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SPD wiring...

I just thought of something. My goal with solar was to be off grid. I'm closing in on that goal. Cut these stupid power poles down. Without the grid, I wouldn't need the 300ac.

Very seldom have I neeed the grid. The inverter is programmed to be off grid and only kicks on when the batteries get down to 10% which hardly ever happens. It doesn't even call on the grid when the ac kicks on but the lights do dim a bit when the upstairs 1.5 ton kicks on. Definitely getting a soft start soon for that.

I could just throw the transfer switch so the grid is off, which is how I ran for the first couple months anyway, and throw it back on should the batteries start getting low.
 
The SPD connected to a 2P breaker on those bus bars, will protect everything from a surge on the grid lines.
But it's pointless, if the grid isn't feeding anything.
It would be better to connect it to the output of the inverter.
Then it's helping, all of the time.
Whether the grid is feeding through or not.
 
Connect it to the output of the inverter? I'm not exactly sure what you mean by this.
If I've got the mppt's covered and no grid power coming in, what would the 300ac spd be protecting the inverter from exactly?
 
I know this will make Tim and others gag, but I think she'll hold. This type of install is actually shown on the last page of midnight solar's instructions. There's a silly amount of space in this wire box.
The spd wires are a little less than 1/2 the original length. I had to make the 3rd strings mppt a bit longer because it was a bit too tight next to #2.

IMG_20240524_171038874.jpg IMG_20240524_171327213.jpg IMG_20240524_170918186.jpg IMG_20240524_171011791.jpg IMG_20240524_171144649.jpg
 
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Like the PV wires, household wires could pick up coupled energy from a nearby lightning strike.

While connected to grid, SPD on output of inverter would seek to limit surge voltage. Is is preferable to have protection upstream, because there will be a voltage drop across impedance of wires and relay, so input monitoring electronics will see higher voltage than output drive transistors, which will see higher voltage than breaker panel with SPD.

I would connect an SPD to input of inverter, or to service entrance.
Ideally there is a hierarchy of protection, including a spark gap at service entrance. And maybe wires coiled to add some inductance. Then various types of SPD after that.

Gotshocked! said:
I know this will make Tim and others gag, but I think she'll hold. This type of install is actually shown on the last page of midnight solar's instructions. There's a silly amount of space in this wire box.

View attachment 217467
Click to expand...

Fat wires in wire nuts - are those a good connection for operating current?
 
That's the funny thing about electricity that I've learned so far. Some would do this, some would do that.
Tim would go to the output of the inverter, Hedges would go to the input of the inverter.

I posted a link on another thread I had going to some electrical folks on another solar site who were totally good with wire nuts and asked why the op was looking at a buchanon connection. This was also for installing spd's for pv's.

Two 10ga and one 14 ga. These are the correct size for the wire. The pv wire insulation is fat, but you know that.
The nuts are rated at 600v and copper to copper.
Every house I've owned has been full of wire nuts. I suppose we'll find out.
 
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Right - I missed that it was PV looking at the zoomed-in picture. Thought it was AC.
PV is moderate current.

So long as the joints are mechanically sound. Some of mine haven't been, but watching a video where multiple stranded wires were twisted tightly, clipped to length, then wire nut, I plan to do better.
 
I actually did do what you wrote.

So, I'm curious which is the best way to install this 300ac spd. I was looking forward to returning it, thinking I've conquered the need for an spd as I'd just shut the damn grid off at the transfer switch, but Tim and you have crushed that dream, so I need to figure out if this spd needs to go to the output or the input of the inverter and then where exactly.

I don't understand how electricity moves, so I cannot imagine how an spd at the inverter would save the inverter and the load panel, but I know you guys know what you're talking about, at least I think you guys know what you're talking about because I do not comprehend most of what your talking about but I do greatly appreciate the knowledge and feedback.

I've attached pictures of my ac and dc sides. Go ahead and laugh at my imo boxes. I got 1 for free anyways.
In laymen's terms please, where do you guys suggest I install this 300ac spd?

Transfer switch (right) ------ Inverter (duh) --------------- Transfer switch --------------- Meter box --------------------- Disconnect (left)
IMG_20231105_163826626.jpg IMG_20231030_205257889.jpg IMG_20231021_165054655.jpg IMG_20231021_165018760.jpg IMG_20231021_165011316.jpg
 
Gotshocked! said:
I know this will make Tim and others gag, but I think she'll hold. This type of install is actually shown on the last page of midnight solar's instructions. There's a silly amount of space in this wire box.
The spd wires are a little less than 1/2 the original length. I had to make the 3rd strings mppt a bit longer because it was a bit too tight next to #2.

View attachment 217464 View attachment 217465 View attachment 217466 View attachment 217467 View attachment 217468
Click to expand...
Looks like a good use of the space, to me.
It can be hard to find a place to install the midnight SPD's, because of their physical size.
 
Gotshocked! said:
Tim would go to the output of the inverter, Hedges would go to the input of the inverter
Click to expand...
I only suggested the output because you said that there's almost never going to be an input.
So that you would get more use out of it, at all times.
(Assuming that you already purchased it)
 
I understand now that input is the dc side & output is ac. Y'all are talking about one or the other, input OR output side. I've got the input side covered, so then I don't have to worry about the output side? But I still have the input of the grid, right? That's why it was suggested by midnight solar to buy the 600's and the 300ac.

timselectric said:
The SPD connected to a 2P breaker on those bus bars, will protect everything from a surge on the grid lines.
But it's pointless, if the grid isn't feeding anything.
It would be better to connect it to the output of the inverter.
Then it's helping, all of the time.
Whether the grid is feeding through or not.
Click to expand...

Where do I install the spd in order to connect it to the output of the inverter? Do I attach it to the lugs that the 4/0 is attached to, going to the panel? After all, supposedly you can attach these spd's to the lugs, though I do not see that instruction in the spd manual.
I've got room in the wire box to do so, on the right side.
 
Gotshocked! said:
I would too but mine's in the drywall, so I'd need to do something like a hole with the metal box midnight solar makes for this purpose, but I don't want to do that for several reasons.
Click to expand...
I know that most people like the midnight SPD's.
As an electrician, I'm not a fan. Because they can be troublesome for the install.

For the AC panel, I prefer the ones that take the place of a 2p breaker.
Just snap it in, and connect the neutral (and or ground) pigtail.
 
Gotshocked! said:
I actually did do what you wrote.

So, I'm curious which is the best way to install this 300ac spd. I was looking forward to returning it, thinking I've conquered the need for an spd as I'd just shut the damn grid off at the transfer switch, but Tim and you have crushed that dream, so I need to figure out if this spd needs to go to the output or the input of the inverter and then where exactly.

I don't understand how electricity moves, so I cannot imagine how an spd at the inverter would save the inverter and the load panel, but I know you guys know what you're talking about, at least I think you guys know what you're talking about because I do not comprehend most of what your talking about but I do greatly appreciate the knowledge and feedback.

I've attached pictures of my ac and dc sides. Go ahead and laugh at my imo boxes. I got 1 for free anyways.
In laymen's terms please, where do you guys suggest I install this 300ac spd?

Transfer switch (right) ------ Inverter (duh) --------------- Transfer switch --------------- Meter box --------------------- Disconnect (left)
View attachment 217491 View attachment 217492 View attachment 217493 View attachment 217494 View attachment 217495
Click to expand...

1) Buy a breaker to fit unused busbars in combined service entrance device, connect SPD to it.
2) Tap off after main breaker and connect SPD there (if one of those ~ 3/0 wires is long enough, and Polaris is large enough to clear insulation, can feed through Polaris to main breaker, leaving spare tap.)
3) Tap off unfused disconnect
4) Tap off fused disconnect
5) Tap off AC in wires of inverter

In general, SPD is supposed to have about 20A OCP and any of these tap points has larger fuse/breaker.

If 20A is available to fit busbars in CSED, that's the simplest. I think those breakers land on line side of main, so should probably have higher AIC than typical 10kA branch breakers, but maybe that's OK if available fault current from utility is limited.

Otherwise, there are DIN rail mount touch-safe fuseholders and breakers.

Hey, if one of those SPD shown by Tim fits the busbar, and has necessary AIC, that is the simplest of all.
 
timselectric said:
I know that most people like the midnight SPD's.
As an electrician, I'm not a fan. Because they can be troublesome for the install.

For the AC panel, I prefer the ones that take the place of a 2p breaker.
Just snap it in, and connect the neutral (and or ground) pigtail.
Click to expand...
I've looked into those. I called and got 2 recommendations from Siemens that would fit my panel but after looking further into which of the 2 to buy, I found that they might not be the best choice for actually protecting stuff. From my research, it appears that midnight solar's spd's are some of if not the most effective residential spd's, but I have no proof either way.
 
Kornbread said:
Does it make any difference how these 'breaker sized' spd are wired if they go in the main panel vs a sub panel? Should they be in the first position, nearest the grid feed, for best protection, or does it make any difference?
Click to expand...
It works in any location.
But preferably close to the source of the expected surge, whenever possible.
As in main panel is better than sub panel, if protecting from a grid surge.
Location in the panel has little impact.
 
First position is slightly better, lower resistance and inductance.
Minimum pigtail length, and definitely not coiled, is better.

But wires leading to sub panel will be more resistance and inductance than busbars.
If you put SPD in main panel, and another at sub-panel, that should result in additional voltage drop at sub-panel.
Just as if electric furnace was fed by main panel, and another device at sub-panel, each causes additional voltage drop. Except, we're talking about voltage drop from 10,000A rather than 40A, so voltage drop clamping a surge is much greater.

Plus, two SPD in parallel means each takes fewer amps, clamps to lower voltage.
I would have liked to get 50kA QO SPD, but it was for PON panel, and for my panel that uses neutral pigtails 25kA was the largest they carry.
 
Gotshocked! said:
I've looked into those. I called and got 2 recommendations from Siemens that would fit my panel but after looking further into which of the 2 to buy, I found that they might not be the best choice for actually protecting stuff. From my research, it appears that midnight solar's spd's are some of if not the most effective residential spd's, but I have no proof either way.
Click to expand...
I'm sure that some offer more protection than others.
More is always better, but enough is always enough.
 
Hedges said:
1) Buy a breaker to fit unused busbars in combined service entrance device, connect SPD to it.
2) Tap off after main breaker and connect SPD there (if one of those ~ 3/0 wires is long enough, and Polaris is large enough to clear insulation, can feed through Polaris to main breaker, leaving spare tap.)
3) Tap off unfused disconnect
4) Tap off fused disconnect
5) Tap off AC in wires of inverter

In general, SPD is supposed to have about 20A OCP and any of these tap points has larger fuse/breaker.

If 20A is available to fit busbars in CSED, that's the simplest. I think those breakers land on line side of main, so should probably have higher AIC than typical 10kA branch breakers, but maybe that's OK if available fault current from utility is limited.

Otherwise, there are DIN rail mount touch-safe fuseholders and breakers.

Hey, if one of those SPD shown by Tim fits the busbar, and has necessary AIC, that is the simplest of all.
Click to expand...
The midnight solar 300ac is recommended to use a 30amp 2 pole.

It is supposedly already fused, so it doesn't actually need a breaker. It can be installed straight to the lugs.

If I tap off the existing wires of the inverter, I can stick this thing at the bottom or to the right side of the inverter which would be swell.

The 4 wires all the way to the right are load and grid.

If I connect to the load lugs, this will also protect the load panel?

IMG_20240524_170918186.jpg
 
On load lugs of course protects devices on protected loads panel.
It only begins to protect devices on main panel when inverter is connected to grid.
Same for AC input circuitry of inverter - not protected when off-grid.

Midnight SPD has thermal over-protection for MOV so they don't catch fire after failing short.
If it says 30A fuse/breaker required, you should connect that.

Best option may be to plug an SPD directly on busbar in CSED. But find its AIC rating, which may be 10kA. Then ask utility what maximum available fault current is.

Next best is 30A breaker (with appropriate AIC rating) on busbar in CSED, then connect lead of SPD. The breaker likely accepts two wires, so could easily connect two SPD for greater protection. Or two of different voltage rating; lower rated one protects against first big strike, shows red LED, higher rated one continues to protect.

Either way, another SPD at AC in of inverter provides additional protection.

SPD on PV protects from induced voltage, as does SPD on AC out of inverter.

If you live in Florida or other high lightning area, go for that 3 or 4 SPD setup. I'm in San Jose, have fraction as much risk. One property has overhead service, while the other is fed underground from an underground transformer. Some of my inverters have MOV in combiner box, others I plan to add (bought loose MOV + PTC fuse for a few bucks each.)
 
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