Midnite Solar SPD Install Questions

[girfold]

Hey all, just got four SPDs for my setup - x1 EG4 6000XP with two PV arrays as input. Typical voltage up to 400V. 48/56V battery array, and AC breaker, no grid tie or grid input.

SPDs - x2 600VDC for the two solar inputs, x1 300VDC for somewhere connecting to the battery (would have liked a 115VDC since it's a 56V max battery setup, so I'm not even sure this SPD will help me?), and x1 300VAC somewhere for my breaker box / inverter.

Few questions..

• The schematics are showing both DC and AC ground wire voltage going to the ground in the AC breaker box. Is that right? With the neutral screw bond in the breaker box, is it ok to set up as such as long as the impedence is lowest on the ground to the exterior ground rod?
• Would the 300VDC SPD serve any purpose here to protect the batteries? My main concern is lightning coming in from the PV lines and surging to the batteries. I'd also have an SPD for the AC in case lightning somehow gets inside via like my minisplit then travels to inverter -> battery that way. Where best to wire the 300VDC if I were to use it? On top of battery box and hooked to the busbars?

 

[seneysolar]

Hey all, just got four SPDs for my setup - x1 EG4 6000XP with two PV arrays as input. Typical voltage up to 400V. 48/56V battery array, and AC breaker, no grid tie or grid input.

SPDs - x2 600VDC for the two solar inputs, x1 300VDC for somewhere connecting to the battery (would have liked a 115VDC since it's a 56V max battery setup, so I'm not even sure this SPD will help me?), and x1 300VAC somewhere for my breaker box / inverter.

Few questions..

• The schematics are showing both DC and AC ground wire voltage going to the ground in the AC breaker box. Is that right? With the neutral screw bond in the breaker box, is it ok to set up as such as long as the impedence is lowest on the ground to the exterior ground rod?
• Would the 300VDC SPD serve any purpose here to protect the batteries? My main concern is lightning coming in from the PV lines and surging to the batteries. I'd also have an SPD for the AC in case lightning somehow gets inside via like my minisplit then travels to inverter -> battery that way. Where best to wire the 300VDC if I were to use it? On top of battery box and hooked to the busbars?

Yes, the grounds for the SPD need to all come to the single main earth ground rod. This is typically easiest to tie in at your AC panel.
The SPD 115 is recommended for anything under 115v, see attachment. So the 115 could be used on the battery side of the charge controller.

The 300 spd might be too far away from the voltage you are trying to protect (48). Perhaps you can trade it in if unopened?

 

[timselectric]

The schematics are showing both DC and AC ground wire voltage going to the ground in the AC breaker box. Is that right?

Yes

With the neutral screw bond in the breaker box, is it ok to set up as such as long as the impedence is lowest on the ground to the exterior ground rod?

Not sure what you are saying, but the N/G bond should be at the first means of disconnect.

Would the 300VDC SPD serve any purpose here to protect the batteries? My main concern is lightning coming in from the PV lines and surging to the batteries. I'd also have an SPD for the AC in case lightning somehow gets inside via like my minisplit then travels to inverter -> battery that way. Where best to wire the 300VDC if I were to use it? On top of battery box and hooked to the busbars?

SPD's should be placed on every circuit that enters the house, at the point of entry. (Or before it reaches any equipment)
AC and DC circuits.
To protect everything in the house. (Which includes the batteries)

 

[Hedges]

I don't think battery itself would pick up anything. Unless battery wires make a long run.
So you're putting SPD on PV and AC, but you're worried something passes through inverter (or SCC) and reaches battery. Yes, a lower voltage one could help clip what comes through as seneysolar suggests.

AC input from grid definitely could use protection. I suppose AC output to wires in the house could pick up induced voltage from nearby lightning strike, especially if old house with knob and tube wiring (loop area) which could get differential mode. Modern house wiring e.g. Romex might get some common-mode voltage, little differential.

Don't know your location, if you expect nearby lightning or just surges from powerline including distant strikes.

 

[girfold]

Thanks all! I think my state is in the top 5-10 states for lightning strikes. Not quite as bad as Florida, but have had a handful of run-ins with lightning in my past to make me cautious of potentially losing 5+ LiFePo4 batteries to. I usually flip the PV disconnect during storms, but may not always be around to do that when the storms show, so would rather have SPDs in case.

Yes, the grounds for the SPD need to all come to the single main earth ground rod. This is typically easiest to tie in at your AC panel.
The SPD 115 is recommended for anything under 115v, see attachment. So the 115 could be used on the battery side of the charge controller.

The 300 spd might be too far away from the voltage you are trying to protect (48). Perhaps you can trade it in if unopened?
View attachment 200950

I think when shopping Signature Solar site, I didn't see 115V, but will look to order one for extra safeguard. I'll reuse the 300V SPD for the PV array on my little "yellow inverter dolly setup" that Will has shown how to make at least. Thanks for the reassurance on having all grounds come together regardless of AC or DC voltages.

Yes

Not sure what you are saying, but the N/G bond should be at the first means of disconnect.

SPD's should be placed on every circuit that enters the house, at the point of entry. (Or before it reaches any equipment)
AC and DC circuits.
To protect everything in the house. (Which includes the batteries)

Thanks for reassurance on the SPD locations. I think one question for the middle part is how to test resistance to make sure that lightning will travel to ground vs going back through the neutral path due to the ground/neutral bond screw? Or are those screws meant to have a moderate resistance versus the full ground. I did choose a much larger copper wire for my ground connection than most of my other connections.

I don't think battery itself would pick up anything. Unless battery wires make a long run.
So you're putting SPD on PV and AC, but you're worried something passes through inverter (or SCC) and reaches battery. Yes, a lower voltage one could help clip what comes through as seneysolar suggests.

AC input from grid definitely could use protection. I suppose AC output to wires in the house could pick up induced voltage from nearby lightning strike, especially if old house with knob and tube wiring (loop area) which could get differential mode. Modern house wiring e.g. Romex might get some common-mode voltage, little differential.

Don't know your location, if you expect nearby lightning or just surges from powerline including distant strikes.

Good to know, lot of lightning strikes here, and a few AC circuits exterior to the building that could act as antennas (the minisplit for instance). Per yours and the above advice, I'll look to add in a 115V eventually for extra safety in case surge gets to the inverter but before the batteries. The batteries are definitely the most costly part of the system, I'd also want to safeguard the inverter of course, but with the life expectancy of 5 years and the same cost as a single battery, it's not the end of the world if it goes and batteries survive. Plus will definitely still be using the 300VAC to hopefully shunt any of that surge to ground.

 

[timselectric]

Thanks for reassurance on the SPD locations. I think one question for the middle part is how to test resistance to make sure that lightning will travel to ground vs going back through the neutral path due to the ground/neutral bond screw? Or are those screws meant to have a moderate resistance versus the full ground. I did choose a much larger copper wire for my ground connection than most of my other connections.

Lightnings only goal is to find its way to the earth.
It will take all paths, but mostly the easiest path to do so.