Transfer Circuit for Generator

I think you could have serious problems under certain sorts of fault conditions you haven't considered.

For example: think of what will happen if a fault on the service side entirely knocks out the "right" phase of the incoming service, and the "left" side suffers a partial brownout (or blinks off momentarily and then comes back on, but perhaps not all the way).

This would cause your "A" relay to open and remain open (it won't pull in with less than half of the usual voltage across it, or none at all if the right side of the service failed "open"), and will fool your entire system into "thinking" that the service voltage is completely gone... but the left side will still be at least partially live. If you then start up the generator without opening the transfer switch, something will go boom for certain. Your fault-detect circuit won't catch this, since there's only partial voltage across the "A" coil in this case (not enough to close A's contacts) and so L won't operate.

Since this incarnation of your circuit seems to be depending on the fault-detection circuit to determine whether you accidentally didn't open the disconnect before starting the generator, you've got a problem. The whole idea of using a fault detector to discover the mistake (after the fact) rather than preventing it (by using a listed transfer switch with the right sorts of purely mechanical interlocks), is a really bad idea.

Even if the fault detector *does* trip, it'll take time to open the C relay... and this is a few milliseconds during which your generator could be short-circuited right across the service power. If you're especially unlucky, the C relay's contacts could arc and weld shut, leaving your generator stuck on the line indefinitely.

The whole reason the codes specify the use of a mechanically- interlocked transfer switch, rather than a complex set of logic (relay or otherwise), is that a mechanical interlock works even in the face of weird fault conditions (power bouncing on and off repeatedly, voltages being low or high, etc.). It's immune to these sorts of things. Your approach is not, and cannot be made so... the more relays and "logic" you throw at it, the more vulnerable it is to strange interactions of voltage and timing.

That's why people don't use this approach... it's fundamentally unsafe.

Please, DO NOT DEPLOY this thing you're working on.

By the way, your recent few versions of the page don't render properly in Mozilla Firefox... the pictures don't show up.

says that there are a total of 17 errors in your page, 9 of which involve improper HTML.

--
Dave Platt                                    AE6EO
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There are a couple of other things. WE are NOT giving him advice on how to do his electrical abomination. You and I are discussing a hypothetical case that does NOT apply to ANY venture Mister Giffen may undertake now or at anytime in the future.

a) You can NOT connect stuff to the hot side of the disconnect switch. EVERYTHING has to be disconnected when that switch is open. Coil A and everything associated with it is BAD.

b) In many residential cases, the main breaker is also the disconnect, so this setup also bypasses the safety mechanism.

b) What happens if a coil fails during use? A disaster. Failure must cause a safe *stop*, NOT activation.

c) In normal AC use, if the disconnect switch is closed, coils A and B are on. That makes the latching relay turn ON, showing an error.

d) A latching relay here makes no sense. You want it to keep a fault signal? OK, but don't use it to work a contact that does something else, besides, as soon as A or B open it gets reset anyway, because it's wired wrong.

d) A reset switch should be of the NC type and in series with a holding contact.

e) There are no overcurrent devices protecting any of his control circuitry.

d) Everything you said...and probably something I've overlooked.

Mister Giffen had told the world that God had designed the ancestor of this thing. That circuit was even worse than this one. Is God incompetent or did Jon lie? Perhaps God wanted KILL Jon and we are inadvertently preventing HIM from carrying out his Divine Will.

mike

He's trolling. But since your post mentions some technical stuff, let's nail his mess right at the "get-go". His schematic is crap. There's no path for current through the load(s) to neutral. Nor is there a path for 240 volt devices across both hot legs. So he's completely wrong, even before a single relay is added.

Next, he adds relays in a (coil) failure prone way. Relays A and B will be energized 24x7x365 (excluding power outages) virtually guaranteeing eventual coil burnout, and failure of either relay coil will prevent his fault circuit from operating. It is also doubtful that he has given any consideration to contact switching current as opposed to carrying current.

His circuit is totally incompetant, to use a gentle term. And then gets even worse when you add in the stuff you, and Mike and many others have pointed out.

In my view, his posts should be ignored, and when people respond to him, they should be warned of his long history of trolling on this subject.

Ed