NEC Wiring Questions

whitet777whitet777 Posts: 10Registered Users
Hi, long time lurker, first time poster.

I've successfully completed 1 solar install on a trailer, and am thirsty for more. So, I've decided to add a small system to my home. It will be off grid to provide full time power to some small off grid loads and provide emergency standby power for those same loads during outages. Loads are a small chest freezer, washing machine, and router, among anything else that I want to power on that power strip. (I've used a Kill A Watt meter to size the system.)

I am the very first person in my small town to want to install solar, so I have created a ruckus with the local building inspector. He's insisted that I get a building permit, which I assume means that he'll want to inspect my work. This makes me a bit more careful about my install. He doesn't have the first clue about what to look for, so he may go overboard.

Here is what I have so far:
1-Helios 7T2-310 panel
1-Meanwell TN-1500-124F Inverter (24V DC Input, 120V AC Output)*
4-Trojan Black golf cart batteries (6V 210Ah each all in series)
1-Blue Sea 150A DC breaker for positive battery cable
(I'm aware that I'll need a DC breaker on the solar panel input into the inverter)

*The Meanwell inverter/charger is pretty neat. It will let me run off grid with AC bypass input for when the solar/batteries are too low; providing consistent power to my critical freezer load.

So, here are my questions:
-I have lots of 3/0 welding wire left over from the trailer install. Apparently, it's not legal for use in a home according to the NEC. Would others agree with this? Has this been a problem for your inspectors? Besides Wind-Sun.com where can I get bulk NEC cable? I want to shop around.
-The solar panel is rated for 45V STC. According to the NEC 125% rule, that puts me over 50V DC. Can I run wire without a conduit or raceway down from my roof into my basement? If so, am I better off using MC4 single conductor solar cables or just running standard 10/2 NEC approved outdoor cable?
-Looks like I have to put ground fault protection in because it's in a dwelling. Can any one concur? What model would you recommend for my application?

Thanks for the help. If I enjoy this install, I may just have to do the whole house some day :)
Tim

Comments

  • BB.BB. Posts: 27,885Super Moderators, Administrators admin
    Re: NEC Wiring Questions

    In general, you should be using the rated solar wiring for the panels/roof runs. UV is very hard on insulation and so can animals (squirrels and other other animals with less good press). So conduit would be a requirement too--And I believe the NEC would require rated conduit into the home until the DC disconnect (and fusing/breakers, if required).

    Using your welding cable for the battery bank may be OK with your inspector. As always, lead acid batteries can output a crazy amount of current (probably over 1,000 amps into a dead short). So insuring that the cables are properly supported, no short metal to cut insulation, and a cover over the battery bank to protect against dropped tools and kids too.

    Now, before we get into the hardware--Let us look back at your needs/existing hardware. Two ways to go--First start with your loads, or second to start with your existing hardware.

    Solar power systems are very difficult to expand in a cost effective manner. And, in your case, starting with a 24 volt battery bank will make it a bit easier to design/build out your system with a good amount of available energy.

    I would suggest that you get a Kill-a-Watt type meter to measure your energy usage (peak watts, average watts, how much energy per day you use in Watt*Hours/kWH).

    To run an energy star rated fridge/freezer and a few other random/small loads, you probably are looking at a 1.5 kWH per day minimum. And I would suggest around 3.3 kWH per day for a serviceable off grid system that could keep you going for months (or longer).

    Since the battery bank is the "heart" of your power system, I like to design a balanced charging system around it. Lets pick 1,000 WH (or 1 kWH) per day as your loads (I cheated, that is what your present battery bank with "ideally" support--but to show the math...). Assume 1-3 days (pick 2 days for "balanced" system) and 50% maximum discharge for long battery life... A battery bank would look like:
    • 1,000 WH per day * 1/0.85 inverter efficiency * 1/24 volt battery bank * 2 days storage * 1/0.50 max discharge = 196 AH @ 24 volt battery bank

    So, close to the battery bank you already have. Next, we need to look at charging that battery bank. Our rule of thumb is ~5% to 13% rate of charge for a happy battery bank. The size of solar array needed would be:
    • 210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 395 Watt array minimum
    • 210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 791 watt array nominal
    • 210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,028 watt array "cost effective" maximum

    So, your present single 310 Watt panel is a bit on the small size... Two to three of your 310 Watt panels would be a much better match for your existing battery bank.

    Now, how much power will an array supply... Using PV Watts and guessing you are around Milwaukee Wisc., with an array tilted to your latitude (tilted from horizontal, fixed array, and you might think of tilting to near vertical in winter if you have a lot of snow for a "self clearing" array), we get:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.32     
    2      3.96     
    3      4.28     
    4      5.11     
    5      5.58     
    6      5.88     
    7      5.66     
    8      5.60     
    9      5.19     
    10      4.34     
    11      2.96     
    12      2.49     
    Year      4.53
    

    Toss out the bottom three months (assume utility power/backup genset use during poor weather), we get February at 3.96 hours of sun (noon time equivalent) per day as the "break even point". A 791 Watt "nominal array" would output a minimum (long term average) of:
    • 791 Watt array * 0.52 off grid system efficiency * 3.96 hours of sun per day = 1,629 120 VAC Watt*Hours per day

    Note that running a freezer on an AC inverter may need the inverter to run 24x7 -- And inverters have significant "tare losses" (power used just because the inverter is "on")--Which can easily be in the 6 to 20+ watt range... For example a 20 watt tare loss (larger inverters have larger losses), that is 480 Watt*Hours per day--Or over 1/4 of your available power in February.

    So, before we go further--What would your plans be for the system (larger array now, or expansion plans later, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    Wow. I wasn't expecting such a thorough first response. Thanks Bill.

    I probably should be more clear with my intentions. First and foremost, this is an experiment. There will be no hardships if this system is undersized.

    I did mention that I used a Kill-A-Watt, but that was buried in my post. I measured 1.2kWhr usage over a typical week. I know I'm on the ragged edge of a bare minimum system. The nice thing about the Meanwell inverter is it will shift to AC bypass mode if I'm out of battery. Also, worst case, I simply take one of the loads plugged into the power strip and will plug it back into the grid.

    So, really my biggest concern is just being code compliant. I'd hate to spend all this time and $ and be told I have to redo everything. I've been trying to convince the city that this really is no different than taking a portable generator and plugging in some loads to it, but they are paranoid because I've used the word solar. In fact, they just put a moratorium on any solar installs beyond mine until they write ordinances to control it.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: NEC Wiring Questions

    If it's not fastened to the house they shouldn't be concerned. It is possible to build a portable solar electric system for experimenting with. When you start "hardwiring" to the existing system is when things need to follow code and get permits/inspected.
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    I think I'm on the fringe with this experiment. The solar will be sitting on a flat portion of my roof, tilted with no penetrations. The wires will penetrate my basement wall though. The loads will all be plugged into an off-grid power strip. I think they are just not clear how to deal with me given I'm the first to install solar in my city and this install is clearly not normal. I'll play nice for a bit unless they get ridiculous.
  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    ...1-Meanwell TN-1500-124F Inverter (24V DC Input, 120V AC Output)*
    ...

    I don't believe this inverter is UL listed for home use I think it is only UL 458 if that (I've read only 'G' models carry UL 458 ) This is for Mobile and Marine use. In theory Home use must have a battery box and conduit from the Battery Box to the inverter. If this will be inspected, ask your inspector about what they require. Even inverters with provisions for these lines run in conduit often are done with out. Home use is UL 1741(me thinks)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    Good catch. It is only rated to UL458 for the model I have with the GFCI outlets. I seriously think the inspector will see UL and think that is good enough.

    For a battery box, I was going to use a Rubbermaid-like container with a lid and vent line to the outside. Good call on the inverter to battery conduit. I'll look into the code a bit more on this. The batteries and inverter will be out of the way and will be protected enough for accidental shorts.

    I fear asking the inspector anything because I know I know more than him on this and if I start asking questions he'll know where to start looking.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    Good catch. It is only rated to UL458 for the model I have with the GFCI outlets. I seriously think the inspector will see UL and think that is good enough.

    For a battery box, I was going to use a Rubbermaid-like container with a lid and vent line to the outside. Good call on the inverter to battery conduit. I'll look into the code a bit more on this. The batteries and inverter will be out of the way and will be protected enough for accidental shorts.

    I fear asking the inspector anything because I know I know more than him on this and if I start asking questions he'll know where to start looking.
    Yeah, till he see a extension cord plugged into the front of it, then he'll wonder why he's even there. What your trying to do is make a UPS with solar support, i don't see where he'd even have a interest. Is he a Building Inspector or a Electrical Inspector ?? I had a run in with a Building Inspector that made me get a structural analysis done for some panels even though they didn't require a permit or his approval to be installed, I just took the path of least resistance and had it done. $600 in the wind for nota.
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    He's a jack of all trades for a small city (2000 people). He inspected some electrical work I had done for a basement remodel and didn't even have a clue about that. Maybe I'm overreacting. I tried to explain that it's a UPS, but that's foreign to him.

    Got to love red tape. Thanks for all the support guys.
  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    Good catch. It is only rated to UL458 for the model I have with the GFCI outlets....

    Does it have a provision to be hardwired as well? I think some of the Meanwell do, in fact I didn't realize this while speaking with someone who had a Prosine 2000 that had both, perhaps since yours has a pass thru and perhaps a charger? it's setup the same way.

    FWIW - I have no inspection and will be using 2 1800 watt Prosine inverters(1 installed now), they can be hard wired and one of them has a UL1741(?) but no provision for battery cables in conduit. I believe they were used in stair lift chairs as a battery backup and perhaps every thing lived in a UL box...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    No hardwire option with the TN-1500-124F.
  • PhotowhitPhotowhit Posts: 4,703Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    No hardwire option with the TN-1500-124F.
    .
    Plugging in your home may create a problem for the electric inspector, odd thing here, I work in a "camping community' and just purchased a modular home. The electric coop is fine with plugging in a camper or mobile home, if it still has the hitch on it, but if you remove the hitch (required for taxing the mobile home with the land) it must be hardwired. No inspection just the electric coop...gotta love Missouri.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • YehoshuaAgapaoYehoshuaAgapao Posts: 280Solar Expert ✭✭
    Re: NEC Wiring Questions

    No permits or inspections in Mesa, AZ for grid-tied solar systems (with or without batteries). They require permit for off-grid systems though because there is no utility design approval or inspection. They city is essentially freeloading off the utility for the inspections but the utilities mostly only inspect the AC side of the system. For bi-modal battery based systems, they are very concerned about how the system behaves in a grid down + batteries full + sun out scenario (AC-coupled battery banks have caused backfeeding problems for SRP in the past) though, but other than that they mostly only care about the AC side.

    Not sure if a permit would be needed for a truck-portable off-grid solar cart though (3 or 6 full size 60-cell 220-260W solar panels, 3 or 6-string combiner box, 60A MPPT charge controller, 1000W pure sine wave inverter, 8 golf cart batteries).
  • YehoshuaAgapaoYehoshuaAgapao Posts: 280Solar Expert ✭✭
    Re: NEC Wiring Questions
    In general, you should be using the rated solar wiring for the panels/roof runs. UV is very hard on insulation and so can animals (squirrels and other other animals with less good press). So conduit would be a requirement too--And I believe the NEC would require rated conduit into the home until the DC disconnect (and fusing/breakers, if required).

    I agree. Don't go cheap on wire size. And do use conduit where it isn't shaded or inside the house. In AZ, even USE-2 gets torn up by the sun in a matter of a few years.
    210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 395 Watt array minimum
    210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 791 watt array nominal
    210 AH battery bank * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,028 watt array "cost effective" maximum

    If you can shift most usage to sun-up hours (like under a utility TOU pricing plan), you probably can push to 0.2 off-grid (higher grid-tie, with curbed charge rate and networked inverter & MPPT). A far second to generator gas, batteries are expensive. Solar is cheap and getting cheaper (inverters seem to be stagnant in pricing change). Batteries are expensive and getting more expensive, and are the most depreciating / short lived component in the system (5-10 years vs 5-20 years for inverters). 2 strings of full-size 60-cell 220-260W panels (6 panels, 1320-1560W) will be around 0.2 rate of charge for 4 golf cart batteries.
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    Thanks. I'll use PVC conduit or a raceway for the Solar DC coming down from the roof where it is exposed to the sun.

    We are also planning on doing most consumption during sunny parts of the day.
  • solar_davesolar_dave Posts: 2,334Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    No permits or inspections in Mesa, AZ for grid-tied solar systems (with or without batteries).

    And just across town there is the other side of the coin. Glendale, AZ requires permits, and inspects everything, including the structural installation. They red tagged our system 3 times, and on the 3rd time the electrician was there to find out exactly what it would take to pass. It was mostly grounding issues with proper bonding to each component.
  • YehoshuaAgapaoYehoshuaAgapao Posts: 280Solar Expert ✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    Thanks. I'll use PVC conduit or a raceway for the Solar DC coming down from the roof where it is exposed to the sun.

    We are also planning on doing most consumption during sunny parts of the day.

    James ran almost all my PV wiring through the attic, in flex metal conduit (code requires metal conduit or raceway for PV in the attic). For the one spot where PV string wiring is in the sun, it is in a schedule 40 PVC conduit (gray electrical).

    You will need your generator on bad weather days if you go PV heavy and battery lite (there aren't many of those in AZ) because you won't have much reserve capacity in the battery bank.

    High density polyethylene and polypropylene are the best materials to house batteries in. If you are in a permit free area and those are high quality containers, by all means use it. Flooded batteries do need ventilation (my batteries are overkill ventilated because i'm ventilating for the 110 degree days and it is 10 degrees cooler on the floor in the garage). Battery acid eats up aluminum and steel like nothing (cotton is candy to battery acid, gets eaten even rubbed up on the side of the battery off of the shipping crate; polyester has mild-moderate resistance - a drip from they hydro, rinse it out and its fine).
  • whitet777whitet777 Posts: 10Registered Users
    Re: NEC Wiring Questions

    You will need your generator on bad weather days if you go PV heavy and battery lite (there aren't many of those in AZ) because you won't have much reserve capacity in the battery bank.

    The Meanwell TN-1500-124F will use AC charging as a last resort if the batteries are low and there is no solar. I am not going off grid, so this is adequate for my experiment. I will not be using a generator.
  • Dave AngeliniDave Angelini Posts: 4,014Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    whitet777 wrote: »
    The Meanwell TN-1500-124F will use AC charging as a last resort if the batteries are low and there is no solar. I am not going off grid, so this is adequate for my experiment. I will not be using a generator.

    Good! You do not need one! I have 4 offgrid homes in Arizona alone that do not need generators. Hard to beat the southwest for reliable power from the sun!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: NEC Wiring Questions
    Good! You do not need one! I have 4 offgrid homes in Arizona alone that do not need generators. Hard to beat the southwest for reliable power from the sun!

    Would be impossible in the North. What is an approximate "Array Size"/"Average Daily Consumption" in these houses?
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: NEC Wiring Questions
    NorthGuy wrote: »
    Would be impossible in the North. What is an approximate "Array Size"/"Average Daily Consumption" in these houses?

    Nah, piece of cake. You just put the array in Arizona and run the wires North. :p
    Okay so you'll need some big wires and a high Voltage charge controller ... Although maybe not by the time it gets here.

    Seriously; we get down to 2 hours usable sun in Winter, and that's not much time to charge a battery in. :cry:
  • northernernortherner Posts: 492Solar Expert ✭✭✭✭✭✭
    Re: NEC Wiring Questions
    Nah, piece of cake. You just put the array in Arizona and run the wires North. :p
    Okay so you'll need some big wires and a high Voltage charge controller ... Although maybe not by the time it gets here.

    Seriously; we get down to 2 hours usable sun in Winter, and that's not much time to charge a battery in. :cry:

    You can solve that problem by converting all your fitness equipment into electrical generators, and send out open invitations for a free workout session. And voile, free power! That is if anyone actually shows up.;)
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: NEC Wiring Questions

    Could be tricky converting a splitting maul into a generator. Hmm. Magnetize the head, and make sure they swing it neatly through the coils of wire ....
  • northernernortherner Posts: 492Solar Expert ✭✭✭✭✭✭
    Re: NEC Wiring Questions
    Could be tricky converting a splitting maul into a generator. Hmm. Magnetize the head, and make sure they swing it neatly through the coils of wire ....

    Well, at least you may have some wood split out of the deal?

    I've heard that a fit person can generate about 200 watts of electrical power on a bike. Lance Armstrong probably around 500 watts.
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: NEC Wiring Questions
    Nah, piece of cake. You just put the array in Arizona and run the wires North. :p
    Okay so you'll need some big wires and a high Voltage charge controller ... Although maybe not by the time it gets here.

    It would be much easier to move to Arizona. In fact, many of my neighbors already go there for winter :p
  • solar_davesolar_dave Posts: 2,334Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    NorthGuy wrote: »
    It would be much easier to move to Arizona. In fact, many of my neighbors already go there for winter :p

    It is the good life! Lots of Canadians here for sure.
  • Dave AngeliniDave Angelini Posts: 4,014Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions
    NorthGuy wrote: »
    Would be impossible in the North. What is an approximate "Array Size"/"Average Daily Consumption" in these houses?

    They are all have different requierments, like the people who live in them. My smallest array is 2KW on a Wattsun single axis.

    It may be impossible where you live but I have a few Alaskans and Canadians who seriously reduce the need to run the beast by using 5 to 10 KW of panels. These are not people who do without the good things we have these days.
    They just learn that there are days that they can choose to not consume energy at a pace that they normally do. There are other things to do besides watch a counter rack up KWH.

    This forum is great for people who are concerned with saving money. I do not necessarily target that group!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: NEC Wiring Questions
    It may be impossible where you live but I have a few Alaskans and Canadians who seriously reduce the need to run the beast by using 5 to 10 KW of panels.

    I would need approximately 30kW array to go solar-only. Most of it would be totally wasted most of the year except 2.5 months in the middle of the winter.

    I have 6kW now. I probably will be installing another 5-6kW, however I'm still not sure. Right now, it looks like the cost of new array is approximately equal to savings from reduced generator runs. I have to watch at least one whole season to make a decision.
  • westbranchwestbranch Posts: 5,087Solar Expert ✭✭✭✭
    Re: NEC Wiring Questions

    NG, except that the $$ outlaid for Solar is a one time expense rather than an annual one. Sounds like you are getting ever so close to that sweet spot where you are not over-solared ...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: NEC Wiring Questions
    westbranch wrote: »
    NG, except that the $$ outlaid for Solar is a one time expense rather than an annual one. Sounds like you are getting ever so close to that sweet spot where you are not over-solared ...

    I count amortized cost. For solar - over 25 years. For generator - over 2000 hours + fuel. If I install more solar, generator will last longer (in theory anyway) and I'll need less fuel.
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