Loop Ground

[Swamprat]

How many of you "loop Ground" your transformers?

By Loop Ground, I mean, Taking the copper groundwire on the transformer thru the H1, or H2 Bushing, down over the top of the pot, Thru the secondary X2 Bushing, thru the tank grounding lug, below the X2 bushing, wrapping it around the transformer, and connecting it to the pole ground. The H1 or 2 bushing Ground is also connected to the pole Ground.

Anybody do that? I personally loved it, as opposed to connecting a single piece of copper to the back of the pot on the tank grounding lug and a single piece of copper to the H1 or H2 bushing. I liked the Loop Ground.

[Bighorn Ape]

we loop ground OH and UG...just in case one bond breaks or becomes loose i suppose.

[Swamprat]

we loop ground OH and UG...just in case one bond breaks or becomes loose i suppose.

THAT is exactly why I like the Loop Ground. And, That is what it's for. Just don't understand why more Utilitys and Corps don't do it.

[gumbo]

How many of you "loop Ground" your transformers?

By Loop Ground, I mean, Taking the copper groundwire on the transformer thru the H1, or H2 Bushing, down over the top of the pot, Thru the secondary X2 Bushing, thru the tank grounding lug, below the X2 bushing, wrapping it around the transformer, and connecting it to the pole ground. The H1 or 2 bushing Ground is also connected to the pole Ground.

Anybody do that? I personally loved it, as opposed to connecting a single piece of copper to the back of the pot on the tank grounding lug and a single piece of copper to the H1 or H2 bushing. I liked the Loop Ground. That is REA spec across the country. I guess putting their nuetral alongside the top of the transformer like they do, they definately want the Txs grounded so the fuses work quickly. It also puts the entire Tx case in an equal potential zone with the nuetral, small as it might be.

[lewy]

On 2 bushing transformers you should always run your H2 from the neutral through the H2 & onto the X2, the X2 should also be connected to the neutral. We have to ground all of our transformers & we run a separate case ground. Not all of our 2 bushing transformers have a ground strap, but we still hook them up that way. On our single bushing transformers we do not run a wire form H2 to X2, but all of our single bushing transformers have ground straps. On the inside, the one side of the primary winding is connected at the same spot as where the H2 is connected on the outside. We always run a wire from X2 to the neutral as well a a separate case ground. On a 2 bushing transformer if you do not also have the loop from neutral to H2 to X2 back to the neutral & that wire breaks from H2 it will be at primary voltage. You do not have this problem on single bushing transformers because you have 3 connections to H2. I do not understand how on new construction, why the transformer has to be so close to the primary & why the neutral can not be below the transformer, for us we have a 10.5' neutral & the bottom of the transformer is 12" above it.

[Swamprat]

I've personally, never liked single bushing transformers Lewy. CSP or with a switch. Just never liked em.

But, bein a contractor, I just built to their spec usin their stuff. "Have tools, will Travel" so to speak.

I liked and still do like the Loop Ground on 2 Bushing transformers.

It creates 3 different neutral connections. 2 to the pole ground, One directly from, H2 to the pole ground, and the other, thru the same wire feed, "looped", thru X2 and Thru the tank ground connected to the pole Ground again. Both connected to the pole ground, and the pole ground was always connected to the primary neutral of course.

Then, when the actual Secondary Neutral lead was installed in X2, and again connected to the Primary neutral, that was #3.

I've worked for utilities, where a single piece of wire, was connected from H2 to the pole ground, and another piece of wire was connected...in the back of the transformer, to the tank ground. Then, the X2 Secondary lead, was connected to the primary neutral. Still a 3 point connection, but I liked the Loop ground theory and look a h$ll of alot better. "Different Strokes", Right?:cool:


On 2 bushing transformers you should always run your H2 from the neutral through the H2 & onto the X2, the X2 should also be connected to the neutral. We have to ground all of our transformers & we run a separate case ground. Not all of our 2 bushing transformers have a ground strap, but we still hook them up that way. On our single bushing transformers we do not run a wire form H2 to X2, but all of our single bushing transformers have ground straps. On the inside, the one side of the primary winding is connected at the same spot as where the H2 is connected on the outside. We always run a wire from X2 to the neutral as well a a separate case ground. On a 2 bushing transformer if you do not also have the loop from neutral to H2 to X2 back to the neutral & that wire breaks from H2 it will be at primary voltage. You do not have this problem on single bushing transformers because you have 3 connections to H2. I do not understand how on new construction, why the transformer has to be so close to the primary & why the neutral can not be below the transformer, for us we have a 10.5' neutral & the bottom of the transformer is 12" above it.

[Fiberglass Cowboy]

Not a good idea to loop ground any transformer in a bank, of any type. Taking a chance of the transformer case paralleling the neutral, and current flowing across the case. Not recommended in the transformer manufacturer books; (i.e. GE, ABB, Solomon, etc.) or any other literature about transformers and their connections. I did not know this until someone told me and I looked it up, just a few years back. You guys should look it up if you find that kind of thing interesting, or just find that having that knowledge is valuable. Figure the engineers that work for the companies that build them have to know something about transformers ....... :cool:

[Swamprat]

Not a good idea to loop ground any transformer in a bank, of any type. Taking a chance of the transformer case paralleling the neutral, and current flowing across the case. Not recommended in the transformer manufacturer books; (i.e. GE, ABB, Solomon, etc.) or any other literature about transformers and their connections. I did not know this until someone told me and I looked it up, just a few years back. You guys should look it up if you find that kind of thing interesting, or just find that having that knowledge is valuable. Figure the engineers that work for the companies that build them have to know something about transformers ....... :cool:

Don't know about "ANY transformer bank", but...

Good point Cowboy. D$mn good point. A little "technical" for me, and I think most in this subject, but...whatever.

Never mentioned that, or thought about it till you brought it up. On a 3 pot Wye bank, we would only wire the center pot, with the loop ground. On a Delta bank...needless to say, only the center pot.

Most times...It's all about how the utility you're workin for...has their specs. If you're a contractor. Ya just work by their Specs.

[lewy]

Swamp on a 2 bushing transformer you would only have 3 connections if you have a ground strap at X2 (which most of ours do not), if not then you your case ground if separate would not be tied into H2 & if you ran 1 wire through the case ground to H2 & onto X2 back to system neutral you would only have 2.
On 3 phase banks we tie in all of our neutrals on the secondary side for 120/208 & 347/600, they do not want us connecting H2 to X2 on single bushing transformers (which most don't anyway) because it would cause circulating current, but on a 2 bushing transformer we would because like I said earlier if the wire coming from the H2 bushing broke & it was not connected at the other end through X2 it would be at line potential.

[kooman]

Swamp on a 2 bushing transformer you would only have 3 connections if you have a ground strap at X2 (which most of ours do not), if not then you your case ground if separate would not be tied into H2 & if you ran 1 wire through the case ground to H2 & onto X2 back to system neutral you would only have 2.
On 3 phase banks we tie in all of our neutrals on the secondary side for 120/208 & 347/600, they do not want us connecting H2 to X2 on single bushing transformers (which most don't anyway) because it would cause circulating current, but on a 2 bushing transformer we would because like I said earlier if the wire coming from the H2 bushing broke & it was not connected at the other end through X2 it would be at line potential.

on single bushing transformers you dont tie h2 and x2 together? please explain because the h2 is connected to the case inside the tank so you dont hook anything to the x2 bushing? i am confused, the reason i ask is because we have some 120/208 banks that are single bushing trans, just wondering if there is something we dont know about.

[lewy]

on single bushing transformers you dont tie h2 and x2 together? please explain because the h2 is connected to the case inside the tank so you dont hook anything to the x2 bushing? i am confused, the reason i ask is because we have some 120/208 banks that are single bushing trans, just wondering if there is something we dont know about.

No you do not have to tie H2 & X2 together they already tied through the tank, if your transformer has a ground strap, all of our single bushing transformers do & I would suspect yours do as well. You have to connect X2 & your H2 separtly to your neutral & on a 3 phase we tie all of the X2s together & run 1 wire to the neutral. The only reason you tie the H2 & X2 together on 2 bushing transformers is for safety reasons, they do not work any better either way, the same with the case ground, it is for safety only.

[Swamprat]

Swamp on a 2 bushing transformer you would only have 3 connections if you have a ground strap at X2 (which most of ours do not).

Yeah, ours didn't come with ground straps either. We put the ground lug below X2. Run the copper thru H2, down the top of the tank, thru X2 then the tank ground, then wrap it around the side of the pot to the pole ground. Then take the actual neutral lead straight down to the primary neutral.

[gumbo]

on single bushing transformers you dont tie h2 and x2 together? please explain because the h2 is connected to the case inside the tank so you dont hook anything to the x2 bushing? i am confused, the reason i ask is because we have some 120/208 banks that are single bushing trans, just wondering if there is something we dont know about. Are there 2.....or 3 secondary bushings on these transformers?? I've never banked a single bushing transformer. I've been told that they for single phase only, although I have seen them in banks from time to time on existing structures. I think that is for when you float your H2 nuetrals for 3rd harmonics. Guess it wouldn't be an issue on a power bank.

It's a wonder some of the West Coast hands aren't chiming in here. In California, they don't ground the case at all. They hang the Tx bolts, head out....nut under the hangers, and use bolt covers on the back side of the pole for isolation purposes in case the Tx case comes hot. There isn't a nuetral available unless you are close to a housing addition with an extensive underground system. Anyone ever worked the California "Phantom Wye"??

[Swamprat]

Are there 2.....or 3 secondary bushings on these transformers?? I've never banked a single bushing transformer. I've been told that they for single phase only, although I have seen them in banks from time to time on existing structures. I think that is for when you float your H2 nuetrals for 3rd harmonics. Guess it wouldn't be an issue on a power bank.

It's a wonder some of the West Coast hands aren't chiming in here. In California, they don't ground the case at all. They hang the Tx bolts, head out....nut under the hangers, and use bolt covers on the back side of the pole for isolation purposes in case the Tx case comes hot. There isn't a nuetral available unless you are close to a housing addition with an extensive underground system. Anyone ever worked the California "Phantom Wye"??

3. Just a standard 2 bushing transformer. H1, H2,...X1, X2, X3.

[Swamprat]

Are there 2.....or 3 secondary bushings on these transformers?? I've never banked a single bushing transformer. I've been told that they for single phase only, although I have seen them in banks from time to time on existing structures. I think that is for when you float your H2 nuetrals for 3rd harmonics. Guess it wouldn't be an issue on a power bank.

It's a wonder some of the West Coast hands aren't chiming in here. In California, they don't ground the case at all. They hang the Tx bolts, head out....nut under the hangers, and use bolt covers on the back side of the pole for isolation purposes in case the Tx case comes hot. There isn't a nuetral available unless you are close to a housing addition with an extensive underground system. Anyone ever worked the California "Phantom Wye"??

Interesting. "Don't ground the case at all."
Is that, like an ungrounded WYE system?

[kooman]

Are there 2.....or 3 secondary bushings on these transformers?? I've never banked a single bushing transformer. I've been told that they for single phase only, although I have seen them in banks from time to time on existing structures. I think that is for when you float your H2 nuetrals for 3rd harmonics. Guess it wouldn't be an issue on a power bank.

It's a wonder some of the West Coast hands aren't chiming in here. In California, they don't ground the case at all. They hang the Tx bolts, head out....nut under the hangers, and use bolt covers on the back side of the pole for isolation purposes in case the Tx case comes hot. There isn't a nuetral available unless you are close to a housing addition with an extensive underground system. Anyone ever worked the California "Phantom Wye"??

we usually use 2 bushing on all banks but we do have some wye banks that have single bushing transformers, and we have alot of open delta banks that have single. any bank that requires you to ground the h2 can use single bushing transformers because the other end of the single bushing is grounded to the tank internally.

[gumbo]

Interesting. "Don't ground the case at all."
Is that, like an ungrounded WYE system? Yes. That is why they call it a "Phantom Wye". When they build a new housing addition, they'll start stringing a nuetral for 15 or 20 spans before and after the entry drives and ground every pole to build a ground grid for the Wye connected underground. All their overhead Txs are Phase to Phase, leading some to believe they are working on a Delta system. I took a lot of money off of Tramps when I was an apprentice. Folks would want to argue about it till I would get them to bet that there weren't 2 volatages available on the primary. You had to check it at a transformer or apparatus pole though. Drank a lot of free beer on that one when it showed 7200 on a 12470. First you tell.......then you show.

[lewy]

Are there 2.....or 3 secondary bushings on these transformers?? I've never banked a single bushing transformer. I've been told that they for single phase only, although I have seen them in banks from time to time on existing structures. I think that is for when you float your H2 nuetrals for 3rd harmonics. Guess it wouldn't be an issue on a power bank.

It's a wonder some of the West Coast hands aren't chiming in here. In California, they don't ground the case at all. They hang the Tx bolts, head out....nut under the hangers, and use bolt covers on the back side of the pole for isolation purposes in case the Tx case comes hot. There isn't a nuetral available unless you are close to a housing addition with an extensive underground system. Anyone ever worked the California "Phantom Wye"??

Our 347/600v transformers are 2 bushings on the secondary side with a ground strap connected to X2.