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Section 9: Study Guide Review Questions / Question #5 Error?
« Last post by Arvore on March 22, 2012, 03:43:30 PM »
From my perspective, this problem should have used "Latitude -15" in its calculation. If we go with the understanding that an "at latitude" tilt results in a 41.53 degree array tilt, then in this example, with the roof being at 26 degrees (which just happens to be 15 degrees less than latitude) we should use a solar irradiation of 4.8 hours based on the "latitude -15". Figure 14 on page 17 bears this out. Any dissenting view points?
Section 8: Case Study Examples / Voltage Drop Calculation
« Last post by DerrickH on March 22, 2012, 11:52:58 AM »
Regarding Case Study Example 1:

We are provided a scenario where an Array on a garage feeds into a combiner box on the same garage at ground level. The PV output circuit is then ran underground to the Inverter, which is located at the main house next to the main panel (Question 7).

My confusion begins at question 8 where we are asked to calculate the distance while maintaining a VD less than 2%. The calculation uses 240v nominal, as opposed to 413v (29.5Vmp x 14 modules). If we are still considering the scenario used in question 7, then why are we not using the maximum power voltage?

Any help on clarifying this would be appreciated.
Section 2: Verify System Design / Section 2.72 Source Circuit (page 66)
« Last post by Arvore on March 17, 2012, 02:54:00 PM »
Where did the 9A of continuous current value come from (paragraph 3). If we're still using the original source circuit example, the continuous current should be 10.5A (8.41 x 1.25).
Section 2: Verify System Design / Re: Calculating Conductor Ampacity
« Last post by Arvore on March 17, 2012, 02:11:55 PM »

This does indeed look confusing at first glance. However, my thinking is that it failed because they opted for a 15A fuse instead of 14A (OCPD calculation resulted in 13.1A which should lead to a 14A fuse). According to NEC 690.9(C), second paragraph, OCPD <15A go in 1A increments. So, technically a 14A fuse should have been used and would have satisfied NEC 690.9(C). But because they went with the 15A fuse it seems to violate NEC 240.4(B), which states,"The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used..."
Section 2: Verify System Design / Bypass Diodes Figure 67 (page 56)
« Last post by Arvore on March 17, 2012, 01:57:15 PM »
The bypass diodes depicted are configured incorrectly, i.e. they're forward biased. During normal (unshaded) operation, bypass diodes are reversed biased (not conducting). During a shading event, the bypass diode corresponding to the shaded cell(s) becomes forward biased and conducts current from the unshaded cells.
Section 2: Verify System Design / Calculating Conductor Ampacity
« Last post by Tony Henderson on March 06, 2012, 08:50:20 AM »
I'm studying the new NABCEP installer resource guide by Brooks and Dunlop, and I have a question on page 65, section 2.72, calculating required ampacity of conductors.

On Step 5, why does 13.93 amps fail because of 690.9(c)?

Tony H.
Thanks for the catch, we are working inserting any missing graphic.
This appears to be fixed.  I find question #7 on page 160.
General PV Discussion / Re: Example Question Corrections
« Last post by jen cooper on February 20, 2012, 06:42:39 PM »
O.k. - on question 3 study guide, its true the AC voltage drop would be greater than a DC run because of the operating voltage; lower voltage higher current... 
I still don't know what is going on with question 6. Anyone have any ideas? 
General PV Discussion / Example Question Corrections
« Last post by jen cooper on February 19, 2012, 01:46:45 PM »
     I'm new to the P.V. study guide forum. I will be sitting for the installers exam in March and couldn't help but notice a few (mistakes?) in the case study and the practice question section of the December 2011 5.1 version Installers Resource Guide. I would love to get some help with these, a second opinion, some clarification, corrections or a revised study guide.

Question number 8, Newark, NJ case study- They are looking for a voltage drop % of less than 2. The Vnom given in the answer is from the inverter (240v) not the P.V. array: (14 modules @vmp = 413v DC).   

Question number 2 in the Sample Questions- They ask where the inverter should be located to maximize system efficiency, performance and to minimize wire size. The answer given is C) at the utility point of connection.... But to minimize wire size, voltage drop and maximize system efficiency you would really want make the DC wire runs as short as possible which would mean that the inverter would be located at the PV array.

Question Number 3 sample questions- there is a voltage drop formula instead of an array shading diagram.

Question Number 6 sample questions- Not really sure what is going on here.  90% of the annual load is 6.21 Kw and @80% system efficiency is equal to 4.96 Kw the given answer is B) 4.43kw...?

Where is question # 7?

If anyone else has had issues with the study guide or knows of any other mistakes please post. My main concern is that if the actual test is written like the example questions are, none of us have a chance of passing. 
 Jen Cooper
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