Wire Type

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Eric Ernst
Eric Ernst Registered Users Posts: 16 ✭
in Advanced Solar Electric Technical Forum #1
I'm putting together a system with a Xantrex 4024 inverter. I need to run two 60amp cables out from my garage, where the inverter is to the house where the main panel is and where the panel powering the inverter loads will be. My question is what kind of insulation do I need.

I intend to attach the cables under a deck type walkway and would perfer to run them without conduit since they are totally protected from any type of damage. Can I use THWN, or do I have to go to a UF that is capable of being buried directly.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Wire Type

    You SHOULD place the inverter as close to the battery bank as possible. Then run 120/240V wires for each circuit, as needed. Power a small load center from the inverter, and run 15 or 20 A circuits as needed.

    Lots of options for 20A (12GA) romex, but to try to carry 60A any distance is silly.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • TnAndy
    TnAndy Solar Expert Posts: 249 ✭✭
    #3
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    Re: Wire Type

    You thinking DC Mike ? 60a AC for 60' isn't that much of a run, simply need to size the wire accordingly for an acceptable voltage on the other end.

    I believe code will require you to use conduit, not exposed THWN......even though you say the wire will be run under a walkway, it pretty much HAS to be exposed at some point, like leaving the inverter, and coming into the panel on the other end.... .....and if you can get under the walkway to run the wire, it IS exposed....if nothing else, you may find rodents love the taste of insulation.
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  • Eric Ernst
    Eric Ernst Registered Users Posts: 16 ✭
    #4
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    Re: Wire Type

    I'd prefer not to do the long cable runs, but the physical location of were the pv panels must be (only south facing roof) and were the main power entry panel (for grid connect) is don't give me any other options. I know that I'll have to run 6 or 8 gage cable for the connections.

    The batteries will be directly below the inverter and the pv modules on the roof directly above it.
    Very good point on rodents. Had them chew up the wires on my tractor once.
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #5
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    Re: Wire Type

    Eric,

    The simplest approach might be to use UF or SE/USE cable. Individual conductors such as THWN will require conduit to meet code. Jacketed cables can usually be run in "exposed" locations so long as they're rated for the location and are not subject to damage (that may be at the discretion of an inspector). For copper UF or any aluminum cables, use #4. Otherwise #6 should be OK for 60A.

    Marc
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  • Pgovetom
    Pgovetom Solar Expert Posts: 30 ✭
    #6
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    Re: Wire Type

    I would suggest you download John Wiles summary of the Solar PV requirements in the NEC. He discusses wire, ampacity, derating, colors, wire type and has examples.

    http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/PVnecSugPract.html

    I presume you care about meeting code or do you just want it to be work?

    If the wires are exposed to light than you need USE-2 wire.

    My opinion is not running these wires in cheap conduit is not a great idea.

    I bought Southwire that with THHN, THWN and THWN-2 ratings all in one at Home Depot. Also check EBAY as Electricians sell off excess wire from big jobs and you can get good wire at 1/4 the retail price.

    In grey schedule 80 conduit you will need THWN-2 probably but I got THWN-2 ( 90 degrees and wet/oil) for THHN price so it doesn't matter in price much.

    You just say 60A but what does that mean? Is that nominal or fully derated or short circuit?

    What percentage of your power do you want to lose due to IR loses. I designed my system with .5% IR power loss on my DC wires. Solar systems will kill for 97% efficiency so wasting 2% in IR ( Ohms law) losses in a cable is not good.

    I would shoot for losing less than 1% or even .5% like I did.

    So what is the 60A. Continuous typical current? If so, multiply the wire gauges resistance x 2 ways by the typical operating current and see how many watts are dissipated in the wire. KEEP it low.

    Don't mess around. Do it right..... You have spent good money and want a good safe system and don't want to violate code or waste power.

    Use either USE-2 or THWN-2 in conduit and keep the resistance Low.

    just my opinion.

    The problem varies depending on whether your AC lines are line tapped or backfed into your service panel. Line tapped has more stringent demands since you are attaching directly to the utility grid. Feeding backfed breakers is looser.

    I presume you mean two hot wires, a neutral and a ground?

    The hot wires are not the same as the neutral and ground.

    You
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  • Eric Ernst
    Eric Ernst Registered Users Posts: 16 ✭
    #7
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    Re: Wire Type

    A lot to consider here. and and great useful references cited. Thanks.

    Yes I want it to meet code. Although I'm electrically smart, I'm code dumb. My electrical experience is military where milspecs rule vice codes. (Besides, my neighbor and friend is a county inspector - not electrical, unfortunately) so it would offend him if I didn't pull permits.

    Pgovotom, you mentioned that you didn't like back fed main panel connects. My plans call for a 60a breaker at the bottom (main is at top) of my main panel. I have the bus bar capacity to do that and it sure makes life (and interaction with the utility company) easier. If there is a down side to that, I'd like to consider it.

    If Run in conduit, which I am now leaning toward, can I run individual wires, and how much do I need to up size the wire? I'm currently looking a AWG 4 as having acceptable ampacity and acceptable IR loss. I assume it is an issue of the cable not being able to get rid of as much heat if put in a conduit. If I'm in a conduit, can I use THHN for the run even though it is mostly outside?

    Thanks for the help and references. This site is a treasure.
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #8
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    Re: Wire Type
    Eric Ernst wrote: »

    If Run in conduit, which I am now leaning toward, can I run individual wires, and how much do I need to up size the wire? I'm currently looking a AWG 4 as having acceptable ampacity and acceptable IR loss. I assume it is an issue of the cable not being able to get rid of as much heat if put in a conduit. If I'm in a conduit, can I use THHN for the run even though it is mostly outside?

    In most situations you're required to use individual conductors in conduit. A jacketed cable inside of conduit causes a greater increase in wire temperature, so it is often forbidden or, if allowed, it is derated. #4 copper THHN is good for 95A according to NEC 310-16, so you're good there...and that is assuming three conductors or less enclosed in conduit, jacketed, or buried. THHN in Sch80 nonmetallic conduit is suitable for most locations, above or below ground. If you're having the installation inspected, pay close attention to the entry and exit points of the conduit and make sure that the conductors aren't exposed at those points.

    Marc
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