Noob grounding question

verdigo

I have been reading that all grounds should go to the same grounding rod. I don't have a problem with this but my shed is about 50 feet from the house and the existing rod. The only part of the system that will be located in the house will be a manual Reliance 6 circuit transfer switch. Batteries, inverter, charge controller, the shed's A/C distribution box, and gen set will be located at the shed. Is there any foreseeable reason to drive another rod into the ground at the shed?

BB.

Re: Noob grounding question

Do you have a chance of lightning strikes in your area?

-Bill

verdigo

Re: Noob grounding question

BB. wrote: »

Do you have a chance of lightning strikes in your area?

-Bill

Oh yeah.... So I should ground all the shed components to include the pv frames to a separate grounding rod at the shed?

BB.

Re: Noob grounding question

Since lightning ground it a complex subject... I like to suggest reading these links to understand the "basics":

BB. wrote: »

A couple threads about Lightning:

Off Grid Grounding Technique?
Another Question, this time about Lightning

Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

And our host's consolidated FAQ page:

www.windsun.com
Lightning Protection for PV Systems

From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

Towards the end of this thread is a very nice discussion of proper generator grounding.

-Bill

As start, ground solar panel frames, external racking/metal work, etc. to a local ground rod at the foundation.

For DC grounding of the solar panel (+/-) power leads--Don't ground them locally (at the remote building). You could get surge suppressors (Midnite's, etc.) to connect from DC to Earth Ground--Would not be a bad idea.

For your 120/240 VAC Neutral... The standard is to ground the neutrals at one point in the system (at the main AC panel typically).

But, for electrical safety, you should connect the neutral to the local metal work (electrical boxes, well head, etc.). And because the neutral is grounded to the local ground rod--you now have two (or more) ground rods in the system.

In theory, that is not supposed to be a good idea (multiple ground rods)... But, in practice, lightning will not travel more than a few 10's of feet down electrical wire before it finds someplace else to go.

And having your same AC system sharing a "green wire ground" makes a short circuit "safer" -- Any short to nearby metal would be grounded to the green wire, and trip the breaker back in the AC panel.

Plus, remember that even a "typical" utility neutral is multi-point grounded too. The transformer neutral is grounded a the pole, and grounded at each of the homes sharing the drop (1-5 or so homes).

So, why "worry" about multi-point AC Neutral to Earth Ground Rods in your home if you have power distributed to various out buildings.

-Bill

verdigo

Re: Noob grounding question

Thanks Mr. BB. I will do the suggested reading.

BB.

Re: Noob grounding question

Just to make clear... The "green wire" safety ground should be shared throughout your AC power system. There should not be a separate AC Green wire and ground rod (for example) in the pump shack.

The green wire ground should come from the home main panel (and tied to AC neutral and Main Ground rod, as well as DC Battery Green wire to main ground rod). And the main AC Green wire should go to the pump shack electrical panels (so a short returns back to the main panel green wire/neutral ground-bonds). And a second local AC neutral to Earth Ground Rod at the pump shack (I am proposing).

Normally, driving "distributed AC ground rods" is something I suggested not doing--If you get a near by lightning strike, the two ground rods are in different locations, and you can inject voltage/current from the two ground rods into your green wire ground. But reading some of the later stuff about grounding has made me think that distributed AC green wire grounding is not the worst thing in the world. At least, it gets any lightning energy into the earth via the shortest path--Pretty much always a good thing.

-Bill

DanS26

Re: Noob grounding question

BB. wrote: »

Just to make clear... The "green wire" safety ground should be shared throughout your AC power system. There should not be a separate AC Green wire and ground rod (for example) in the pump shack.

The green wire ground should come from the home main panel (and tied to AC neutral and Main Ground rod, as well as DC Battery Green wire to main ground rod). And the main AC Green wire should go to the pump shack electrical panels (so a short returns back to the main panel green wire/neutral ground-bonds). And a second local AC neutral to Earth Ground Rod at the pump shack (I am proposing).

Normally, driving "distributed AC ground rods" is something I suggested not doing--If you get a near by lightning strike, the two ground rods are in different locations, and you can inject voltage/current from the two ground rods into your green wire ground. But reading some of the later stuff about grounding has made me think that distributed AC green wire grounding is not the worst thing in the world. At least, it gets any lightning energy into the earth via the shortest path--Pretty much always a good thing.

-Bill

Bill, great advice here, you really know your stuff!

I currently have fifteen ground rods at my electrical location. I know, that sounds excessive, but I have multiple outbuildings and a ground mount solar array. But the key to this arrangement is that all the rods are bonded together to create a massive grounding ring that protects all my buildings and solar array. The rods are all bonded together so that differences in electrical potential are minimized throughout the property. In effect I have a large "single point" ground.

Years ago before I realized the dangers of differences in electrical grounding potential, I learned the hard way---equipment destruction. I lost a microwave oven, a stereo system and speakers, a couple satellite TV receivers, a fence charger, an oven and multiple computers. I had all these ground rods but they were not protecting my equipment because they were separate from each other. Then I realized my mistake, all the rods were at different electrical potential. Voltage spikes anywhere in the system would seek the least resistance ground and flow through my equipment with destructive force.

BB.

Re: Noob grounding question

And one part I am concerned about is the multiple tie points between Earth Green Wire Safety and AC neutral... That is simply going to force some AC current into the parallel current path. Against all code.

I don't know... A purist could put isolation transformers to "regenerate" an isolated neutral--and ground bond locally in the remote shed (prevent shared neutral/green wire current). But who would want to speed hundreds of dollars and additional losses for each outbuilding served by a transformer.

-Bill

DanS26

Re: Noob grounding question

BB. wrote: »

And one part I am concerned about is the multiple tie points between Earth Green Wire Safety and AC neutral... That is simply going to force some AC current into the parallel current path. Against all code.

I don't know... A purist could put isolation transformers to "regenerate" an isolated neutral--and ground bond locally in the remote shed (prevent shared neutral/green wire current). But who would want to speed hundreds of dollars and additional losses for each outbuilding served by a transformer.

-Bill

Just to be clear, I spent a lot of time and money to avoid parallel paths. Neutral and ground is bonded only at the service entrance as per code.

BB.

Re: Noob grounding question

So you are "multi-point" grounding the "green wire" and local sheet metal/electrical boxes/etc. at the out buildings?

And you have (for example) 6 awg wire connecting all the ground rods together? Ring around the property? Shortest run between rods, or what??? Tried any surge suppressors (Delta, Midnite, etc.)?

Always nice to hear from somebody that has been successful at reducing the lightning damage to the equipment.

-Bill

verdigo

Re: Noob grounding question

BB. wrote: »

Just to make clear... The "green wire" safety ground should be shared throughout your AC power system. There should not be a separate AC Green wire and ground rod (for example) in the pump shack.

The green wire ground should come from the home main panel (and tied to AC neutral and Main Ground rod, as well as DC Battery Green wire to main ground rod). And the main AC Green wire should go to the pump shack electrical panels (so a short returns back to the main panel green wire/neutral ground-bonds). And a second local AC neutral to Earth Ground Rod at the pump shack (I am proposing).

Normally, driving "distributed AC ground rods" is something I suggested not doing--If you get a near by lightning strike, the two ground rods are in different locations, and you can inject voltage/current from the two ground rods into your green wire ground. But reading some of the later stuff about grounding has made me think that distributed AC green wire grounding is not the worst thing in the world. At least, it gets any lightning energy into the earth via the shortest path--Pretty much always a good thing.

-Bill

My setup is not a pump shack. I will have batteries, charge controller, inverter, autotransformer, with panels on the roof and an adjacent ground mount(s). If I read you right I should connect all of the A/C equipment green wires to the house grounding rod. Would I be alright driving an additional rod at the shed for PV frame grounds, and DC negatives?

BB.

Re: Noob grounding question

verdigo wrote: »

My setup is not a pump shack. I will have batteries, charge controller, inverter, autotransformer, with panels on the roof and an adjacent ground mount(s). If I read you right I should connect all of the A/C equipment green wires to the house grounding rod.

Would I be alright driving an additional rod at the shed for PV frame grounds,

To that point--Yes. Bring the green wire from the home (and/or metal conduit grounds, etc.) from main AC panel (where, I presume, AC Neutral is connected to main ground rod and you have Grid/Utility Power?).

Driving ground rods at the remote shed to connect AC green wire ground, and connect metal structures, AC Power Panels, Solar panel frames/racking to local ground rod... All fine. Usually, each "major" ground should have its own run directly to local ground rod (panel frames/rack to local ground rod; green wire AC ground to local ground rod; etc.).

Optional--bury a ~6 awg (bare is fine) wire from the remote shack ground rod to the main AC ground rod. This will ensure that any AC short in your power systems will have a return back to the source and be able to pop a circuit breaker (this earth ground is in parallel to the green wire AC ground--and is sort of redundant--But the buried exposed to earth 6 awg wire does some of its own grounding too).

and DC negatives?

Now it gets a bit more complex. First, is this a True Sine Wave inverter with "floating/isolated" AC output or a MSW (modified sine wave) inverter with (typically) a non-isolated AC output (with respect to battery power). You may need to read the manual to figure out if your inverter output is isolated or not (i.e., do they say you can ground bond the Neutral/White wire to earth ground?).

Will your AC Inverter output be only used in the shed, or will you have a outlets in the house for "back up power". And/or will you have an AC transfer switch somewhere for AC fail over?

Generally, the DC negative battery bus is tied to the local ground rod (which is already tied via green wire/optional buried 6 awg ground wire back to the house ground rod).

For any DC related conduit/equipment/metal (battery racks, etc.). Your DC Bus ground may have to larger diameter than the 6 awg used for typical AC grounds.

Depending on the capacity of your battery bank and size of AC inverter--You may have 200-300 Amp fuses in the system. A 6 awg wire will fuse around 600 amps... Which is fine with a 100 amp fuse (or possibly to a 200 amp fuse). For larger fuses/breakers, I would suggest going up 3 AWG in wire size for every doubling of fuse size.

For example (being conservative)... Say 100 amps through 6 AWG is good; then 200 amps would be 6-3=3 awg minimum wire. 400 amps would be 6-3-3=0 awg wire, etc...

If you are comfortable with 6 awg and a 200 amp breaker/fuse--Then 3 AWG would be find with up to a 400 amp breaker. NEC might have a table on wire size for safety grounds (I think it does)--Following those recommendations should be fine.

Unfortunately, grounding is a complex set of questions and answers to "do right".

The major issue is the AC neutral bonding from the AC inverter... If TSW--not a big issue.

If MSW, if you ground the DC Bank negative (or even positive) terminal to the ground rod, and ground bond the White wire "neutral" from the MSW AC output--It creates a dead short through the MSW inverter and can smoke it (and/or trip fuses/breakers).

-Bill

verdigo

Re: Noob grounding question

BB. wrote: »

To that point--Yes. Bring the green wire from the home (and/or metal conduit grounds, etc.) from main AC panel (where, I presume, AC Neutral is connected to main ground rod and you have Grid/Utility Power?).

Driving ground rods at the remote shed to connect AC green wire ground, and connect metal structures, AC Power Panels, Solar panel frames/racking to local ground rod... All fine. Usually, each "major" ground should have its own run directly to local ground rod (panel frames/rack to local ground rod; green wire AC ground to local ground rod; etc.).

Optional--bury a ~6 awg (bare is fine) wire from the remote shack ground rod to the main AC ground rod. This will ensure that any AC short in your power systems will have a return back to the source and be able to pop a circuit breaker (this earth ground is in parallel to the green wire AC ground--and is sort of redundant--But the buried exposed to earth 6 awg wire does some of its own grounding too).



Now it gets a bit more complex. First, is this a True Sine Wave inverter with "floating/isolated" AC output or a MSW (modified sine wave) inverter with (typically) a non-isolated AC output (with respect to battery power). You may need to read the manual to figure out if your inverter output is isolated or not (i.e., do they say you can ground bond the Neutral/White wire to earth ground?).

Will your AC Inverter output be only used in the shed, or will you have a outlets in the house for "back up power". And/or will you have an AC transfer switch somewhere for AC fail over?

Generally, the DC negative battery bus is tied to the local ground rod (which is already tied via green wire/optional buried 6 awg ground wire back to the house ground rod).

For any DC related conduit/equipment/metal (battery racks, etc.). Your DC Bus ground may have to larger diameter than the 6 awg used for typical AC grounds.

Depending on the capacity of your battery bank and size of AC inverter--You may have 200-300 Amp fuses in the system. A 6 awg wire will fuse around 600 amps... Which is fine with a 100 amp fuse (or possibly to a 200 amp fuse). For larger fuses/breakers, I would suggest going up 3 AWG in wire size for every doubling of fuse size.

For example (being conservative)... Say 100 amps through 6 AWG is good; then 200 amps would be 6-3=3 awg minimum wire. 400 amps would be 6-3-3=0 awg wire, etc...

If you are comfortable with 6 awg and a 200 amp breaker/fuse--Then 3 AWG would be find with up to a 400 amp breaker. NEC might have a table on wire size for safety grounds (I think it does)--Following those recommendations should be fine.

Unfortunately, grounding is a complex set of questions and answers to "do right".

The major issue is the AC neutral bonding from the AC inverter... If TSW--not a big issue.

If MSW, if you ground the DC Bank negative (or even positive) terminal to the ground rod, and ground bond the White wire "neutral" from the MSW AC output--It creates a dead short through the MSW inverter and can smoke it (and/or trip fuses/breakers).

-Bill

Thank you. I have not bought an inverter yet. I pretty much decided on an Xantrex XW 4548 or maybe the 6048. The system will pretty much function as grid tied with battery/generator backup. I like the idea of two grounding rods inter-connected, and hope this would prevent a lightning strike or at least a near miss to go to ground without bring it into the house or shed. I know nothing is 100
% though.

BB.

Re: Noob grounding question

The XW is a very nice (complex and configurable) unit. You should not have any "issues" with neutral bonding because if the inverter (is TSW inverter with isolation).

You will have to really think through this configuration in detail (lots of paper design) to make sure you do not build yourself into a corner (I think).

My first question is around where you will place the XW inverter/system. In general, the XW is setup like a giant whole house UPS system.

You plug the AC input to your Grid (and AC2 to backup genset). And the AC Output to your "protected" sub panel (i.e., everything you wish to run from solar/battery power when the utility power is down). For example, you may put all your lights and most of the 120 VAC receptacles and 240 VAC well pump on the XW. However (for sake of this example), you may choose not to put the A/C system and electric water heater on the XW Inverter.

So--As you can see, the XW+Sub Panel really should be at the "center" of your AC wiring distribution.

If, you were to put the XW in an out building... You would have to run 240 VAC (50-60 amp 240 VAC circuit or so) to the XW. Then you would have to run a 60 amp 240 VAC circuit (protected--aka battery backed emergency inverter+genset circuits) back to the home AC protected sub panel and then make your connections there.

You end up with an extra round trip of 120/240 VAC ~60 amp cabling from the home to the outbuilding and back to the home.

An alternative is to put the XW next to your main AC panel and put the protected sub panel there too--So it is easier to move your branch circuit connections from the main panel to the sub panel.

However--You are now left with the question of the DC Battery Bank and its cabling. 6kW of 120-240 VAC power translate into 168 amps (210 amp minimum rated DC cabling+breakers)... So the DC wiring is much heavier (roughly 3-4x the amount of copper) and, because of the lower voltage, you have less available "voltage drop" on the DC side (i.e., ~4 volts on a 48 volt battery bank is significant drop. 4 volts of drop on a 240 vac circuit is nothing to worry about).

So, can you put the battery bank inside the home or in a box outside the home (acid fumes, worry about fire)--Or is putting the system in the outbuilding and an extra round trip run of 120/240 VAC the better solution--I don't know.

One suggestion is not to put all of your eggs in one basket. For example, if you have a back up genset and fuel--Put that in a separate structure from your home and battery/solar/XW shed. Generators can catch fire you you don't want to lose "everything" (or all of your batteries+solar panels).

Does not happen often--But it does happen.

Anyway--Some things to think about. Detailed paper drawings/parts lists (even just back of the envelope sketches) will be helpful. These can be quite complex and the more work you do ahead of time--The fewer "surprises" later.

-Bill

verdigo

Re: Noob grounding question

i don't have the inverter yet so I don't have all the detail either. My plan is to yes run 240 volts from the house to the shed/inverter and then again another 240 volt A/C out to a 6 circuit transfer switch and do exactly as you said run the water heater and air conditioning (maybe not concurrently) during a power outage. The house is very small and really there is really not enough room to house everything. The shed is around 50 ft away from the house, and the existing A/C panel.

BB.

Re: Noob grounding question

Sounds like a plan. Will your utility allow "net metering"? Grid Tied solar is a good deal for many utility customers (at the present time). Rate plans and rules can be complex. And many smaller utilities do not allow net metered Grid Tied systems. And a few will not allow Net Metering for Hybrid solar systems (such as the XW + Battery bank).

Regarding A/C and water heating...

There are newer "inverter" Mini-Split systems which can be very off grid friendly. One unit (Sanyo, no longer available) ran at 120 volts and if set at low speed would no draw no more than 300 watts at 120 VAC. And the heat pump version has been very successfully used for heating the home even with snow on the ground.

Sanyo mini split AC (inverter/variable speed)

There are another units out there--But most are 240 VAC and I have read less about them--But they are very efficient and seem to work well for off grid users (both as A/C and for heating too).

And for Water Heaters... You can run a desuper heater from your A/C system.

Or even get heat pump water heaters, or even retrofit heat pumps for existing electric water heaters:

GE Geospring Water Heater Testing
General Electric Geospring
Is this hard on my Geospring waterheater?
Nyle Geyser Heat Pump Water Heater
Opportunity Load - Heat Pump Water Heater - Anyone do it ...
Too Good To Be True Project

In general, a heat pump water heater is 2-3x more efficient vs a resistive type water heater. And most are good down to ~55F ambient temperature before their efficiency drops. A "typical" heat pump water heater will raise the water temperature slower (~1,000 watts of heat vs ~2,000+ watts for a standard water heater) and the Geospring (for example) does have a backup resistance heater for faster heating when needed (can be disabled from control panel--I think).

Heat pump water heater's waste is "cold/dry air" (i.e., air conditioning). Great for hot climates--May be an issue for colder climates/cool basements (some installers/people have been forced to duct outside air to the heat pumps to keep the rooms from getting too cold). And for many people, solar electric power systems (GT and Off Grid) + heat pump water heaters are better than installing solar thermal panels, pumps, storage tanks, etc. (less plumbing/maintenance).

Anyway--I am a big believer in doing extreme conservation first--Before installing solar power. Conservation is almost always a better "investment" vs installing a larger solar power system (off grid, GT, or hybrid). This thread has some links to various conservation projects and other sources of solar RE information.

-Bill

DanS26

Re: Noob grounding question

BB. wrote: »

So you are "multi-point" grounding the "green wire" and local sheet metal/electrical boxes/etc. at the out buildings?

And you have (for example) 6 awg wire connecting all the ground rods together? Ring around the property? Shortest run between rods, or what??? Tried any surge suppressors (Delta, Midnite, etc.)?

Always nice to hear from somebody that has been successful at reducing the lightning damage to the equipment.

-Bill

All 15 rods are interconnected by 6 awg or greater. It is not a true ring but a large semi-circle. The area I live in seems to be susceptible to lightning strikes. My neighbors believe it is something in the ground that is attractive. All I know is that I was losing equipment rapidly and had to do something.

First I brought everything up to the latest electrical code, of course that meant 4 wire service to all the outbuildings. After doing some research on lightning protection, I realized that all the ground rods on the property should be at the same electrical potential. The only way to do that is to electrically tie them together.

Then I installed surge suppressors. The local REMC was kind enough to put a suppressor on the transformer at no cost. Then I placed another under the meter. Then a whole house suppressor on the main panel and another on the sub-panel in the garage. Of course all my sensitive electronic equipment is on point of use suppressors.

The solar system is protected by both Delta DC and AC suppressors. The ground mount array is protected by four rods, one at each corner and then tied together in a continuous loop by #6 awg solid copper. Used the WEEB system.

I know a direct strike will not be defeated, but I feel much better about mitigating voltage spikes. So far no lost equipment since the upgrade.

westbranch

Re: Noob grounding question

You might just want to view this video comparing your arrestors to the MN Solar SPDs. Most enlightening...

http://www.midnitesolar.com/video/videoPlay.php?video_ID=9&videoCat_ID=8

DanS26

Re: Noob grounding question

westbranch wrote: »

You might just want to view this video comparing your arrestors to the MN Solar SPDs. Most enlightening...

http://www.midnitesolar.com/video/videoPlay.php?video_ID=9&videoCat_ID=8

Thanks, saw that video last year. Would love to see a response from Delta or an unbiased comparison from a recognized independent electrical engineer.

verdigo

Re: Noob grounding question

BB. wrote: »

Sounds like a plan. Will your utility allow "net metering"? Grid Tied solar is a good deal for many utility customers (at the present time). Rate plans and rules can be complex. And many smaller utilities do not allow net metered Grid Tied systems. And a few will not allow Net Metering for Hybrid solar systems (such as the XW + Battery bank).

Regarding A/C and water heating...

There are newer "inverter" Mini-Split systems which can be very off grid friendly. One unit (Sanyo, no longer available) ran at 120 volts and if set at low speed would no draw no more than 300 watts at 120 VAC. And the heat pump version has been very successfully used for heating the home even with snow on the ground.

Sanyo mini split AC (inverter/variable speed)

There are another units out there--But most are 240 VAC and I have read less about them--But they are very efficient and seem to work well for off grid users (both as A/C and for heating too).

And for Water Heaters... You can run a desuper heater from your A/C system.

Or even get heat pump water heaters, or even retrofit heat pumps for existing electric water heaters:

GE Geospring Water Heater Testing
General Electric Geospring
Is this hard on my Geospring waterheater?
Nyle Geyser Heat Pump Water Heater
Opportunity Load - Heat Pump Water Heater - Anyone do it ...
Too Good To Be True Project

In general, a heat pump water heater is 2-3x more efficient vs a resistive type water heater. And most are good down to ~55F ambient temperature before their efficiency drops. A "typical" heat pump water heater will raise the water temperature slower (~1,000 watts of heat vs ~2,000+ watts for a standard water heater) and the Geospring (for example) does have a backup resistance heater for faster heating when needed (can be disabled from control panel--I think).

Heat pump water heater's waste is "cold/dry air" (i.e., air conditioning). Great for hot climates--May be an issue for colder climates/cool basements (some installers/people have been forced to duct outside air to the heat pumps to keep the rooms from getting too cold). And for many people, solar electric power systems (GT and Off Grid) + heat pump water heaters are better than installing solar thermal panels, pumps, storage tanks, etc. (less plumbing/maintenance).

Anyway--I am a big believer in doing extreme conservation first--Before installing solar power. Conservation is almost always a better "investment" vs installing a larger solar power system (off grid, GT, or hybrid). This thread has some links to various conservation projects and other sources of solar RE information.

-Bill

I am not sure about a net metering deal with the local utility. The grid after all the fees and what not come to around ten cents per KWH. This is in large part a hobby and learning experience for me. I have been doing some reading on mini split heat pumps and the heat pump water heaters as well. My current water heater is in need of new heating elements. Chris Olson mentioned in a different thread that he had replaced his with lower wattage elements. I wan't to say he is using 2000 watt elements instead of typical 4500 watt units.

As for extreme conservation... While I know it would be logical to do this first I am a bit anxious to skip the foreplay and go directly to the good stuff.

Anyway thanks for the help with grounding. I just ordered an Iron Ridge setup today for PVs being mounted on the shed roof. I got the weebs components for grounding as well. I probably could have fabricated the mounts but I think the Iron Ridge setup will save me a lot of time. I would like to at least charge some batteries before winter. I need to get these solar panels out of the living room.

Dennis

northerner

Re: Noob grounding question

BB. wrote: »

And one part I am concerned about is the multiple tie points between Earth Green Wire Safety and AC neutral... That is simply going to force some AC current into the parallel current path. Against all code.

I don't know... A purist could put isolation transformers to "regenerate" an isolated neutral--and ground bond locally in the remote shed (prevent shared neutral/green wire current). But who would want to speed hundreds of dollars and additional losses for each outbuilding served by a transformer.

-Bill

Could you not run 2 parallel ground wires (ie taped together) down from the remote shed to ground? Have one connected to a small rod or separate sheet of metal, located up high, to direct a static surge to the local ground. But not such a big lightning rod which may attract a strike. The other runs from the panel frames almost to ground without making a direct connection (ie within an inch or so). In theory, that should direct a major surge down to the local ground and give electrical isolation, so that you could run the ground wire over and through your main system (house ground wire) and then finally to a ground rod. That way, you would just have the one neutral to ground bond at the service entrance. This is something I'm considering to do, even though my panels are nearby, on my roof, and the equipment is inside the house. Thoughts?

DanS26

Re: Noob grounding question

northerner wrote: »

Could you not run 2 parallel ground wires (ie taped together) down from the remote shed to ground? Have one connected to a small rod or separate sheet of metal, located up high, to direct a static surge to the local ground. But not such a big lightning rod which may attract a strike. The other runs from the panel frames almost to ground without making a direct connection (ie within an inch or so). In theory, that should direct a major surge down to the local ground and give electrical isolation, so that you could run the ground wire over and through your main system (house ground wire) and then finally to a ground rod. That way, you would just have the one neutral to ground bond at the service entrance. This is something I'm considering to do, even though my panels are nearby, on my roof, and the equipment is inside the house. Thoughts?

Grounding theory and practice gets complex. But lets break it down.

The green wire (or bare copper) serves two purposes as far as electrical code is concerned. First purpose is for personal safety and secondly is for damage control.

First the "ground" is to serve as the EGC (equipment grounding conductor), thus stray voltage on any equipment or any energized part of an electrical system is taken to source and trips the OCPD (over current protection device) ie circuit breaker or fuse. Safety first.

Secondly the "ground" protects your equipment from high voltage surges, such as lightning, by directing the surge to ground at the best and most convenient place. This is accomplished by constructing a low impedance path to earth in as many places as possible and as short as possible. Most homes only need a single point of entrance. But if you have outbuildings and ground mounted solar arrays, etc., multiple grounding points are necessary and desired.

In response to your comments, parallel paths are NOT desired, you need only one low impedance path to ground. If you have multiple grounding points they must be tied together so that they have the same electrical potential as all grounding points in the system. Without this electrical sameness, voltage surges will seek the low impedance route over all others, which maybe through your inverter or other sensitive electrical equipment.

IMHO lightning rods and grounding rods do not attract strikes. I find it hard to believe a bolt, after traveling miles in air will find a piddling copper rod to earth itself. A direct hit cannot be mitigated, but you can mitigate the side strikes and utility surges which are much more numerous.

And finally, do you really want to direct a voltage surge originating at your solar array into your house?

northerner

Re: Noob grounding question

DanS26 wrote: »

In response to your comments, parallel paths are NOT desired, you need only one low impedance path to ground. If you have multiple grounding points they must be tied together so that they have the same electrical potential as all grounding points in the system. Without this electrical sameness, voltage surges will seek the low impedance route over all others, which maybe through your inverter or other sensitive electrical equipment.

IMHO lightning rods and grounding rods do not attract strikes. I find it hard to believe a bolt, after traveling miles in air will find a piddling copper rod to earth itself. A direct hit cannot be mitigated, but you can mitigate the side strikes and utility surges which are much more numerous.

And finally, do you really want to direct a voltage surge originating at your solar array into your house?

If you follow the NEC, you will be bringing the lightning and/or surges into your home, that's the problem. The ground from your panel frame must run through your equipment ground before it makes it to a grounding rod. What I proposed with the 2 parallel ground wires, is essentially a short circuit to ground for a high voltage surge, but is not physically connected to ground, and conforms to the safety ground requirement by the NEC. And the very small lightning rod is not intended to attract a lightning strike, but direct a surge down to the local grounding rod, if there is a local static buildup. Ideally, if there are 2 or more grounding rods, they should be connected together as you mention. Do you see the proposal now?

DanS26

Re: Noob grounding question

northerner wrote: »

If you follow the NEC, you will be bringing the lightning and/or surges into your home, that's the problem. The ground from your panel frame must run through your equipment ground before it makes it to a grounding rod. What I proposed with the 2 parallel ground wires, is essentially a short circuit to ground for a high voltage surge, but is not physically connected to ground, and conforms to the safety ground requirement by the NEC. And the very small lightning rod is not intended to attract a lightning strike, but direct a surge down to the local grounding rod, if there is a local static buildup. Ideally, if there are 2 or more grounding rods, they should be connected together as you mention. Do you see the proposal now?

I understand what you are trying to do, but I have to ask why an "inch or so" sparking gap? Why not 1/2 inch or 6 inches? I don't think you will accomplish anything. A better route would be to invest in quality surge suppressors in your main panel and at your point of use.

Cariboocoot

Re: Noob grounding question

Cut-and-paste my own post from another thread here as it is somewhat relevant.

This is called "playing with fire", or more accurately "playing with lightning".

Nothing will prevent damage from a direct strike.

However, when there are strikes in the area the air gets saturated with stray Voltage. High frequency, high Voltage that can jump from place to place and damage things even though it doesn't make the big flash and deafening roar.

Grounding helps. If give the equipment some protection. More protection can be had from lightning arrestors properly installed. http://www.solar-electric.com/suprde.html Nothing can provide 100% protection, but you can reduce the risks. You're lucky you only had a temporary outage (momentary increase in the sensed Voltage on the DC side cause the inverter to detect "over Voltage" condition and turn off, most likely).

Grounding should be to one rod only, or more accurately to a single point (which may be constructed of multiple rods in order to get sufficient contact with Earth). The biggest disagreement here is that the NEC required the panel/mount ground to go in to the house with the DC lines and connect to ground there, whereas most of us prefer that ground be kept outside the building to reduce the risk of introducing the high Voltage to the interior. If the single point ground is outside the structure then everyone should be happy.

It is unlikely that grounding alone would have prevented your shutdown, but in conjunction with arrestors it would not have happened. That's the trouble with lightning: totally unpredictable in its effect.

northerner

Re: Noob grounding question

DanS26 wrote: »

I understand what you are trying to do, but I have to ask why an "inch or so" sparking gap? Why not 1/2 inch or 6 inches? I don't think you will accomplish anything. A better route would be to invest in quality surge suppressors in your main panel and at your point of use.

I already have a surge arrestor in place, both at the PV connect box and at the inverter O/P.

The 2 parallel ground wires would be there to divert a surge away from sensitive equipment, and minimize entry into the house. It would also help to take a good portion of the surge load off the lightning arrestors, if it is a significant current. The lightning arrestors I have are rated to handle 115,000 amps (@ 8/20 micro sec) per device. A significant surge could exceed that, and diversion would help significantly, would it not?

In the event of a close strike, the line with the rod would act as the main diversion path to ground. The panel frames would likely be energized as well, and the 2nd wire in parallel would bleed off some of that, rather than taking the ground path that goes through the house (NEC requirement). The 1 inch gap is arbitrary, and could be 1/4 inch, so long as it doesn't contact the ground rod (and create a parallel path to ground).

I realize that no protection can be 100%, but just attempting to offer the best protection possible for the system.

Cariboocoot

Re: Noob grounding question

Additional grounding will not take any surge load off arrestors: they pick up high Voltage spikes on the power conductors and direct it to ground. Another ground wire will not be connected to the conductors, so it wouldn't divert any stray Voltage that hits them. You can not divert the strike before it happens.

There is a great deal of discussion and disagreement about how lightning rods work and how effective they are. Since you never know what happens until it does happen, you can't say for sure what the effectiveness of any plan will be. The system could survive nearby strikes with absolutely no grounding, arrestors, or other protection and with all protection possible in place it could still be fried.

The problem with parallel ground wiring is that it is more likely to create problems than solve any, as it can lead the high Voltage back along the parallel path rather than sink it to Earth thus energizing sections that otherwise would be safe.

The general consensus is, I believe, that arrestors on the PV wires at the junction box connected to the panel/frame ground wire running outside the building to the single point ground is the best you're going to do.

BTW, these lightning-induced stray Voltages are not high in current but are high in Voltage and frequency.

northerner

Re: Noob grounding question

Cariboocoot wrote: »

The problem with parallel ground wiring is that it is more likely to create problems than solve any, as it can lead the high Voltage back along the parallel path rather than sink it to Earth thus energizing sections that otherwise would be safe.

That did cross my mind that there could be induction into the 2nd wire.
Wouldn't the parallel wires act as a single conducting path for a larger surge? I would think that the surge arrestor should clamp any stray voltages, irregardless.

I've heard that a direct strike likely means disaster for a solar setup, but have also heard that radio antenna and other installations are routinely struck by lightning and there is protection built in for the associated equipment??? Could it be that we are not offering the best protection possible? I know that a Farad cage improves the shielding of a system which essentially consists of numerous diversion paths around the equipment to an equi potential ground.

Cariboocoot

Re: Noob grounding question

northerner wrote: »

That did cross my mind that there could be induction into the 2nd wire.
Wouldn't the parallel wires act as a single conducting path for a larger surge? I would think that the surge arrestor should clamp any stray voltages, irregardless.

The surge arrestor will clamp any high Voltage spikes on the power conductors, not the ground wire. If the ground wire becomes 'hot' the only thing that will save it and what it is attached to is a good connection with Earth. Otherwise you have the same situation you're trying to prevent: high Voltage traveling wherever it wants to go instead of being controlled.

With two parallel wires you have two varied resistances (they will never be the same) and as such, some of the Voltage may go down the path of least resistance and some down the other, meaning both are 'live' for a given Voltage potential in respect to other points in the system. Multiple grounding points are frowned on for this same reason: not all of the power may be dissipated to Earth at one point, meaning it can "come back up" the other wire and energize equipment.

I've heard that a direct strike likely means disaster for a solar setup, but have also heard that radio antenna and other installations are routinely struck by lightning and there is protection built in for the associated equipment??? Could it be that we are not offering the best protection possible? I know that a Farad cage improves the shielding of a system which essentially consists of numerous diversion paths around the equipment to an equi potential ground.

Ah, the myth of surviving a direct strike. Think of it like this: on one end of the spectrum there is no lightning. At the other end is Voltage high enough to jump through miles of air and enough power to melt rock. In between are an infinite number of variations on the power level. So what is a "direct strike"? Airplanes get hit by lightning often, without damage, because there is no current path to ground. It is entirely possible to have a conductor in the air which will get hit (perhaps "touched" is a better word) by lightning and suffer no damage. As a rule, a piece of metal can withstand a huge amount of Voltage but not current. Whereas electronic components can be damaged by either. Since lightning inherently is high Voltage and not current, if you can 'clamp' the Voltage nothing gets damaged. But what you clamp it with has to be able to survive the strike or else it only takes some of the power potential away. Hence the arguments about which arrestor is better.

A Faraday cage is meant to shield sensitive components for all sorts of EMP's and RFI. It would effectively block damage from most strikes around it, but if it were to get hit by a direct lightning strike it would melt too. The cage functions quite differently from just two wires, as it is a continuous "skin" of conductors capable of carrying off high frequency electricity. Lightning is high frequency, btw, and you may note that lightning rod conductors are "woven" flat wires as this works best for conducting that type of power: it actually "dances on the surface".

northerner

Re: Noob grounding question

Cariboocoot wrote: »

The surge arrestor will clamp any high Voltage spikes on the power conductors, not the ground wire. If the ground wire becomes 'hot' the only thing that will save it and what it is attached to is a good connection with Earth. Otherwise you have the same situation you're trying to prevent: high Voltage traveling wherever it wants to go instead of being controlled.

With two parallel wires you have two varied resistances (they will never be the same) and as such, some of the Voltage may go down the path of least resistance and some down the other, meaning both are 'live' for a given Voltage potential in respect to other points in the system. Multiple grounding points are frowned on for this same reason: not all of the power may be dissipated to Earth at one point, meaning it can "come back up" the other wire and energize equipment.

Yes, I agree that the surge arrestor will clamp voltage spikes on the power conductors, as it's the difference in potential on those conductors that may/will cause the damage to sensitive equipment. Diverting the surge should allow the arrestor to handle those voltage spikes. If the surge is large enough (ie a direct or very close strike, the arrestor could easily be overwhelmed.

I also agree that it's imperative to have a good connection with ground, as this will help dissipate the surge away from your equipment.

A Faraday cage is meant to shield sensitive components for all sorts of EMP's and RFI. It would effectively block damage from most strikes around it, but if it were to get hit by a direct lightning strike it would melt too. The cage functions quite differently from just two wires, as it is a continuous "skin" of conductors capable of carrying off high frequency electricity. Lightning is high frequency, btw, and you may note that lightning rod conductors are "woven" flat wires as this works best for conducting that type of power: it actually "dances on the surface".

Faraday cages are very effective in diverting surges. Automobiles and aircraft have often been struck by lightning directly, and the cage around them doesn't melt. In some cases, I have heard that it leaves a pinhole where the lightning enters/exits, but the cage doesn't melt. And the occupants inside are usually not impacted by a direct strike in a vehicle. And yes, I'm aware that woven wires work best for conducting the RF of lightning surges.

http://science.howstuffworks.com/nature/natural-disasters/lightning8.htm

Cariboocoot

Re: Noob grounding question

Before I completely give up I'll just remind anyone reading this thread that electrical safety ground procedures are not meant to handle the effects of lightning/stray Voltage and vice-versa.