Why would a residential generator panel switch and interlock the neutral?

[hwy17]

Schneider has a new model of home "generator" panels which are basically split bus.

But, the new models have an interlocked breaker with a switched neutral.

This breaks my brain a bit, all my DIY training has focused me on keeping the one true house neutral and ground bond system intact at all times.

Is this related to some new code or something?

Maybe I just need time to process this. Does the GN bond actually stay the same place the whole time, and you wouldn't actually notice the neutral switching?

CHGP605638100 - Generator panel, Homeline, 68 spaces, 100A main breaker, NEMA1, CSA | Schneider Electric USA

Schneider Electric USA. CHGP605638100 - Generator panel, Homeline, 68 spaces, 100A main breaker, NEMA1, CSA.

www.se.com

 

[ricardocello]

That thing is ridiculously expensive at $843 list price.

Most portable generators today have a Ground-Neutral bond, and sometimes it cannot be removed.
This approach guarantees that the circuits on the bottom half either get the house neutral, or the generator neutral on a separate bus.
The top circuits get the house neutral.

Ground is common to everything.
So guaranteed to be code compliant.

 

[hwy17]

Maybe this solves a problem I was never sure about in my head: If two independent power sources are connected to a common neutral and separated by an open breaker, is there two 120v potentials in that breaker that are going in out of phase due to the frequency differences? And so as they pass 180 out of phase you've got a truly 240v (RMS) potential within the breaker between the two opposing 120v sources.

The riddle of the above is if they are from two different sources do they even have the potential to short circuit into each other? Power only returns to it's source says no, but they share a common neutral so does that say yes?

Maybe the answer to the riddle is yes they can, and we're finally recognizing it so we're switching neutrals. Or maybe I'm lost.

 

[Hedges]

I see a 3-pole interlocked switch (breaker?) in the drawing.
Is it documented as switching neutral more explicitly?

I could see that if used with a generator that is already bonded. Or mobile inverter that switches & bonds. You could always hardwire across if desired.

That thing is ridiculously expensive at $843 list price.

Almost the cheapest thing I've ever seen on Schneider website.
Anything carried at home improvement store is a fraction of msrp.

Compare with this, $1249

QO142M200P - Load center, QO, 1 phase, 42 spaces, 52 circuits, 200A convertible main breaker, PoN, NEMA1, UL | Schneider Electric USA

Schneider Electric USA. QO142M200P - Load center, QO, 1 phase, 42 spaces, 52 circuits, 200A convertible main breaker, PoN, NEMA1, UL.

www.se.com

And compare to two panels.
Now if available retail around $400, would be really good.

 

[ricardocello]

Maybe this solves a problem I was never sure about in my head: If two independent power sources are connected to a common neutral and separated by an open breaker, is there two 120v potentials in that breaker that are going in out of phase due to the frequency differences? And so as they pass 180 out of phase you've got a truly 240v (RMS) potential within the breaker between the two opposing 120v sources.

If they are truly independent power sources, they will not be phase synchronized, and if you connect them, BOOM.

The riddle of the above is if they are from two different sources do they even have the potential to short circuit into each other? Power only returns to it's source says no, but they share a common neutral so does that say yes?

Not with their design, there is a mechanical interlock where only one breaker can be on at a time.
Here are part of the instructions. This documentation is really poor.
The Note at the bottom is the BOOM part.

Maybe the answer to the riddle is yes they can, and we're finally recognizing it so we're switching neutrals. Or maybe I'm lost.

See @Hedges response above.

All they are doing is acknowledging that lots of people have two Neutral-Ground bonds when they connect a generator.
This prevents that.

 

[hwy17]

All they are doing is acknowledging that lots of people have two Neutral-Ground bonds when they connect a generator.

That doesn't sound right to me. It would be more dangerous for someone to connect an unbonded generator to an unbonded panel, than for the opposite.

I see a 3-pole interlocked switch (breaker?) in the drawing.
Is it documented as switching neutral more explicitly?

It's got a big N written on it.

 

[ricardocello]

It would be more dangerous for someone to connect an unbonded generator to an unbonded panel

That's for sure!
But most panels are bonded correctly, and so are most portable generators these days.

The problem with portable generators is that they can be used standalone, where you want the N-G bond for GFCI reasons,
or they can be fed into an inlet for the house, where you don't want a N-G bond in the generator.

 

[ricardocello]

It's got a big N written on it.

Yes it does. Maybe it is a Z?

 

[ricardocello]

Finally found the load center schematic (en Francais and Anglais).

 

[hwy17]

Yes it does. Maybe it is a Z?

Ahh, it's the Z axis phase. For the fancy neighborhoods with their fiber optic cable and three dimensional power.

 

[hwy17]

Finally found the load center schematic (en Francais and Anglais).

Hot dangit you're right. Now I sound like a crazy person sharing my two power source problem. It's not actually about the breaker closing out of phase, it's about whether the arc potential across the open breaker is 0, 120, or 240.

 

[ricardocello]

Anything carried at home improvement store is a fraction of msrp.
Compare with this, $1249

Maybe they establish a list price to charge the government. Sheesh.

 

[Hedges]

Yes it does. Maybe it is a Z?
View attachment 209012

Oops!

And I was about to connect Neutral to the middle one.

 

[ricardocello]

And I was about to connect Neutral to the middle one.

Seems like a more natural position for neutral being between L1 and L2.
I couldn't buy this thing, my OCD would get to me.

 

[Hedges]

I would go for the QO series.

200A:

QOGP3P604436200P - Generator panel, QO, 1 phase, 40 spaces, 80 circuits, 200A main breaker, PoN, NEMA1, cover with door, CSA | Schneider Electric USA

Schneider Electric USA. QOGP3P604436200P - Generator panel, QO, 1 phase, 40 spaces, 80 circuits, 200A main breaker, PoN, NEMA1, cover with door, CSA.

www.se.com

100A:

QOGP3P604436100P - Generator panel, QO, 1 phase, 40 spaces, 80 circuits, 100A main breaker, PoN, NEMA1, cover with door, CSA | Schneider Electric USA

Schneider Electric USA. QOGP3P604436100P - Generator panel, QO, 1 phase, 40 spaces, 80 circuits, 100A main breaker, PoN, NEMA1, cover with door, CSA.

www.se.com

$1000.

Gotta pay extra for that copper busbar.


And "normally stocked". Something funny about the one you found "not normally stocked".

Here's a Homeline for $843 and "normally stocked"

CHGP605638200 - Generator panel, Homeline, 68 spaces, 200A main breaker, NEMA1, CSA | Schneider Electric USA

Schneider Electric USA. CHGP605638200 - Generator panel, Homeline, 68 spaces, 200A main breaker, NEMA1, CSA.

www.se.com

All these are indoor only.
The 3R enclosures aren't available with these dual sets of busbars, just small panels with interlocked breakers.

 

[hwy17]

Here's my above question illustrated. Take two split phase independent power sources, 120/240, bond them by their neutral. Let's say one is at 60hz and the other's at 60.0001hz. Maybe it could be called riddle, maybe it's just the modest limits of my understanding.

Now what is the potential between their two hot wires. Is it 0 because they're separate sources, or is it fluctuating between 0 and 240 as they go in and out of phase 120 apart? And if you closed the hot wires together, apart from any phase difference violently meeting, would power flow between them in a short circuit?

 

[hwy17]

I would go for the QO series.

I've already got $400 into Homeline GFCI/AFCI breakers, I can't switch now!

 

[ricardocello]

Is it 0 because they're separate sources, or is it fluctuating between 0 and 240. And if you closed the hot wires together, apart from any phase difference violently meeting, would power flow between them in a short circuit?

Let's assume the initial phase difference between the two independent power sources is exactly 0 degrees, so nothing blows up immediately.

One of them is slightly faster, so it "walks away" in phase from the other. You have them 0.1 milliHz different in frequency in your example.
After 5000 seconds (10000/2), they will be 180 degrees out of phase with respect to each other. Math is wrong, sorry. You get the idea.
So over those 5000 seconds, the power will keep increasing until BOOM.

OK 60 Hz is 16.66666666... msec time interval, and 60.0001 Hz is 16.667 msec exactly.
So every cycle the phase shifts by 0.000333333... msec, or 0.02 msec per second.
So after 416.6666 seconds, the two power sources will be 180 degrees out of phase (8.33333 / 0.02).
Then they will be back together in phase after another 416.666 seconds.

Now I'm waiting for the wrath of the math gods on this forum.

 

[hwy17]

Let's assume the initial phase difference between the two independent power sources is exactly 0 degrees, so nothing blows up immediately.

One of them is slightly faster, so it "walks away" in phase from the other. You have them 0.1 milliHz different in frequency in your example.
After 5000 seconds (10000/2), they will be 180 degrees out of phase with respect to each other.
So over those 5000 seconds, the power will keep increasing until BOOM.

So if the blue arrows represent an open breaker, and that breaker is rated for 120v, does two power sources bonded by their neutral expose the open breaker contacts to 240v potentials, potentially exceeding the breaker's voltage rating?

 

[Hedges]

Neutral switched or not, if each has neutral bonded to ground, neither is floating.
If L1 connected to L1, they will fight when out of phase.

You either switch off generator before connecting to grid, or you synchronize before connecting (what inverters do, and I suppose utility scale generators.)


Sure, will be holding off 240V. I don't think that is a problem with no current flow, just don't try to open with current flow and 240V apart.

The grid is expected to have 2kV spikes, and "isolator", large gap in breaker, ensures it doesn't jump across and bite someone working on a locked-out circuit.