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- Sep 25, 2021
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Hey @timselectric - great thread, thanks for posting and knowledge sharing. I bench tested this with a 5000ES-US unit from SS and found an unfortunate shortcoming, at least with my implementation which seems pretty much identical to yours. If you're using a NC AT relay and going from off-grid back to on-grid, the time it takes for the two relays (ice cube and AT contactor) to actuate leaves the AT in a ground loop with the grid for a short period of time.
At least with my scenario, this short period of time is enough to run a significant amount of current through the AT (since it's grid balancing during the transition), causing OCPD trips. A word of warning to anybody else attempting this - connecting an AT in parallel to the grid could expose you to thousands of amps of balancing current. I was hoping this imbalance was going to be a few amps tops, but it's easily enough to trip the 15A breaker, and relying on a NC contactor to not weld itself shut while trying to interrupt this current is (imo) a serious safety concern. Appreciate your thoughts if you've got any.
Unrelated - I've got a neutral and voltage protection setup that seems to be working quite well for the AT (for not grid-balancing currents, heh) and I think might be useful to you if you're interested.
At least with my scenario, this short period of time is enough to run a significant amount of current through the AT (since it's grid balancing during the transition), causing OCPD trips. A word of warning to anybody else attempting this - connecting an AT in parallel to the grid could expose you to thousands of amps of balancing current. I was hoping this imbalance was going to be a few amps tops, but it's easily enough to trip the 15A breaker, and relying on a NC contactor to not weld itself shut while trying to interrupt this current is (imo) a serious safety concern. Appreciate your thoughts if you've got any.
Unrelated - I've got a neutral and voltage protection setup that seems to be working quite well for the AT (for not grid-balancing currents, heh) and I think might be useful to you if you're interested.