Ground cable question

mryimmers

Hi everyone,
I set up my small system a while back, for a ground cable I used a copper cable that I took off of an old house that was attached to the lightening rods.

It is equal in diameter to a 2/0 cable, but is the flat ribbon/ loosely woven type of cable, is this considered to be adequate for this type of use?

The cable runs from my mini disconnect out to the ground rod (15 ft), and another piece from the array to the same ground rod.

Thanks.

Cariboocoot

Re: Ground cable question

Electrically it should work, providing it's not all corroded. The ESG does not care about the shape of the wire: lightning protection does; the flat, woven design carries the RF energy from strikes better.

Will it pass inspection? Probably not because AHJ's can be very single-minded: most do not understand the principles behind the regulations they only enforce them. Sometimes incorrectly.

vtmaps

Re: Ground cable question

Cariboocoot wrote: »

Will it pass inspection? Probably not because AHJ's can be very single-minded: most do not understand the principles behind the regulations they only enforce them. Sometimes incorrectly.

There's a good reason why braided (and even stranded, in some jurisdictions) does not pass inspection, and you did mention it: Corrosion.

Another reason that solid is preferred is fusing... braided is more likely to melt than stranded, and stranded is more likely to melt than solid.

--vtMaps

Cariboocoot

Re: Ground cable question

vtmaps wrote: »

There's a good reason why braided (and even stranded, in some jurisdictions) does not pass inspection, and you did mention it: Corrosion.

Another reason that solid is preferred is fusing... braided is more likely to melt than stranded, and stranded is more likely to melt than solid.

--vtMaps

No.
And since it is a ground cable there are no fusing issues because ground cables are not fused due to the fact they normally carry zero current and have zero Voltage potential.

vtmaps

Re: Ground cable question

Cariboocoot wrote: »

No.
And since it is a ground cable there are no fusing issues because ground cables are not fused due to the fact they normally carry zero current and have zero Voltage potential.

"fuse" was not meant as OCP, it was meant as "melt" or "vaporize". High surge currents (lightning) are more likely to melt/vaporize a braided conductor than a solid conductor of similar resistance.

--vtMaps

mryimmers

Re: Ground cable question

It's off in the bush, no inspection.

Cariboocoot

Re: Ground cable question

vtmaps wrote: »

"fuse" was not meant as OCP, it was meant as "melt" or "vaporize". High surge currents (lightning) are more likely to melt/vaporize a braided conductor than a solid conductor of similar resistance.

--vtMaps

Well as has to be repeated so often on the forum the main purpose of grounding is not for lightning protection. If it were, your statement does not stand since it is multi-strand braided wire that is used for lightning protection. Someone has been feeding you incorrect information. The fact is multi-strand wire is less likely to suffer complete failure because it can suffer partial failure and continue to work. Lightning is not high current either. It is high Voltage and high frequency.

Do you know why solid wire is used? Because it is cheaper than stranded. So in an application where mechanical interference is unlikely (i.e. inside a wall or conduit) it becomes a better value.

Do you know why stranded wire is used? Because it is flexible and can withstand movement better than solid. In cases where the wire is 'exposed' solid wire may fail completely if subject to mechanical force whereas the stranded will just move with that force.

Take, for example, ground conductor from a service panel to a earthing rod. Examine as many as you can find. Most if not all will be 6 AWG stranded wire exposed and connected above ground to the rod. Likewise the lines feeding a house from the power transformer: stranded wire. This is so that it can flex in the wind. Welding cable is fine strand because it is expected to need to flex a lot.

Electrically there is no difference in the conductivity or current handling of similar sized stranded and solid wire. One will not 'melt' before the other, and as I mentioned the stranded can suffer partial failure and still conduct sufficiently (indeed the tiny strands in welding cable often break yet the cable as a whole remains a viable conductor for very high Voltage and current). If solid wire breaks inside you can get partial connection as it touches end to end, arcs, and starts a fire.

jcheil

Re: Ground cable question

Cariboocoot wrote: »

Do you know why stranded wire is used? Because it is flexible and can withstand movement better than solid. In cases where the wire is 'exposed' solid wire may fail completely if subject to mechanical force whereas the stranded will just move with that force.

A perfect example is something I run into a lot. People make up a "plug" to connect to their generator to feed their cabin/inverter/etc and use solid wire. After a while (sometimes just hours or days), the solid wire will rattle out of the connector in the plug. Use stranded wire and the connector holds firm forever.

inetdog

Re: Ground cable question

jcheil wrote: »

A perfect example is something I run into a lot. People make up a "plug" to connect to their generator to feed their cabin/inverter/etc and use solid wire. After a while (sometimes just hours or days), the solid wire will rattle out of the connector in the plug. Use stranded wire and the connector holds firm forever.

Just do not tin the wire solid to make it fit properly under the screw. Twist it and handle it properly instead.
Some plugs (attachment caps) are designed to securely accept stranded wire, having a pressure plate or washer. Other devices, including receptacles designed to put into wall boxes, do not handle stranded nearly as well.

vtmaps

Re: Ground cable question

Cariboocoot wrote: »

Well as has to be repeated so often on the forum the main purpose of grounding is not for lightning protection. If it were, your statement does not stand since it is multi-strand braided wire that is used for lightning protection. Someone has been feeding you incorrect information.

It's certainly possible that I have been fed incorrect info. It's also possible that I receive good info but misinterpret it.

From http://ecmweb.com/code-basics/grounding-and-bonding-part-3-3

The purpose of the grounding electrode conductor (GEC) is to help direct lightning induced energy to the earth. But the purpose of an equipment grounding conductor (EGC) is to provide a low-impedance ground-fault current path to the source to operate overcurrent devices in the event of a ground fault.

These conductors serve entirely different purposes, so it is understandable that their sizing requirements differ. The sizing of an EGC depends on 250.122, while GECs are sized according to 250.66.

Because these conductors have different rules, different sizing requirements, and different installation requirements, the 2011 NEC added 250.121 to clarify that an EGC must not be used as a GEC.

I'm still trying to track down an authoritative reference for solid vs stranded GEC... perhaps the solid is required in the grounding of towers and other large commercial installations where high current lightning strikes are a possibility.

--vtMaps

jcheil

Re: Ground cable question

inetdog wrote: »

Just do not tin the wire solid to make it fit properly under the screw. Twist it and handle it properly instead.
Some plugs (attachment caps) are designed to securely accept stranded wire, having a pressure plate or washer. Other devices, including receptacles designed to put into wall boxes, do not handle stranded nearly as well.

Yeah, that is what I was talking about, the plugs (that I have seen) generally have that pressure plate/washer combination. If they just have a screw terminal.

Cariboocoot

Re: Ground cable question

inetdog wrote: »

Just do not tin the wire solid to make it fit properly under the screw. Twist it and handle it properly instead.
Some plugs (attachment caps) are designed to securely accept stranded wire, having a pressure plate or washer. Other devices, including receptacles designed to put into wall boxes, do not handle stranded nearly as well.

Tinning solid wire won't cause much of a problem as tinning is a very thing coating of solder. There's usually no reason to do it for a screw connection any way.

Tinning stranded wire will be a problem because you can't really tin each individual strand. Invariably you end up with a wire end that is a mixture of hard copper and soft solder. Guess what happens when you tighten a screw against that? Holds for a while, but the softer material succumbs to force and the connect will loosen.

vtMaps: try eight years at university and see if that helps. Although apparently it doesn't. :roll:

Cariboocoot

Re: Ground cable question

jcheil wrote: »

Yeah, that is what I was talking about, the plugs (that I have seen) generally have that pressure plate/washer combination. If they just have a screw terminal.

Hey, you know why? 'Cause they're meant to take stranded wire as is recommended for cords whereas outlets are meant to take solid wire just for the reasons I've already explained.

But no one has to listen to me. Find out for yourselves. Just warn the neighbours and alert the fire department first.

vtmaps

Re: Ground cable question

Cariboocoot wrote: »

vtMaps: try eight years at university and see if that helps. Although apparently it doesn't. :roll:

Do you care to comment on the information/misinformation that I quoted in post #10 in this thread? It might save me quite a few years at university.

--vtMaps

Cariboocoot

Re: Ground cable question

vtmaps wrote: »

Do you care to comment on the information/misinformation that I quoted in post #10 in this thread? It might save me quite a few years at university.

--vtMaps

You mean this?

The purpose of the grounding electrode conductor (GEC) is to help direct lightning induced energy to the earth. But the purpose of an equipment grounding conductor (EGC) is to provide a low-impedance ground-fault current path to the source to operate overcurrent devices in the event of a ground fault.

These conductors serve entirely different purposes, so it is understandable that their sizing requirements differ. The sizing of an EGC depends on 250.122, while GECs are sized according to 250.66.

Because these conductors have different rules, different sizing requirements, and different installation requirements, the 2011 NEC added 250.121 to clarify that an EGC must not be used as a GEC.

Entirely accurate and in keeping with what I said. What's the problem?
Okay in my day the EGC was called ESG (electrical safety ground) and was 'brand new'. But yes, the purpose of the two is entirely different. I've explained this numerous times - like whenever someone talks about grounding for lightning protection.

And again the flat, braided wire is used for lightning protection because it conducts the high-Voltage, high-frequency RF energy of lightning better than standard wire. In fact if you were to observe the 'skin effect' of this energy on standard wire you'd see that essentially it reduces the wiring size by about 1/3 whereas with the flat, braided wire the full equivalent amount of copper is used for conducting. Electrically the 'lightning wire' can be used for ESG, but regulations say it can't. Nor should it be interpreted that stranded wire is automatically that type of wire, even though it technically is a type of stranded wire.

Keep in mind there are tons of regulations about grounding. They have been changed numerous times over the years and are still debated as to which is the most efficacious. The point I'm trying to make is that understanding the underlying principles behind the rules is not the same as simply being able to quote them (like most inspectors do).

Several of us here would argue nose-to-nose with Mr. Wiles on may regulations. Just because he writes the rule book doesn't mean he's always right. And just because someone claims they help write it doesn't mean they're telling the truth.

P.S.: If you do find yourself committed to university remember: when you go chasing women, some of them are very fast and some of them won't run at all. The latter type are the most dangerous.

vtmaps

Re: Ground cable question

Cariboocoot wrote: »

Entirely accurate and in keeping with what I said. What's the problem?

No problem now, but the OP asked about his GEC, and you wrote "the main purpose of grounding is not for lightning protection". I thought that in the context of this thread you were referring to the GEC.

Cariboocoot wrote: »

P.S.: If you do find yourself committed to university remember: when you go chasing women, some of them are very fast and some of them won't run at all. The latter type are the most dangerous.

I've already had 35 years at university... 10 as student and 25 as faculty.
Chasing women was fun for 10 years, but the university does not permit faculty to chase women... neither does the woman I caught.

--vtMaps

Cariboocoot

Re: Ground cable question

vtmaps wrote: »

No problem now, but the OP asked about his GEC, and you wrote "the main purpose of grounding is not for lightning protection". I thought that in the context of this thread you were referring to the GEC.

I've found they like to keep changing terminology for no reason other than they like changing terminology.

I've already had 35 years at university... 10 as student and 25 as faculty.
Chasing women was fun for 10 years, but the university does not permit faculty to chase women... neither does the woman I caught.

--vtMaps

Yeah, they can be funny like that.

niel

Re: Ground cable question

i understand what coot wrote and i'm unsure why you don't. the ground rod has 2 purposes, but the primary reasoning wasn't for lightning as it was for an electrical equipment safety ground. if lightning does strike it will most likely destroy all it goes through and the rod is at that point just the path for the destruction. there is also the secondary aspect of lightning that people like wiles and a certain 'king' don't fathom well and that is the emp effects of lightning. this also can follow a path to that ground rod and it is well into the rf range this energy exists in. the fact that emp reduction is a separate issue it is also the reason why a separate ground rod for the spd on the midnite thread was said by me as it has no bearing on proper functionings of the electrical system wiring itself. the spd will not have a low resistance path to ground anyway unless a certain potential is reached. it only grounds out high voltage surges, period.

a solid wire is not the strongest wire either and when one looks at the surface area of a solid wire it is not as vast in surface area as that which a stranded wire with equal amounts of copper per foot (and thus the same awg) can wield. the surface areas of all of the strands affords more area over a solid same awg wire would present and reduces the impedance (ac resistance) to the rf flow. can one go too far with stranding? yes. i would not want a #2/0 made up of #40 individual strands as corrosion would be capable of destroying those fine strands much easier, but remember that larger strands won't be destroyed as readily. make no mistake here that this corrosion occurs on solid wires too and they are not immune to corrosion. if over time corrosion goes say 20 microns then that is not as significant on the larger individual strands rather than the smaller individual strands. all ground wires will corrode and need checked upon after so much time passage and all ground wires in a full strike are apt to be vaporized. even after the wires hit the vaporization point the air is loaded with copper atoms and the lightning will continue to follow the path through them to ground so the stupid argument of the microsecond differences in the points of vaporization is moot in the big scheme of things. if you are hit with a strike all bets are off even for solid wires.

simply stated would be the use of stranded wire is good if not too fine as it does add strength to the wire while affording more flexibility and a tad less ac resistance to the emp of lightning being lightning is loaded with radio frequency ac. protection from lightning directly is a misnomer unless you are in a faraday cage with no leaks in the path to the interior of the cage.

vtmaps

Re: Ground cable question

niel wrote: »

it is also the reason why a separate ground rod for the spd on the midnite thread was said by me as it has no bearing on proper functioning of the electrical system wiring itself.

For those readers who are not familiar, here is the link to the midnite thread that Niel is referring to:
http://midniteforum.com/index.php?topic=1716

If you use a surge protector and ground rod at your array, and do NOT bond that ground rod to the main system ground rod, I agree with you that there are no issues with safety grounding. I agree with you that there is no issue with bleeding static to ground. And I agree that there is no issue with a direct lightning strike, because in that case you're toasted no matter what you do.

The issue I see is that if lightning strikes the ground in your neighborhood, the two ground rods can be 1000's of volts apart.

niel wrote: »

the spd will not have a low resistance path to ground anyway unless a certain potential is reached. it only grounds out high voltage surges, period.

That's exactly the point... if the ground rods are 1000 volts apart the SPD can become a conductor and allow current to flow between the ground rods through your power cables.

If I had a drilled well I would also bond the casing to my system ground with bare wire in the trench, for all the same reasons... I don't want the power cables (to the pump) to relieve the potential difference between the well casing and my system ground rod.

I'm no code expert and I have no idea what code demands in these circumstances. There is a benefit to be gained by bonding the two ground rods, but there is also a cost.

When I weighed the cost and benefit for my system, I decided to put 100 ft of bare #6 in the trench.

Loosen up Niel, I'm not saying your approach is wrong... I just weigh the costs and benefits differently than you.

In that midnite thread there was at least one other person in a lightning prone area that weighs the costs and benefits as I do:

Halfcrazy wrote:

VTMaps
I think I agree if there are multiple ground rods they really need to be bonded together. Induced voltage from lightning is a nasty thing and I have had several paid (By me) educations on this subject as I live on a rock at a high elevation.

--vtMaps

niel

Re: Ground cable question

vtmaps,
i follow what you say, but it is very unlikely the lightning energy will go up the ground paths to do harm. normally i do agree with you about tying rods together, but in that thread there was unlikely to be that kind of potential in the ground due to the distances involved between the different buildings as the soil resistance would quell any such high voltage from developing.

you can be relieved that i am not aiming all of this at you either as i hinted without getting into that side show so fear not, but i do hope it is clear on what all i was trying to convey to you.

mryimmers

Re: Ground cable question

OK guys, thanks for the responses, I'm gonna go with the assumption that it's OK then, thanks again !!!