Disconnect

CopperkingCopperking Registered Users Posts: 17
Quik Question
I have the required square D fused disconnect which is placed between the Inverter and the back fed breaker in the service panel. Now which side is the load?
AC is feeding into the disconnect from both directions. The disconnect is labeled load and line side. My guess was that the Inverter was the source and thus the Line.
But - unless I can coil some wire in the disconnect box there will not be enough slack to swap ends if the Inspector disagrees.

So - does it matter?

Comments

  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Disconnect

    Ask your inspector. Here, the utility co. mandates that, of course, they are the line.
    The main thing is that the utility people are on the side of the switch blades that is visibly disconnected to satisfy their lockout-tagout rules.
    Since GT inverters can't run without the grid anyway, the whole question is safety 1st nitpicking.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Disconnect
    Copperking wrote: »
    Quik Question
    I have the required square D fused disconnect which is placed between the Inverter and the back fed breaker in the service panel. Now which side is the load?
    AC is feeding into the disconnect from both directions. The disconnect is labeled load and line side. My guess was that the Inverter was the source and thus the Line.
    But - unless I can coil some wire in the disconnect box there will not be enough slack to swap ends if the Inspector disagrees.

    So - does it matter?

    Yes, it matters and you have it wrong. The utility goes on the line side. Otherwise, when you open the switch the fuses are still hot.

    I am told that getting this backwards is the single most commonly occurring error flagged by PV inspectors.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Disconnect
    Copperking wrote: »
    I have the required square D fused disconnect which is placed between the Inverter and the back fed breaker in the service panel.

    I understand that is is probably required by codes, but I wonder why.

    The breaker in the service panel works as a fuse and as a disconnect at the same time. Why a separate fused disconnect is needed?
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: Disconnect

    In the "olden days"--The utility wanted a way to "lock off" a Grid Tied system if the power was down and their linemen where working on the poles. Either you had an external lockable disconnect (bare breakers in a main panel are not usually designed to lock) or they would pull your meter and kill power to the whole home--and reconnect you when they had the free time.

    Today, at least PG&E (northern California), (last I heard) did not require the external lockable box. They trust that the GT Inverters are not going to back drive a dead utility drop (and be a hazard for their crews).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnect

    Let me see if I have this right: you have a fused disconnect and a separate back-feed breaker?

    That is redundant and useless. You only need the breaker.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Disconnect
    Let me see if I have this right: you have a fused disconnect and a separate back-feed breaker?

    That is redundant and useless. You only need the breaker.

    well I have both a well marked external disconnect and the back feed breaker plus a AC combiner with a pair 30 amp breakers. Crazy huh!
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Disconnect
    Let me see if I have this right: you have a fused disconnect and a separate back-feed breaker?

    That is redundant and useless. You only need the breaker.
    There you go again using common sense... :D

    Many AHJ's (A's HJ?) still require a lockable AC disconnect between the inverter and the interconnect, I guess because they don't fully trust anti-islanding. Never mind that (IMO, anyway) it would be impossible to design an inverter that wouldn't shut down when presented with a virtual dead short on its output terminals.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Disconnect
    ggunn wrote: »
    Never mind that (IMO, anyway) it would be impossible to design an inverter that wouldn't shut down when presented with a virtual dead short on its output terminals.
    How true!
    From what I have seen, the biggest part of the effort in building the anti-islanding circuitry is to shut the GTI down in the event of an open circuit from the grid combined with a wildly improbable, but still theoretically possible, combination of local loads that exactly balance the power output of the GTI and include some resonant loads which serve to stabilize the frequency.
    In which case disconnecting the GTI from the house wiring would only have to happen momentarily even if there were a hypothetical matched load present. :-)
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Disconnect
    inetdog wrote: »
    How true!
    From what I have seen, the biggest part of the effort in building the anti-islanding circuitry is to shut the GTI down in the event of an open circuit from the grid combined with a wildly improbable, but still theoretically possible, combination of local loads that exactly balance the power output of the GTI and include some resonant loads which serve to stabilize the frequency.
    In which case disconnecting the GTI from the house wiring would only have to happen momentarily even if there were a hypothetical matched load present. :-)
    Yeah. Anti-islanding is often mentioned as a protection for line workers trying to fix an outage, as if you are going to light up your local grid with your 5kW inverter. :D
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Disconnect
    ggunn wrote: »
    Yeah. Anti-islanding is often mentioned as a protection for line workers trying to fix an outage, as if you are going to light up your local grid with your 5kW inverter. :D
    You might light up your local service wiring if it were disconnected from the transformer. :-)
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Disconnect
    inetdog wrote: »
    You might light up your local service wiring if it were disconnected from the transformer. :-)
    How would you know? :D
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Disconnect
    ggunn wrote: »
    How would you know? :D

    You would not, but the guy on the pole might if you were on your own transformer and the primary circuit had been opened.
    SMA SB 3000, old BP panels.
  • CopperkingCopperking Registered Users Posts: 17
    Re: Disconnect

    Thanks Ggun
    In the end I wired it as you suggest with the Utility as the Line.
    This Disconnect is not required by the County, but is by my local Elec Co-op.

    Now if it wasn't for the snow falling sideways I would be putting up Panels today.
    Oh well.

    G
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Disconnect
    inetdog wrote: »
    You would not, but the guy on the pole might if you were on your own transformer and the primary circuit had been opened.
    Serves him right for trying to cut off my power. :D
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