Garage or subpanel with loads allowed?

aj164aj164 Solar Expert Posts: 116 ✭✭✭
Refer to this thread on 'detached garage':
http://forum.solar-electric.com/showthread.php?t=3300

The situation is a breaker sub-panel that distributes power to loads, such as in a detached garage. The idea is to wire an inverter to this sub-panel instead of wiring the inverter separately all the way back to the main service panel.

This would save a lot of work, but it appears to violate 690.4 (B) "Conductors of Different Systems. Photovoltaic
source circuits and photovoltaic output circuits shall not be
contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as feeders or branch circuits of other systems, unless the conductors of the different systems are separated by a partition or are connected together."

By connecting an inverter to your sub-panel, it seems that the circuit feeding that sub-panel then becomes a "photovoltaic output circuit". So if at any point after the main breaker panel that wire shares a conduit/raceway or junction box with other wiring, this code is technically violated. That's what it seems to me... ??

Otherwise, if this is acceptable, it sure would make some installations much easier.

-AJB

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,970 ✭✭✭
    Re: Garage or subpanel with loads allowed?

    The code you quote is in reference to mixing AC & DC conductors in the same conduit. You can have a gridtie unit on a sub panel but you must check that both the sub panel and breaker in the main panel meet the back feed requirements ( mostly relating to the bus-bar limits )
  • aj164aj164 Solar Expert Posts: 116 ✭✭✭
    Re: Garage or subpanel with loads allowed?

    This is yet another area I got tagged on, sharing the same conduit to get the PV output to the breaker panel as circuits going to other loads in the home. The inspector said it mixes source circuits with load circuits; That it creates a hazard because someone could, in theory, cut power to the home, believing that the wires in the conduit would be dead, but then would be in danger because of the potentially-live PV output circuit.

    I realize the grid-tie inverter here shuts down when there is no grid connection, but he did not allow that as an exception here. It seems nit picky, but I guess if someone were to upgrade the inverter in the future with a battery-backup system... :roll:
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Garage or subpanel with loads allowed?

    you really have a winner of an inspector. he really didn't want you to connect.
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: Garage or subpanel with loads allowed?
    aj164 wrote: »
    This would save a lot of work, but it appears to violate 690.4 (B) "Conductors of Different Systems. Photovoltaic
    source circuits and photovoltaic output circuits shall not be
    contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as feeders or branch circuits of other systems, unless the conductors of the different systems are separated by a partition or are connected together."
    aj164 wrote: »
    This is yet another area I got tagged on, sharing the same conduit to get the PV output to the breaker panel as circuits going to other loads in the home. The inspector said it mixes source circuits with load circuits; That it creates a hazard because someone could, in theory, cut power to the home, believing that the wires in the conduit would be dead, but then would be in danger because of the potentially-live PV output circuit.

    I realize the grid-tie inverter here shuts down when there is no grid connection, but he did not allow that as an exception here. It seems nit picky, but I guess if someone were to upgrade the inverter in the future with a battery-backup system... :roll:

    From my reading, you are correct and the inspector is wrong...

    The circuits, if isolated (such as a battery based PV system DC side vs the Inverter output and/or with substantially different voltages/currents/uses where the insulation differences, say insulation rated for 12 volts vs insulation rated for 600 volts) cannot be mixed together...

    In your case, the wires are all connected together, through breakers. They are not isolated networks. And they all have the same insulation requirements.

    In this case, the grid tied inverter cannot power the box/wiring/bus bars unless the utility power is present--the whole reason for the UL rating.

    There is no way--that I can see--where they can make a valid argument about separating wiring (for example, generator backed wiring vs Grid Tied Inverter wiring isolation) for something that is not even planned for the future.

    If, you were going to build a battery backed UPS type system--that would require a transfer switch and (probably) a sub panel... No way that type of system would be confused with what you are doing.

    No matter the failure type (utility mains fail, main home breaker opens, CB on one branch circuit opens, or CB on inverter circuit opens) would there be any sort of "live/energized" circuit in your shared conduit/box area...

    And, technically, I would even argue the case that the PV side of a Xantrex Grid Tied system is tied with the Output of the inverter--they have a common ground (and in the US, safety ground and neutral are tied together in the wiring box)--although the Xantrex PV side is sort of "isolated" through a 1 amp ground fault detection fuse. Since the PV side is electically connected (via safety ground/neutral connections in house wiring), and the PV side is using the same rated wiring (600 Volts RMS Max) as the 240 VAC output of the inverter--they are the "same circuit" in the NEC sense... So no isolation barrier or separate wiring box would be required...

    And, if you look in a Xantrex GT inverter (at least my Xantrex 3.0 GT model), there is no barrier between the 240 VAC wiring and the 200-600 VDC PV wiring. The wiring all goes in the same box, and depending on where the PV and Output wiring comes in via the knockouts--the wiring will cross each other (which they do in my box).\

    I would only argue for the PV DC vs AC output wiring isolation (separate conduit/metal barrier) if there was a UL approved barrier between the PV DC and the Inverter Output (i.e., UL approved transformer with double insulation and/or internal ground screen). But since the NEC PV code (as written by our "friends") requires grounding the PV panels inside the inverter--they have "voided" and isolation between the input and output sides of a GT inverter (normally, I would have to pass a ~1,800 VAC--don't remember the exact voltage requirement--highpot test between the GT input and output to achieve "proper and meaningful isolation".

    In the end, there is no valid reason (that I can see at this point) for disapproving co-locating GT inverter output wiring and other normal branch wiring as in your installation. As you say--the UL regulations prevent the inverter from energizing during any power failure. And if the GT where to energize its output with a mains AC and/or local Circuit Breaker failure--then the UL testing/requirements are bogus and the whole idea of NEC approved GT solar should be killed as being too dangerous.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • aj164aj164 Solar Expert Posts: 116 ✭✭✭
    Re: Garage or subpanel with loads allowed?

    I tried to look this up in PV and the 2005 NEC, but Wiles' wording still could be interpreted in different ways. He says "...as PV source conductors...". So does PV source mean literally source (DC) from the PV, or can it mean that AC output from the inverter is a "PV source"?

    The text: (link)

    (22) Panelboards, Enclosures, and boxes
    a. Disconnect and overcurrent devices shall be mounted in listed enclosures, panelboards, or boxes [240III]. Wiring between these enclosures must us a NEC-approved method
    [110.8].
    b. Conductors form different systems such as utility power, gas generator, hydro, or wind shall not be placed in the same enclosure, box, conduit, etc., as PV source conductors unless the enclosure is partitioned [690.4(B)].
    c. The AC outputs of a specific PV system may be routed in the same conduit or raceway as the DC PV source conductors from the same system providing that all conductors meet the insulation requirements of 300.39 ( C)(1).
    d. Dead front-panelboards with no exposed current-carrying conductors, terminals, or contacts
    are generally required [408.38].
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Garage or subpanel with loads allowed?

    wiring an inverter to a subpanel is just like to the main panel and is really only an extension of the main panel. what i believe your inspector is saying is that this creates a mixing of souce and utility power and is therefore a no-no. the guy is an idiot because pv source power is dc and not ac and the whole idea is to get them to mix when the dc is finally inverted to ac. no shock hazards exist due to the anti islanding built into the inverters that will shut the inverter down in the abscence of utility power.
    the problem with interpreting anything is that if you don't know what all the terms mean then misinterpretations take place. being the pv source power is a dc power, then can he say that the ac output from the inverter is a dc source power? he might try, but at that point it is an ac source power independent of the utility meant to be connected to the utility and is only operational when it is connected to the utility power and ultimately becomes one and the same power. he can't make the determination as to where it combines with the utility because one could then say the utility ends at your pole connection and the pv(dc) power source enthers the utility there. picture 2 batteries in parallel even though one of them may have a higher voltage. you run say 15ft of wire between them to connect the + to + and - to -. how can you determine where one connection stops and the other begins? the voltage will appear to be the same everywhere as they average each other out. you can't say where it starts or stops and neither can that inspector. even though the connection is desirable between the 2 he is saying their interconnection is illegal because of different sources.
    the bottom line here is the man doesn't know what he's doing and is looking for anything to disallow the connection. if this isn't so then ask him just how these 2 different sources as he defines them are to meet as he is deeming the connection between the 2 to be illegal and hence an inverter by his definitions is illegal to connect to the utility anywhere if his definitions of pv source and utility power apply.
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