New Solar Inspector - Worried solar = fire

The word is that a warning letter circulated among utility solar rebate programs and solar inspectors recently about a large solar PV fire on a department store roof.

Our local inspector is now very concerned (paranoid?), and believes we need to have some means of disconnecting DC before it enters the building. (This is so fire fighters can turn off the DC.)

The trouble is the department store fire was traced to a DC arc fault. Now our inspector thinks this is a potential hazard on all our little 3kW residential DC circuits. (If I heard correctly, the store fire had bunches of DC all bundled together and sharing one big conduit...)

I think it is sufficient to point out that turning off the AC on our GT systems will cause the inverter to shut down immediately. This shutdown also brings the current in the DC circuit to zero, which will extinguish all but the rarest types of arc faults.

The only arc fault that might benefit from a rooftop disconnect would be a direct + to - short. Any place this could occur would be inside of a metal box or EMT conduit. We use 1" EMT with typically one or two circuits inside (#10 or #12 THWN-2) + gnd. With this arrangement, what are the chances that an arc fault could burn through the EMT and start a fire?

Thanks,
AJ

Comments

  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: New Solar Inspector - Worried solar = fire

    This is one of the reasons we will be switching to the new Solaredge system on almost all of our new installations. It has distributed powerboxes no each module that all shutdown when the inverter is switched off. Good to have everything off for installation as well. And has better efficiency as too.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: New Solar Inspector - Worried solar = fire

    Another fine case of a bureaucrat thinking he knows more than an engineer.
    Most electrical fires in structures are started by AC, so maybe we should ban electricity altogether. It's dangerous stuff. Even when installed properly and to code, sometimes things go wrong. You can not foresee every eventuality. If you can, tell me the next winning numbers in the Lotto 6/49 please!

    I was under the impression that there was supposed to be a fire-fghter accessible DC disconnect on grid-tie systems. Perhaps that code varies from location to location? I don't know; I don't do grid-tie.

    You can have AC arc faults too: Canada has recently implemented law that requires arc-fault breakers to circuits in bedrooms. This is to prevent the 0.00000000000000000000001% (sarcasm) of fires that start that way. However, there is still no regulation putting fusing into lamp-cord extension cords so you can still burn your house down the old fashioned way by over-loading one of those.

    Curiously, this issue is related to another posting on here about paralleling panels and why it's a bad idea to circumvent NEC regs by scrimping on panel fuses. In the case of arc-fault, the typical fuse wouldn't do much for protection. One wonders if they'll investigate this to find the true cause; it wasn't because of it being DC as this inspector seems to believe.

    Although here again we run into the puzzle I posed elsewhere which so far no one has got the answer to. :p

    I expect I'll now be told I'm completely wrong, as it seems I can't get a single answer right these days. :confused:
  • mike95490mike95490 Solar Expert Posts: 9,035 ✭✭✭✭✭
    Re: New Solar Inspector - Worried solar = fire

    Where's John W on this ??
    Won't a 3 ga ground wire to the water line on the firetruck solve this ?:roll:

    no, it has to be in conduit. :roll::p:p
    sorry as i couldn't resist. niel
    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 ||
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  • aj164aj164 Solar Expert Posts: 114 ✭✭✭
    Re: New Solar Inspector - Worried solar = fire

    Good one :D

    Is someone working for Solaredge here? ;)

    The required DC disconnect (in our area) is at the bottom of the inverter. That will interrupt the circuit and bring the power to zero, but the voltage is still present on the wiring. So, if you saw into the metal conduit, you still might get shocked.
  • BB.BB. Super Moderators, Administrators Posts: 31,072 admin
    Re: New Solar Inspector - Worried solar = fire

    In theory, all of the metal parts are supposed to be bonded with their very own ground wire which is run back to a ground rod/water pipe grounding. So, you should not be shocked by a conduit in any normal situation.

    There is no way around the fact that solar panels generate power when exposed to sun... Just like there is no way to turn off batteries (short of flooding the case with fresh water and purging the electrolytes).

    Is there a possibility of fire if everything is built/installed correctly... Yes.

    Is the possibility high enough that "I" would not install solar... No, not for me.

    Similar question--what could go wrong with insulating an attic... In Australia, 4 people killed and somewhere around 120-160 homes burned down (metalized foil insulation, attic wiring, guys with staple guns, special government program with lots of free money to ensure a fast roll-out--what could not go wrong).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: New Solar Inspector - Worried solar = fire

    There's a pretty good analysis here:

    http://irecusa.org/fileadmin/user_upload/NationalOutreachPubs/InspectorGuidelines-Version2.1.pdf


    "6) Provisions for the photovoltaic power source disconnecting means:
    The 2005 NEC states in 690.14(C)(1), “Location. The photovoltaic disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the system conductors. The photovoltaic system disconnecting means shall not be installed in bathrooms.”

    i) Readily accessible—Article 100 states, “Accessible, Readily (Readily Accessible). Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth.

    ii) Readily accessible provision is primarily for emergency operation. If the disconnect is not mounted in close proximity of the service entrance disconnect (usually within 10 feet of the meter location or service disconnect switch), then a diagram or directory must be provided to clearly identify where the disconnect is located.

    iii) A rooftop disconnect on a residential roof will normally not qualify as a readily accessible disconnect. A new exception to this requirement has been added to provide additional clarification for residential and building integrated PV systems. This exception reads: “Exception: Installations that comply with 690.31(E) shall be permitted to have the disconnecting means located remote from the point of entry of the system conductors.”

    690.31(E) states:
    “(E) Direct-Current Photovoltaic Source and Output Circuits Inside a Building. Where direct current photovoltaic source or output circuits of a utility-interactive inverter from a building-integrated or other photovoltaic system are run inside a building or structure, they shall be contained in metallic raceways or enclosures from the point of penetration of the surface of the building or structure to the first readily accessible disconnecting means. The disconnecting means shall comply with 690.14(A) through 690.14(D).”

    Although metal-clad cable is not specifically called out in 690.31(E), many jurisdictions consider installations with metal-clad cable as meeting the intent of this new provision. Note that this new section specifically mentions building-integrated systems. The way the 2002 NEC was written, a roof-integrated PV system cannot reasonably comply the 690.14(C)(1) as written.

    13
    Those jurisdictions that remain on the 2002 NEC need to consider two alternative approaches to the provisions of 690.14(C)(1). Suggested alternative approaches:

    (1) Follow the new exception in the 2005 NEC and require that all wiring once within the building be installed in metallic raceways or enclosures, or metal-clad cable from the point of penetration of the building to the first readily accessible disconnecting means.

    (2) Consider applying the requirements of NEC 440.14 for Air-Conditioning and Refrigerating Equipment only requires that the disconnect be “readily accessible from the air conditioning or refrigerating equipment.” Following this provision would require a clearly marked rooftop disconnect that can be easily operated by emergency personnel on the roof with an appropriate sign at the service entrance providing (1) a warning of voltage, (2) how to shut down system prior to getting on roof, and (3) location of disconnect on the roof."




    But that's code...personally, I think that ALL power coming into a building should be disconnect-able from outside. Firefighters might not be able to get into a building if it's too hot, or might not be able to get to wherever in the building the disconnect is located.

    And if it is outside, then it has to be readily accessible which means ground level not on the roof.

    I gotta go with the inspector on this one.
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