disconnect disagreement

Hello forum.

I was recently installing a system with another electrician and we had a disagreement about how to wire the AC disconnect, after the inverter, before feeding the back-fed breaker. 

It is my understanding that my bare #6 copper bonding the array (#6 insulated after roof) should run uninterrupted to my ground bar in my service panel or ideally bond with the #6 at my ground rod. The Neutral generated at my inverter should not be landed in the disconnect, but should go directly to the neutral bar at my main breaker panel. The disconnect should be grounded and that the inverter and disconnect can be grounded together, then a separate grounding conductor (#10 in my case) should run back to the service panel and land at the ground bar from the inverter/disco.

The other electrician told me to land both the Neutral from the inverter and the #6 ground from the array at the grounding bar in the fused disconnect. I think this is wrong because I believe they are only supposed to touch at 1 location in a residence (at the service panel).

thanks for any info.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    If lightning is a concern, Run array frame ground from Array to ground rod at base of array (or if near home main ground rod, to the home ground rod). If second ground rod is installed for solar array, then tie with 6 AWG the two (or more) 6 AWG ground rods together with their own cable.

    If lightning is not a major concern, you can run the array safety ground to the local safety ground bonding are in the disconnect box.

    Using Surge Protectors at the disconnect box (and tied to local ground rod) is highly recommended if lightning is a concern for your area.

    http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/suprde.html

    You are correct that the Neutral to Earth bond for AC grounding should only take place in one location--Typically the main service panel. If you have two (or more) bonding points, you can have neutral (return) current flowing in parallel in both neutral and earth/safety ground wiring (conduit, cold water pipes, etc.).

    If this is a pure Grid Tie AC inverter (and not an off grid/hybrid inverter)--There is no reason to tie the GT inverter neutral to any earth bond other than at the main panel.

    In my case, I had an "older' GT Inverter that was pure 240 VAC output and did not even have a neutral connection. Later, I had a replacement GT inverter of newer construction--Where the new GT inverter used the neutral to "qualify" the AC power (i.e., 240 VAC between black and red hot wires, and 120 VAC between neutral and Black/Red hot wires). Because there was no AC neutral from panel to GT inverter, the installer replacing the GT inverter tied the GT inverter neutral to safety (green wire) ground. Because there was no current flow in the neutral, the inverter simply measure the ground voltage the same way it would measure neutral voltage to qualify the safety of the installation (i.e., there was no break between Neutral and Earth bond back at the AC main panel).

    If you have a Hybrid Inverter and/or backup AC genset and/or an RV/Boat/Vehicle installation--Then grounding can get a lot more complicated (with AC transfer switches and such). Still want a single AC Neutral to Earth connection--But sometimes you have to "switch" the bonding on/off depending on how the system is operating (AC mains or off grid for example).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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