Solar PV 120% 690.64(B)(2)

[ty]

What is the ACTUAL AC output of the inverters at What voltage?

There is a formula to use and specific Codes.

What is the Power Factor of each inverter???

You are not giving enough info.

 

[davedottcom]

Ty, like I said, it's not an actual situation so i don't have any specs on the inverters & I said to assume the 40 amp breakers are correctly sized per manufacturer's specs.

How would the inverter specs enter into the "Sum" formula?

690.64 refers only to the sum of the breakers.

 

[ty]

OK. I just drew it out on paper.

You would be OK with 150A Main on 200 Amp Buss with your (3) 2-pole 40's

 

[ty]

But, why not use a Main Lug Only loadcenter?

I'll give you an examle in a few minutes.

Oh, and the voltage would make a difference, because SMA inverters at 277/480 are 1-pole breakers, while 208 and 240 are 2-pole.

 

[SeanD]

SeanD,

It's hard not to start an argument around here!

Excellent point, 690.64(B) goes into describing which panels fall under this rule...

"...where this distribution equipment is capable of supplying multiple branch circuits or feeders or both the interconnecting provisionsfor the utility-interactive inverter(s) shall comply with (B)(1) through (B)(7)."

So... what makes a panel "capable of supplying circuits"? Available spaces?

I don't see any thing that mentions that labeling the panel "Solar Equipment Only" is even acceptable or by doing so would make the panel Not capable of supplying other circuits.

I was confused for a second there. I forgot we are speaking about the 2008 code. 2005 doesn't include this section, so it is significantly more vague. :grin: It's good to know about the upcoming changes. 2008 doesn't come into effect here until the end of the year.

 

[davedottcom]

But, why not use a Main Lug Only loadcenter?

I'll give you an examle in a few minutes.

Oh, and the voltage would make a difference, because SMA inverters at 277/480 are 1-pole breakers, while 208 and 240 are 2-pole.

Ty,

let's say 208 volts & it is a main lug only panel. You still have to add the sum of the breakers feeding the busbar. whether the 125 amp breaker is located in the sub panel or in a main distribution panel doesn't matter, it's the same 125 amp value either way.

Ok, examples are good!

 

[ty]

OK.

Say we are using (3) SMA Sunnyboy 7000Watt Inverters on a 3 phase 208 service.
Using a PV only panel (which will basically be a combiner box) to feed into the Main Distribution Panel (as you suggested in your example).

Let's start using a 200A Main Lug Only Loadcenter:

3*7000= 21,000w.

Volts*sq rt 3*PF of inverter
208*1.73*.98=
352.64

21,000/352.64=
59.55

59.55*1.25=
74A so next size breaker is 80amp.

80A 3phase breaker in main distibution panel.

Now each inverter:
P/V=I
7000/208=33.65

33.65*1.25=42A
So next size up is 45Amp breaker for each inverter

80+45+45=170A
Under the 200amp buss rating.


Same specs but using a 200A Main Breaker Loadcenter:
200*120%= 240A buss rating
200+45+45= 290Amp! No Good

Same using 200Amp MB Loadcenter with 150A Main:
200*120%=240A Buss rating
150+45+45= 240A. Barely OK, but makes it.



Now, using 277/480:
480*1.73*.98=
813.79

21,000/813.79=
25.81
25.81*1.25= 32.26A next size up is 35A Breaker
So, 3-pole 35A feeding MDP

Inverters:
P/V=I
7000/480= 14.58
14.58*1.25= 18.23
Next size up is 20A for each inverter.

These will be single pole 277volt breakers.
35+20=55A

 

[davedottcom]

Barely OK, but makes it.

That was funny!

I think what you meant to say is... It would be 100% 2008 NEC Code compliant! :grin:

But, what do you gain by doing it that way? It's a pass / fail situation. It's still a 7,000 watt inverter on a 45 amp breaker & as long as it is within the 120% rule of the busbar in the panel it's backfeeding what's the difference?

Seriously though, I am going to work out all of your examples, & thanks.

 

[ty]

That was funny!

I think what you meant to say is... It would be 100% 2008 NEC Code compliant! :grin:

But, what do you gain by doing it that way?

By using the MLO panel, you would spend less $$$$$.

You wouldn't have to pay for a 200A MBL and a 150 breaker,
your wize size would be smaller, conduit would be smaller, etc...

 

[davedottcom]

OK!

OK!

Ahhhh $ Gotcha!

I guess it could also be a major factor when trying to design a PV system for an existing service.

Thanks

 

[davedottcom]

I see the big picture now...

My way is fine, but your way is better!

I guess "slimming" down the numbers as much as possible will always be to your benefit.

Thanks!

 

[ty]

No problem.

good luck.

 

[davedottcom]

I would really like to go back and discuss SeanD's reply. No one else commented on his statement or my reply to him and I think it's the most important part of this thread.

SeanD's quote:

Just for the purpose of starting an argument. If this 200 amp subpanel is for solar only. Would this really be considered a "Connection to other source" (Title of NEC section VII)? Or if the panel is marked "Solar Only" would this be considered part of the solar system?

If this is considered part of the solar system, 690.64 wouldn't apply. You could then size the sub-panel to the appropriate size for combining the AC outputs of the inverters (100 amp panel w/ 100 amp main, I think. I don't work with 3-phase). You would then apply 690.64 to your interconnection at the main.

My response:

Excellent point, 690.64(B) goes into describing which panels fall under this rule...

"...where this distribution equipment is capable of supplying multiple branch circuits or feeders or both the interconnecting provisionsfor the utility-interactive inverter(s) shall comply with (B)(1) through (B)(7)."

So... what makes a panel "capable of supplying circuits"? Available spaces?

I don't see any thing that mentions that labeling the panel "Solar Equipment Only" is even acceptable or by doing so would make the panel Not capable of supplying other circuits.

This is important to clarify. 690.64(B) mentions that 690.64(B)(2) is only applicable to panels that are "capable" of supplying other circuits and/or feeds. This tells me they do not consider all panels to be capable.

So, my question remains:

What makes a panel capable or not capable?

Is it capable if it has empty spaces that are available?
Is it not capable if you hang a sign on it saying this panel is not capable?
Is it only not capable if no other spaces are available?
Is it capable only if it already has other circuits already in it?

Article 100 doesn't define capable, I just looked!

 

[ibew501ed]

I agree with the ambiguity
solar courses say say label the combiner panel "solar only"
but that clearly won't prevent future screw ups. Maybe a proposal for next code cycle
or maybe its clarified in 2011

 

[ty]

What makes a panel capable or not capable?

Is it capable if it has empty spaces that are available?
Is it not capable if you hang a sign on it saying this panel is not capable?
Is it only not capable if no other spaces are available?
Is it capable only if it already has other circuits already in it?

Article 100 doesn't define capable, I just looked!

Valid points, to the million dollar question.

IMO:

If you are using a 200A 3-phase MBL as a combiner for your (3) 2pole 40's,
it is going to be at least 12 spaces.
Now this panel will be in the parameter of 2008NEC 690.64(B)
...it is "capable of supplying multipl branch circuits or feeders"...

So, your concern is 690.64(B)(2)?

We have determined this loadcenter is 'Capable', so you can use it for your (3) 2-pole 40's, and size the buss accordingly.

There is no mention of sizing for possible future load to this panel.

690.64(B)(4) says it shall be marked.

I would size this loadcenter accordingly, size the buss accordingly, and label it accordingly.
(and hope the inspector sees it the way that I do)
I would call before hand, but this is how I see it, and so does alot of other installers and instructors.

 

[davedottcom]

Attention All Forum Members!

If anyone here has a panel
that is Not Capable of supplying any circuits
other than PV inverters
please take a picture of it for me...
I want to see what one looks like!
:grin:​

 

[davedottcom]

If an uncapable panel does exist, I bet it's made by Federal Pacific!