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)
14. What if you had a 200A Main
Breaker and a 200A Main
Buss??
15. 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!!!
16. 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!!!
17. What if you had a 200A Main
Breaker and a 225A Main
Buss??
…AND you needed to put in a 20A OCPD, but the opposite
end of the panel was already filled up?
Could you do it?
18.
19. Yes!! Total supply to
the BUSS (220A) is
less than the BUSS is
rated for (225A)!!
20. Side note on Fastener
Requirement for OCPD
NEC 408.36(D):
21. Side note on Fastener
Requirement for OCPD
Exception to this provided by 705.12(D)(6)
22. What if you had a 200A Main
Breaker and a 200A Main
Buss??
…AND you really wanted to use that 13KW inverter that
requires a 70A OCPD?
Could you do it?
23. What if you had a 200A Main
Breaker and a 200A Main
Buss??
…AND you really wanted to use that 13KW inverter that
requires a 70A OCPD?
Could you do it? Maybe… There are two ways it can be
achieved.
24. What if you had a 200A Main
Breaker and a 200A Main
Buss??
…AND you really wanted to use that 13KW inverter that
requires a 70A OCPD?
Could you do it? Maybe…
1. Do a load analysis on the facility and if you determine
that you can reduce your Main Breaker down to 150A, then
that gives you 90A of PV supply OCPD head room:
(200A Main Buss * 1.2) – 150A Main Breaker = ?A
240A – 150A = 90A
25.
26. What if you had a 200A Main
Breaker and a 200A Main
Buss??
…AND you really wanted to use that 13KW inverter that
requires a 70A OCPD?
Could you do it? Maybe…
OR, 2. Do a line-side tap.
31. In this example with the
service size being 200A,
then the maximum size
line-side tap OCPD would
be 200A.
Maximum current from PV
array? 200A/1.25= 160A
PV Supply!!!
Wattage?? 160A x 240V =
38,400 Watts!!
32. 705.12 (D)(2) Exception
Now hold on there!!!… The specifications of my 6KW
240V bimodal inverter (grid-tied with battery backup) is
asking for a 60A OCPD in the main panel. I’ve got a 200A
Main Breaker and a 200A which gives me just 40A PV
supply OCPD headroom… I sure don’t want to downsize
my main. Is there any hope for me??
YES… there is.. It is the exception listed in 705.12(D)(2).
34. 705.12 (D)(2) Exception
(rationale)
Because the charging current required from the grid for the
batteries can be greater than the current supplied by the
inverter and PV array, the size of the backfed breaker must
be larger.
However, the 120-rule is concerned with the supply currents
to the main buss, not the load currents leaving the buss.
They therefore allow 125% of the inverter’s supply current
to be used instead of OCPD size to determine the buss
loading as it pertains to the 120-rule.
35. 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 = 40A
allowable.
31.25A< 40A so it is GOOD!!!
36. Charging
currents
Actual currents with
exception factor = 32.5A
32.5A < 40A so we are good!
37. Last Minute Resources
Home Power Magazine: Code Corner Articles, Mehalic Article
on Load Side Connections, and the one on Line-Side
Connections
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
38. Drilling Down
Web Reader iPhone App – reads
articles to you!
Listen passively to article voice-
overs. Good for driving, chores,
etc.
NEC Code Book – Know where
things are and where related
information is!!!
Tables
Index
Definitions, Article 100
39. 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
40. How to Attack the Questions
For a question requiring no calculations that you have
complete confidence in the answer you’ve provided put a
star next to it.
For a question that you are not sure about the answer
you’ve 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 don’t 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 don’t mix up your answers or put them where they
shouldn’t be.
41. Time Management
4 hours, 70 questions (60 count, 10 are pilot questions)
First time through – Recommend NOT to spend more than
3 minutes on each question!
Need to be able to get through the test at least one time and
have time to go back
42. Next Test Insurance
Do your best! BUT, no matter what, this is a window into
the NEXT test!
Stay the FULL 4 hours, NO MATTER WHEN YOU
FINISH!
Do you best to memorize as many questions as possible so
that if you fail this time, you can use those questions as a
study aide for the next test!! (just keep them to yourself).
44. Be sure to buy the Casio fx260
Buy the Calculator:
Casio fx260 – about $5-
10.00
Get familiar with the
function keys
(especially trig and
arctan)
45. Why arctan??
Arctan is the function you use to convert a rise over run
value to an actual value of pitch of the roof in degrees.
For example: What if you had a roof with a 2/12 pitch?
56. 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 you
will not be able to bring anything into the exam
A lot of page turning, distractions: FOCUS!!!
57. “You Got This!!!”
Yes, this is a difficult test.
26% pass rate (rumor has it)
Experience helps, but don’t
count on it (solely)
Code, Code, Code
49/70 = 70%
