Extra/Auxilary grounding rods..... Don't do it.

[Quattrohead]

The local electrical inspector required I put ground rods at each one of my ground mounts. It was the only electrical inspection I have ever failed. I also didn’t have the electrical conduit secured every three feet.

But if those rods are all connected together then that is great, again this is what all transmitter sites do.
Look, you can have a hundred grounding rods if you want as long as they are all bonded together.

 

[timselectric]

But if those rods are all connected together then that is great, again this is what all transmitter sites do.
Look, you can have a hundred grounding rods if you want as long as they are all bonded together.

For electrical safety, yes.
But not if you want to avoid the gradient pulse, generated by a nearby lightning strike.

 

[timselectric]

Auxiliary grounding electrodes are not required, because they don't improve electrical safety.
Auxiliary grounding electrodes are allowed, because they don't reduce electrical safety.

 

[AntronX]

In case the MOV's (or one of them) will be activated, it will in fact connect the PV wire to ground. Will the FET's of the floating MPPT charger blow in such a situation?

MOVs don't connect to ground they conduct at their clamping voltage which is 2x working voltage. So if surge happens to drive voltage across 600V 10kA rated MOV to 1200V it will conduct 100A. That's not very healthy for your AIO inverter with 650V IGBTs inside. I don't think MOV-only based SPDs are enough for full lightning protection.

 

[740GLE]

For electrical safety, yes.
But not if you want to avoid the gradient pulse, generated by a nearby lightning strike.

By having multiple ground rods all connected together how does that increase the gradient pulse otherwise known a step hazard? It would reduce it

A lightning strike wants to seek ground, if there is a nice juicy ground source close to a strike, source and sink, it helps mitigate the pulse travel back to your service panel ground.

This is the exact same reason utility poles have down grounds and lightning arresters tided to said down ground, to help prevent any sort of pulse travel down the service line to your service panel ground.

 

[AntronX]

For electrical safety, yes.
But not if you want to avoid the gradient pulse, generated by a nearby lightning strike.

Multiple ground rods at transmitter sites are for lightning protection, not just for electrical safety. If AM transmitting tower gets hit you want to direct that energy straight down as soon as possible and not have it all traverse hundreds of feet over coax transmission line. Gradient pulse is unavoidable and is mitigated by bonding remote ground rods with a conductor that can survive it.

 

[timselectric]

SPD = Surge Protection Device
Protection from surges, not lightning.
This is what people need to understand.

 

[timselectric]

By having multiple ground rods all connected together how does that increase the gradient pulse otherwise known a step hazard? It would reduce it

It doesn't increase the gradient pulse. It just gives it an easier path.(right towards your equipment)
Nothing to do with step hazzard.
When lightning strikes the earth. It sends out a gradient pulse, similar to ripples in a pond from a thrown rock.
This pulse dissipates as it radiates outward. An reduces quickly due to the high resistance of earth. When you place two electrodes in the earth and connect them together. You create a lower resistance path, which allows the pulse to travel further. And aiming it right at your equipment, appliances, and home.

 

[AntronX]

Protection from surges, not lightning.

Lightning causes voltage surges so SPD protects from both.

 

[timselectric]

Multiple ground rods at transmitter sites are for lightning protection, not just for electrical safety. If AM transmitting tower gets hit you want to direct that energy straight down as soon as possible and not have it all traverse hundreds of feet over coax transmission line. Gradient pulse is unavoidable and is mitigated by bonding remote ground rods with a conductor that can survive it.

I will assume that this tower is made of metal. And mounted on large concrete pillars. With large anchor bolts and rebar in the concrete.
If so, then it's already bonded to the earth, better than any amount of rods can do.
But you are talking about a direct lighting strike. Not a gradient pulse.

 

[timselectric]

Lightning causes voltage surges so SPD protects from both.

Do you have a link to an SPD that can survive a direct lightning strike?
Or protect against it?

 

[AntronX]

If so, then it's already bonded to the earth, better than any amount of rods can do.

Letting it go through concrete can crack it and let water inside which will rust and expand the rebar which will crack the concrete structure. There is a spark gap under the tower that connects to many ground rods to dissipate the strike.

 

[740GLE]

SPD = Surge Protection Device
Protection from surges, not lightning.
This is what people need to understand.

So lightning isn’t a surge? I’ll admit a cheap surge protector isn’t worth buying and won’t protect everything.

It doesn't increase the gradient pulse. It just gives it an easier path.(right towards your equipment)
Nothing to do with step hazzard.
When lightning strikes the earth. It sends out a gradient pulse, similar to ripples in a pond from a thrown rock.
This pulse dissipates as it radiates outward. A reduces quickly due to the high resistance of earth. When you place two electrodes in the earth and connect them together. You create a lower resistance path, which allows the pulse to travel further. And aiming it right at your equipment, appliances, and home.

it radiates out if there is poor ground resistivity (high impedance).

How to you reduce ground resistivity, a better sink? You install more ground rods and deeper ground rods.

You ever set up an electric fence? The first thing you do to help it’s kick is improve the ground path.

 

[AntronX]

Do you have a link to an SPD that can survive a direct lightning strike?
Or protect against it?

Nope, none of them are designed to fully protect power electronics and that's why inverters still blow up from direct strikes. MOV based SPDs are good for protecting dumb electrical equipment like motors and transformers from insulation breakdown. Much tighter voltage surge clamping is needed for electronic devices.

 

[740GLE]

I will assume that this tower is made of metal. And mounted on large concrete pillars. With large anchor bolts and rebar in the concrete.
If so, then it's already bonded to the earth, better than any amount of rods can do.
But you are talking about a direct lighting strike. Not a gradient pulse.

That’s an improper assumption, concrete is a decent insulator (in the grand scheme of things)

Also foundation cages maybe 10-15’ below grade, 30’-40’ ground rods are very very common.

 

[timselectric]

Letting it go through concrete can crack it and let water inside which will rust and expand the rebar which will crack the concrete structure. There is a spark gap under the tower that connects to many ground rods to dissipate the strike.

I'm not sure why everyone keeps going to direct lightning strikes. When discussing electrical grounding. The two have nothing to do with each other.
We are discussing electrical grounding on solar systems.
Lightning protection is a completely different system. And not worth discussing in this situation. As most people aren't going to spend the extra money for an expensive lightning protection system for solar panels that are cheaper to just replace, if the rare direct strike actually happens.

 

[timselectric]

So lightning isn’t a surge?

Of course it is. A huge surge.

How to you reduce ground resistivity, a better sink? You install more ground rods and deeper ground rods.

If you want to do that, go right ahead.
All that I am saying is that you don't want to connect that mess to your equipment or home.

 

[AntronX]

I'm not sure why everyone keeps going to direct lightning strikes.

Cause two go hand in hand. You even keep bringing up ground gradient from nearby lightning strike. Leaving array without ground rods will not protect against ground gradient unless your array sits on top of insulators. Lightning current will find a way to close that ground loop and if you don't bond and install properly designed voltage clamping devices at the right places your equipment will get damaged.

 

[740GLE]

I'm not sure why everyone keeps going to direct lightning strikes. When discussing electrical grounding. The two have nothing to do with each other.
We are discussing electrical grounding on solar systems.
Lightning protection is a completely different system. And not worth discussing in this situation. As most people aren't going to spend the extra money for an expensive lightning protection system for solar panels that are cheaper to just replace, if the rare direct strike actually happens.

But you reduce gradient by reducing impedance to ground by installing more ground rods?

Why does a houses plumbing (old copper days) have to be grounded? So it’s tied to the closest ground source.

 

[FilterGuy]

I wonder what will happen in case of a non-isolated, floating AIO design in case of a surge event. Usually non of the PV+ or PV- is allowed to be connected to ground in such an AIO design. In case the MOV's (or one of them) will be activated, it will in fact connect the PV wire to ground. Will the FET's of the floating MPPT charger blow in such a situation?
If yes, could the surge protection be done different for a floating non-isolated charger? Maybe adding a (small resistor in series with the MOV to reduce the surge current in such a case)? But I think, this would only help a bit if the MOV's will switch back to high resistance after the surge is over... but I don't know.
A fuse at the charger side may help in such a case?

All good questions. If the voltage spikes high enough to trigger the MOVs, shunting the energy is still a good thing to do, but will the cure be as bad as the problem?? I have no good answer.

This is something worth investigating.