ground sizes

[BULLogna]

I realize fault current is the main factor but when your going to a 1/0 neutral whats the purpose? A relay is lookin for excessive current so am i being protected by a 4/0 phase to phase short ? otherwise my ground fault neutral should be at least the same size as my ground. I also wonder if the ground is assuring me that the line is dead and my lock out tag is protecting me from energizing but I have had lines heated up on my grounds. Either way I am not arguing the ground fault capability is important. I am just wanting to know if most hands are trusted to pick the proper ground size for what your groundin. right now I am breakin my company rules if I choose to find a smaller ground for grounding #6cu or even #8cu 12kv which we still have in the air. Thanks for the input guys


"its better to be lookin down than lookin up"

[BULLogna]

I know short ground theory is important but I can only carry so many sizes. And using single point grounding I like to have the grounds long enough to transfer with out having to re ground usually about 12'. You have to pay attention when you got hot under build and cover things up.


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"better to be lookin down than lookin up"

[old lineman]

Coiling ground leads is a big no, no. It causes high impedence to the flow of current. Perhaps your only coiling a couple of loops which you can get away with but if the grounding cables are stored on a drum everything should be stripped off.
By the way high impedence will cause high heat which in turn will melt the cable cover.
As for size of cable most utilities standardize on 2/O because there will be fault currents on their system that requires this size.
Generally 4/O is reserved for the substation setting. Sometimes the substation crews will be required to parallel 2/O cables due to the fault current available.
I found that IEC (europe) standards are slightly more stringent than ASTM standards. Their information must be readily available on the web.
Any supplier will provide the fault current vs. cable size info without question. Your engineering department can provide the available fault current information.
The Old Lineman

[old lineman]

As you all know current cuses heat. The only method of preparing a high flex cable to be treminated is by compressing on a ferrule before tightening it into the grounding clamp.
Never sweat any fittings using lead.
Lead will melt out and the connection will fail before the protection clears it in some cases.
The Old Lineman

[Special ED]

Back in Louisville we only had 2/0 grounds. I would usually keep 12 ground chains on my truck mostly 6 foot and a few longer ones. I believe OSHA has a standard on minimum sizes and 2/0 is it if I'm not mistaken. Atleast thats what the office told us..

As for coiling the grounds... Yeah thats a huge no no... It builds up too much heat and in some cases will act like the coils in a transformer and blow up. We had a saftey video the apes had to watch and on our trucks the ground was coiled up and hung in the rear bin on the truck with the lead made up to the frame on the other side of the bin. Well the video showed the ground only taken out enough to make it to the neutral and they put a fault on it. WOW you talking bout one hell of an explosion!! They also showed the same sceanareo on one of them automatic ground reels on the back of a truck.. Same thing only it didn't put a bin door in orbit.

[JAKE]

i remember seein that video, remember the ground rod shooting out of the ground like a rocket!!

we use ep grounds here quite a bit when ya only gotta put one up it can be quicker depending on circumstances. i still think its safer also. when i first saw it i was a sceptic also, we just happened to put a new sub in with nothing on it so we set it up in real life on a 14.4 line put a pot on the line to act like a person put my fluke 189 hooked up to the pot, had the ep ground setup and closed the sub in she hit and there wasnt the slightest bump on that meter after that test i definately belive in it. i wanted to try it with bracket grounding but after the boss saw the line buckin like it did he didnt let us

[Special ED]

Speakin of the ground rods shootin out of the ground.. We used to have the old screw grounds and the forman instructed the guys to use it on the tensioner ground and rolling grounds while we reconductored a hot 12Kv route. They just barely put the screw in the ground and made everything up. Well needless to say with the windy day and the boss being in a rush the new wire would occassionally bump the energized circuit and everytime the screw ground would jump and through dirt in the air. Boss insisted on pulling anyways and never did knock out the line. Since then they banned the use of the screw grounds and everything is made up to the system neutral.. They used to ground to pole grounds as well but thats a no no now as well.

[mainline]

Driven ground rods are not a really good ground. I can speak from experience. We sounded one out, about 4 feet when it hit ledge. We then hooked it up to a running ground on our wire trailer. What we didn't know was that the P-line was wrapped around a phase, when the wire got there it energized the trailer. It burned three out of the eight tires flat. It also burned a tire on the digger truck we had hauled the trailer with. I was on the trailer for the ten minutes it took to for a lineman to get through a work zone and kill the circuit at the sub. The recloser never even bumped. We now only use the system neutral for a ground. Strangely enough we have to use a 2/0 ground to ground our equipment for pulling though we only use #2 for personal protection during restoration. Go figure.

[wtdoor67]

Anybody ever seen that ......I think it was AB Chance training Video on Omni potential Grounding? I saw it in the early 90's, 93 I think it was.

The one with the little fake 3 ft. line and the lightbulbs connected with alligator clips?

Does anybody out there ACTUALLY DO...Omni Potential Grounding? Is it "Hocus Pocus", or what.

It sure looked good in Theory.

and then again in about 87 or 88. It was not made mandatory at either place I was working. It as just kind of presented as perhaps a good method. Seemed to me it worked but I don't recall anybody using it. I had actually forgotten what it was called but Omni Potential sounds like it.

[BULLogna]

Didn't that video compare a cluster ground assembly to single point grounds that were too long?






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"better to be lookin down than lookin up"