Corner Ground Delta

[Joethemechanic]

The rural utility company I work around the most doesn't have any corner ground systems that I am aware of. They made an effort back in the 80's maybe into the 90's to eliminate all of them. Many irrigation services had such a supply. This was a cooperative and publicly owned utility (still is) and part of the benefits of such ownership was they would bring the service conductors out to the equipment served. With irrigation it often was maybe 1500 feet from the source. They didn't do it for free but were doing it for less than any contractor would charge to do the same thing. Little story to understand the situation here. The problem they created when they decided to get rid of corner ground delta was you needed a fourth conductor. Most those long runs I mentioned they buried a fourth individual conductor in the neighborhood of 10 to 20 feet away from the other three for most of the run. This not only creates more impedance during a fault condition but a problem I have run into in more recent years is when locate requests come in for other excavating this fourth grounded conductor doesn't get located and the excavator plows through it not knowing they hit it. I happened to find this when I was locating a underground problem with one of the ungrounded conductors one time more recently. In that process I discovered the grounded conductor was lost as well. End result was it was about 10-15 feet from the other conductors so I knew it was likely a system converted from corner ground delta, the break was right where a fiber line had been plowed in maybe 10 years earlier. My best guess they located the ungrounded conductors using simple 60 Hertz detection function of a locator and had no idea the grounded conductor was not in same vicinity so it was never marked. Makes me wonder how many other of those done like that had been compromised because of other excavation activity and failure to locate said grounded conductor.

If I was doing it the way I wanted and I was out in farm country I think I'd set a pole line and run two phase conductors and a MGN for the medium voltage out to the pump site. Do you think they don't do that because of balance problems. I'm not sure how large of pumps these are. Are we talking deep wells with big line shaft pumps that need to make a lot of head pressure?

 

[tortuga]

If I was doing it the way I wanted and I was out in farm country ..

I have always wondered why so many stick with such a low voltage like 480.
Since the NEC now allows up to 1000 volts as low voltage distribution, I'd promote 1000y/577 or at least 600y/347.

 

[Birken Vogt]

I have always wondered why so many stick with such a low voltage like 480.
Since the NEC now allows up to 1000 volts as low voltage distribution, I'd promote 1000y/577 or at least 600y/347.

I think it might be increasingly restrictive safety standards.

I went to a new 10 story building a while ago where it was all fed from the basement at 120/208. Multiple huge mains. Some of the mains had something like 13 parallel MC going off to distribution.

No transformers and nothing over 120 to ground.

 

[Joethemechanic]

I have always wondered why so many stick with such a low voltage like 480.
Since the NEC now allows up to 1000 volts as low voltage distribution, I'd promote 1000y/577 or at least 600y/347.

They aren't going 1,500 feet at low voltage are they?

We've come a long way since the REA farm services of 80 years ago

600y/347.

They use that a lot up in the Chemical Valley (Sarnia Ontario Canada), don't they?

 

[winnie]

If the pump site is in the middle of the field, with rotating irrigation, then overhead poles might not work well

 

[WD40]

I think it might be increasingly restrictive safety standards.

I went to a new 10 story building a while ago where it was all fed from the basement at 120/208. Multiple huge mains. Some of the mains had something like 13 parallel MC going off to distribution.

No transformers and nothing over 120 to ground.

Agreed we had a project here changed at the last minute from 480 to 208 the reason was the NFPA 70E, @480V staff would have had to wear a moon suit to open a panel.

 

[kwired]

If I was doing it the way I wanted and I was out in farm country I think I'd set a pole line and run two phase conductors and a MGN for the medium voltage out to the pump site. Do you think they don't do that because of balance problems. I'm not sure how large of pumps these are. Are we talking deep wells with big line shaft pumps that need to make a lot of head pressure?

A majority of those pumps are 60 to 100 HP. There is occasionally a 125 HP. I've seen 200 HP but never wired one up new. There is also occasional 20 to 50 HP pumps, mostly where higher water table exists and they only need to pump volume and not raise the water much. Pressure can vary depending on sprinkler package design, but most tend to be designed between 40 and 60 PSI as their optimal pressure. But depth of water and flow rate is biggest factors in determining what size of motor is needed.

Where I live my domestic water well has the pump at about 150 feet deep, the static water level last time I checked was around 120 feet down. Then there is a place about 4 miles away from me where in a wet season the static water level is above grade in some low areas and water just stands there.

 

[Joethemechanic]

A majority of those pumps are 60 to 100 HP. There is occasionally a 125 HP. I've seen 200 HP but never wired one up new. There is also occasional 20 to 50 HP pumps, mostly where higher water table exists and they only need to pump volume and not raise the water much. Pressure can vary depending on sprinkler package design, but most tend to be designed between 40 and 60 PSI as their optimal pressure. But depth of water and flow rate is biggest factors in determining what size of motor is needed.

Where I live my domestic water well has the pump at about 150 feet deep, the static water level last time I checked was around 120 feet down. Then there is a place about 4 miles away from me where in a wet season the static water level is above grade in some low areas and water just stands there.

Yeah I worked on a few deep municipal wells. 0.433 PSI per foot just to get the water to the top. And that is just static, there is a "friction head" to also consider. Flow in the pipe is turbulent, not laminar, so friction head can be significant. Almost all the municipal wells were line shaft with a large electric motor at the top and hundreds of feet of shafting with threaded couplers. Ratchet on top of the motor to prevent reverse rotation. Last thing you need is to spin them the wrong way and undo the couplers and maybe even have to pull the pump

 

[ptonsparky]

Did a small village well that pumped to a tower. Started it up and the clay valve started to move away from the well head. Talk about sh..your pants... The valve was plumbed wrong.

 

[kwired]

Almost all the municipal wells were line shaft with a large electric motor at the top and hundreds of feet of shafting with threaded couplers. Ratchet on top of the motor to prevent reverse rotation. Last thing you need is to spin them the wrong way and undo the couplers and maybe even have to pull the pump

Most these irrigation wells are the same thing

 

[hillbilly1]

Agreed we had a project here changed at the last minute from 480 to 208 the reason was the NFPA 70E, @480V staff would have had to wear a moon suit to open a panel.

Bad engineering there, clearing time is the biggest factor, not voltage. I’ve seen 120/208 volt panels have a higher rating than the 277/480 volt panel next to it.

 

[Joethemechanic]

They are really taking all the fun out of work. Remember when working hot was normal? And you could close medium voltage switchgear by taking a shot of Jack, saying 3 Hail Marys, and taking a deep breath and holding it in?