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Thread: A/C disconnect: Which conductors are considered the "line"?

  1. #1
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    A/C disconnect: Which conductors are considered the "line"?

    When installing a disconnect on the A/C side of an inverter -- usually adjacent to the utility meter box -- which side is considered the "line" and which is the "load" ??

    I figure that the "line" side should be the premises wiring panel, and the "load" should be the inverter, even though the current will be flowing in the opposite direction.

    Since the inverter will disconnect itself if it senses the loss of utility power, putting its output on the load side of the disconnect won't end up with energized blades exposed with the disconnect in the "off" position.

    Do you have a preference, or a valid reason why it should be the other way around?

  2. #2
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    Quote Originally Posted by kbsparky View Post
    When installing a disconnect on the A/C side of an inverter -- usually adjacent to the utility meter box -- which side is considered the "line" and which is the "load" ??

    I figure that the "line" side should be the premises wiring panel, and the "load" should be the inverter, even though the current will be flowing in the opposite direction.

    Since the inverter will disconnect itself if it senses the loss of utility power, putting its output on the load side of the disconnect won't end up with energized blades exposed with the disconnect in the "off" position.

    Do you have a preference, or a valid reason why it should be the other way around?
    You have to label it as hot on both sides.

    My preference would be utility on the top, inverter on the bottom as very shortly after you open the switch the inverter will shut down.

  3. #3
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    Your thinking is correct. On both the AC and DC sides you want the load terminals to be on the inverter side.

  4. #4
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    The inverter has a dual-disconnect switch that is integral with the unit. Switching it off disconnects both the AC and DC lines -- complying with any disconnecting requirements that may be applied. It also has a built-in combiner assembly with up to 4 inputs from connected solar arrays.

    In this case, the local POCO requires a separate safety switch adjacent to their meter for the AC output from the inverter, even though the integral disconnect switch of the inverter is right there next to it!

  5. #5
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    I agree with everyone else on the load vs. line side.

    Quote Originally Posted by kbsparky View Post
    The inverter has a dual-disconnect switch that is integral with the unit. Switching it off disconnects both the AC and DC lines -- complying with any disconnecting requirements that may be applied. It also has a built-in combiner assembly with up to 4 inputs from connected solar arrays.!
    That sounds a lot like an SMA combiner/disconnect. The thing is, SMA's current product is only a DC disconnect. (It used to do both, but they changed that.) Are you sure the integrated disconnect disconnects the AC?

  6. #6
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    I'm going back to that job tomorrow, and will verify that the SMA disconnects both the AC and DC lines.

  7. #7
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    Quote Originally Posted by kbsparky View Post
    I'm going back to that job tomorrow, and will verify that the SMA disconnects both the AC and DC lines.
    If it was made after (I believe) 2009, it only disconnects the DC. It's going to be hard to verify by looking at it, but if you call SMA tech support that's what they will tell you.

  8. #8
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    You are correct. I took a close look at it yesterday, and it does indeed only disconnect the DC side, after the combiner assembly. The AC side feeds right through without connection to that switch.

    From first glance (and my prior experience), it looked like it was designed to disconnect both.

    Well, we did install the AC disconnect with the "line" side connected to the service panel, and the "load" side connected to the inverter. For good measure, the facilitator had sent out a lightning arrestor, and we connected that to the line side as well.

    I installed a label on the disconnect box stating, "Photovoltaic System Disconnect"

  9. #9
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    disconnects on ac side

    Quote Originally Posted by kbsparky View Post
    You are correct. I took a close look at it yesterday, and it does indeed only disconnect the DC side, after the combiner assembly. The AC side feeds right through without connection to that switch.

    From first glance (and my prior experience), it looked like it was designed to disconnect both.

    Well, we did install the AC disconnect with the "line" side connected to the service panel, and the "load" side connected to the inverter. For good measure, the facilitator had sent out a lightning arrestor, and we connected that to the line side as well.

    I installed a label on the disconnect box stating, "Photovoltaic System Disconnect"
    The solar farm which I worked at also because of the high current on the 13,800 volt side of the Xformer after the inverters was t-body bolt on elbows which are not easily disconnected like a simple loadbreak elbow isolating the ac side of the inverter. The primary AC side had to be shut down from the substation and may have shut down up to 5 power blocks (inverters ) on a circuit. SMA Sunny Central inverters.
    The tail does NOT wag the dog.

  10. #10
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    Quote Originally Posted by kbsparky View Post
    The inverter has a dual-disconnect switch that is integral with the unit. Switching it off disconnects both the AC and DC lines -- complying with any disconnecting requirements that may be applied. It also has a built-in combiner assembly with up to 4 inputs from connected solar arrays.

    In this case, the local POCO requires a separate safety switch adjacent to their meter for the AC output from the inverter, even though the integral disconnect switch of the inverter is right there next to it!
    I agree with the local POCO on their decision. If the meter needs to be pulled or replaced for some reason, or something happens to the line, they want a simple disconnect. Most POCO's preach visual opening.

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