What AWG wire gauge are you running from inverter to circuit breaker box?

softdown
softdown Solar Expert Posts: 3,896 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I had a solar pro make this connection for me. Told him I had:
10/2
10/3
and 6/3

He used to 6/3 to run to the diesel genset....almost made it too. Ran the 10/3 to my circuit breaker box. Probably figuring a single guy couldn't use too many circuits at once and that is what I had.

Well....the 6/3 to the diesel genset wasn't a bad choice. My batteries got low and I used a 20' 12 AWG power cord to complete the run to the genset. Looked pretty fried (copper wire got dark) and was very warm after a couple hours. Ready to run #6 AWG all the way to genset now.

I'm figuring copper THHN 4 AWG to the circuit breaker box....a 12 foot run. Rated around 100 amps as I seem to recall...

Would have probably gone larger but running low on room on the connection lug for the negative.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
· Share on Twitter

Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Hi soft..,

    The rating of the circuit PROTECTION -- the circuit breaker -- determines the minimum size of the conductors connected to it.

    There is probably a breaker on the genset, that protects the output connections to the genset. What is the rating of this breaker?

    Also, from the sound of your reference to the negative connection lug, you may have more than one wire in a single lug. If so, this is not good practice. You could use busbars for Neutral, L1, and L2, if there is a L2 lead from the genset (yes, know that you have 120 VAC inverter, from appearances).

    Busbars are available:
    http://www.solar-electric.com/instal...tebus/tbb.html

    ... White for Neutral, Black for L1 (usually), and, if needed, Red for L2. Ground connections can be made to the bare busbar without insulating mounts, that is screwed directly and solidly to the electrical box ...

    FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #3
    Outback makes a fine Manual, found here!

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • softdown
    softdown Solar Expert Posts: 3,896 ✭✭✭✭
    #4
    Didn't look easy to get into the circuit breaker on the genset. I don't know the rating. But I can't seem to recall a 110/120 circuit breaker rated at over 20 amps. So why did my 12 awg 20' extension cord get so warm?

    Inverter is a 3648. So a wire that rated for ~40 amps should be fine I would think.

    Vic wrote: »
    Hi soft..,

    The rating of the circuit PROTECTION -- the circuit breaker -- determines the minimum size of the conductors connected to it.

    There is probably a breaker on the genset, that protects the output connections to the genset. What is the rating of this breaker?

    Also, from the sound of your reference to the negative connection lug, you may have more than one wire in a single lug. If so, this is not good practice. You could use busbars for Neutral, L1, and L2, if there is a L2 lead from the genset (yes, know that you have 120 VAC inverter, from appearances).

    Busbars are available:
    http://www.solar-electric.com/instal...tebus/tbb.html

    ... White for Neutral, Black for L1 (usually), and, if needed, Red for L2. Ground connections can be made to the bare busbar without insulating mounts, that is screwed directly and solidly to the electrical box ...

    FWIW, Vic

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
    · Share on Twitter
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
    softdown wrote: »
    Didn't look easy to get into the circuit breaker on the genset. I don't know the rating. But I can't seem to recall a 110/120 circuit breaker rated at over 20 amps. So why did my 12 awg 20' extension cord get so warm?

    Inverter is a 3648. So a wire that rated for ~40 amps should be fine I would think.

    Hi soft..,

    First, only the most clairvoyant could know anything about your generator, other than that it IS a Diesel.

    Some gensets have outlets and circuit breakers built in. Others have a Terminal Strip, which is commonly fed from a circuit breaker. In either case, access to the genset output would be easy.

    It is most likely that an OB 3648 has a maximum capability of directly accepting #6 AWG cable, as it has a 60 A Transfer Switch, built-in. This implies that no larger cable for the generator input to the 3648 would be # 6 AWG. If your cable runs from the genset are long, #4 AWG (Copper) would be suggested.

    A single OB VFX 3648 inverter has a battery charge capability of about 45 DC Amps continuous. This represents only about 3500 watts of AC input, with charger inefficiencies. Adding loads that might be on the AC output of the inverter, a single 3648 would probably only be able to use about 6 -7 kW from the genset. This is close to 60 A maximum at 120 VAC.

    Given that your location might be at a relatively high altitude, the genset's maximum output would normally be de-rated at about 3% per 1000 feet of altitude above about 1000 feet (commonly).

    Questions;

    1. What is the make and model of the diesel genset that you are using on this system?
    2. What is its maximum output rating in kVA or kW?

    In general terms, # 12 AWG Copper cable is Rated for about 20 A in general applications. It should really be capable of handling about 25 - 30 A maximum.
    EDIT: However, should have added that black SO cord laying in the Summer sun can get hot with no current flowing, so it would be customary to derate the Maximum current to accommodate the ambient temperature that the cable is experiencing<<.

    Battery charging is often, a long slog, and can stress many system components, over a long period of time, especially with additional AC loads that are down-stream from the inverter will add to the current that the genset, and any cable connecting it to the inverter must supply ... this can cause overheating of components.

    Any circuit breaker on the genset shout be readily visible on its main panel, and should be labeled as to its Maximum current rating.

    BTW, AC circuit breakers in single pole and double pole versions are commonly available at Big Box stores, with Ratings to 60 Amps for Branch Circuits, and to 200 or so Amps as Main breakers, IIRC.

    All FWIW. You WILL get all of this figured out in time ... we are all learning. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
    · Share on Twitter

Categories