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Old 12-24-2012, 09:13 PM   #21
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Originally Posted by InPhase277 View Post
You could mount a microswitch on the main, such that when the main is on, the relay coil is dead
True and put two 120V relay coils in series with each other (fused) and put the relay contacts in series with each other. This would ensure the relays would drop out if "single phasing" occured or a coil burned out.

Also, it's un-likely both relays would have welded contact problems at the same time.

But, the bottom line is why take the risk? Even the best design (better than a listed ATS) would not be listed and could bring the AHJ down on the EC.
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Old 12-24-2012, 11:06 PM   #22
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I guess a bit more info from the Doc would help.

In any case, there is no difference between a DPDT relay and a DP ATS. When wired correctly, both will prevent backfeed from the gen to the utility.

Suppose the relay supplies two branch circuits. The NO contacts of the relay are connected to the load side of two breakers. The common of the relay is connected to the loads. The NC contacts are connected to the gen. The coil is connected to the utility, ahead of the main.

When the utility is hot, the relay coil is energized. The NO contacts are closed, sending power from the breakers in the panel to the loads. The NC contacts are open, isolating the gen from everything.

Utility fails. Now the NO contacts are open, isolating the panel breakers from everything. The NC contacts are open, allowing the gen (if it's running) to supply the loads.

If the main is closed, and utility comes back up hot, the relay contacts change state, NO becomes closed, NC becomes open. The panel breakers are now supplying the loads, and the gen is isolated. Whether it's running or not doesn't matter. Its power is on two contacts that are open.

Same thing happens when the main is open, but in this case, there's no power available at the panel. And the gen is isolated.

I'm sorry that I can't make this any more clear; I'm not good at writing......
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Old 12-24-2012, 11:13 PM   #23
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I guess a bit more info from the Doc would help.

In any case, there is no difference between a DPDT relay and a DP ATS. When wired correctly, both will prevent backfeed from the gen to the utility.

Suppose the relay supplies two branch circuits. The NO contacts of the relay are connected to the load side of two breakers. The common of the relay is connected to the loads. The NC contacts are connected to the gen. The coil is connected to the utility, ahead of the main.

When the utility is hot, the relay coil is energized. The NO contacts are closed, sending power from the breakers in the panel to the loads. The NC contacts are open, isolating the gen from everything.

Utility fails. Now the NO contacts are open, isolating the panel breakers from everything. The NC contacts are open, allowing the gen (if it's running) to supply the loads.

If the main is closed, and utility comes back up hot, the relay contacts change state, NO becomes closed, NC becomes open. The panel breakers are now supplying the loads, and the gen is isolated. Whether it's running or not doesn't matter. Its power is on two contacts that are open.

Same thing happens when the main is open, but in this case, there's no power available at the panel. And the gen is isolated.

I'm sorry that I can't make this any more clear; I'm not good at writing......

What you wrote isn't hard to understand and is plain as day to me.
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Old 12-24-2012, 11:26 PM   #24
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Originally Posted by micromind View Post
I guess a bit more info from the Doc would help.

In any case, there is no difference between a DPDT relay and a DP ATS. When wired correctly, both will prevent backfeed from the gen to the utility.

Suppose the relay supplies two branch circuits. The NO contacts of the relay are connected to the load side of two breakers. The common of the relay is connected to the loads. The NC contacts are connected to the gen. The coil is connected to the utility, ahead of the main.

When the utility is hot, the relay coil is energized. The NO contacts are closed, sending power from the breakers in the panel to the loads. The NC contacts are open, isolating the gen from everything.

Utility fails. Now the NO contacts are open, isolating the panel breakers from everything. The NC contacts are open, allowing the gen (if it's running) to supply the loads.

If the main is closed, and utility comes back up hot, the relay contacts change state, NO becomes closed, NC becomes open. The panel breakers are now supplying the loads, and the gen is isolated. Whether it's running or not doesn't matter. Its power is on two contacts that are open.

Same thing happens when the main is open, but in this case, there's no power available at the panel. And the gen is isolated.

I'm sorry that I can't make this any more clear; I'm not good at writing......
What you wrote makes perfect sense to me too, unfortunatley that is not what the OP installed.
So what you are saying is correct, it just does not apply to this situation.
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Old 12-24-2012, 11:30 PM   #25
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Rob, your setup is great and safe for a few circuits. But the OP is going to backfeed a whole panel through a DP breaker. But since you got me thinking, add a fail safe relay in case the main held relay fails. Hmmmm....

You could get a 12 circuit panel, cut the bottom 4 spaces off the buss bars to make some room. Double pole contactors (the dreaded and forbidden definite purpose kind!) are less than $15... Mount four of them, and you have an 8 circuit ATS...hmmm
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Old 12-24-2012, 11:35 PM   #26
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Rob, your setup is great and safe for a few circuits. But the OP is going to backfeed a whole panel through a DP breaker. But since you got me thinking, add a fail safe relay in case the main held relay fails. Hmmmm....

You could get a 12 circuit panel, cut the bottom 4 spaces off the buss bars to make some room. Double pole contactors (the dreaded and forbidden definite purpose kind!) are less than $15... Mount four of them, and you have an 8 circuit ATS...hmmm

My GOD sell the man a turnkey standby generator installation and be done with it.
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Old 12-24-2012, 11:36 PM   #27
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Shockdoc just pulled the mother of all trollings on you guys.
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Old 12-24-2012, 11:46 PM   #28
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Shockdoc just pulled the mother of all trollings on you guys.
Nah, nobody here on this thread has rented a U-Haul yet. But I'd rather reply to the Doc's bologna threads than Cletis'. Taking part in a Cletis thread makes me feel unclean. Like the kind of unclean that only crying deeply in the shower will ease.
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Old 12-24-2012, 11:50 PM   #29
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Nah, nobody here on this thread has rented a U-Haul yet. But I'd rather reply to the Doc's bologna threads than Cletis'. Taking part in a Cletis thread makes me feel unclean. Like the kind of unclean that only crying deeply in the shower will ease.

I stopped clicking on cletis threads long ago. I feel so much smarter now for some reason?
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Old 12-24-2012, 11:52 PM   #30
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Nah, nobody here on this thread has rented a U-Haul yet. But I'd rather reply to the Doc's bologna threads than Cletis'. Taking part in a Cletis thread makes me feel unclean. Like the kind of unclean that only crying deeply in the shower will ease.
Cletis is the new forum attention whore.
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Old 12-24-2012, 11:54 PM   #31
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Rob, your setup is great and safe for a few circuits. But the OP is going to backfeed a whole panel through a DP breaker. But since you got me thinking, add a fail safe relay in case the main held relay fails. Hmmmm....

You could get a 12 circuit panel, cut the bottom 4 spaces off the buss bars to make some room. Double pole contactors (the dreaded and forbidden definite purpose kind!) are less than $15... Mount four of them, and you have an 8 circuit ATS...hmmm
I must have missed the backfeed a 2 pole breaker. Yeah, that's not a good idea at all. If so, I can just about guarantee backfeeding the utility at some point. Homeowners are horrible at remembering to turn stuff on and off.
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