Ground Straps - ECN Electrical Forums

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Bill, I haven't been and won't be able to participate in the forums for a while as I am working out of town and zillion hours a week. A few weeks ago I posted a topic about a silver soldered ground strap. I thought some of you might be interested in some pictures.

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Picture one: Rolling off the reel.

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Picture two: Turning a corner. The PVC is there two maintain a wide radius and keep the back hoe from crushing it flat. Later this week we will be auguring the chemical ground rods and making the silver solder connections at the corners. I'll post pictures of this when I get a chance.

- Nick

Hi, Nick:
Interesting pix. One question (and pardon my ignorance, please); Would the strap be impaired, or broken, if it were to be flattened at the corner? Anyone else know...?

Mike (mamills)

[This message has been edited by mamills (edited 06-14-2002).]

just curious what type of installation requires something like this. Just that I have never seen a ground strap used like this for a grid.

mamills
The reason for not letting it crushed flat is that is it designed to carry stray currents in the giggaHZ range. It flows better with more surface area and it doesn't like sharp bends. (Kind of like lightning) The other option is to cut and splice at the corners but there are two down falls.
1) The fewer splices there are the more integrity the system has.
2) A 12" to 12" bolted and silver soldered splice takes a man that is experienced an hour to one and one half hours to make. Quite a bit longer than mearly rounding the corner!

elektrikguy,
This is a TV station/Studio with tons of digital television equipment. The strap is a reference for that equipment and is a spec for this particular client. This is the second installation I have done for them like this. The first was the national master control center for the USA network. I was disappointed to find out that 2 years after we completed the project Telemundo bought them out and cleaned the place out. What do ya do?!
I can send more PICS of other aspects of the project if the people here are interested. Just let me know.

Very interesting work! Send what you can. Are you installing the grounding grid for towers/dishs.

Wow, that looks weird, but sounds like the designer has specific ideas on how he wants it done. Copper coil stock and silver solder—sounds like armed-guard duty. Hopefully a few yards of ready mix is on the way.

I bet you'll find plenty of gold-plated connectors on the equipment itself, as well.

Interesting photoes. I've never saw anything like that before. I did work at a power house once where we laid copper wires in the ground to form a grounding grid. I think they call it cathodic grounding.

Nick:
Thanks for the answer.

YES, please send some more pix!

Mike (mamills)

[This message has been edited by mamills (edited 06-16-2002).]

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I have tons of pics of regular construction stuff but rather than bore everyone with that I am waiting till we do some of the unusual stuff. I did think you might enjoy these.

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Picture one: One (of two) 300KVA Mirus harmonic canceling duel output transformer. This transformer has two 180KVA outputs phase shifted 30Deg from each other. One is 15 degrees out from the primary the other is 45 degrees out. The concept here is that the two outputs create a common mode rejection point to cancel 3rd 5th 7th etc. harmonic currents rather than allowing them to circulate in the primary delta winding as a normal transformer would. This eliminates the need for a high K rated transformer and filters noise out of the grounding system. Notice all the secondary terminals!

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Picture two: The point where the 12" ground strap emerges from outside into the building. You can see one of the four rows of seismic rack bases for this room. At each one we will bolt and silver solder a 12" tap run down the inside of the bases. Each rack has a ground bus in it with a 2" copper strap silver soldered to it which we will silver solder to the 12" under the bases. Pics will follow.

PS: The silver solder we are using costs $32.00 per pound!

- Nick

Hello E-C.Net Webmaster— Thanks indeed for the pics.

In the photo of an opened-up drytype, is the upper horizontal bar on glastic knobs {a/k/a johnny balls} the neutral bus? It’s not unheard of busbars are specifies to be of silver-plated copper stock. It looks like the bottom six bus stubs on the fiberglass rail may be the lowside six phase leads. Is that correct?

No reflection on you personally, but in that drytype image, the white-textured jumpers remind me of old ones that were commonly asbestos covered.

Looks like a very interesting jobsite, but I imagine the Divison-16 paper on this project must be at least a foot thick...

[This message has been edited by Bjarney (edited 06-19-2002).]

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We augured the holes and set the XIT ground rods today. In the pictures you will see the the 12" strap attached to the ground rod (bolted with stainless steel hardware and silver soldered of course). We made this connection before dropping them in the hole. The 4/0 copper that comes standard on these rods will not be used except for on the one by the electric room. It will be used to bond the system to the building ground system. The next step is to bolt and silver solder the tails you see coming off the rods to the buried strap in the previous pictures.

Bjarney,

Yes the bussbar in which you are referring is the neutral buss. The three behined it are the primary termination pads. The six on the bottom are the duel outputs I referred to. X1,X2,X3 and Y1,Y2,Y3. The white over the jumpers is a vinyl covering installed at the factory.

Actually this is a design build job. We (I) are engineering the job. The specs come from the client whom we did a job like this for before. Despite the last part of our name, "Electrical Contractors and Engineers" we do not have a PE on staff at this time. We hired an engineering firm to help out and provide stamped drawings for the AHJ and as a CYA.

- Nick

Nick— Sounds like the work could make for some interesting and profitable repeat business. A minor aside—on ANSI terminal markings for three-winding transformers… H1-H2-H3 primary; X1-X2-X3(-X0) secondary; Y1-Y2-Y3(-Y0) tertiary. Anther oddity for this type of transformer is that on the secondary and tertiary terminals, there will be typically six 120-volt ø-n measurements, but also you’ll be able to sort out six 120-volt ø-ø readings. The two 208Y/120V “groups” are interleaved, for lack of a better term.

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For anyone interested here is a couple of pictures of the completed ground
straps.

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XIT ground rod connection to the 12" strap

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2" strap connection from the rack buss to the 12" strap.

- Nick

Isn't silver solder prone to chemical attack? I read in a radio engineering magazine where a process called "cadwelding" is used for joining grounds.

Has anyone heard of that process? Apparently you join the two ends inside a crucible filled with some high-temp burning powder that melts the two metal ends together permanently.

AKA Thermite welding.

Uses a graphite form which is placed around the conductors, and filled with a mixture of powdered filler metal (copper for electrical work), an oxidizer, and a top layer of some kind of ignitor powder (magnesium powder?).

Used for creating "radial" ground systems at AM broadcast tower bases, and other places where the highest connection reliability is desired. Also used for welding rebar, railroad tracks, etc.
http://www.cadweld.com/erico_public/product/Cadweld.asp

Nick, thanks for the great pics!

How far down do those XIT rods go? Do the straps simply get covered over in concrete?

SvenNYC—as far as I can tell, the usual “45%” silver-brazing materials are not at all corrosive after installation. [Athough the flux paste can sting a little if wet and gets in cuts on the hand.] A fluoride-based flux is used for installation, but the residue seems to be quite inert.

An alternative is “15%” sil/phos brazing rod—needing no additional flux for copper-to-copper joints, but requires somewhat more heat in joint makeup. It has a higher melting point compared to the 45% material, but a very wide glass temperature for void filling. The after-sweat flux remains are very small, and although I have not used it to salt my fries, I’ve never found it to be the least concern, much less significantly visible after joint sweating.

[This message has been edited by Bjarney (edited 08-22-2002).]

ThinkGood—as far as I can tell, chemical rods are not intended to be concrete encased, but backfilled with a diatomaceous-earth slurry to a few inches below the top, with the accessible but subsurface upper end is placed in a valve box for venting and testing/inspection.

Sandwiched between the copper tube and “the earth,” conductive, chemically charged “veins” form in the hardened slurry and adjacent soil through the several inches of intermediate conductive slurry, and is a key part of a desirably low-resistance system.