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I don't know about solars but my windows had to be 55 PSF plus large object impact protection.


Greg Fretwell
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Most of the inverters require input power to function, for safety reasons, I suppose. However, I install a two pole contactor with the coil powered by the normal source. If utility power drops off line, the contactor de-energizes and disconnects the invertor from the grid. I don't like to rely on electronics to keep people safe. There is also the issue of a disconnect at the point where the power enters the structure and labeling indicating multiple sources of power at the panelboard.

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I agree with you 100%. I doubt if any electronic switch could be called a "disconnect". I sure wouldn't trust it.


Greg Fretwell
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i thought we had art 690 for this...?

~S~

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Originally Posted by homer
Most of the inverters require input power to function, for safety reasons, I suppose. However, I install a two pole contactor with the coil powered by the normal source. If utility power drops off line, the contactor de-energizes and disconnects the invertor from the grid. I don't like to rely on electronics to keep people safe. There is also the issue of a disconnect at the point where the power enters the structure and labeling indicating multiple sources of power at the panelboard.
Isn't the inverter in parallel with the utility, though? It seems as though the contactor would be self-sustanining, with the inverter powering its own coils even if utility power is lost. You couldn't even use directional CTs, as loss of utility power would be indistinguishible from selling power back to the grid.

Does this method rely on the impedance of backfeeding the grid to be so low that internal resistance depowers the coils below the sustainment threshold?


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There are different causes for loss of utility power. At one extreme your service drop is knocked down by a tree. Your inverter or generator could keep those wires hot without any significant current drawn. Someone picking it up could die.

If there is no damage in your area/town but the upstream transmission grid is what is out, you should see about the impedance of your nearest utility transformer. Unless we are talking about a solar/wind farm, it is likely all the other customers are going to overload the system. Current going too high and/or voltage going too low should ideally trip the disconnect.

Now you can monitor the utility for power restoration. But there is a new risk: someone else's power system could make it look like the utility is back.

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NJwirenut, There's also Sol Rosenberg. He thinks the world revolves around him too....

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I'm sure I've been an electrician for my entire working life; but when I read 'solar system' I thought - 'who can get out there to check outside of Earth?' and 'well, at least the rest of the Galaxy, and the Universe, have been left alone for now.' - photovoltaic arrays didn't even enter my mind.

Frenchy I'm figuring the 'fly apart' concerns regarding Florida wind generation would pertain to hurricane safety.

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I think designing a wind generator for 150 MPH winds is within the technology but wind borne debris is another problem. I would have the same concerns anywhere that has tornadoes, even the little "dust devils" some east coast folks call tornadoes. (compared to the mid west monsters)


Greg Fretwell
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