Course ---NEC Article 690 Highlights 10

11 Some of the definitions Photovoltaic Source Circuit. Circuits between modules and from modules to the common connection point(s) of the dc system. Photovoltaic Output Circuit. Circuit conductors between the photovoltaic source circuit(s) and the inverter or dc utilization equipment. September 2014 PV Installer's Course ---NEC Article 690 Highlights 11

690.5 Ground-Fault Protection. Roof-mounted dc photovoltaic arrays located on dwellings shall be provided with dc ground-fault protection to reduce fire hazards.

12 690.5 Ground-Fault Protection. Roof-mounted dc photovoltaic arrays located on dwellings shall be provided with dc ground-fault protection to reduce fire hazards. (A) Ground-Fault Detection and Interruption. The ground-fault protection device or system shall be capable of detecting a ground fault, interrupting the flow of fault current, and providing an indication of the fault. September 2014 PV Installer's Course ---NEC Article 690 Highlights 12

13 There are 4 things we have to use NEC in PV system design on a regular basis 1) DC Voltage of PV as a function of temperature 2) Voltage drop 3) Ampacity of wires, fuses and breakers 4) Grounding September 2014 PV Installer's Course ---NEC Article 690 Highlights 13

14 Hyundai 250 W Voltages and currents are given at standard test conditions and are NOT the maximums! September 2014 PV Installer's Course ---NEC Article 690 Highlights 14

15 September 2014 PV Installer's Course ---NEC Article 690 Highlights 15

16 These IV Curves show the effect of temperature on the output DC voltage These IV Curves show the effect of irradiance on the output DC current September 2014 PV Installer's Course ---NEC Article 690 Highlights 16

17 690.7 Maximum Voltage. (B) Direct-Current Utilization Circuits. The voltage of dc utilization circuits shall conform with (C) Photovoltaic Source and Output Circuits. Over 600 V not allowed in 1 and 2 family dwellings (D) Circuits Over 150 Volts to Ground. NOT accessible to other than qualified persons 1 and 2 family dwellings Item D means you must make the wiring on a residential groundmount inaccessible to unqualified persons. For example, on a poletop array, make it tall enough that a ladder would be needed to be able to touch the inter-module wiring. Put all other wiring in a conduit. September 2014 PV Installer's Course ---NEC Article 690 Highlights 17

18 Voltage Rules Summary PV system voltage (V NEC ) is the V oc x w Systems over 600 volts cannot be installed in 1 & 2 family dwellings. w Systems over 250 volts must use 600 volt equipment and conductors. w Systems over 150 volts, installed in 1 & 2 family dwellings, must be locked. w Systems over 50 volts must be grounded. w Systems less then 50 volts must use 12 AWG conductors (or larger). September 2014 PV Installer's Course ---NEC Article 690 Highlights 18

19 690.8 Circuit Sizing and Current. The wires from the PV modules to the inverter or charge controller must be able to carry 15625% of the Isc Because we must size the wires larger by 125% for continuous duty 125% for irradiance greater than 1000 W/square meter Math reminder: 125% x 125% = 15625% 125% = 1.25 AND 15625% = Ditto: for sizing the charge controller unless it is rated for continuous current as per 690.8(B)(1) exception September 2014 PV Installer's Course ---NEC Article 690 Highlights 19

20 PV Circuit Current And a quick reminder that you must add the CURRENT for parallel wiring NEC 690.8(A)(2) Circuit current is the sum of the parallel source circuits maximum current as calculated in 690.8(A)(1). September 2014 PV Installer's Course ---NEC Article 690 Highlights 20

21 Example module September 2014 PV Installer's Course ---NEC Article 690 Highlights 21

22 690.8(B) The PV source current (I NEC ) is the short circuit current (I sc ) multiplied by 125%. Isc = 7.7 A NEC PV Source Circuit Current = (I NEC ) = I sc X 125% Example: (I NEC ) = 7.7 Amp X 1.25 = = 10 Amps NEC Over-current Device Current Rating (I od ) I od > 125% X I NEC September 2014 PV Installer's Course ---NEC Article 690 Highlights 22

23 690.8(B) The PV source current (I NEC ) is the short circuit current (I sc ) multiplied by 125%. Isc = 7.7 A NEC PV Source Circuit Current = (I NEC ) = I sc X 125% Example: (I NEC ) = 7.7 Amp X 1.25 = = 10 Amps NEC Over-current Device Current Rating (I od ) I od > 125% X I NEC Example: 125% X 10 Amps = 12.5 Amps > 13 Amps (I od ) The wire also has to be able to take 13 A September 2014 PV Installer's Course ---NEC Article 690 Highlights 22

24 Overcurrent Protection Use the rules in Article 240 Considerations: Ampacity Temperature AC or DC Overcurrent Protection. (A) Circuits and Equipment. (B) Power Transformers. (C) Photovoltaic Source Circuits. (D) Direct-Current Rating. (E) Series Overcurrent Protection. September 2014 PV Installer's Course ---NEC Article 690 Highlights 23

25 690.9 Overcurrent Protection. (C) Photovoltaic Source Circuits. Use of fuses or breakers is OK. They have to be accessible You must pick the amperage rating to the nearest 1 amp (D) Direct-Current Rating. Make sure the fuses or breakers are RATED FOR DC September 2014 PV Installer's Course ---NEC Article 690 Highlights 24

26 A fuse for each series string, all 500 of them! September 2014 PV Installer's Course ---NEC Article 690 Highlights 25

27 Overcurrent protection sizing (see article 240) While the wording of some of the rules for this may seem confusing, the bottom line for all of them is: Make sure the fuse will blow BEFORE the wire melts! And a corollary: Make sure the fuse will blow before the equipment is damaged. September 2014 PV Installer's Course ---NEC Article 690 Highlights 26

28 For PV source circuits Recall that the current we had to consider for wire sizing Is 1.25 x Isc. For the overcurrent device, we have to use 1.25 x the current Rating found for the wire. This leads to x Isc. Then we have to pick the nearest fuse size. Finally, we have to go back and check that the fuse will protect the wire size we chose. September 2014 PV Installer's Course ---NEC Article 690 Highlights 27

29 The PV modules are to be connected in series with a single conductor cable. September 2014 PV Installer's Course ---NEC Article 690 Highlights 28

30 The PV modules are to be connected in series with a single conductor cable. The ambient temperature could be 170 F (77 C) between the roof and the module. September 2014 PV Installer's Course ---NEC Article 690 Highlights 28

31 The PV modules are to be connected in series with a single conductor cable. The ambient temperature could be 170 F (77 C) between the roof and the module. So the temperature rating of all terminals, devices, conductors and cables should be 90ºC. September 2014 PV Installer's Course ---NEC Article 690 Highlights 28

32 Recall that for a module with Isc=7.7 A we had: The PV source current (I NEC ) is the short circuit current (I sc ) multiplied by 125%. NEC PV Source Circuit Current = (I NEC ) = I sc X 125% Example: (I NEC ) = 7.7 Amp X 1.25 = = 10 Amps NEC Over-current Device Current Rating (I od ) I od > 125% X I NEC September 2014 PV Installer's Course ---NEC Article 690 Highlights 29

33 Recall that for a module with Isc=7.7 A we had: The PV source current (I NEC ) is the short circuit current (I sc ) multiplied by 125%. NEC PV Source Circuit Current = (I NEC ) = I sc X 125% Example: (I NEC ) = 7.7 Amp X 1.25 = = 10 Amps NEC Over-current Device Current Rating (I od ) I od > 125% X I NEC Example: 125% X 10 Amps = 12.5 Amps > 13 Amps (I od ) September 2014 PV Installer's Course ---NEC Article 690 Highlights 29

34 PV Conductor Ampacity So we know that the current could be as high as 10 A under certain irradiance conditions and the over current device is sized with another factor of 1.25 because the PV current is continuous. So now we must have a wire that can carry AT LEAST the amount of current it is protected for (13 A). Now we have to consider the temperature conditions. September 2014 PV Installer's Course ---NEC Article 690 Highlights 30

35 Table (B)(3)(c) But what ambient temp do you use? September 2014 PV Installer's Course ---NEC Article 690 Highlights 31

org Useful link to design temp tables: http://www.copper.

36 Use the Outdoor design temperatures for the ambient temperature mentioned in (b)(3)(c) Find the table at Copper.org Useful link to design temp tables: September 2014 PV Installer's Course ---NEC Article 690 Highlights 32

37 Now you take the design temp + temp adder from NEC table (B)(2)(c) = the temperature you will need to de-rate to in NEC table In Binghamton, the design temp = 84 F. For a conduit sitting on the roof, you have to add 60 F. So the temperature to de-rate for is 144 F. September 2014 PV Installer's Course ---NEC Article 690 Highlights 33

38 September 2014 PV Installer's Course ---NEC Article 690 Highlights 34

39 A design temp of 144 means a de-rate factor of 0.58 September 2014 PV Installer's Course ---NEC Article 690 Highlights 35

40 Take the ampacity you need and divide by 0.58 to get the 30 C ampacity. For our 13 A we need on the roof-top, take = A: AWG #12 THWN-2 Using 0.41 instead of 0.58 is still OK, because it is more conservative. September 2014 PV Installer's Course ---NEC Article 690 Highlights 36

41 What if there are more than 3 current carrying conductors in the conduit? Now you have to de-rate again using table (b)(3)(a) September 2014 PV Installer's Course ---NEC Article 690 Highlights 37

42 If there are more than 3 current carrying conductors, use table (b)(3)(a) September 2014 PV Installer's Course ---NEC Article 690 Highlights 38

43 Take your 30 C current and divide by de-rate factor in table (b)(2)(a) For our A, we would need = A if there are 4 to 6 current carrying conductors in the conduit. AWG # 12 is still OK. September 2014 PV Installer's Course ---NEC Article 690 Highlights 39

44 Switch or Circuit Breaker. The DC disconnect Must have correct rating for DC and current Located where readily accessible Outside or inside nearest the point of entrance of the system conductors This pertains small wires such as on solar shingles In (G), if the PV wiring comes into an inaccessible location, such as the attic, the wires must me in metal conduit or metal-clad cable until they get to the first disconnect And it can t be in the bathroom September 2014 PV Installer's Course ---NEC Article 690 Highlights 40

45 DC disconnect Rated for up to 600 V DC Readily accessible and There is plenty of working space September 2014 PV Installer's Course ---NEC Article 690 Highlights 41

46 New in NEC 2014: Rapid Shutdown September 2014 PV Installer's Course ---NEC Article 690 Highlights 42

47 New in NEC 2014: Rapid Shutdown This is not required if the regular disconnect is more than 10 from the PV array or more than 5 feet from where PV wires enter inside. For example, this is not needed for micro-inverters. As of September 2014, there is only one supplier of rapid disconnects and code officials are mostly not requiring them. But that will change over the coming year. September 2014 PV Installer's Course ---NEC Article 690 Highlights 43

48 Section IV Wiring methods (B) Single Conductor Cable. Types SE, UF, USE, and USE-2 single-conductor cable shall be permitted in photovoltaic source circuits where installed in the same manner as a Type UF multi-conductor cable in accordance with Article 339. Where exposed to sunlight, Type UF cable identified as sunlight-resistant shall be used. September 2014 PV Installer's Course ---NEC Article 690 Highlights 44

49 Connectors. 1) Must have polarity (labeled + and -) 2) Must have protected tips 3) Must latch together so they can t be disconnected accidentally September 2014 PV Installer's Course ---NEC Article 690 Highlights 45

50 Voltage drop from PV array to inverter In addition to sizing the wires for ampacity, we also have to consider voltage drop. September 2014 PV Installer's Course ---NEC Article 690 Highlights 46

51 About Voltage Drop Wires should be sized to reduce resistive (heating) loss to less than 2%. This loss is a function of the SQUARE of the current x the resistance. This is another manifestation of Ohm s law: V= I x R. So I = V/R. And resistive loss is I x I x R = V/R x V/R x R = V x V/R = our old friend, V x I = Watts! So resistive loss equals power loss, a bad thing. Use a wire-sizing table to choose the size wire for the current and voltage you are working with. September 2014 PV Installer's Course ---NEC Article 690 Highlights 47

52 Where: Computing voltage drop formula (0.2 x d x I /V) x (Ω/kf) = %Voltage Drop I is the circuit current, which for source circuits is usually taken as the maximum power current, Imp, d = one way distance in feet V is the voltage at which you want to find VD, and Ω/kft is the wire s resistivity in Ohms per 1000 feet and is found from NEC Chapter 9, Table 8, Conductor Properties. Math note: 2d is the round trip distance. To convert to %, one multiplies by 100, but to convert feet to kilo-feet, one divides by x 100/1000 = 0.2 September 2014 PV Installer's Course ---NEC Article 690 Highlights 48

53 Grounding See also, article 250 September 2014 PV Installer's Course ---NEC Article 690 Highlights 49

Grounding: the big picture + - 1) + - 11) 4) 1) + - + - 3) 1) 5) 9) 3)

8) bond wire from new ground rod to existing ground rod or water pipe

54 Grounding: the big picture + - 1) ) 4) 1) ) 1) 5) 9) 3) 2) - G ) G 3) line load 3) load 7) line 3) L1 L2 N 200 A 30 A G 8) bond wire from new ground rod to existing ground rod or water pipe 3) September 2014 PV Installer's Course ---NEC Article 690 Highlights 50

55 [250.4] Bonding and grounding requirements for non-current carrying conductive components: Must be connected together (bonded) Must be permanent and continuous Must be connected to earth (grounded) Must be connected to the electrical source Must be in accordance with manufactures instructions. [110.3(B)] September 2014 PV Installer's Course ---NEC Article 690 Highlights 51

56 Equipment Grounding. Exposed non current carrying metal parts of module frames, equipment, and conductor enclosures shall be grounded in accordance with or (A) regardless of voltage. From article 250: don t forget that the equipment ground has to be continuous. September 2014 PV Installer's Course ---NEC Article 690 Highlights 52

57 Size of Equipment Grounding Conductor. Use table EQUIPMENT GROUNDS Size of Equipment Grounding Conductors. Equipment grounding conductors for photovoltaic source and photovoltaic output circuits shall be sized in accordance with (A) or (B). (A) General. Equipment grounding conductors in photovoltaic source and photovoltaic output circuits shall be sized in accordance with Table Where no overcurrent protective device is used in the circuit, an assumed overcurrent device rated at the photovoltaic rated short-circuit current shall be used in Table Increases in equipment grounding conductor size to address voltage drop considerations shall not be required. The equipment grounding conductors shall be no smaller than 14 AWG. September 2014 PV Installer's Course ---NEC Article 690 Highlights 53

58 EQUIPMENT GROUNDS September 2014 PV Installer's Course ---NEC Article 690 Highlights 54

59 EQUIPMENT GROUNDS September 2014 PV Installer's Course ---NEC Article 690 Highlights 55

60 EQUIPMENT GROUNDS ILSCO Lug Wiley Electronics September 2014 PV Installer's Course ---NEC Article 690 Highlights 56

61 EQUIPMENT GROUNDS September 2014 PV Installer's Course ---NEC Article 690 Highlights 57

62 SYSTEM GROUNDS [ ] The Grounding Electrode Conductor to be no smaller then the largest conductor but not smaller the #8 AWG for DC systems. September 2014 PV Installer's Course ---NEC Article 690 Highlights 58

63 SYSTEM GROUNDS September 2014 PV Installer's Course ---NEC Article 690 Highlights 59

64 VI. Marking Signs, signs, everywhere there s signs September 2014 PV Installer's Course ---NEC Article 690 Highlights 60

65 Some markings are already there such as on modules. Others, you have to put on, such as: Photovoltaic Power Source. A marking, specifying the photovoltaic power source rated as follows, shall be provided by the installer at the site at an accessible location at the disconnecting means for the photovoltaic power source: (1) Operating current (2) Operating voltage (3) Maximum system voltage (4) Short-circuit current September 2014 PV Installer's Course ---NEC Article 690 Highlights 61

66 Interactive System Point of Interconnection. Label the breaker PV is tied in to Photovoltaic Power Systems Employing Energy Storage. State Max voltage Identification of Power Sources. Indicate where the disconnects are (B)(4) and (5). Label the breaker which is back-fed by PV system and that it IS back-fed. September 2014 PV Installer's Course ---NEC Article 690 Highlights 62

67 September 2014 PV Installer's Course ---NEC Article 690 Highlights 63

68 And from earlier code sections: For the any switch that could be energized on the line or load side, put on this sign WARNING. ELECTRIC SHOCK HAZARD. DO NOT TOUCH TERMINALS. TERMINALS ON BOTH THE LINE AND LOAD SIDES MAY BE ENERGIZED IN THE OPEN POSITION. September 2014 PV Installer's Course ---NEC Article 690 Highlights 64

69 For a 120 V stand-alone, put this sign on the load center: WARNING SINGLE 120-VOLT SUPPLY, DO NOT CONNECT MULTIWIRE BRANCH CIRCUITS! It s a good idea to have plenty of labeling. Label the inverter ( INVERTER ) Label the j-boxes as to DC or AC and voltage Label the conduits Label the PV source circuits for easy trouble-shooting Use laminated cards or engraved plaques for long-lasting labels. A paint pen works well to fill in the voltage and current info on a laminated card for the specific system. September 2014 PV Installer's Course ---NEC Article 690 Highlights 65

70 Point of interconnection (A) Supply Side. A photovoltaic power source shall be permitted to be connected to the supply side of the service disconnecting means as permitted in (5). September 2014 PV Installer's Course ---NEC Article 690 Highlights 66

71 (B) Load Side. September 2014 PV Installer's Course ---NEC Article 690 Highlights 67

72 Example: A customer has a 200 A load center and wants to install A 10 kw PV system. If he uses (4) SMA 2500 W inverters, The sum of the PV breakers will be 60 A. 200 A + 60 A = 260 A. This is greater than 120% of 200 (which Is 240). What do we do then? Solution A) Downsize the main breaker to 150 A. Then the sum Of = 210 which is less than 240. Solution B) Create a branch off the service entrance and go to A dedicated PV load center. September 2014 PV Installer's Course ---NEC Article 690 Highlights 68

73 How to build a branch From meter September 2014 PV Installer's Course ---NEC Article 690 Highlights 69

74 Wiring schematic for a tap 8) service panel fed by PV 9) power distribution block 11) disconnect switch 12) existing service panel 14) THWN-2 wire in conduit September 2014 PV Installer's Course ---NEC Article 690 Highlights 70

75 Another way to derate main September 2014 PV Installer's Course ---NEC Article 690 Highlights 71

76 Putting in a new, smaller main breaker 8) Existing service panel 10) To grounding electrode 12) New main panel 13) Utility meter Reminder: Neutral and grounds for circuits must be separated in all sub-panels. September 2014 PV Installer's Course ---NEC Article 690 Highlights 72

77 VIII. Storage Batteries Highlights: High-voltage (over 50 V) not allowed unless terminals are inaccessible Guard live parts. Make sure there is a fuse or breaker in the + wire of the battery bank. There has to be disconnect switch Wet cells must have sufficient ventilation. See Article 480. Check Article for working space rules. Don t put the power panel directly above the battery bank. Use battery cables of the correct type. September 2014 PV Installer's Course ---NEC Article 690 Highlights 73

78 Related codes If batteries are being installed where there is propane, check the local propane code. Usually, you cannot install a battery bank within 3 of a propane fired appliance. If the battery box vent goes thru the wall, install a power vent. September 2014 PV Installer's Course ---NEC Article 690 Highlights 74

79 Daily NEC for PV There are some things that come up in every installation. Other items are taken care of for you. Already figured: Module interconnect size GFP fuse comes with inverter Series string fuse specified on module AC breaker size specified in inverter instructions You have to do: Size wires and conduits for wiring from PV array to inverter. Consider ampacity, temperatures and voltage drop. Size wires from inverter to load center. Put the ground wiring on correctly September 2014 PV Installer's Course ---NEC Article 690 Highlights 75

80 Neatness keeps inspectors happy September 2014 PV Installer's Course ---NEC Article 690 Highlights 76

Know the Code: PV and NEC

Know the Code: PV and NEC More than half of all fires are caused by electricity. --NFPA 1 First National Electrical Code 1881 2 The National Electrical Code was invented to reduce the risk of FIRE And