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Hollywood, FL

1 edit
reply to warwick

Re: OT - Simple Disconnect/Isolation Switch

Thanks for the replies.

Nunya: Will get the particulars of the transfer switch tomorrow lord willing - however I imagine it's your average 3 pole break before make switch, the amperage rating should be 600 @ 240vac.

bburley: while I agree, I wasn't the one who initially designed and spec'd the system - If it were my call it would have been done differently. The only thing I can do at this point is to ensure that "fail-safe" mechanisms are in place which would protect human life and prevent property damage.

The grid tie inverters in this scenario are UL 1741 rated for the intended application which means they MUST cease to produce power once it senses the mains is out of sync. (I.e. a power loss or another fault condition) However I'll sleep better at night knowing there is no physical connection in the event the mains is disrupted which is why I'm looking for the switch in question.

To note: there are a few things missing from the diagram above.

Load = Primary Breaker panel.
Alternate AC input amperage: 31.5 @ 240 vac. (Single Phase)
Necessary breakers.

Mains "sensor wire": Should be the wire which measures line frequency and voltage before the transfer switch. This would signal the "isolation switch" to either cut on or off.

LXI 483
O Fallon, MO
I was asking about the ATS because many have auxiliary contacts. You could accomplish what you need with a simple definite purpose contactor.
The contactor would be wired in a N.O. state between the Aux Source and the load. If the budget allows, and the Aux Source current is low enough, I would spring for a solid state contactor.
The coil would be powered off of utility power. However, once utility power is restored, it usually takes the ATS some time to switch back over. That's where the ATS comes into play. If properly equipped, you could loop the utility fed coil power through the ATS N.C. terminal(s) to keep the Aux Source from coming back online until after the generator goes off line.
E.G., the Aux Source only works when utility power is on line and generator is completely off line. Both conditions would have to be met.
Most decent ATS's have auxiliary contacts available.
If someone refers to herself / himself as a "guru", they probably aren't.


Hollywood, FL
Hmm, thought about that as well. Didn't know those beasts came with aux. contacts. If I'm lucky the logic board will have these contacts in place and maybe I can put the corresponding relay in place.

Really overlooked the fact that the ATS really controls what is what, I.e. the ac could be fine and well however the ATS could still send Gen power to the load (haven't checked the delay).

Will do a more detailed drawing with relays and thingamajigs when I take a look at the transfer switch internals.

Preventing backfeeding* and the destruction of the Generator or PV system is paramount at this point.

Thanks for the help.