Where to install SPD's and how many required for proper protection?

ligwydligwyd Posts: 58Registered Users ✭✭
Hello  there,

I would like to know where to install the SPD,s, what type of SPD to use for each location and of course the best way to wire them in?
I've already watched all the videos on the Midnite website and I  will read through the posts re: SPD's on the Forum, but also thought I'd better post my questions directly, as it pertains to my situation in particular, for greater clarity.
As of now I have one MNSPD-115, one MNSPD-300-AC and two MNSPD-300-DC's in boxes ready to be installed.

The equip I have set up now that my require SPD's installed:

MNPV6-Disco (for the solar array)

MNDC250-L (battery bank disconnect)

Schneider XW+ 6848

Two - Schneider MPPT 60/150's

A 60 amp load center that only runs a few 120V outlets in the power room

I also have Schneider Battery Monitor, SCP, Combox and AGS.

Thank you for any support and direction that may be avail through this forum.


  • mcgivormcgivor Posts: 2,206Solar Expert ✭✭✭✭✭
    DC SPD's at both ends if long runs used, mounted outside at home end, AC SPD's  at distribution on both ungrounded conductors if applicable. Using grounded metallic conduit wherever possible will reduce the effects of induction, avoid unshielded overhead outdoor  runs, don't coil excess cables and install a lightning mast to direct the path of a strike away from the array. Attached pdf is very useful  
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • ligwydligwyd Posts: 58Registered Users ✭✭
    My longest run of 10 awg PV wire is 37 feet one way so I am guessing that I only need protection at the combiner.
    Question: I am using two Schneider Mppt 60 150's. Since I have split the positive bus bar in the combiner and the negative has separate bus bars as well do I need two 300VDC SPD's on my combiner box? I would think so but god to ask? :)
    Looking forward to studying the document from SolarEdge.

  • mcgivormcgivor Posts: 2,206Solar Expert ✭✭✭✭✭
    The 37' run is short at the combiner should suffice, as the feeds as isolated each will need it's own SPD, the Solar Edge file is for grid inverters but the fundementals are the same, remember SPD's offer little to no protection against a direct strike, if in an area of high risk a lightning  rod will help but no gaurentee is possible. My rod was hit four days after installation, lost an inverter due to overhead lines on the AC side, no SPD installed at that point in time, a year later another hit took out a charge controller SPD'S didn't help. Using devices which match the voltage used is important for example with a 60-150 it should be as close to the maximum allowable voltage 150V, the ones I used were too high, I have since sourced a manufacturer who will supply any voltage customized to specific needs and will replace existing ones, before the next rainy season, lessons learned the hard way.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • ligwydligwyd Posts: 58Registered Users ✭✭
    edited October 10 #5
    1.What was the product you sourced?

    2.Does your lightning rod go direct to ground separate of the equip ground?
    You'd think that the clamp voltages of the SPD's produced by Midnite Solar would be dialed in right to where they need to be for the majority of applications? I watched all the videos on the Midnite website re: their SPDs and If I remember correctly (verify for yourself of course) the solar equip is designed to handle a certain threshold of voltage/ current spikes (check manufacturers spec of equip of course) and thus the SPD's are designed to clamp anything above what the equip was designed to handle. I'm sure there is nothing wrong with an SPD that is closer to the max voltage of the equip being protected but is it necessary? Here is the video that discussed this.

    3.Also, what is the best method of terminating the 12 awg SPD wires to the positive bus bars in the combiner. If that is a stupid question I'll just do it sensibly. Be nice if there was a place for it to terminate. Maybe drill a small hole if the bus bar and use a small stainless machine screw with lock washer and a crimp on ring connector? I don't like the idea of putting the 12 awg wire in with the 6awg main wire going from combiner bus bar to the PDP.

    4.Can the SPD's be mounted on the top of the combiner if it is outside? Putting holes in the top of the combiner when there are holes provided in the sides might be silly but I think it might look better, less chance of someone hanging off a side mounted unit and the rubber washer would seal the combiner against water leakage? Thoughts?

    5.Re: the AC side, is it simply a matter of talking the shortest path to ground, when determining whether to run the green SPD wire to Neutral bus bar or Ground bus bar?

    Thanks for the discussion :)

  • mcgivormcgivor Posts: 2,206Solar Expert ✭✭✭✭✭
    edited October 11 #6
    1 Product searched is this http://www.spd-zp.com , bare in mind in in Thailand so these products may or may not be accepted in the US or     other locations 
    2 My lightning rod has 2 × 3 meter isolated  ground rods driven into the soil bonded to each other as well as the reabar used in the foundation, the steel  mast is 6 meters high with an air terminal on top.

    3 Best not to use a single terminal for 2 conductors, if crimp on use quality lugs, alternatively use screw terminals.

    4 If outdoors exposed to weather, it's good practice to never enter on the top of a box

    5 The AC  SPD I used is a Schneider device which occupies a single breaker slot in the panel, single phase 230V with a pigtail to the ground bus, as per installation instructions  

    With regards to the voltage thresholds, the equipment lost was on a 24V nominal PWM system, SPD's rated at these voltages are a little harder to obtain, my logical thinking is it would be better to be as close to the rated system voltage.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • ligwydligwyd Posts: 58Registered Users ✭✭
    edited October 12 #7

    Noted. Thanks mcgivor.

    Did you ground your array/ panels to system ground or also isolated and to its own ground rod? I've heard that it might not be a bad idea  in the event that a strike misses your rods and hits the array/ panels?

    Also in the battery box disconnect, can I run the red wire from the SPD to the line or the load lug on the 250 amp DC breaker and can the black SPD wire run to either the battery stud of the shunt or system stud of the shunt. Is is one location better than the other?

    Almost got them all wired in today :)

  • mcgivormcgivor Posts: 2,206Solar Expert ✭✭✭✭✭
    Array is grounded at the array by means of a ground rod bonded to the steel frame and rebar in the concrete pad, as far as the batteries are concerned lead acid probably don't need to be protected due to lack of sensitive electronics, but you got me thinking because with LFP there are electronics involved, the BMS to be specific. Hopefully the SPD's outside will prevent migration inside, but when a direct strike occurs, it pretty well dose what it wants, which begs the question are you in a high risk area? From what I've read 80% of all lightning occurs within the tropics, 80% of ground strikes within the tropics occur at elevations above 3000'/1000m, other than that, low lying land near the ocean can receive ground strikes more frequently despite being outside the tropics, Florida is a good example. My particular location is 17°N at an elevation of 200 meters ~700' above sea level, 400Km 250 miles west of the Vietnam coast, we get violent storm cells passing through during the rainy season but for the most part lightning is intercloud, or cloud to cloud, Ironically I went for 8 years wit no protection and no problems, go figure, as soon as I address the potential problem I somehow get hit, or is it the law of averages, who knows? 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • ligwydligwyd Posts: 58Registered Users ✭✭
    Thanks for the comments mcgivor.

    I've got two more Midnite Solar 115V SPD's to install today in the battery box disconnects (two separate systems). I have Scnheider Batter Monitor, SCP, Combox and AGS and some LED liights in the battery box running directly off a DC to DC converter. It would be nice to know I've at least done what I can to protect the electronics with proper surge suppression. Not sure if the Schneider electronics can handle what the Midnite SPD's may let through. Need to do a little more research. You'd think that the big solar component manufactures would be mass producing SPD's that clamp closer to system voltages but maybe there is a reason that they are not that I am not aware off.
    I have found the tech suppport through https://www.solar-electric.com/ to be very helpful and informative as well as this forum. I'll keep on digging.

    Thanks again mcgivor and have a great day :)

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