Exterior disconnects

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VolcanoSolar
VolcanoSolar Solar Expert Posts: 56
Hi everyone,

I'm adding exterior disconnects for both my battery bank and panels, and since I haven't seen much reference here or in various literature I'm wondering if it's a common thing to do. These disconnects are in addition to the circuit breakers that are panel-mounted indoors.

My thinking (as a former volunteer firefighter) is that in the event of any kind of fire or emergency I want to have a couple of big, obvious throw switches to shut off all power to the house. So I went and purchased a pair of exterior disconnect switches, which I'm about to wire up.

For the battery bank: a 200-amp, 600-volt monster-sized switch; for the panels a 30-amp, 600-volt unit. With each of the three poles on the 30-amp unit I plan to disconnect the hot side (only) of each solar panel array; these will have a combiner box and circuit breakers further downstream, inside the house.

Thoughts? Comments?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,491 admin
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    Re: Exterior disconnects

    Probably not a bad idea... I have seen battery disconnects occasionally on buses and such...

    My questions... Are the switches rated for DC (voltage and current)? DC arcs are surprisingly nasty vs those from AC circuits. Would the switches weld shut in the event of an over current (batteries can supply huge amounts of current)?

    Your battery area is well vented and any issues in the "battery box" well isolated from your home (well vented, separate building, lots of nice thick sheet rock, etc.).

    If you already have properly sized DC breakers--just placing signs (outside/on panel) good enough? I am not too sure I would worry a lot about the solar panels. Sounds like you have a large enough system that your solar charge controller would shutdown in the event the battery bus went dead.

    As always, the cables are tied out of harms way, battery/bus bars covered/protected to prevent wrenches/metal objects from falling and shorting, battery building is locked to prevent kid access, etc...

    My 2 cents worth...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Roderick
    Roderick Solar Expert Posts: 253 ✭✭
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    Re: Exterior disconnects

    What comes to mind with an exterior battery disconnect is, do you have to run a long length of wire to get to the switch outside? If so, I would not want to take the potential loss (or spend the money for fat wire). I would expect primary protection from a circuit breaker or fuse.

    From the firefighter's view, do you really want to disconnect the batteries, or would it be sufficient to disconnect the AC from the house? I would think the latter is enough, but I'm not qualified to answer.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,491 admin
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    Re: Exterior disconnects

    I probably would try for a metallic cable/fire resistant cord rather that running too much cable to mount the switch on the outside of the building--if possible. But then you get into the issue of the cable/rope burning before it
    can be used as an emergency disconnect. And if the burned cable falls onto an exposed bus bar--more issues...

    Circles inside of circles when you try to do this safety stuff... Kind of back to the KISS principle (Keep it simple s......)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: Exterior disconnects

    Here’s how I think the NEC addresses the issue PV disconnects:

    1) NEC 690.56 requires a permanent plaque stating the facility includes a PV system and indicating the location of the disconnects.
    2) 690.14 requires that a PV disconnect be located in a readily accessible location outside the building or inside nearest the point of entrance.
    3) 690.53 requires that DC PV array specs (Voc, Vmp, Isc, Imp) be marked at the disconnect.
    4) Square D has obtained a special listing on their three-pole, 600-volt fused (H361/H362/H363) and unfused (HU361/HU362/HU363) Heavy Duty Safety Switches that allows them to be used on PV systems with only one switch pole per string of PV modules or one switch pole per inverter where the maximum currents are less than about 18 amps (rated short-circuit currents less than 11 amps) for the 361’s and 60 or 100 amps for the 362 and 363 respectively. Example: http://www.affordable-solar.com/dc.disconnect.60a.600vdc.square,D.htm
    5) Here are links to relevant articles by John Wiles: http://www.iaei.org/subscriber/magazine/06_e/wiles.html and http://www.iaei.org/subscriber/magazine/07_c/wiles.html

    The DC battery breaker is likely to be pretty large. It’s not practical to have an remote battery disconnect. All interior PV system disconnects should be grouped together.

    HTH,
    Jim / crewzer
  • VolcanoSolar
    VolcanoSolar Solar Expert Posts: 56
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    Re: Exterior disconnects
    BB. wrote: »
    My questions... Are the switches rated for DC (voltage and current)? DC arcs are surprisingly nasty vs those from AC circuits.

    Would the switches weld shut in the event of an over current (batteries can supply huge amounts of current)?

    Your battery area is well vented and any issues in the "battery box" well isolated from your home (well vented, separate building, lots of nice thick sheet rock, etc.).

    If you already have properly sized DC breakers--just placing signs (outside/on panel) good enough? I am not too sure I would worry a lot about the solar panels. Sounds like you have a large enough system that your solar charge controller would shutdown in the event the battery bus went dead.

    As always, the cables are tied out of harms way, battery/bus bars covered/protected to prevent wrenches/metal objects from falling and shorting, battery building is locked to prevent kid access, etc...

    My 2 cents worth...

    -Bill


    I couldn't find anything directly listed for DC as such; standard commercial units are rated either 240-volt AC or 600-volt AC, so I went with 600-volt AC.

    As for welding shut, the Outback 175-amp breaker would presumably trip before then.
  • VolcanoSolar
    VolcanoSolar Solar Expert Posts: 56
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    Re: Exterior disconnects
    Roderick wrote: »
    What comes to mind with an exterior battery disconnect is, do you have to run a long length of wire to get to the switch outside?

    Actually in this case no -- it adds maybe a few feet of cable, as it just breaks up the run from the exterior battery box to the interior inverter.
  • VolcanoSolar
    VolcanoSolar Solar Expert Posts: 56
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    Re: Exterior disconnects
    crewzer wrote: »
    Here’s how I think the NEC addresses the issue PV disconnects:

    1) NEC 690.56 requires a permanent plaque stating the facility includes a PV system and indicating the location of the disconnects.
    2) 690.14 requires that a PV disconnect be located in a readily accessible location outside the building or inside nearest the point of entrance.
    3) 690.53 requires that DC PV array specs (Voc, Vmp, Isc, Imp) be marked at the disconnect.
    4) Square D has obtained a special listing on their three-pole, 600-volt fused (H361/H362/H363) and unfused (HU361/HU362/HU363) Heavy Duty Safety Switches that allows them to be used on PV systems with only one switch pole per string of PV modules or one switch pole per inverter where the maximum currents are less than about 18 amps (rated short-circuit currents less than 11 amps) for the 361’s and 60 or 100 amps for the 362 and 363 respectively. Example: http://www.affordable-solar.com/dc.disconnect.60a.600vdc.square,D.htm
    5) Here are links to relevant articles by John Wiles: http://www.iaei.org/subscriber/magazine/06_e/wiles.html and http://www.iaei.org/subscriber/magazine/07_c/wiles.html

    The DC battery breaker is likely to be pretty large. It’s not practical to have an remote battery disconnect. All interior PV system disconnects should be grouped together.

    HTH,
    Jim / crewzer

    Thanks, useful information. The DC battery breaker that I'm wiring in (not remote, just inserted between the exterior battery box and the house) happens to be a Square D H364, picked up on ebay for under $200. It is pretty large, but manageable.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: Exterior disconnects

    The 364 is a 200 A switch. It also appears to be DC rated. See page 6: http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches/Heavy%20Duty/H%20and%20HU%20Switches/3110CT9601.pdf You still want appropriately sized circuit breakers between the battery and all other power sources and loads.

    HTH,
    Jim / crewzer
  • VolcanoSolar
    VolcanoSolar Solar Expert Posts: 56
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    Re: Exterior disconnects
    crewzer wrote: »
    The 364 is a 200 A switch. It also appears to be DC rated. See page 6: http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches/Heavy%20Duty/H%20and%20HU%20Switches/3110CT9601.pdf You still want appropriately sized circuit breakers between the battery and all other power sources and loads.

    HTH,
    Jim / crewzer

    Right, these exterior disconnects are in addition to Outback AC and DC breaker panels.