Ground wire from panel mounts

[merc4]

With the PV on top of my Pole barn, what's the best, code safe way, to run the solid copper ground down to the ground rod? on the exterior, in conduit, and all alone, I would assume?

[inetdog]

With the PV on top of my Pole barn, what's the best, code safe way, to run the solid copper ground down to the ground rod? on the exterior, in conduit, and all alone, I would assume?

Do not run a ground electrode conductor inside ferrous metal (magnetic) conduit unless you bond the copper solidly to the conduit at each end. And at that point you are really just using the conduit itself for the ground conductor.
The problem is that high frequency current (such as that induced by a near lightning strike or --heaven forefend-- a direct strike) will see the wire going through the metal core as an inductor and will develop a high enough voltage drop to cause the current to jump to some other path. Exactly what you do not want.
If you need mechanical protection, use PVC or aluminum. But if there is no likelihood of mechanical damage, bare copper in a size of #4 or larger should be just fine on its own.

[Sunking]

Use solid #6 AWG using non-ferrous clips or use PVC pipe.

[merc4]

PVC is always my preference anyhow, thanks guys!! Actually had it done already, cuz we had thunderstorms coming in yesterday/last night.

[mapmaker]

Use solid #6 AWG using non-ferrous clips or use PVC pipe.

Why solid? I thought stranded, and even braided works better for the high frequencies of lightning.

--mapmaker

[Sunking]

Why solid? I thought stranded, and even braided works better for the high frequencies of lightning.

--mapmaker

Good and fair question. The kind I like to see and answer because it shows me you know a little something and using your head for something other than a hat rack.

With lightning it is all about impedance, thermal capacity, and logevity. There is no virtually no significant difference between the impedance of a solid wire and stranded of a given gauge. Stranded wire just has more surface area to counter Skin Effect. For example a 10 foot long #4 AWG solid @ 100 Mhz exhibits about 2.6 K-oms of resistance, and Class H Stranded 2.4 K-Ohms. Not enough to make a squat bit of difference. Witht hat said flat solid buss bar is a different story and used in Radio Towers to ground coax, SPD's to hatch plates. Let's not go there as it has nothing to do with your question.

That leaves us thermal capacity and longevity. This is where solid far outperforms stranded wire especially in the dirt. When you get above say #2 AWG you have to use stranded Class B strand only because above # 2 you cannot get solid because they do not lease gorillas from the zoo to work with it. Stranded will corrode and erode at a must faster rate than stranded. Solid has much higher thermal capacity the stranded. Keep in mind lightning current is in the 10's of thousands of amps. It is very short duration, bu twill fry stranded much faster than solid.

Hope that helps.

[SolarShadow]

I hate to burst your bubble, but.........

Stranded is better even if not by much. It resists breakage better being stranded while allowing some flexibility. Braiding is good too, but uses very fine wires that will corrode through faster than stranded or solid.Plus, the larger surface area of stranding/braiding decreases the impedance to allow radio wave frequencies of the lightning EMP to pass to ground easier, being radio waves travel more on the surface than deep within a wire, meaning stranded wire enhances the skin effect and that is a good thing. Only the dc resistance shall remain the same between stranded and solid wire of the same gauge.

It is important to point out that neither the solid or stranded wire of the same gauge will survive a full lightning stroke so we are talking about the EMP effects of lightning.

Why you make mention of burial I don't know as it can attach to the ground rod a few inches above the surface of the ground with the proper connectors, but some corrosion will occur over time in either case so burial does not matter terribly as both need to be checked periodically.

As to capacity, both wires have the same amount of copper per length so both have the same capacity. For the same reason both will have the same thermal capacity excepting the bare comparison will have the stranded edge out the solid by a minute amount due to a slightly larger surface area exposed to the air.

[Sunking]

I hate to burst your bubble, but.........

You are not busting my bubble, you are just over looking too many things and making wrong assumptions.

Stranded is better even if not by much.

As I stated the performance difference is insignificant, and the extra material and labor cost cannot be justified for such little performance benefit.

It resists breakage better being stranded while allowing some flexibility.

That is a halve truth. It resist mechanical vibration fatigue better but has less sheer and tensile strength. Ground electrode conductors are most often supported only by their own physical strength attached to a surface only using clips. Use braided and now you have to use some sort of pipe to protect it from damage. You have to comply with:

250.64 Grounding Electrode Conductor
Installation

(B) Securing and Protection Against Physical Damage.
Where exposed, a grounding electrode conductor or its enclosure
shall be securely fastened to the surface on which it
is carried. Grounding electrode conductors shall be permitted
to be installed on or through framing members. A 4
AWG or larger copper or aluminum grounding electrode
conductor shall be protected if exposed to physical damage.
A 6 AWG grounding electrode conductor that is free from
exposure to physical damage shall be permitted to be run
along the surface of the building construction without metal
covering or protection if it is securely fastened to the construction;
otherwise, it shall be protected in rigid metal conduit
(RMC), intermediate metal conduit (IMC), rigid
polyvinyl chloride conduit (PVC), reinforced thermosetting
resin conduit (RTRC), electrical metallic tubing (EMT), or
cable armor. Grounding electrode conductors smaller than 6
AWG shall be protected in RMC, IMC, PVC, RTRC, EMT,
or cable armor.

Braiding is good too, but uses very fine wires that will corrode through faster than stranded or solid.Plus, the larger surface area of stranding/braiding decreases the impedance to allow radio wave frequencies of the lightning EMP to pass to ground easier, being radio waves travel more on the surface than deep within a wire, meaning stranded wire enhances the skin effect and that is a good thing.

No argument there as I said braid will corrode faster then stranded, stranded will corrode faster than solid. You got that right. As for the impedance and Skin Effect, I did say the finer strands do have slightly lower impedance, but is insignificant and I gave an example of a #4 Solid and Stranded wire of 10 foot length @ 100 Mhz being 2.6 and 2.4 Kohms. That i snot enough to make any difference.

Why you make mention of burial I don't know as it can attach to the ground rod a few inches above the surface of the ground with the proper connectors, but some corrosion will occur over time in either case so burial does not matter terribly as both need to be checked periodically.

And this is where you loose the argument. Connection to a ground rod shall be buried below the frost line. If you knew electrical code you would have known that. Direct from the NEC

250.53 Grounding Electrode System
Installation


(A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate
electrodes shall meet the requirements of 250.53(A)(1)
through (A)(3).


(1) Below Permanent Moisture Level.
Rod, pipe, and plate electrodes shall be embedded below
permanent moisture level. Rod, pipe, and plate electrodes
shall be free from nonconductive coatings such as paint or
enamel.

Now with all that said there is nothing to prohibit you from using stranded cable or braiding. I made mention once you get above #2 AWG we do use Stranded Class B strands. Above ground bonding jumpers are almost always use stranded insulated cable for flexibility and facilitating terminations where exothermic termination is not practical. If you would like to see how pros do grounding like ar say cell sites here you go. Take noted the solid wire you see is #2 AWG solid tinned copper. Being tinned adds corrosion resistance, and you will not see any mechanical or clamping connections. All of it is exothermic welded, and this particular cell phone company, like most of them can afford any method. They choose to use the most proven effective methods.

[SolarShadow]

So what as putting a ferrule on it isn't the deal breaker you make it out to be.

BTW, they do use stranded cables on bridges because it is more flexible and thus offers more resistance to breakage.

Sorry as that DOES NOT SAY the connection itself is to be below the frost line. It also does not mean that if one has a 3 foot frost line, as I do, that the entire rod must be below that frost line either. It simply means that the rod or whatever is being used for a grounding element must have a portion of it that is not subject to normally being frozen. That means for example that a 10 foot copper plated ground rod in an area with a 3 foot frost line and sticks up 3 inches above ground for ground wire connection will have 6 feet 9 inches below the frost line and is legal.

Please refrain from taking guesses at what the NEC is saying.

[russ]

Please refrain from taking guesses at what the NEC is saying.

Back at you and use caution.

[Sunking]

Sorry as that DOES NOT SAY the connection itself is to be below the frost line. It also does not mean that if one has a 3 foot frost line, as I do, that the entire rod must be below that frost line either. It simply means that the rod or whatever is being used for a grounding element must have a portion of it that is not subject to normally being frozen. That means for example that a 10 foot copper plated ground rod in an area with a 3 foot frost line and sticks up 3 inches above ground for ground wire connection will have 6 feet 9 inches below the frost line and is legal.

Please refrain from taking guesses at what the NEC is saying.

It is exactly what it means. I use to sit on Code Panel 9 which writes Article 250. I did make one error and said Frost Line when I should have said Below Moisture Level. Any licensed electrician will tell you the rod must be below the Moisture Level. All of it not part of it. Leaving a rod above ground exposes it to physical damage. In addition the minimum requirement is a rod must be in contact a minimum of 8 feet below the moisture level and if you leave part of the rod above ground you cannot meet that requirement unless you use 10 foot or longer rods.

Here is a very good discussion on the subject on Mike Holt Code forum that I moderate. The Forum is for professionals only, but you can read the topics. Take note it is an Inspector posting the question.

[Mike90250]

.... In addition the minimum requirement is a rod must be in contact a minimum of 8 feet below the moisture level .....

So, how do they do that in Palm Springs, unless the house is next to a golf course, there is no moisture level?

Or My house pad, which is about 25' of packed gravel (extending 10' beyond the foundation perimeter). No moisture in it unless it's raining. I guess the Code is still not totally de-bugged.

[SolarShadow]

It is exactly what it means. I use to sit on Code Panel 9 which writes Article 250. I did make one error and said Frost Line when I should have said Below Moisture Level. Any licensed electrician will tell you the rod must be below the Moisture Level. All of it not part of it. Leaving a rod above ground exposes it to physical damage. In addition the minimum requirement is a rod must be in contact a minimum of 8 feet below the moisture level and if you leave part of the rod above ground you cannot meet that requirement unless you use 10 foot or longer rods.

Here is a very good discussion on the subject on Mike Holt Code forum that I moderate. The Forum is for professionals only, but you can read the topics. Take note it is an Inspector posting the question.

Breaking my promise to say nothing..............
So tell me then why is a ground wire allowed to be above the ground then? It is more prone to damage than a few inches of rod sticking up. My example mentioned the 10 foot rod as I recognize you'd have said at least 8 feet needed to be below ground level. If you are helping to make NEC rules and say such things here then it explains some things coming out of the NEC. Is there not a test of knowledge to be on the NEC making rules? Also, who came up with the term moisture level to be put into the rules? What an asinine vague term.

[russ]

Breaking my promise to say nothing..............

Last chance - be polite and not a wise ass if you wish to participate.

[mapmaker]

It is exactly what it means. I use to sit on Code Panel 9 which writes Article 250. I did make one error and said Frost Line when I should have said Below Moisture Level. Any licensed electrician will tell you the rod must be below the Moisture Level. All of it not part of it. Leaving a rod above ground exposes it to physical damage. In addition the minimum requirement is a rod must be in contact a minimum of 8 feet below the moisture level and if you leave part of the rod above ground you cannot meet that requirement unless you use 10 foot or longer rods.

Here is a very good discussion on the subject on Mike Holt Code forum that I moderate. The Forum is for professionals only, but you can read the topics. Take note it is an Inspector posting the question.

Thanks for the Mike Holt link. It seems to be not quite as black and white as you indicate in this forum. Consider this quote by 'infinity' the chief moderator:

No one seems to know what "If practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level" actually means. IMO the rod needs to go into the ground 8' and nothing more.

--mapmaker