Delta and Wye ?

[johnbellamy]

I understand that some do not ground the case on pots from what people have posted here, but I still dont understand why.

In my apprentiship, or in my journeyman written test, If you didn't show you grounded the case it was an automatic failure, so this makes no sense to me.

I have worked mostly on single phase, single bushing pots, so that is why we would run a loop thru x2 and thru sometimes two case grounds, depending on the size of the pot, back to a pole ground that was attached to the system neut.

On a two bushing single phase, we would do the same other than running it thru the h1 or h2 primary depending on worked better clearance wise.

By doing this, you would have alot of failed connections for the can to be energized.

So help me undrstand, I you don't have the case of any devise grounded what happens if these devices become energized? and on a transformer , are you releying on your x2 connection, because that connections fails alot.

Another question on a delta system, on a pole with a transformer, if you do not run a pole ground or ground the case, dose that mean you are releying on the customers grounds to get your reference?

[lewy]

On a single bushing tx the other end of the primary winding is attached to the case where the H2 connection is.
You should run a wire directley from there to your neutral
X2 (if you have a ground strap) should go directly to your neutral
case ground should attach to the down ground which is connected to system neutral
On a single bushing tx you are wasting wire & time connecting H2 to X2
If you do not have a ground strap on X2 & no case ground & your h2 connection fails your tx case is at line potential that is why we connect them this way
As far as delta primary I have no experience with them, but I would have thought that there would be a pole ground connected to the case just to keep everything at the same potential in case you touch the tx

[BigClive]

From what I've been told, they do not ground any single phase in California. Not certain about reclosers etc... They cover every bolt with plastic to protect climbers from coming in contact with any bolts. I believe they give the customer a ground reference at their meter panel.

If they actually do that I wonder what their justification for doing so is. I'd have thought that a grounded pot was the first line of defense against an internal failure or external contact by primary. Without a clean short to ground the risk of the whole can being energised at primary voltages could lead to pole damage through tracking from the pots bracket or perhaps worse still, the primary arcing onto the secondary connections due to the lower amount of insulation on the secondary connections and a high fault current seeking earth through the properties ground.

Perhaps this is a misinterpretation of seeing plastic caps on stud ends used to protect climbers from being cut on sharp thread ends? (Nothing quite like a chop saw for leaving the end of threaded rod razor sharp.)

Then again... I have noticed that interpretation of electrical regulations varies widely between different states in the US.

There's nothing quite like grounding of plant to start an interstate flame war.

[lewy]

On a 2 bushing tx you should loop from H2 to X2 for safety reasons, the tx will work with or without the loop, but the case ground should be seperate, again it will work without the case ground it is just there to keep the case at ground potential.
You are using 1 for your neutral which will have current flow & the other for your case ground which under normal conditions should have no current flow

[johnbellamy]

I"m not really a fan of Single Bushing Transformers, I've hung a bunch, but don't really like them. Honestly? I've always thought they were a cheap way of not using another insulator. And I never "Liked" the concept of the return path....being the whole pot so to speak. No matter how "electrically sound" it may be.

I worked for a Muni in Florida years back, and they used all 2 bushing pots on their 13.8 Wye syestem.

There rule was a "Loop", on all single pots and a "Loop" on the Lighting pot of all Closed or open Delta banks.

We'd go from the pole ground, with #6 Soft drawn, thur H2, down the insulator and across the top of the pot to X2, thru X2, thru the Tank grounding lug, and straight to the Primary neutral. The back tank ground was also connected to the pole ground, and the pole ground....needless to say, was connected to the Primary neutral.

There theory, I think....was never loosing a ground or neutral.

Does anybody do the "Loop" thing anymore?

That was our spec, I still do it today, works for me, others have told me it is not necessary, well alot of things aren't but I do them anyway. The problem is I work in windy territory so the pole ground, system neut connection breaks from wind fatigue. I have worked alot of high neut, 8ft arms single phase and alot of three phase, 10ft arm 4 wire flat construction. So it isn't easy to bring x2 down to a 7ft neut. So when that connection fails from wind fatigue, what happens to the case if you don't have it attatched to the poleground? So guys keep talking about a ground strap attached to x2, but isn't that strap the same potential as the case? So if you loose that broken pole ground high neutral connection, then what happens?

[lewy]

On a single bushing tx with a ground strap , if X2 H2 & your case ground are seperate if any 1 breaks you are still connected because everything is connected to the case you would need all 3 to break in order to have the tx not work & your tx would be at line potential.

[johnbellamy]

If they actually do that I wonder what their justification for doing so is. I'd have thought that a grounded pot was the first line of defense against an internal failure or external contact by primary. Without a clean short to ground the risk of the whole can being energised at primary voltages could lead to pole damage through tracking from the pots bracket or perhaps worse still, the primary arcing onto the secondary connections due to the lower amount of insulation on the secondary connections and a high fault current seeking earth through the properties ground.

Perhaps this is a misinterpretation of seeing plastic caps on stud ends used to protect climbers from being cut on sharp thread ends? (Nothing quite like a chop saw for leaving the end of threaded rod razor sharp.)

Then again... I have noticed that interpretation of electrical regulations varies widely between different states in the US.

There's nothing quite like grounding of plant to start an interstate flame war.

I have grounded every case of every device I have installed for the vary reasons you have stated, That is why I don't get the reasons for not doing it, These "plastic caps" I don't even know while they are installed, the plastic inserts are to protect the threads for when you screw in your case ground lugs, so they are not painted over to keep a cleaner connection.

[ghostdog]

We have single bushing transformers on some of our system, but we replace them when we can. We use all 2 bushing transformers now and it is written in our standards that everything gets "looped".

[BigClive]

We've been forced to install plastic caps over the end of screwed rod (stud) when it's been used in an area where an individual could make head contact with it and get slashed. Having gashed my head open and torn clothing in the past on razor sharp screwed rod I can understand that precaution. This is a situation more prevalent with cut rod as opposed to bolts though.

[lewy]

Thanks lewy, you taught me something. I have a few questions for you, These type of industral banks, they are a wye, delta installation correct? How large are these banks, and do you have any pictures, I would like to see the constuction, it dosen't matter where I travel I can't help but look at other systems, the work quality and constuction, any other info on these type of banks would be appricated.

I am not very good at this picture thing