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October 2012 PV Installer's Course ---NEC Article 690 Highlights 2
First National Electrical Code 1881
October 2012 PV Installer's Course ---NEC Article 690 Highlights 3
The National Electrical Code was invented to reduce the risk of
FIREAnd
ELECTROCUTION
October 2012 PV Installer's Course ---NEC Article 690 Highlights 4
Get the NEC Handbook: Order it on-line At
www.nfpa.org/Catalog/
Photovoltaic Power Systems and the National Electrical Code: Suggested Practices
Read John Wiles book about article 690 (which applies to PV)
This is on-line at http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/PVnecSugPract.html
Electrical Safety
October 2012 PV Installer's Course ---NEC Article 690 Highlights 5
Chapter 1 GeneralChapter 2 Wiring and ProtectionChapter 3 Wiring Methods and MaterialsChapter 4 Equipment for General UseChapter 5 Special OccupanciesChapter 6 Special EquipmentChapter 7 Special ConditionsChapter 8 Communications SystemsChapter 9 Tables
National Electrical Code
October 2012 PV Installer's Course ---NEC Article 690 Highlights 6
Each Chapter has many sections
Chapter 6 Special Equipment600 Electric Signs and Outline Lighting ............ 70–477604 Manufactured Wiring Systems ................... 70–481605 Office Furnishings (Consisting of Lighting Accessories and Wired Partitions) ............... 70–482610 Cranes and Hoists .................................. 70–483620 Elevators, Dumbwaiters, Escalators,Moving Walks, Wheelchair Lifts, and Stairway Chair Lifts ................................ 70–488625 Electric Vehicle Charging System ............... 70–498630 Electric Welders .................................... 70–502640 Audio Signal Processing, Amplification,and Reproduction Equipment .................... 70–504645 Information Technology Equipment ............ 70–509647 Sensitive Electronic Equipment ................. 70–511650 Pipe Organs ......................................... 70–512660 X-Ray Equipment .................................. 70–513665 Induction and Dielectric Heating Equipment ........................................... 70–515668 Electrolytic Cells ................................... 70–516669 Electroplating ....................................... 70–519670 Industrial Machinery .............................. 70–520675 Electrically Driven or Controlled Irrigation Machines ................................. 70–521680 Swimming Pools, Fountains, and Similar Installations .......................................... 70–523685 Integrated Electrical Systems .................... 70–537690 Solar Photovoltaic Systems ...................... 70–538692 Fuel Cell Systems .................................. 70–547692 Fire Pumps .................................. 70–550
October 2012 PV Installer's Course ---NEC Article 690 Highlights 7
690 Solar Photovoltaic Systems ...................... 70–538 (this is the page number)
I. General ........................................... 70–538
690.1 Scope
690.2 Definitions
II. Circuit Requirements ........................... 70–540
III. Disconnecting Means .......................... 70–542
IV. Wiring Methods ................................. 70–543
V. Grounding ........................................ 70–544
VI. Marking .......................................... 70–545
VII. Connection to Other Sources ................. 70–545
VIII. Storage Batteries ................................ 70–546
IX. Systems Over 600 Volts ....................... 70–547
Then there sub-headings and sub-sub-headings
October 2012 PV Installer's Course ---NEC Article 690 Highlights 8
Who Makes the Code?NATIONAL ELECTRICAL CODE COMMITTEE
CODE-MAKING PANEL NO. 3Articles 300, 527, 690, 692
Raymond W. Weber, Chair, Dept. of Commerce, WI [E], Rep. International Association of Electrical Inspectors
Joseph J. Andrews, Electrical Safety Resources, Inc., SC [U], Rep. Institute of Electrical & Electronics Engineers, Inc.Charles W. Beile, Allied Tube & Conduit/Tyco, IL [M], Rep. National Electrical Manufacturers AssociationWard I. Bower, Sandia Nat’l. Laboratories, NM [U], Rep. Solar Energy Industries Association(VL 690)Paul Casparro, Scranton Electricians JATC, PA [L], Rep. International Brotherhood of Electrical WorkersCharles W. Forsberg, OH [M], Rep. Society of the Plastics Industry Inc.Jack A. Gruber, Wheatland Tube Co., PA [M], Rep. American Iron and Steel InstituteDennis B. Horman, PacifiCorp, UT [UT], Rep. Edison Electric InstituteKenneth Krastins, Plug Power, Inc., NY [M], Rep. US Fuel Cell Council(VL 691)George M. Kreiner, Underwriters Laboratories Inc., IL [RT]Ronald E. Maassen, Lemberg Electric Co., Inc., WI [IM], Rep. National Electrical Contractors AssociationSteven J. Owen, AL [IM], Rep. Associated Builders and Contractors, Inc.David A. Pace, Olin Corporation, AL [U], Rep. American Chemistry Council
October 2012 PV Installer's Course ---NEC Article 690 Highlights 9
There are several other articles referenced in690 Solar Photovoltaic Systems
n Chapter 1 Generalu Article 100 – Definitionsu Article 110 – Installation Requirements
n Chapter 2 Wiring and Protectionu Article 200 – Grounded Conductoru Article 210 – Branch Circuitsu Article 230 - Servicesu Article 240 – Overcurrent Protectionu Article 250 - Grounding
n Chapter 3 Wiring Methods u Article 310 – Conductorsu Article 314 – J-Boxes sizingu Article 338 –Service Entrance cables
§ Chapter 4 Equipment for General Useu Article 445 – Generatorsu Article 450 – Transformersu Article 480 – Storage Batteries
§ Chapter 6 Special Equipmentu Article 690 – Photovoltaic Systemsu Article 692 – Fuel Cell Systems
§ Chapter 7 Special Conditionsu Article 705 – Interconnected Power Sourcesu Article 720 – Circuits less then 50 volts
October 2012 PV Installer's Course ---NEC Article 690 Highlights 11
Some of the definitions
Photovoltaic Source Circuit. Circuits between modulesand from modules to the common connection point(s) ofthe dc system.
Photovoltaic Output Circuit. Circuit conductors betweenthe photovoltaic source circuit(s) and the inverter or dcutilization equipment.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 12
690.5 Ground-Fault Protection. Roof-mounted dc photovoltaicarrays located on dwellings shall be provided withdc ground-fault protection to reduce fire hazards.
(A) Ground-Fault Detection and Interruption. Theground-fault protection device or system shall be capable ofdetecting a ground fault, interrupting the flow of fault current,and providing an indication of the fault.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 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
October 2012 PV Installer's Course ---NEC Article 690 Highlights 14
Sharp 185
Voltages and currents are given at standard test conditions and are NOT the maximums!
October 2012 PV Installer's Course ---NEC Article 690 Highlights 17
690.7 Maximum Voltage.
(B) Direct-Current Utilization Circuits. The voltage ofdc utilization circuits shall conform with 210.6. (C) Photovoltaic Source and Output Circuits.
Over 600 V not allowed(D) Circuits Over 150 Volts to Ground.
NOT accessible to other than qualified persons
October 2012 PV Installer's Course ---NEC Article 690 Highlights 18
Voltage Rules Summary
PV system voltage (VNEC) is the Voc x 1.25.
wSystems over 600 volts cannot be installed in 1 & 2 family dwellings.
wSystems over 250 volts must use 600 volt equipment and conductors.wSystems over 150 volts, installed in 1 & 2 family dwellings, must be locked.wSystems over 50 volts must be grounded.
wSystems less then 50 volts must use 12 AWG conductors (or larger).
October 2012 PV Installer's Course ---NEC Article 690 Highlights 19
690.8 Circuit Sizing and Current.
The wires from the PV modules to the inverter or charge controller must be able to carry 156% of the Isc
Because
125% for continuous duty
125% for irradiance greater than 1000 W/square meter
125% x 125% = 156%
125% = 1.25
156% = 1.56
Ditto: for sizing the charge controller unless…
October 2012 PV Installer's Course ---NEC Article 690 Highlights 20
690.8 Circuit Sizing and Current.
Exception: Circuits containing an assembly, together withits overcurrent device(s), that is listed for continuous operationat 100 percent of its rating shall be permitted to beutilized at 100 percent of its rating.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 21
NEC® 690.8(A)(2)
Circuit current is the sum of the parallel source circuits maximum current as calculated in 690.8(A)(1).
PV Circuit CurrentSlide credit: Jerry Flaherty, Electrical Inspection Services
October 2012 PV Installer's Course ---NEC Article 690 Highlights 22
Example module
Astropower 120(now GE120)
October 2012 PV Installer's Course ---NEC Article 690 Highlights 23
The PV source current (INEC) is the short circuit current (Isc) multiplied by 125%. Isc = 7.7 A
NEC PV Source Circuit Current = (INEC) = Isc X 125%
690.8(B)
Example: 125% X 10 Amps = 12.5 Amps > 13 Amps (Iod)
The wire also has to be able to take 13 A
NEC Over-current Device Current Rating (Iod)
Iod > 125% X INEC
Example: (INEC) = 7.7 Amp X 1.25 = 9.625 = 10 Amps
October 2012 PV Installer's Course ---NEC Article 690 Highlights 24
Overcurrent Protection 690.9Use the rules in Article 240
Considerations:•Ampacity•Temperature•AC or DC
690.9 Overcurrent Protection.(A) Circuits and Equipment. (B) Power Transformers.(C) Photovoltaic Source Circuits. (D) Direct-Current Rating. (E) Series Overcurrent Protection.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 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
October 2012 PV Installer's Course ---NEC Article 690 Highlights 26
A fuse for each series string, all 500 of them!
October 2012 PV Installer's Course ---NEC Article 690 Highlights 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.
If there is only ONE or TWO series strings feeding the inverter,You DO NOT need series string fuses.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 28
Recall that the current we had to consider for wire sizingIs 1.25 x Isc.
For the overcurrent device, we have to use 1.25 x the currentRating found for the wire. This leads to 1.56 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.
For PV source circuits
October 2012 PV Installer's Course ---NEC Article 690 Highlights 29
The PV modules are to be connected in series with a single conductor cable.
So the temperature rating of all terminals, devices, conductors and cables should be 90ºC.
The ambient temperature could be 170°F (77 C) between the roof and the module.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 30
The PV source current (INEC) is the short circuit current (Isc) multiplied by 125%.
NEC PV Source Circuit Current = (INEC) = Isc X 125%
Recall that for a module with Isc=7.7 A we had:
Example: 125% X 10 Amps = 12.5 Amps > 13 Amps (Iod)
NEC Over-current Device Current Rating (Iod)
Iod > 125% X INEC
Example: (INEC) = 7.7 Amp X 1.25 = 9.625 = 10 Amps
October 2012 PV Installer's Course ---NEC Article 690 Highlights 31
PV Conductor AmpacitySo 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.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 32
New temperature calculations in NEC 2008
Table 310.15(B)2(c)
But what ambient temp do you use?
October 2012 PV Installer's Course ---NEC Article 690 Highlights33
Use the Copper Development Association’s “Outdoor design temperatures”
October 2012 PV Installer's Course ---NEC Article 690 Highlights 34
Now you take the design temp + temp adder from NEC table 310.15(B)(2)(c)
= the temperature you will need to de-rate to in NEC table 310.16
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.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 36
A design temp of 144 means a de-rate factor of 0.58
October 2012 PV Installer's Course ---NEC Article 690 Highlights 37
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 13 ÷ 0.58 = 22.41 A: AWG #12 THWN-2
Using 0.41 instead of 0.58 is still OK, because it is more conservative.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 38
What if there are more than 3 current carrying conductors in the conduit?
Now you have to de-rate again using table 310.15(b)(2)(a)
October 2012 PV Installer's Course ---NEC Article 690 Highlights 39
If there are more than 3 current carrying conductors, use table 310.15(b)(2)(a)
October 2012 PV Installer's Course ---NEC Article 690 Highlights 40
Take your 30 C current and divide by de-rate factor in table 310.15(b)(2)(a) For our 22.41 A, we would need
22.41 ÷ 0.8 = 28.01 A if there are 4 to 6 current carrying conductors in the conduit. AWG # 12 is still OK.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 41
Article 690.10 Stand-Alone Systems
If the inverter output is 120 V, multi-wire branch circuits are not allowed
October 2012 PV Installer's Course ---NEC Article 690 Highlights 42
690.17 Switch or Circuit Breaker.
The DC disconnect•Has to be within 5 ft of where wires enter the building.•Must have correct rating for DC and current •Located where readily accessible
And it can’t be in the bathroom
October 2012 PV Installer's Course ---NEC Article 690 Highlights 43
DC disconnectRated for up to 600 V DC
“Readily accessible” andThere is plenty of “working space”
October 2012 PV Installer's Course ---NEC Article 690 Highlights 44
Section IV Wiring methods
690.31 (B)Single Conductor Cable. Types SE, UF, USE, andUSE-2 single-conductor cable shall be permitted in photovoltaicsource circuits where installed in the same manneras a Type UF multi-conductor cable in accordance with Article339. Where exposed to sunlight, Type UF cable identifiedas sunlight-resistant shall be used.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 45
690.33 Connectors.
1) Must have polarity (labeled + and -)
2) Must have protected tips
3) Must latch together so they can’t be disconnected accidentally
October 2012 PV Installer's Course ---NEC Article 690 Highlights 46
Voltage drop from PV array to inverter
In addition to sizing the wires for ampacity, we also have to consider voltage drop.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 47
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.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 48
Computing voltage drop formula
(0.2 x d x I /V) x (Ω/kf) = %Voltage Drop
Where:
• 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 1000. 2 x 100/1000 = 0.2
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bond wire from new ground rod to existing ground rod or water pipe
October 2012 PV Installer's Course ---NEC Article 690 Highlights 50
Grounding: the big picture
October 2012 PV Installer's Course ---NEC Article 690 Highlights 51
[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)]
October 2012 PV Installer's Course ---NEC Article 690 Highlights 52
690.43 Equipment Grounding. Exposed non–current carryingmetal parts of module frames, equipment, and conductorenclosures shall be grounded in accordance with250.134 or 250.136(A) regardless of voltage.
From article 250: don’t forget that the equipment groundhas to be continuous.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 53
690.45 Size of Equipment Grounding Conductor. Use table 250.122
690.45 Size of Equipment Grounding Conductors.Equipment grounding conductors for photovoltaic source and photovoltaic output circuits shall be sized in accordance with 690.45(A) or (B).
(A) General. Equipment grounding conductors in photovoltaic source and photovoltaic output circuits shall be sized in accordance with Table 250.122. 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 250.122. 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.
EQUIPMENT GROUNDS
(B) Ground-Fault Protection Not Provided. For other than dwelling units where ground-fault protection is not provided in accordance with 690.5(A) through (C), each equipment grounding conductor shall have an ampacity of at least two (2) times the temperature and conduit fill corrected circuit conductor ampacity.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 56
Wiley Electronicswww.we-llc.com
ILSCO Lug
EQUIPMENT GROUNDS
October 2012 PV Installer's Course ---NEC Article 690 Highlights 58
[250.166] The Grounding Electrode Conductor to be no smaller then the largest conductor but not smaller the #8 AWG for DC systems.
SYSTEM GROUNDS
October 2012 PV Installer's Course ---NEC Article 690 Highlights 60
VI. Marking
Signs, signs, everywhere there’s signs
October 2012 PV Installer's Course ---NEC Article 690 Highlights 61
Some markings are already there such as on modules. Others, you have to put on, such as:
690.53 Photovoltaic Power Source. A marking, specifyingthe photovoltaic power source rated as follows, shall beprovided by the installer at the site at an accessible locationat the disconnecting means for the photovoltaic powersource:
(1) Operating current(2) Operating voltage(3) Maximum system voltage(4) Short-circuit current
October 2012 PV Installer's Course ---NEC Article 690 Highlights 62
690.54 Interactive System Point of Interconnection. Label the breaker PV is tied in to
690.55 Photovoltaic Power Systems Employing EnergyStorage.
State Max voltage
690.56 Identification of Power Sources.Indicate where the disconnects are.
690.64 (B)(4) and (5).Label the breaker which is back-fed by PV systemand that it IS back-fed.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 64
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 ENERGIZEDIN THE OPEN POSITION.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 65
For a 120 V stand-alone, put this sign on the load center:
WARNINGSINGLE 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 voltageLabel the conduitsLabel 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 cardfor the specific system.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 66
690.64 Point of interconnection
(A) Supply Side. A photovoltaic power source shall bepermitted to be connected to the supply side of the servicedisconnecting means as permitted in 230.82(5).
October 2012 PV Installer's Course ---NEC Article 690 Highlights 68
Example:
A customer has a 200 A load center and wants to installA 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 (whichIs 240). What do we do then?
Solution A) Downsize the main breaker to 150 A. Then the sumOf 150 + 60 = 210 which is less than 240.
Solution B) Create a branch off the service entrance and go to A dedicated PV load center.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 69
How to build a branch
From meter
October 2012 PV Installer's Course ---NEC Article 690 Highlights 70
Wiring schematic for a tap
8) service panel fed by PV9) power distribution block11) disconnect switch12) existing service panel14) THWN-2 wire in conduit
October 2012 PV Installer's Course ---NEC Article 690 Highlights 72
Putting in a new, smaller main breaker
8) Existing service panel10) To grounding electrode12) New main panel13) Utility meter
Reminder: Neutral and groundsfor circuits must be separated in allsub-panels.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 73
VIII. Storage BatteriesHighlights:
•High-voltage (over 50 V) not allowed unless terminalsare 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 110.26 for working space rules. Don’t put the
power panel directly above the battery bank.•Use battery cables of the correct type.
October 2012 PV Installer's Course ---NEC Article 690 Highlights 74
If batteries are being installed where there is propane, check thelocal 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.
Related codes
October 2012 PV Installer's Course ---NEC Article 690 Highlights 75
Daily NEC for PVThere 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
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