Battery box and conduit required

PV and the NEC - John Wiles says you need a battery box or similar to protect battery terminals from accidental shorts.

I cannot find whether conduit is mandatory on the battery cables to/from the batteries and inverter, but he does mention conduit can be used...

We have four 120A-H AGM (sealed) batteries: 12V in series for 48V nominal. Do I need a box and conduit?

Thanks,
AJB

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,655 ✭✭✭✭✭
    Re: Battery box and conduit required

    "need" is an interesting word here...

    I don't think there is a code requirement for a battery box, I would like one for reasons of protecting from accidental shorts, and if you had a flooded battery for spill control and gassing reasons. Also to seperate controler and inverter from the out gassing (as explosive and as a corrosive)

    Hopefuly your controler and inverter are close to the battery box, requiring only a pass-through. Typically you don't want long DC runs, for lower voltage reasons as well as the battery to inverter usually being heavy(expensive) cable.

    Hopefully someone who does installs can answer directly if code requires a battery box.
    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.
  • aj164aj164 Solar Expert Posts: 116 ✭✭✭
    Re: Battery box and conduit required

    The batteries are directly below the inverter, but I still wonder if I'm supposed to have even those short runs in some sort of conduit.
    Photowhit wrote: »
    "need" is an interesting word here...

    Hopefuly your controler and inverter are close to the battery box, requiring only a pass-through. Typically you don't want long DC runs, for lower voltage reasons as well as the battery to inverter usually being heavy(expensive) cable.

    Hopefully someone who does installs can answer directly if code requires a battery box.
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Battery box and conduit required

    The reality is
    1. how easy do you think it would be to damage the cable
    2. if the cable melted from over current (no fusing), is the area wood or concrete and dry wall
    3. if there are no fuses/breakers in the battery bus--add them. Probalby more important than conduit by itself.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Battery box and conduit required

    As far as the conduit goes, I think you have to look up the type of conductor and find the uses permitted and not permitted. In general, I think the standard is 300.4 "Where subject to physical damage, conductors shall be protected."

    690.71 Storage Batteries, Installation

    (B) Dwellings

    (2) Guarding of Live Parts. Live parts of battery systems for dwellings shall be guarded to prevent accidental contact by persons or objects, regardless of voltage or battery type.
  • audredgeraudredger Solar Expert Posts: 272 ✭✭
    Re: Battery box and conduit required

    On the battery box part of this question; it is my understanding that NEC requires spill containment. Containment must equal the volume of at least one battery. Am I wrong?
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Battery box and conduit required
    audredger wrote: »
    On the battery box part of this question; it is my understanding that NEC requires spill containment. Containment must equal the volume of at least one battery. Am I wrong?

    Sounds like a good practice and perhaps it's in the NEC somewhere, but I can't find that requirement.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Battery box and conduit required

    Conduit is cheap, use it anyway !!!

    As to the box, look at a large Rubbermaid container. If not, just protect the terminals.

    I have my terminals covered, wire between the batteries and wall. Then in conduit from last battery to CB box.
  • aj164aj164 Solar Expert Posts: 116 ✭✭✭
    Re: Battery box and conduit required

    UPDATE:

    The batteries sit about 2' below the inverter wiring box.
    I installed the batteries (AGM, sealed) in a battery box, and I ran 1" FMC conduit from each side of the battery box, up the drywall, and into the inverter wiring cabinet. On the left side is my negative 4/0 cable in 1" FMC, and on the right is the positive 4/0 in FMC.

    The inspector comes along and says I can't separate my conductors in two different conduits. He says I must run both pos and neg battery cables in one conduit from the battery box to the inverter wiring box.

    There is no fuse protection or fusible link in the battery box or wiring leading up to the inverter wiring box. The first means of disconnect and over-current protection is a 250A DC breaker in the wiring box (Xantrex XW).

    To run the battery cables in one raceway, while not necessarily unsafe, seems _less_ safe than two metallic raceways. (This is all in a garage.) Say a driver loses control and runs into the wall and pinches the conduit (unlikely, yes). If both cables are in one conduit, sparks fly...

    The inspector's reasoning was this: "You don't see service conductors leading up to a home separated in two conduits..." True, but is this a fair analogy?

    Cheers,
    AJ
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Battery box and conduit required

    I believe the NEC was corrected long ago about this requirement...

    You do not run the same AC Line/Neutral or L1/L2 circuits in separate conduit or through two different penetrations into a metal box. The reason is that with AC current it creates circulating AC currents (transformer/AC coupling of changing magnetic fields) in the associated metal conduit/box sheet metal and it can cause over heating of the metal components.

    DC currents make a (more or less) fixed magnetic field and do not create circulating currents in the sheet metal / conduit if you run the cables separately. So it is OK to run the DC +/- cables in separate metal conduit and or through separate penetrations into a metal box.

    Although, electrically, it is better to keep +/- DC cables close to each other. This reduces impedance of cables (less "resistance" to surge currents) and reduces the antenna effect of the cables (reduces radio emissions and possible coupling of lightning energy/radio waves into your DC power system).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery box and conduit required

    you guys may be right in the interpretation, but the inspector, unless mandated by the city or town, can say or require anything he likes. as bill said that was to address ac and not dc and as such ask the inspector if he is going by the nec (what version too) and to show you in black and white this requirement. the inspector may be using a previous nec version as law there and they do not have to use the latest nec version or the nec at all if they elect not to. reasoning as it was meant for ac requirements would be a talking point, but he can require you to do nearly anything he wants as long as nobody above him is ruling otherwise.
  • RCinFLARCinFLA Solar Expert Posts: 1,398 ✭✭✭✭
    Re: Battery box and conduit required

    I looked up the sections in the 2009 NEC code and see no statement requiring conduit for less then 50 volt nominal system (ie. up to 48 vdc batteries).

    As to separating the battery lines, you want to keep them close together to cancel out their magnetic fields. The battery cable inductance goes up as they are separated which causes greater voltage ringing at the inverter when load transients occurs.

    You also need a fuse in each series string of batteries. You can put it between any of the batteries in the string that is convenient and easily accessable.
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