Is my SPD plan solid?

Started by Megunticook, August 28, 2020, 11:59:45 AM

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Megunticook

Hello--aiming to protect my Outback FlexPower FPR-8048A-01 grid-tie system with battery backup from lightning. I've done research and spoken with a MNS tech so I think I've got a good plan but just wanted to cross-check with the forum experts.

A couple details: my battery bank is 48V, 420Ah flooded lead acid. The batteries and Outback system are housed in a shed about 30 feet from the house. There are two arrays, one on the roof of the shed and one on the house roof, and two charge controllers.

The house array has an accessible combiner box inside the attic. The PV circuit (in conduit) runs from the attic down to the first floor near the main service entrance, then underground to the shed.

AC circuits are all underground--from the grid at the street to the service entrance, and from the service entrance to the shed.

All EGCs are properly grounded as per NEC. An additional ground wire runs from each rooftop array directly to a ground rod that's bonded to the ground rods at the main service panel and the Outback system (in other words all ground rods are bonded together). This is just to provide lightning a direct path to ground in the event either array gets hit, rather than having the surge travel through the combiner boxes, into the house, equipment, etc.)

I've installed a Siemens SPD inside the main service panel to protect against any surges from the grid.

Here's what I think I need from Midnite Solar:


  • 1 MNSPD-300-DC for each combiner box (mount at combiner boxes or mount at charge controllers?).

    1 MNSPD-300-AC for the AC side of the inverter (mount at backup load panel in house or at inverter?)

    1 MNSPD-115 to protect the battery bank (not sure this is essential--tech. says battery bank can absorb surges)
Thanks for your thoughts/advice.



Kent0

Quote1 MNSPD-300-DC for each combiner box (mount at combiner boxes or mount at charge controllers?).
Best protection for the charge controller is to locate the SPD at the charge controller. One SPD for each charge controller input. Best protection for the combiner to charge controller wiring is to locate a SPD at the combiner box. But putting a SPD only at the combiner box only can make surges at the charge controller worse, so a SPD at each location is best.
Since the shed is a separate structure, it should have a ground electrode, and an equipment ground running with the PV array wiring.

Quote1 MNSPD-300-AC for the AC side of the inverter (mount at backup load panel in house or at inverter?)
On the AC load side of the inverter you should have a 4-wire SPD (probably like the Siemens unit on the service panel) or two MNSPD-300-AC SPDs. If the load center is a long ways away another 4-wire SPD there will provide better protection for circuits in the house.

Quote1 MNSPD-115 to protect the battery bank (not sure this is essential--tech. says battery bank can absorb surges)
Because of their location in the power system batteries are the least likely item to be damaged. However, I have seen small batteries with the side blown out by lightning. If you have a small battery bank, if you have AGM batteries, or if you are using lithium batteries, a MNSPD-115 on the battery cables is a good idea. If you have large FLA batteries, then they can withstand a hefty surge without damage.




schroew

The SPD can be mounted on a classic on the pv side?

boB

Quote from: schroew on January 28, 2022, 08:30:56 PM
The SPD can be mounted on a classic on the pv side?

Actually, I think it can be mounted there !   

There is a knockout hole with a plastic plug or filter plug and it might just fit in there.

I have not done that myself so I would find the documentation and see if that hole size is correct.

boB
K7IQ 🌛  He/She/Me

schroew

Cool, I think it will fit that little vent hole. I will have to see if I have the space between the classics.
Thx!!

boB

Quote from: schroew on January 29, 2022, 01:10:07 AM
Cool, I think it will fit that little vent hole. I will have to see if I have the space between the classics.
Thx!!

Yes, THAT is the only thing I was wondering about  😁😀
K7IQ 🌛  He/She/Me

Megunticook

I'm wondering if I should use the MNSPD115 rather than the MNSPD300DC to protect the DC side of my system. The Clamping voltage on the 115 is considerably lower (295V vs 775V) so I'm thinking that would better protect my equipment. The charge controllers are Outback FM80s which apparently are quite sensitive to voltage spikes.

The MCOV on the 115 is listed as 180V. My system never exceeds 120V so that should be fine.

Should I use the 115 instead of the 300?