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Type: Posts; User: ggunn

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1. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### That's what 310.15(B)(3)(c) does as an adjustment...

That's what 310.15(B)(3)(c) does as an adjustment to the ambient temperature. If we still must make the same calculation, why not leave the table in the code? Why fix it if it ain't broke?
2. ## Thread: inspectors doing electrical- learned something new

by ggunn
Replies
52\$\$
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1,467

### Discrediting an inspector in a jurisdiction in...

Discrediting an inspector in a jurisdiction in which you work is like shooting a tiger. You'd better take him out with your first shot or he will have you for lunch. :D
3. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### I get it, but it makes no sense to me. When the...

I get it, but it makes no sense to me. When the ambient temperature is 100 degrees the temperature on a rooftop in areas exposed to sunlight can easily be 140 degrees. We derate for the 20 degree...
4. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### So, we will have to figure out what temperature...

So, we will have to figure out what temperature the conductors will get to and derate accordingly? How is that different from using 310.15(B)(3)(c)?
5. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### It's not that there is a problem, per se. My...

It's not that there is a problem, per se. My issue is that if the ambient temperature is 100 degrees F we have to derate 90 degree conductors by 0.91; if the temperature on the roof is 140 degrees do...
6. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### It started for me in 2008 when I began working in...

It started for me in 2008 when I began working in the solar (PV) industry.
7. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### It just doesn't make much sense to me to have...

It just doesn't make much sense to me to have different conductor ampacity derate numbers for every 5 degrees of ambient temperature and then disregard the substantial heating over ambient of...
8. ## Thread: When did rooftop table 310.15(B)(3)(c) appear in the code?

by ggunn
Replies
30\$\$
Views
875

### Then why derate for temperature at all? Anyone...

Then why derate for temperature at all? Anyone who puts conduit on a roof can tell you that conduits exposed to sunlight on a rooftop (and therefore the conductors inside it) get a whole lot hotter...
9. ## Thread: supply side PV connection

by ggunn
Replies
119\$\$
Views
2,842

### IMO your best bet is to make an appointment for a...

IMO your best bet is to make an appointment for a preconstruction meeting with the AHJ and ask how they want it done. They may not care, but the two AHJ's I deal with most have definite and opposing...
10. ## Thread: supply side PV connection

by ggunn
Replies
119\$\$
Views
2,842

### One thing I think we can all agree on (maybe!) is...

One thing I think we can all agree on (maybe!) is that the central issue here is that Distributed Generation (PV, et al.) throws new variables into a complex system of interrelated rules that were...
11. ## Thread: 120 % rule

by ggunn
Replies
11\$\$
Views
386

### It's no big deal, but the NEC is...

It's no big deal, but the NEC is (uncharacteristically, some might say) clear about the calculations pertaining to the 120% rule. The OP was correct in his math; 120% of the bus rating minus the...
12. ## Thread: 120 % rule

by ggunn
Replies
11\$\$
Views
386

### The inspector would never be correct in using the...

The inspector would never be correct in using the rating of the backfed breaker multiplied by 1.2 in any 120% rule calculations.
13. ## Thread: 120 % rule

by ggunn
Replies
11\$\$
Views
386

### Section 705.12(D)(2)(3)(b) of the 2014 code is...

Section 705.12(D)(2)(3)(b) of the 2014 code is clear. 125% of the maximum inverter current plus the rating of the main breaker cannot exceed 120% of the rating of the busbar. Any calculation...
14. ## Thread: Multiple Inverters in "Combiner" Panel 705.12(D)(2) Application Commercial/Industrial

by ggunn
Replies
9\$\$
Views
261

### Sure, but I was under the impression that the...

Sure, but I was under the impression that the OP's followup Q was about the MDP.

Aside: one of my very first contributions to my present company (on my first day) was to point out that they had...
15. ## Thread: Multiple Inverters in "Combiner" Panel 705.12(D)(2) Application Commercial/Industrial

by ggunn
Replies
9\$\$
Views
261

### Yes, 125% of the inverter max output current (not...

Yes, 125% of the inverter max output current (not the value of the backfed breaker) counts toward the 120% rule (subsection (b)) in every panel in series all the way back to the service, and if the...
16. ## Thread: Red tape on white wire?

by ggunn
Replies
25\$\$
Views
891

### I am talking about single phase residential...

I am talking about single phase residential panels.
17. ## Thread: Red tape on white wire?

by ggunn
Replies
25\$\$
Views
891

### What about in the walls of a house? That's where...

What about in the walls of a house? That's where I am seeing it (in residential panelboards).
18. ## Thread: Voice signal power amplifier.

by ggunn
Replies
33\$\$
Views
910

### Not really. The purpose of humbuckers is to buck...

Not really. The purpose of humbuckers is to buck hum (hence the name) not to reduce distortion. Any EM noise picked up and injected into the circuit from the environment by coil A is canceled by the...
19. ## Thread: Multiple Inverters in "Combiner" Panel 705.12(D)(2) Application Commercial/Industrial

by ggunn
Replies
9\$\$
Views
261

### I agree; see 705.12(D)(2)(3)(c) in NEC2014....

I agree; see 705.12(D)(2)(3)(c) in NEC2014. That's the language that legitimizes AC combiner panels for PV. 705.12(D)(2)(3) does apply, in any case. It gives you three (four really, but use (d) with...
20. ## Thread: Red tape on white wire?

by ggunn
Replies
25\$\$
Views
891

### Red tape on white wire?

Something I have seen several times lately is a white wire with red marking tape connected to a breaker in a panel. Is that NEC compliant? I didn't think you could do that.
21. ## Thread: SolarEdge 20kW Inverter Grid Connection Riddle

by ggunn
Replies
6\$\$
Views
285

### The only way I know of is to install a 1:1 delta...

The only way I know of is to install a 1:1 delta to wye isolation transformer with a grounded neutral between the service and the inverter. I'd be interested to hear if there is another way.

by ggunn
Replies
48\$\$
Views
1,413

### Why wouldn't it be? I have seen 1P3W panels on A...

Why wouldn't it be? I have seen 1P3W panels on A and C on a high leg service; what's the diff?

by ggunn
Replies
15\$\$
Views
738

### How does anyone consider this outlet to be...

How does anyone consider this outlet to be grounded? The hack would have been better off just connecting a bare copper conductor to the green screw and shoving the other end of it out of the back of...
24. ## Thread: Co-Op or Work

by ggunn
Replies
8\$\$
Views
772

### My experience was a little out of the ordinary;...

My experience was a little out of the ordinary; my BSEE was my second degree. My first was BSChem, which was the same education as some of the process engineers had in the fab I worked in as a Co-Op....