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Blown fuse in AC disconnect?

gg576

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Mar 19, 2021
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Solar edge is running clipping as it does at noon this time of year. See that I have no generation from that time onward. Check the inverter and it will not turn on.

It was like 93 degrees today. Go to the AC disconnect and pull the two bussman fuses. One is blown. First time in the 8 years I have had the system.

Now I know I can get a new fuse and maybe that is it. I am more concerned why it failed. Do these fuses have a certain lifespan and this is within reason?

I just added a whole home surge suppressor yesterday. I don think that would have done anything.

Thanks for any suggestions in advance.
 
Solar edge is running clipping as it does at noon this time of year. See that I have no generation from that time onward. Check the inverter and it will not turn on.

It was like 93 degrees today. Go to the AC disconnect and pull the two bussman fuses. One is blown. First time in the 8 years I have had the system.

Now I know I can get a new fuse and maybe that is it. I am more concerned why it failed. Do these fuses have a certain lifespan and this is within reason?

Not really. but as you know a fuse is using a thermal limit to trigger.
Is your AC disconnect outside and is it in the sun ?

If you have a hot day (93 is hot imo) with high ambient temperatures _and_ the AC disconnect also is in direct sun light and you have 8 years of oxidation on the fuse & fuse holder (== heat buildup) , I could see it melt down at some point.

I just added a whole home surge suppressor yesterday. I don think that would have done anything.
It shouldn't (famous last words). The voltage would have to go up so much out of the ordinary to trigger, I doubt that was the case .
 
Appreciate the confirmation.
Once you have the fuse replaced, just before noon go in and take IR temperature reading of both the fuse in the middle and the 2 spots where it is in the holder. If you see higher temperatures there, there might be some oxidation. If the resistance would go from 0.01 -> 0.05 (not measurable with normal meters) it would be visible with an IR thermometer.
You say it is clipping, does it even go near of the rating of the fuses?
 
So the SE 7600 inverter has a max listed at 30 amps. Run amperage is listed at 23.7 amps. We figured out that the fuses were 40 amp fuses.

Replaced this morning and inverter is up and running. New problem is that one of my optimizers is not being recognized. Did a re pairing as well and now I am short one. Think a blown optimizer could cause the fuse to go?
 
So the SE 7600 inverter has a max listed at 30 amps. Run amperage is listed at 23.7 amps. We figured out that the fuses were 40 amp fuses.
7600 watt / 240 volt = 31.6 Amp. that ofcourse only during the peak of the day.
With cloud focusssing you could easily see 25% more for less than a minute.
That would be 39.6 amps.
I agree that 40 amp fuse is the right value.

Replaced this morning and inverter is up and running. New problem is that one of my optimizers is not being recognized. Did a re pairing as well and now I am short one. Think a blown optimizer could cause the fuse to go?
No
an optimizer is in the DC chain at the input of the inverter.
You are having a problem with the AC chain behind the inverter to the grid.
If/when an optimizer fails, it goes to bypass mode so you won't have the power of the attached panel, but it should definitely not have any result on blowing an AC fuse imo.
 
Thanks for the clarification. Stared a warranty request with SE but they need I for from my installer. Might be better of just buying one myself.
 
When you installed surge suppressor, did the wires to fuse get disturbed, maybe affecting their contact resistance?

30A max current rating x 1.25 = 37.5A minimum fuse, so 40A is good.

Fast blow or slow? It could be fatigued by repeated motor-starting surges.
There are many types of fuses, often fit same fuse holder. Some rated for connection direct to grid, others not. Fuse holders can be designed or have inserts to reject fuses with lesser protection.

What gauge wire to the fuse?
Wiggle to test if it is loose (power off while doing this). Re-tighten, wiggling wire until screw stops turning.

Temperature, as FromPort says.
 
Thanks for all the suggestions. I am out of town and of course it looks like it blew again. Will know more when I get back tomorrow. Same thing. Just before noon. Max generation then data stops.

I added 6 425w panels to the system in March. The AC disconnect was installed for the original 25 327w panels.

Is it safe to upgrade the fuses in the disconnect to 50 amps? I will check connections and wire gauge now that this is not a one off issue.
 
Thanks for all the suggestions. I am out of town and of course it looks like it blew again. Will know more when I get back tomorrow. Same thing. Just before noon. Max generation then data stops.

I added 6 425w panels to the system in March. The AC disconnect was installed for the original 25 327w panels.

Is it safe to upgrade the fuses in the disconnect to 50 amps? I will check connections and wire gauge now that this is not a one off issue.
25*327=8175 W / 240V = 34 amps
6*425=2550 W /240V = 10.625 amps
Total 10725W /240V = 44.68 amps

The extra panels is essential info you forgot to mention in your initial post ?!
I am not surprised your fuse blows

Most of the time the fusible ac disconnects are 60 amps so probably no problem there.
But you have to figure out wire size to see if you can upgrade your fuses.
What is needed is 44.7*1.25= 56 amps so 60 amp fuse and i would go for #6 wire.
 
I just figured I got through three months of peak production and no problems. And I never even thought about the fuses. So you are correct that was definitely a lack of oversight.

Ok I will max my fuse to the wire size, ideally 60 amps if possible.

Again thanks for the help!
 
I'm dealing with similar, but I think it is current imbalance between two parallel runs bypassing inverter from grid to load. Also aged thermal breakers tripping below rating.
I'd like to get 63A or 70A DIN-rail magnetic/hydraulic 2-pole AC breakers, but I'm seeing prices of $200 to $250 and some instances of no stock. Midnight's CBI breakers rated 60A are $45, may use those but can't have quite as much current. It is claimed they can run 100% of rating, so maybe up to full 56A is OK.
 
I'm dealing with similar, but I think it is current imbalance between two parallel runs bypassing inverter from grid to load. Also aged thermal breakers tripping below rating.

@gg576 is pushing 44 amps through a 40 amp fuse.
His system is _not_ below rating ;-)


I'd like to get 63A or 70A DIN-rail magnetic/hydraulic 2-pole AC breakers, but I'm seeing prices of $200 to $250 and some instances of no stock. Midnight's CBI breakers rated 60A are $45, may use those but can't have quite as much current. It is claimed they can run 100% of rating, so maybe up to full 56A is OK.
Worth it though in the end ;-)
 
Ok so this is why I think I was confused.
Solaredge 7600 inverter gets capped at 7600w. So either the optimizers or inverter limits down the current leaving the inverter towards the AC disconnect?

So even though I am over paneled I thought the inverter would limit what makes it to the grid.

You cannot bruise my ego if you explain why I am not getting it.

Thanks.
 
7600W / 240V = 31.67A, should be just 80% of 40A breaker rating. At nominal 240V grid voltage.
Usually we see higher voltage when producing, but if yours is pulled lower, current would be a bit higher. Not enough to reach 40A, but cuts into the margin.

Weather, wire connections, etc. could boost heat a bit.

If this was a PV fuse or battery fuse I could come up with ways to trip it below expected wattage.

Just a 40A fuse for 7600W inverter? Two fuses, one for each phase?
You don't get 208VAC, do you? (only other models, according to data sheet)


What exact model number fuse? There may be some fast-blow that can't take some sort of surge. Not sure what surge would be on the AC side of a transformerless inverter ...
 
Ok so this is why I think I was confused.
Solaredge 7600 inverter gets capped at 7600w.
Technically it is capable of producing 7600Watt AC power.

So either the optimizers or inverter limits down the current leaving the inverter towards the AC disconnect?
optimizers optimize, inverters invert. The only thing limiting the power is the inverter.
You did not mention how you connected things.
Since you have so many different brand/watts panels added to your system i kind of guessed you used micro inverters
So even though I am over paneled I thought the inverter would limit what makes it to the grid.
that is what it should do
Solar edge even has a technical document about this:

SolarEdge allows DC/AC oversizing of up to 155% 345 depending on the inverter model according to below
specifications:
For Single Phase Inverters up to (and including) SE6000, DC/AC oversizing of up to 135% is allowed.


You cannot bruise my ego if you explain why I am not getting it.
With the new info (you could have put the new panels with micro inverters parallel to the SE) we now know that your 40 amp breaker should not melted again.
I did ask for some extra info in my first reply that you never answered so I will ask them again:
a)
Is the AC disconnect in direct sunlight
b)
did you use some sandpaper and take the oxidation off from both the fuses contacts & the fuse holder?
As an extra you might spray some oxidation cleaner on the copper contacts.

A fuse is a thermal breaker. if the environment (direct sunlight & ambient temp) & electrical resistance because of oxidation gives extra extra heat, the fuse will pop without reaching the actual 40 amps that is rated for.
 
Yes it is in direct sun during peak hours. I did not see any oxidation but I will give them a shine before I add new ones.

Thanks for the link and your additional info. Very helpful.
 
So as you suspected. Oxidation and evidence or arching/heat damage on the black conductor. The fuse on the left was the bad one installed a week ago. Sandpapered what I could. Put a 50 amp time delay fuse. Will do some observing during peak time tomorrow and will take some temps with IR gun.
 

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Wires work loose or settle. Torque, wait a while, re-torque. Rotate wire back and forth while torquing.

 
So as you suspected. Oxidation and evidence or arching/heat damage on the black conductor. The fuse on the left was the bad one installed a week ago. Sandpapered what I could. Put a 50 amp time delay fuse. Will do some observing during peak time tomorrow and will take some temps with IR gun.
Few things feedback:

a)
Did you check what wire size you have fitted? looks like beefy wire and might be #6.
If it is #8 your 50 amp fuse is not allowed and would be an issue if your house burns down and they discover that fuse.

b)
The fuse you replaced is already a 40 amp time delay fuse and can handle 44 amps for a few hours normally.
Technically it should be enough for your system, I don't like the idea of putting a 50 in.

c)
As you can see in this picture, I highlighted where the fuse holder contacts the fuse and where the current is transferred
Screenshot from 2022-08-14 16-24-03.png
Those surfaces should be sanded/cleaned as well. but they might be live so please take the utmost care.
And also on the top of course.
Screenshot from 2022-08-14 16-48-43.png

d)
the real problem seems to be with the switch blade, not the fuse or the fuse holder since I don't see any evidence of arching/black.
But the discoloring of the switch blade says enough:

Screenshot from 2022-08-14 16-51-54.png
That has been *HOT*
Screenshot from 2022-08-14 16-52-30.png

I would go as far as to advise you to replace the fused disconnect with a new one, stay with 40 amp fuse and try and get a warranty on this unit.
It is not like this was a loose wire or anything (based on the info provided with these pictures)
Replacing the fuse with a 50 amp will not make the arcing go away. and it might end up in producing a fire at the switch blade.
I would take no chances with this one.

Just my $0.02
 
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