Need Help With 3 Line Drawing And Calcs For City Of Tucson

LHawes

I am applying for permits from the city of Tucson for a 10kW system and one requirement is a 3 line drawing with calcs for wire sizes. I have a set of drawings from an older California install that includes a 3 line drawing (that I can probably duplicate) so I get the general look and format but the calcs are a concern.

I know there's a wire size calculator here on the forum and I think I can get the wire sized properly (and I can always be conservative and up the wire size) but how would I show the actual calcs for arriving at that wire size? Anyone with experience with the City of Tucson?

Thanks

Larry

(Hope I chose the correct forum)

EDIT: System is (2) arrays of (30) Sharp 170U1 panels and (2) Sunny Boy 4000US or 5000US. One system will sit right over its inverter with perhaps a 15 ft. run from the panels and the other will have around a 30 ft. run from panels to inverter.

mike95490

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

The inspectors are liklely looking for the std wires sizes they are familar with, and the wattage/amps you calc your solar to be.
14ga =15A max
12ga =20A
10ga =30A

The more wires you add into conduit, the more heat you generate, and need to up-gauge the wire.
Outdoors and in outdoor conduit, needs to be UV and hot water rated too.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Thanks Mike,

I'm pretty comfortable getting the sizes right and work with inspectors a lot but I need to get the permit first and that requires the 3 line and calcs.

I found this site www.brooksolar.com and they have

this PDF file of what looks like a calculator of sorts used to create the 3 line but I'm still pretty lost. I'm thinking this is a jump into the deep end but willing to learn.

Larry

peterako

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

For anybody trying to follow the pdf link remove the symbol after .pdf

Greetings from Greece

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Fixed it, thanks...

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

This is what I finally came up with. Sorry i couldn't post the PDF (even zipped). Is there another way to get larger files posted?

Attachment not found.

niel

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

can't make out that one either. sorry, but the site only handles so much resolution. i don't know if it can be raised or not and maybe windsun will say here or drop him a pm yourself on it as this is the 3rd diagram you tried that we can;t seem to get well enough. maybe somebody else has a suggestion for you to try on this to make it readable.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

I hosted it on one of my web sites - probably not perfect but we're going to the city with to see what happens.

3 Line Drawing

Solar Guppy

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Pretty sure you can't have 7 #10 AWG's in a single 3/4 conduit ... I'm to lazy to go look it up, but your probably going to be limited to a single active pair plus ground in a 3/4 conduit due to the NEC limits on fill factor

lorelec

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Larry,

If I understand this correctly, you have ten modules in each parallel string? Each module has an Isc of 5.47A -- that's 54.7A per string. There's no way 10AWG wire is going to handle that.

Marc

Solar Guppy

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

He is running in series for an SMA4000 gridtie inverter, 10 panel , then the 3 strings down down in one conduit ( can't do that ) to the inverter

FL SUN

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Details, details.

Looking at the drawing, the integrated DC disconnects are breaking the negative and not the positive wires from the array. Should be the other way around.

Inverter output should be designated with 'L1' and 'L2' for 240 VAC and not '+' or '-'.

lorelec

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Solar Guppy wrote: »

He is running in series for an SMA4000 gridtie inverter, 10 panel , then the 3 strings down down in one conduit ( can't do that ) to the inverter

Ahhh...makes a lot more sense now. Thanks.

Marc

niel

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

it seems he combined them at the combiner and is now running 3x the current of a single string with a single pair of #10 wires and a #10 ground wire through the 3/4" conduit. i don't remember if he figured it for just 1 string's worth of current there or all 3, but in any vase the voltage drop does need to be taken into account as the 3x current will cause a 3x voltage frop to occur in the wire. the voltage drop also increases over distances so this is also a factor in what to go with. in most cases keeping voltage drops in check will be well within any complicated procedures wiles would come up with in his nec rulings.
btw, it's nice to finally be able to view the drawing.:D

Solar Guppy

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Niel, the diagram has quantity of 6 listed for the power leads from each array ... its is confusing, the diagram that is

niel

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

ok you're right on him feeding all 6 through it and you're also right as that won't be allowed in a 3/4" conduit. not sure of how big a single pair and ground would be allowed through 3/4" though as my idea isn't that bad as often a larger wire size is allowed because of the physical constraints of less insulation that would be present. not sure of those nec details off hand though and most likely he'll need larger conduit regardless.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Marc,

Each string of 10 panels is wired in series, the amps stay at 5.47 for all 10 modules.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Solar Guppy wrote: »

Pretty sure you can't have 7 #10 AWG's in a single 3/4 conduit ... I'm to lazy to go look it up, but your probably going to be limited to a single active pair plus ground in a 3/4 conduit due to the NEC limits on fill factor

Thanks for heads up. We'll definitely size the conduit appropriately on the job.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

niel wrote: »

it seems he combined them at the combiner and is now running 3x the current of a single string with a single pair of #10 wires and a #10 ground wire through the 3/4" conduit. i don't remember if he figured it for just 1 string's worth of current there or all 3, but in any vase the voltage drop does need to be taken into account as the 3x current will cause a 3x voltage frop to occur in the wire. the voltage drop also increases over distances so this is also a factor in what to go with. in most cases keeping voltage drops in check will be well within any complicated procedures wiles would come up with in his nec rulings.
btw, it's nice to finally be able to view the drawing.:D

Very good points and thanks so much for the feedback. My intent was not to use a combiner box but merely a junction box that would preserve all the initial amperages and voltage all the way to the inverter.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Solar Guppy wrote: »

He is running in series for an SMA4000 gridtie inverter, 10 panel , then the 3 strings down down in one conduit ( can't do that ) to the inverter

Is the 'can't do that' part because the conduit is too small?

Thanks

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Solar Guppy wrote: »

Pretty sure you can't have 7 #10 AWG's in a single 3/4 conduit ... I'm to lazy to go look it up, but your probably going to be limited to a single active pair plus ground in a 3/4 conduit due to the NEC limits on fill factor

I'd like to run all 7 wires through the proper size conduit and I'll up the size to match the wire fill regs.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

FL SUN wrote: »

Details, details.

Looking at the drawing, the integrated DC disconnects are breaking the negative and not the positive wires from the array. Should be the other way around.

Inverter output should be designated with 'L1' and 'L2' for 240 VAC and not '+' or '-'.

I'd really like to understand this. I have a system installed at my home that uses negatively grounded panels (which I understand almost all are - SunTechs being an exception?) and the 3 line that we used to install that system had the DC disconnect breaking the negative wire. What's the science and how is that determined?

Here's the DC disconnect section of the manual on the Sunny Boy

Thanks

Solar Guppy

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

LHawes wrote: »

I'd like to run all 7 wires through the proper size conduit and I'll up the size to match the wire fill regs.

OK, dug into my NEC2005 book

Chapter 9 deals with the conduit fill and de-ratings

For more than 2 conductors, maximum fill is limited to 40% ( 70-625 )

The EMT table lists a maximum of 6 conductors and you must include ground in the count for 10 AWG ( Table C.1 70-658 ) for wire types THHW THW THW-2

If you use 90C wire ( THWN which is what I get at Home Depot ) your OK with upto 10 conductors, so 3/4 would work BUT

I would suggest you go with 1" EMT it will be an easier job to pull the wires, your conduit from a pull prospective can never be to big and your permit reviewer will be happy you were conservative on the fill.

FL SUN

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

LHawes wrote: »

I'd really like to understand this. I have a system installed at my home that uses negatively grounded panels (which I understand almost all are - SunTechs being an exception?) and the 3 line that we used to install that system had the DC disconnect breaking the negative wire. What's the science and how is that determined?

Here's the DC disconnect section of the manual on the Sunny Boy

Thanks

I have been working on a three line drawing for a 6kw GT system we've been putting together. Our first, and I've been in Article 690 of the NEC for a good portion of the day. I cannot for the life of me find where it says to disconnect the positive, and not the negative in pv output circuits. 690.13 says "to disconnect all current carrying conductors of a pv power source from all other conductors in a building or other structure." The grounded conductor of course cannot be disconnected. 'Ground' of course cannot be confused with the 'negative' output of a pv circuit

The integrated disconnect of the Sunny Boy may disconnect both positive and negative of the pv output circuit. I don't know this at this point. We are using a Sunny Boy 6000 for ours BTW, so I'll find out soon as we get into the installation of our system.

Looking at the link on the SB wiring you provided, it looks like the pv output circuit can be configured for either positive or negative grounding to accomodate any pv application out there. Maybe the inspector overlooked the switched negative portion of the drawing.

Solar Guppy

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

You can't switch the negative as this is bonded to ground for safety reasons ( and compliance ). If you switch the ground, you have turned off the ground fault protection to the array. Now this is pre 2008 code and I don't have the new book to see how it deals with ungrounded arrays ... maybe someone with the 2008 can fill in the details

Now for Sunpower systems, you would switch the negative leg as the positive run is what gets bonded to ground for that same fault protection

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

Solar Guppy wrote: »

.....so 3/4 would work BUT

I would suggest you go with 1" EMT it will be an easier job to pull the wires, your conduit from a pull prospective can never be to big and your permit reviewer will be happy you were conservative on the fill.

Yeah I agree, we always up size for ease of pulling.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

FL SUN wrote: »

I have been working on a three line drawing for a 6kw GT system we've been putting together. Our first, and I've been in Article 690 of the NEC for a good portion of the day. I cannot for the life of me find where it says to disconnect the positive, and not the negative in pv output circuits. 690.13 says "to disconnect all current carrying conductors of a pv power source from all other conductors in a building or other structure." The grounded conductor of course cannot be disconnected. 'Ground' of course cannot be confused with the 'negative' output of a pv circuit

The integrated disconnect of the Sunny Boy may disconnect both positive and negative of the pv output circuit. I don't know this at this point. We are using a Sunny Boy 6000 for ours BTW, so I'll find out soon as we get into the installation of our system.

Looking at the link on the SB wiring you provided, it looks like the pv output circuit can be configured for either positive or negative grounding to accomodate any pv application out there. Maybe the inspector overlooked the switched negative portion of the drawing.

Our permits and the 3-line have not been approved as of yet so I'll keep this thread informed and like I said in a previous post I have an approved 3 line from another system, and system designer. that shows the negative broken and really the only reason I duplicated that in my 3 line.

I put in a system with Open Energy roof tile panels and a PV Powered 3500 inverter. The inverter clearly stated that with negative grounded panels proceed in this manner and with positive grounded panels proceed in this way. I called the panel manufacturer to find out how their panels were grounded and the technician said negative and that almost all panels are.

I'm not exactly sure how that bears within the conversation here but before we commit to the final set-up within the Sunny Boy I'll contact both the panel manufacturer and the folks at Sunny Boy to be sure we get it right.

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

We got our plans approved through the city of Tucson yesterday. Thanks so much for all your help. I hope i can follow up with this install and post any problems and solutions we might come across.

Thanks again

LHawes

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

I thought I'd follow up on this install. Everything went very well with the install and we're seeing about 4200 Watts max from each inverter and it's been HOT (100+) over the last few days. I have a question about heat loss I might post in a separate thread but was wondering if there's a chart or formula to figure heat losses from ambient heat?

Thanks to everyone here for the help on this project.

I'll cross post this in the other forum where I asked a different question re: this system.


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lorelec

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

LHawes wrote: »

I have a question about heat loss I might post in a separate thread but was wondering if there's a chart or formula to figure heat losses from ambient heat?

Loss is going to depend on the resistance of the wire. As the temperature of the wire increases, it's resistance will also increase (and so will its loss). The formula for figuring the resistance of a wire as a function of temperature is:

Ro = Rb [1 + c(To-Tb)]

where
Ro = the resistance of the wire in Celcius at the operating temperature To
Rb = the resistance of the wire at a baseline temperature Tb (usually at 25degC)
c = the temperature coefficient of the wire (for copper, this is about 0.0039)
To = the operating temperature of the wire in Celcius
Tb = the baseline temperature for which Rb is given (usually 25degC)

So, for example, a 10AWG wire has a resistance of 1.02 ohms per 1000 feet at 25degC. Say you want to figure the resistance of the wire at 65degC:

Ro = 25 [1+.0039 (65-25)] = ~1.18 ohms/1000feet, or about .0012 ohms per foot.

The complication here is that both the ambient and the heat generated by the wire itself will cause an increase in resistance. How hot the wire gets due to self-heating will depend on the thermal resistance of the wire and insulation to air, and that can be really difficult to determine.

Once you have the resistance per foot, multiply it by the length of the wire, and then multiply that result by the square of the current through the wire -- which will give you your power loss in watts. (P = I^2[R])

Marc

BB.

Re: Need Help With 3 Line Drawing And Calcs For City Of Tucson

You can also use the Wiring Calculator in this thread to check your losses at various temperatures (typically, design for less than 3% total loss at worst case temperature).

The other place where you will have losses is the solar panels themselves. There Vmp output voltage falls with increasing temperature (the current rises a little bit with increasing temperature--but you can ignore the effect with little error).

My system (GT 3 kW) seems to vary from a cool spring day (60 degrees or so) to hot spring day (95F)--by about 5-10% output drop at higher temperatures (could also include the typically hazy sky we have in hot weather).

You can look up your panel's Vmp and temperature coefficient and plug the numbers into:

P=V*I=[Vmp @77F - Vtcf(77F-xxF panel temp)] * Imp

I think that will work for you--I have to go.

-Bill

PS: Fix to "-" in middle of equation.

Also change from "ambient temp" to panel temperature.