041813 rs 120 rule and test taking strat

• 1. NABCEP PV Installer Exam120 Rule & Test-takingStrategiesRichard StovallSolPowerPeople, Inc.Austin, TX April 18, 2013

2. Todays Topics 120-Rule Last Minute Articles &Resources Test-taking Strategies Time Management What to Expect 3. 120-Rule: Question fromNABCEP 2009 Study Guide 4. Problem 64 NEC 705.12 (D) (2) 5. Problem 64 Rating of the buss bar = 225 amps 225 A x 1.20 = 270 amps Rating of the breaker serving the utility = 200 amps 270 amps - 200 amps = 70 amps is the maximum breaker size for the PV system Divide by 1.25 from NEC 690.8 70 amps / 1.25 = 56 amps is the maximum inverter output Answer (c) 6. Problem 64 NEC 690.8(B)(1)(a) 7. 70A * .8 = 56Ainverter output max! 8. 70A * .8 = 56A56A * 240V = 13,440 Watts max! 9. NEC 705.12 (D)(7) 10. What if you had a 200A Main Breaker and a 200A Main Buss?? 11. What if you had a 200A Main Breaker and a 200A Main Buss?? What would your OCPD max be? (200A Buss x 1.2) 200A Breaker = ? 240A 200A = 40A 40A OCPD maximum!!! 12. What if you had a 200A Main Breaker and a 200A Main Buss?? What would the most current allowable from your inverter? 40A OCPD/ 1.25 = 32A current from inverter MAXIMUM!!! 13. What if you had a 200A Main Breaker and a 225A Main Buss?? AND you needed to put in a 20A OCPD, but the oppositeend of the panel was already filled up? Could you do it? 14. Yes!! Total supply tothe BUSS (220A) isless than the BUSS israted for (225A)!! 15. Side note on Fastener Requirement for OCPD NEC 408.36(D): 16. Side note on FastenerRequirement for OCPD Exception to this provided by 705.12(D)(6) 17. What if you had a 200A Main Breaker and a 200A Main Buss?? AND you really wanted to use that 13KW inverter thatrequires a 70A OCPD? Could you do it? 18. What if you had a 200A Main Breaker and a 200A Main Buss?? AND you really wanted to use that 13KW inverter thatrequires a 70A OCPD? Could you do it? Maybe There are two ways it can beachieved. 19. What if you had a 200A Main Breaker and a 200A Main Buss?? AND you really wanted to use that 13KW inverter thatrequires a 70A OCPD? Could you do it? Maybe 1. Do a load analysis on the facility and if you determinethat you can reduce your Main Breaker down to 150A, thenthat gives you 90A of PV supply OCPD head room: (200A Main Buss * 1.2) 150A Main Breaker = ?A 240A 150A = 90A 20. What if you had a 200A Main Breaker and a 200A Main Buss?? AND you really wanted to use that 13KW inverter thatrequires a 70A OCPD? Could you do it? Maybe OR,2. Do a line-side tap. 21. Various ways to do Supply-Side Tap 22. How big can I go with a supply-side tap? 23. In this example with theservice size being 200A,then the maximum sizeline-side tap OCPD wouldbe 200A.Maximum current from PVarray? 200A/1.25= 160APV Supply!!!Wattage?? 160A x 240V =38,400 Watts!! 24. 705.12 (D)(2) Exception Now hold on there!!! The specifications of my 6KW240V bimodal inverter (grid-tied with battery backup) isasking for a 60A OCPD in the main panel. Ive got a 200AMain Breaker and a 200A which gives me just 40A PVsupply OCPD headroom I sure dont want to downsizemy main. Is there any hope for me?? YES there is.. It is the exception listed in 705.12(D)(2). 25. 705.12 (D)(2) Exception 26. 705.12 (D)(2) Exception(rationale) Because the charging current required from the grid for thebatteries can be greater than the current supplied by theinverter and PV array, the size of the backfed breaker mustbe larger. However, the 120-rule is concerned with the supply currentsto the main buss, not the load currents leaving the buss.They therefore allow 125% of the inverters supply currentto be used instead of OCPD size to determine the bussloading as it pertains to the 120-rule. 27. Sooo In our example 6000W 240V inverter will produce a maximum of 25A. 1.25 (per the 705.12(D)(2) exception) x 25A= 31.25A (200A Main Buss x 1.2) 200A Main Breaker = 40Aallowable. 31.25A< 40A so it is GOOD!!! 28. Chargingcurrents Actual currents with exception factor = 32.5A32.5A < 40A so we are good! 29. Last Minute Resources Home Power Magazine: Code Corner Articles, Mehalic Articleon Load Side Connections, and the one on Line-SideConnections Solar Pro Articles Hren/Mehalic Issue 4.3 Code Red: Notable Changes to 2011 NEC Leblanc/Yates Issue 2.4 Can We Land? load vs. supply side interconnection Q & A Sections All issues SolarABCs.org Expedited Permit Process Workbook Cross reference to the Code Book as you prepare 30. Drilling Down Web Reader iPhone App readsarticles to you! Listen passively to article voice- overs. Good for driving, chores, etc. NEC Code Book Know wherethings are and where relatedinformation is!!! Tables Index Definitions, Article 100 31. Test-Taking Strategies Core Dump upon arrival Write out formulas you know I-V Curve, PIE chart, write it down before you get going CIRCLE what the question is asking you to figure out! Multiple Choice the right answer is there!!! Look for clues in other questions 32. How to Attack the Questions For a question requiring no calculations that you have complete confidence in the answer youve provided put a star next to it. For a question that you are not sure about the answer youve provided, or involves a calculation that you want to double-check later, put a circle. For a question with a circle that gets revisited later and you are confident of the answer, put a check in the circle. If you dont think you need to visit again, put a star. For a question that you skip, put a circle. BE CAREFUL: When filling out the answer sheet that you dont mix up your answers or put them where they shouldnt be. 33. Time Management 4 hours, 70 questions (60 count, 10 are pilot questions) First time through Recommend NOT to spend more than3 minutes on each question! Need to be able to get through the test at least one time andhave time to go back 34. Next Test Insurance Do your best! BUT, no matter what, this is a window intothe NEXT test! Stay the FULL 4 hours, NO MATTER WHEN YOUFINISH! Do you best to memorize as many questions as possible sothat if you fail this time, you can use those questions as astudy aide for the next test!! (just keep them to yourself). 35. NABCEP Code of Ethics 36. Be sure to buy the Casio fx260 Buy the Calculator:Casio fx260 about $5-10.00 Get familiar with thefunction keys(especially trig andarctan) 37. Why arctan?? Arctan is the function you use to convert a rise over runvalue to an actual value of pitch of the roof in degrees. For example: What if you had a roof with a 2/12 pitch? 38. First we must understand what 2/12 means? 39. It refers to the rise over the run212 40. For every 2 of rise, there is 12 of run212 41. So how do we solve for the angle? 2?12 42. We know that the tangent of the angle is equal to the opposite over the adjacentOpposite 2?12Adjacent 43. Therefore, 2 divided by 12 is thetangent of the angle which is0.1666Opposite 2?12Adjacent 44. How to solve In order to convert from the tangent of an angle toOpposite the actual angle value use the arctan function 2 ? 12Adjacent 45. Arctan functionPress shiftor 2nd key 46. Arctan functionArctan is thetan-1 key 47. What to Expect Scratch paper is either the exam cover sheet limited They supply pencils, you can ask for more sharpened They supply a copy of the NEC 2011 Tight Security varies by location, but you can be sure youwill not be able to bring anything into the exam A lot of page turning, distractions: FOCUS!!! 48. You Got This!!! Yes, this is a difficult test. 26% pass rate (rumor has it) Experience helps, but dontcount on it (solely) Code, Code, Code 49/70 = 70%