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Thread: Solar disconnect wiring

  1. #11
    Join Date
    Nov 2010
    Location
    North east Ohio
    Posts
    74

    Default Re: Solar disconnect wiring

    caribocoot,
    " ... it's easy to interrupt alternating current since it essentially hits zero Volts sixty times per second ..."

    At my house, the AC crosses zero volts 120 times per second.


    Also,
    Does there need to be a fuse near/at the BAT + terminal?
    What protects those heavy gauge wires from shorting and starting a fire?

  2. #12

    Default Re: Solar disconnect wiring

    Quote Originally Posted by NEOH View Post
    Also,
    Does there need to be a fuse near/at the BAT + terminal?
    What protects those heavy gauge wires from shorting and starting a fire?
    There most definitely should be some form of circuit protection on the battery wire, whether fuse or circuit breaker. It is also a good idea to have it as close to the battery as possible for just the reasons you mention. Blue Sea makes some nifty terminal-mount fuses that work well for this, and there are also breakers and standard "inverter" fuses that can be used. It's all about finding something that has a rating suitable for the current expected (based on wire size; the circuit protection must always be the "weakest link") and that fits in with your particular mounting limitations.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #13

    Default Re: Solar disconnect wiring

    So do I still need the fuse at battery even though everything goes through a breaker before battery?

  4. #14
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,525

    Default Re: Solar disconnect wiring

    I do not believe in double fusing/fuse-breaker on the same wire...

    The issue is to keep the fuse/breaker as close to the battery as practical (some specs. are like 18 inches or so)... Basically, look at how things may fail decide if the + wire from the battery to the first battery breaker/fuse is short/safe from damage. If so--then your current breaker is probably "good enough".

    If, for example, the + wire can get cut by something falling on it, pinched in a metal door, cut by sharp sheet-metal, etc.--Then you may want to look at a fuse/breaker closer to the battery.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  5. #15

    Default Re: Solar disconnect wiring

    Batteries are about 3' away from breaker. There is nothing that will damage cable. The fuses Cariboocoot mentions are not expensive, is there any reason not to put one at the battery? If not what size? My cables are 1/0, I think that is 150A. 100A fuse?

  6. #16
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,525

    Default Re: Solar disconnect wiring

    A 150 Amp cable can use a 150 amp fuse and should carry a maximum of:
    • 150 amps * 0.80 NEC derating = 120 amps maximum continuous current


    You should have a couple extra fuses stored with the application...

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  7. #17

    Default Re: Solar disconnect wiring

    Thank you Bill.

  8. #18

    Default Re: Solar disconnect wiring

    Here's a nit to pick.

    Quote Originally Posted by Vic View Post
    From the Midnite Forum, this FAQ adds some deatil, escpcially the polarity of the breaker that connects the output of a Charge Controller (MPPT) to the battery bank.
    http://midnitesolar.com/smf_forum/index.php?topic=113.0
    Vic
    I disagree with Halfcrazy (from Midnite) on one point:
    "In a PV combiner the + sign marked on the breaker connects to the PV positive output."

    Here is why:
    - "The + sign designates the highest potential should be conneced there."
    - "The main job of this output breaker is to trip when and if there is a catastrophic failure."
    - "Since these two terminals inside the charge controller are normally connected up to a very large battery bank, you have a direct short across the battery bank if the controller fails. During this condition, the controller is acting like a piece of wire."

    This says to me that the PV combiner breakers should be hooked up with the + marks towards the charge controller.( towards the inverter for batteryless) Because if one string in a multi-string installation has a fault it will receive current, backfed through the combiner circuit, with all available current from all of the other strings or by current comming from the battery via. a faulted charge controller.

    Alex Aragon

  9. #19
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,525

    Default Re: Solar disconnect wiring

    I agree with Alex/SolaRevolution on that interpretation. The "excess" current source is the Solar Array common bus.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #20
    Join Date
    Jun 2007
    Location
    Center of Nowhere, NOR CAL
    Posts
    1,681

    Default Re: Solar disconnect wiring

    Alex,

    To further pick a nit ...

    Quoting from the linked MN FAQ, "In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus".

    I read this to mean that in the case of the PV Combiner, the + breaker terminal is connected to the PV module's + wire. THE + on the PV module, NOT the CC's PV INPUT + terminal.

    So, IMHO, you and HC are in agreement. Vic
    Off-Grid, Sys1: 1280 AH 48 V bat, 5.250 KW STC PV, Classic 150, WBjr, MX-60, MN KID, Xantrex Stacked SW+ 5548s; EU6500isa, 21KW Kubota diesel gens, misc Honda Eu gens
    Sys2: 1280 AH 48 V 4KS25 Surrettes, 5.88 KW STC, Two Classic 150s, WBjr, MX-60, MN SPDs, Stacked X SW+ 5548s; Kohler 18 KW LP, EU 3000isa gens, HB DC Charger, Midnite Breakers/boxes. Thanks for this great Forum!

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