SPD success stories

[rustyrotors]

my only experiences are back when i first installed my system, i ignorantly had two separate ground rods for the DC and AC sides, separated by about 100ft. i also had no surge protection. my system is installed outdoors, and the only thing entering the house is split phase AC to a dedicated offgrid breaker panel. it was not long before i had a nearby lightning strike, power went out for a second but recovered quickly. my inverter reset itself, but the only casualty was my internet cable modem died. the cable modem was on a surge protector power strip, i suspect the cable line had a surge. after that, i realized my grounding was inadequate, and i needed add surge protection

so now everything is grounded to a single ground rod at grid service entrance, there is a DIN style SPD on the solar DC input, an SPD in both grid and offgrid AC breaker panels, and also surge protector power strips at most appliances. last major storm, we had another nearby lightning strike, this time i heard a snap sound near my TV, a second later BOOOM from the lightning strike. inverter did not reset this time, everything was fine. not really sure where the snap sound came from, maybe the cable modem again, but still works fine

 

[Daddy Tanuki]

This may sound stupid, but I guess one question I have never askedis: If you do not have a ground (older construction) and never install a ground can the lightening strike damage your equipment?

 

[OzSolar]

This may sound stupid, but I guess one question I have never askedis: If you do not have a ground (older construction) and never install a ground can the lightening strike damage your equipment?

I've wondered about this several times and I think you possibly are more likely to get damaged by lightning.

Here's my theory: If you've ever played with your DVM trying to see what the voltage was from the hot of an outlet to a concrete floor or even the dirt you likely would have gotten some odd reading. For example: you might get 20v to the floor from the hot 120V outlet. That's because even though those surfaces aren't great conductors they are still conductors.

So instead of having a single point ground for your building you have an iffy ground in all sorts of places. Multiple grounds are bad to due to induced voltage between them. Probably a whacky theory, perhaps smarter folks will be along to educate us!

 

[Daddy Tanuki]

I've wondered about this several times and I think you possibly are more likely to get damaged by lightning.

Here's my theory: If you've every played with your DVM trying to see what the voltage was from that the hot of an outlet to a concrete floor or even the dirt you likely would have gotten some odd reading. For example: you might get 20v to the floor from the hot 120V outlet. That's because even though those surfaces aren't great conductors they are still conductors.

So instead of having a single point ground for your building you have an iffy ground in all sorts of places. Multiple grounds are bad to due to induced voltage between them. Probably a whacky theory, perhaps smarter folks will be along to educate us!

yeah i was not trying to be a smartaleck . not an electrician myself so just curious. the ground is there for the safety of the end user and protection of components is a secondary benefit.

 

[robbob2112]

Look, the object of an earth ground is to get all the equipment cases to the same potential and the tie to the earth through the ground rod is to prevent you from shocking yourself or others if they touch the equipment and are standing on the ground. Say you like to work in flip flops, or run out to reset a breaker at 2am barefoot... or god forbid a child is touching something he/she isn't supposed to and gets electrocuted.

Tying it all together and to ground prevents any of those things.

If there is only a single ground and there is a nearby strike the voltage level of the rod, the equipment and the ground will all have a momentary rise to many thousand volts and come back down... in that case everything is together and nothing is harmed because there is no voltage gradient. Now with distance between array and inverter the SPD will burn through to try and protect you from the lightning, but if you take a straight strike nothing will protect things. If you are smart you ground things, ground the SPD to that same system and use an SPD at both ends of the long wires especially outside... put them at equipment you want to protect and put them at all building entrances.

IF and ONLY if you are in something mobile sitting on tires and there are no panels attached ground mounted you don't add a ground rod. If you plug into shore power you get a ground through that.


Also,

Ever wonder while in some combiner boxes you see PV wires going to 2 fuses or 1 fuse or 2 pole breakers or single pole... in some the negatives are combined and some they are not?

I did digging the other day and here is what I came up with.... I hope I am right, but if I am wrong, someone will point the way

IF you are mobile and you have a combiner - then you have your battery negative tied to the chassis ground. You also have the combiner negative tied to chassis ground. The positive goes into 1 pole breaker or fuse. Panel frames are attached to th chassis ground. Everything is basically floating the ground and using chassis as reference. SOOOO - you touch any piece of metal or any part of the system and everything is at the same potential. Just hope you aren't one foot on the step and one foot on the ground when lightning strikes. Of course if the leveling jacks are down that could easily provide a ground verse floating.



For perm mount/home mount everything is tied to the ground system which is referencing the ground rod verse floating. All the grounding is as listed above, but no tie to a chassis .... This means you DON"T have the negative from the panels tied to the ground system of the house, instead you have it in a 2 pole DC isolator and then in the combiner you have it going into a 2-pole breaker or a 2 fuse holder. You want to pop the OCPD if either wire shorts out to the conduit the wires are in... the conduit is tied to that ground system from the house.

It is always the same answer, if there is a way to have a difference of potential when you touch two metal enclosures they get tied together... metal roof and metal racking - tied together... metal cage around the equipment - tied together.... all tied to house ground system.

 

[user2562]

Look, the object of an earth ground is to get all the equipment cases to the same potential and the tie to the earth through the ground rod is to prevent you from shocking yourself or others if they touch the equipment and are standing on the ground. Say you like to work in flip flops, or run out to reset a breaker at 2am barefoot... or god forbid a child is touching something he/she isn't supposed to and gets electrocuted.

Tying it all together and to ground prevents any of those things.

If there is only a single ground and there is a nearby strike the voltage level of the rod, the equipment and the ground will all have a momentary rise to many thousand volts and come back down... in that case everything is together and nothing is harmed because there is no voltage gradient. Now with distance between array and inverter the SPD will burn through to try and protect you from the lightning, but if you take a straight strike nothing will protect things. If you are smart you ground things, ground the SPD to that same system and use an SPD at both ends of the long wires especially outside... put them at equipment you want to protect and put them at all building entrances.

IF and ONLY if you are in something mobile sitting on tired and there are no panels attached ground mounted you don't add a ground rod. If you plug into shore power you get a ground through that.


Also,

Ever wonder while in some combiner boxes you see PV wires going to 2 fuses or 1 fuse or 2 pole breakers or single pole... in some the negatives are combined and some they are not?

I did digging the other day and here is what I came up with.... I hope I am right, but if I am wrong, someone will point the way

IF you are mobile and you have a combiner - then you have your battery negative tied to the chassis ground. You also have the combiner negative tied to chassis ground. The positive goes into 1 pole breaker or fuse. Panel frames are attached to th chassis ground. Everything is basically floating the ground and using chassis as reference. SOOOO - you touch any piece of metal or any part of the system and everything is at the same potential. Just hope you aren't one foot on the step and one foot on the ground when lightning strikes. Of course if the leveling jacks are down that could easily provide a ground verse floating.



For perm mount/home mount everything is tied to the ground system which is referencing the ground rod verse floating. All the grounding is as listed above, but no tie to a chassis .... This means you DON"T have the negative from the panels tied to the ground system of the house, instead you have it in a 2 pole DC isolator and then in the combiner you have it going into a 2-pole breaker or a 2 fuse holder. You want to pop the OCPD if either wire shorts out to the conduit the wires are in... the conduit is tied to that ground system from the house.

It is always the same answer, if there is a way to have a difference of potential when you touch two metal enclosures they get tied together... metal roof and metal racking - tied together... metal cage around the equipment - tied together.... all tied to house ground system.

If you have a long distance between inverter and panels, can you just ground the panel SPDs to a local ground (but ground the panels to the same ground as inverter, as required)?

 

[robbob2112]

If you have a long distance between inverter and panels, can you just ground the panel SPDs to a local ground (but ground the panels to the same ground as inverter, as required)?

If there is a distance between the inverter and panels you need the pv wires and an EGC (equipment ground conductor). This wire should be run along side the pv wires inside the same conduit. In general it should be the same size as the pv wires. It connects to the pv panel racking and frames, but not to either the positive or negative current carrying conductor. If it is a shorter distance you can downsize the EGC a bit.

You should NOT have a second ground rod out at the array. If the posts are set in concrete you can't help having a ground, but don't drive a rod out there.

PV wire size is 156% of the expected current from the panels. At the array the EGC needs to be bare copper 6awg solid wire. Inside the conduit the simplest is to use stranded THHN/THWN. You don't need to worry about voltage drop but any drop is wasted power, so you may want to upsize the wire gauge for it, but not the EGC.

 

[Daddy Tanuki]

my building (shop is all metal) the racking is metal bolted to the frame of the shop frame is 4x4 box steel 3.2mm thick which is cast into concrete. currently i have a (admitedly shitty) ground rod driven into the ground next to the shop which then goes to the building frame and bussbar for the shop, house, and inverters, scc's etc. Do you think it is OK not to run a seperate wire to the panels as they are mounted on the roof metal on metal.

Panel metal frame -> metal racking -> metal roof -> metal frame of building.

thoughts?

 

[robbob2112]

Were it me I would probably still run a bare copper wire back to the ground system and in the process tie it to each different item along the way. If there are high impedance joints at any point you could have a voltage gradient. And shock hazard.

Now, if the building were here in the states you would probably be able to find bonding straps connecting the frame parts together that aren't welded. Then the sheet metal screws to it with insulated screws a lot of the place, but at least a couple are penetrating from sheet metal to some portion of the frame that is bonded back to the posts in cement. This can also be accomplished with bolts holding everything together so long as the resistance from one thing to the next is near zero ohms.

BUT, if any of that fails and you get across two different parts you could get a shock.

The vendor doesn't want folks to get shocked into being sue happy so they make sure everything is grounded good.

And as you have probably seen @timselectric mention more than once metal in cement is an excellent conductor to attach ground wire to, better than a puny weak ground rod that isn't gonna do so much. Many commercial buildings are done this way.

 

[ThaiTaffy]

Not a success story but i thought it was relevant and interesting,