diy solar

diy solar

Correct wiring for Solar Panel SPD

B

burgerking

New Member
Joined
Apr 6, 2022
Messages
368
Location
Subic, Philippines
Which of these two wiring diagram is the correct method of installing a DC SPD for Solar Panels?
Please give your reason.


1654441460404.png


Assume that the above listed components are inside a single box.


Thanks
Dan
 
Last edited:
burgerking said:
Which of these two wiring diagram is the correct method of installing a DC SPD for Solar Panels?
Please give your reason.


View attachment 97323


Assume that the above listed components are inside a single box.


Thanks
Dan
Click to expand...
commercial combiner boxes all seem to do Circuit B. The reason for this is that if there are multiple strings, you would need a separate SPD per string. With a single string as shown above, the only difference I can see is that if the SPD is before the fuse, it will no longer protect your charge controller once the fuse is blown. (but if the fuse is blown, the need for protection of the controller is drastically reduced).
 
B


When using string protectors such as fuses, DC breakers or string diodes together with SPDs, the SPD must be installed between the
fuses and the inverter, otherwise the PV strings would be unprotected if the fuse is triggered.
 
mopat said:
B


When using string protectors such as fuses, DC breakers or string diodes together with SPDs, the SPD must be installed between the
fuses and the inverter, otherwise the PV strings would be unprotected if the fuse is triggered.
Click to expand...
I came to the same conclusion that the SPD should be between the fuse and charge controller, but not to protect the strings. Instead, it is to protect the charge controller. (Once the fuse blows, the string will no longer be connected to the SPD.
 
timselectric said:
This brings up the question of the location of the SPD.
Near the panels or the inverter.
In both cases, I chose the same as this diagram. Connected directly to the long wiring.
Click to expand...
Midnight is saying to put one in the junction box and another near the inverter. If you trace it out, they are in parallel and on the same circuit.

Overkill? I think so but that is just my opinion.

If you are using just one there are arguments both ways. It is always better to dump the surge closer to the source.... so that argues to put it closer to the panels. However, the ground wire up to the combiner box is going to offer a fair amount of impedance to the path and reduce the effectiveness of the SPD.
 
Last edited:
FilterGuy said:
Midnight is saying to put one in the junction box and another near the inverter. If you trace it out, they are in parallel and on the same circuit.

Overkill? I think so but that is just my oppinion.

If you are using just one there are arguments both ways. It is always better to dump the surge closer to the source.... so that argues to put it closer to the panels. However, the ground wire up to the combiner box is going to offer a fair amount of impedance to the path and reduce the effectiveness of the SPD.
Click to expand...
Mine is close to the SCC, with the breaker between the two. In my opinion the "source" for the SPD is the possible surge. Which in a nearby lighting strike, would be the long wires. I believe that either end would probably protect equally. But, I have Mine at the end closer to the ground rod.
 
FilterGuy said:
Here is a summary.

View attachment 97360

You choose.
Click to expand...

Circuit A.
There is a chance that the surge is strong enough it destroyed the SPD, and the surge long enough it now travels freely through the MCB/fuses and into the SCC.

Personally I choose Circuit B.
My reasoning is that, if there is a surge strike, the SPD will short the output of the MCB/Fuse forcing the latter to trip, fully disconnecting the SCC/Inverter from the troubled circuit.
FilterGuy said:
(but if the fuse is blown, the need for protection of the controller is drastically reduced).
Click to expand...
Exactly what I was banking on putting the SPD between the panels and SCC/Inverter: The MCB/Fuse will become an open circuit no more surge to pass to SCC/inverter.

LittleFuse also recommended putting the SPD between the Fuse and SCC.

It is true that in this setup, the SPD will not protect the panels; however I opined that the surge already damaged the panel (panels) before the surge gets to the wires for any 'protecting' could be done.


re Location: near panels, or near SCC/Inverter?
Considering I'd be putting one combiner box up in the roof, and a disconnect box near the SCC, it does not hurt to add another SPD and have two of them each on both ends.
 
Last edited:
FilterGuy said:
They do like selling their overpriced SPDs!!

Notice that they put the SPD after the fuse.
Click to expand...
But they've got those pretty blue LED's on them!

Once upon a time I did a bit of research and based on my limited understanding Midnite's SPD are about the best value out there. But that was a while ago and I get quickly distracted by shiny things. I believe thier "joules" rating was clearly the highest for the money that I could find. We do use the heck out of them and haven't had any problems.

I'll dig around here and find some Delta's that have the guts blown clean out them and send a picture someday. Equipment survived though!

edit to fix typos
 
Last edited:
You should always have some form of over-current protection between the surge arrestor and the energy source (So circuit B).

The reason being that MOVs wear out, each surge they kill reduces the trigger voltage slightly, eventually the trigger voltage goes below the circuit operating voltage and they stay "on" and potentially dissipate a lot of energy. Most have some form of overheat limiter (which also triggers the "fault" flag in the little window) but best to be safe.

Also, of course, your panels don't have an "off" switch, I'd rather not be wrestling a MOV cartridge out of a live holder (our DIN mount MOVs have replaceable cartridges).

I think I may have mentioned it before, but our Sofar inverters detect the leakage in the MOV long before the "fault" flag even thinks of triggering so the issue of the beast cooking up isn't going to occur, until it does ...
 
Delta's can go to thousands of volts.
My uderstanding is that it's just an air gap in sand. Not particularly useful for sensitive electronics. MOV protectors are much better at limiting surge voltage.
Electrician installed deltas at my place, strike 150' from the house wiped out a bunch of electronics, about $6000 loss.
I will be installing MOV SPD's and quite a few of them. IMO Midnite is a decent value in that space.
 
According to NEC

285.24 Type 2 SPDs. Type 2 SPDs shall be installed in accordance with 285.24(A) through (C).

(A) Service-Supplied Building or Structure. Type 2 SPDs shall be connected anywhere on the load side of a service disconnect overcurrent device required in 230.91, unless installed in accordance with 230.82(8).

(B) Feeder-Supplied Building or Structure. Type 2 SPDs shall be connected at the building or structure anywhere on the load side of the first overcurrent device at the building or structure.

(C) Separately Derived System. The SPD shall be connected on the load side of the first overcurrent device in a separately derived system.
Click to expand...

definitive instruction where it should/must be installed.
 
Last edited:
You must log in or register to reply here.

Similar threads

Rob_in
Are multiple SPDs really required when panel to MPPT wiring is longer than 33ft/10m?
Replies
4
Views
567
timselectric
T
G
SPD location at main panel or at inverters feeding main panel
Replies
5
Views
147
timselectric
T
G
Midnite Solar SPD Install Questions
Replies
5
Views
463
timselectric
T
C
SPD wiring...
2 3
Replies
51
Views
2K
Gotshocked!
Gotshocked!
K
Best placement for SPD
Replies
13
Views
627
Bananaman321
Bananaman321

diy solar

diy solar
Back
Top