Other MidNite Electronics > MidNite SPD (Lightning arrestor)

Is my SPD plan solid?

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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:

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


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


--- Quote ---1 MNSPD-115 to protect the battery bank (not sure this is essential--tech. says battery bank can absorb surges)
--- End quote ---
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.



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