Open delta question

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at a old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
L1 is either intentionally or accidentally grounded. If intentionally, it should be treated as a neutral.

L1 may be switched or go through a 3-pole breaker, but should not go through an individual fuse.
 
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at a old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
Hold on, what is this "neutral" you are measuring to?
 

MTW

Senior Member
Location
SE Michigan
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at a old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
Read up on corner grounded systems. They were common back in WWII plants. Not too many still in existence today.
Once Wye systems became prevalent newer trade workers never had the occasion to learn about them. Seems very strange at first when you connect one of the phase legs to ground. But it used to be a popular method. Your facility may have corner grounded or an ungrounded delta system . Use your search engine to study up on both types of systems. It can make your job much easier and safer if you understand the differences in both types of systems.

Some starter links for you.

https://forums.mikeholt.com/threads/corner-grounded-delta-madness.34504/

https://duckduckgo.com/?t=ftsa&q=corner+grounded+delta+explained&ia=web
 

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
L1 is either intentionally or accidentally grounded. If intentionally, it should be treated as a neutral.

L1 may be switched or go through a 3-pole breaker, but should not go through an individual fuse.
There's 4 wires red black blue and white and everything is working it's just really confusing me. So what would I do with the neutral if I treat the other as a neutral and wouldn't I have to track the circuit to see how it was used in other systems. There's 3 wires going to the contacts red black and blue or sometimes white. Are they interchangeable. Also why don't I get 480v when I test the two 240v lines together like you do when you test two 120v lines. I also looked at our transformer coming into the building there is only one hooked to three primary poles and each one has their own little unit attached to the outside of it looking like there's one each attached to a primary in series.
L1 is either intentionally or accidentally grounded. If intentionally, it should be treated as a neutral.

L1 may be switched or go through a 3-pole breaker, but should not go through an individual fuse.

Hold on, what is this "neutral" you are measuring to?
It is connected to the neutral bus that in some parts of the plant are connected to the ground also it's like they use the blue and white wire interchangeably
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at an old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
As stated above, it’s a corner grounded bank.
You say neutral.. what exactly are you measuring to? Or is it a bond?

I expect to see l-l 240,240,0
 

Birken Vogt

Senior Member
Location
Grass Valley, Ca
Is this a utility supplied open delta or something like an in-plant 480 -> 240 transformation?
So this is utility supplied, which makes for an interesting decision process. In these cases we have to decide whether to design around distributing loads for conductor ampacity or transformer capacity. OF course some will say the utility transformers are not our problem, but in practice there are cases when we want to avoid utility hassles, costs, and upgrades, so maybe we want to have some concern for the transformer loading.
That's where I was going, my answer was going to be, who cares. But you may have reason to care.

At my work we have a 50 kva pot for lighting and 25 for power. This is a pretty big open delta. But the actual loads are maybe 1- 5HP air compressor, 1- 5HP exhaust fan on 3 phase. A couple of air conditioners and a propane dispenser distributed across the high leg, single phase, all else is on the low pot. We don't know which phase is real and which is phantom.

Utility tx have a very large overload capacity, several hours per day.

How big are the tx now, if they exist yet?

I agree if you know which ones are real you can spread the 1ph loads across the two but I would just put them all on the low tx and be done with it, that way everyone understands how it works.
 

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
There's 4 wires red black blue and white and everything is working it's just really confusing me. So what would I do with the neutral if I treat the other as a neutral and wouldn't I have to track the circuit to see how it was used in other systems. There's 3 wires going to the contacts red black and blue or sometimes white. Are they interchangeable. Also why don't I get 480v when I test the two 240v lines together like you do when you test two 120v lines. I also looked at our transformer coming into the building there is only one hooked to three primary poles and each one has their own little unit attached to the outside of it looking like there's one each attached to a primary in series.



It is connected to the neutral bus that in some parts of the plant are connected to the ground also it's like they use the blue and white wire interchangeably
I get 240v from line 2 or 3 regardless if I test from the line one to 2 or line 1 to 3 or line 2 to the white taped wire hooked to the neutral bar or line 3 to neutral I still only get 240v hot line 2 to hot line 3 instead of 480v unlike in residential when you measure the two 120v lines and get 240v. I'm assuming the two 240v lines are 180 out of phase that's why it still reads 240v across both the hots unlike the two 120v lines in phase. If the two 240v lines were in phase I'd get 480v right
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
No. To put it simply, the three 240v secondaries are connected in a triangle, not a straight line.

My first guess is the grounded phase is white where unswitched and blue where switched.

I suggest searches for things like "1 phase vs 3 phase" and "wye vs delta" and similar terms.

The only thing that makes a conductor X volts to ground is another conductor being grounded.
 
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I get 240v from line 2 or 3 regardless if I test from the line one to 2 or line 1 to 3 or line 2 to the white taped wire hooked to the neutral bar or line 3 to neutral I still only get 240v hot line 2 to hot line 3 instead of 480v unlike in residential when you measure the two 120v lines and get 240v. I'm assuming the two 240v lines are 180 out of phase that's why it still reads 240v across both the hots unlike the two 120v lines in phase. If the two 240v lines were in phase I'd get 480v right
I agree with the others your voltages sound like a corner grounded system, but it doesn't seem to be set up right. Corner grounded system should look like single phase, but your service conductors consist of four wires? Can you see what happens to the white wire as you trace it upstream to the utility transformers? Could be you have two grounded conductors.
 
That's where I was going, my answer was going to be, who cares. But you may have reason to care.

At my work we have a 50 kva pot for lighting and 25 for power. This is a pretty big open delta. But the actual loads are maybe 1- 5HP air compressor, 1- 5HP exhaust fan on 3 phase. A couple of air conditioners and a propane dispenser distributed across the high leg, single phase, all else is on the low pot. We don't know which phase is real and which is phantom.

Utility tx have a very large overload capacity, several hours per day.

How big are the tx now, if they exist yet?

I agree if you know which ones are real you can spread the 1ph loads across the two but I would just put them all on the low tx and be done with it, that way everyone understands how it works.
The lighter is a 100 and the teaser is a 50. Everything is fine right now, but they are still building out the building and adding things, and one floor I don't even have a plan yet. I'll just keep an eye on the loading and see what happens. The reason I am caring more than I normally would about this one is upgrading the service would be really problematic. There is just not room for a vault and even adding a pole would be very difficult. The existing serving Pole is a fair ways away and the conduit goes under the street which then enters the building under a concrete ramp. On top of that the meters are inside which they do not like, and I'm nearly certain they would make me move the meters outside to do any changes to the service. The service lateral is a single set of 500 AL which is sized about right to those transformers so they probably can't really upgrade the transformers without upgrading the lateral. On top of all that, I just not sure I have the energy right now to deal with Seattle City light 🥺
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at an old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
Ok. I know there are a couple of posts after this, but..

1) what color is L1, L2,L3, and of course the white wire.
Example.
L1 is red
L2 is blue
Etc..

Once you have that, then list the voltages
Example
L1 to L2 240V
L1 to white 240V
L2 to white (5V or nothing)

Where I’m going here is a corner grounded delta with a fourth wire added that is tied together somewhere.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Grounded deltas have EGs, or should. The 4th wire. Someone used the EG and Grounded Conductors interchangeably because they went to the same place at the service. No different than when we come across whites being used as EGs or greens as Neutrals in a residential setting.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Grounded deltas have EGs, or should. The 4th wire. Someone used the EG and Grounded Conductors interchangeably because they went to the same place at the service. No different than when we come across whites being used as EGs or greens as Neutrals in a residential setting.

What I’m also wondering here is similar to what your saying.

The fourth wire, is it solidly connected to the corner ground
OR
It there a fault to ground somewhere in the facility that unintentionally makes it a corner grounded bank..
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at a old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
Sounds like normal corner grounded Delta operation.
What I’m also wondering here is similar to what your saying.

The fourth wire, is it solidly connected to the corner ground
OR
It there a fault to ground somewhere in the facility that unintentionally makes it a corner grounded bank..
Could be the 4th was for fault management on an ungrounded delta. But that wouldn't explain a 0V to ground on L1.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
I'm sorry guys this probably has nothing to do with what you're discussing but I'm so confused and I really need help. I work at a old pre fifties factory that is only 240v. There's three lines in l1 to neutral with the meter on volts reads little to nothing sometimes 5v l2 to neutral 240v l3 to neutral 240v l1 to l2 240v l1 to l3 240v line to line still 240v and it's a ungrounded circuit. What is going on with this place.
I am unsure what this system really is. I am leaning towards an unintended grounded system
We need all the possible voltages:
L1 - L2
L2 - L3
L3 - L1
L1 - N
L2 - N
L3 - N
L1 - G
L2 - G
L3 - G
N - G

Our industry slang may be getting in the way again. Many electricians hear '240V and delta' and immediately think of 240/120V 3 phase 4 wire being fed by an open delta transformer bank with a center tap, but this is only one possible system.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Sounds like normal corner grounded Delta operation.

Could be the 4th was for fault management on an ungrounded delta. But that wouldn't explain a 0V to ground on L1.
It does but.
What if the fourth wire was faulted to ground somewhere making it a corner grounded bank where it is originally an u grounded delta?
 

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
I am unsure what this system really is. I am leaning towards an unintended grounded system
We need all the possible voltages:
L1 - L2
L2 - L3
L3 - L1
L1 - N
L2 - N
L3 - N
L1 - G
L2 - G
L3 - G
N - G

Our industry slang may be getting in the way again. Many electricians hear '240V and delta' and immediately think of 240/120V 3 phase 4 wire being fed by an open delta transformer bank with a center tap, but this is only one possible system.
I was told this is a ungrounded system cause of chemicals and gases being used so the process isn't interrupted and this building was built in the 1930s. That being said L1-L2 240v L2-L3 240v L3-L1 240v L1-N? 0-5v L2-n 240v L3-n 240v and that's it only 4 wires 3 black a fourth black with white tape on the end connected on the only bar on the right side. This is the only place I see 4 wires in the control panels there's only 3 black wires numbered 1 2 and 3 or two are marked with red and blue tape on the end being a black red and blue. It seems no matter how I test I only get a 240v reading or 0-5 on the L1-N. I've only done residential and they really only taught us 480v in school for industrial maintenance and other places I've worked were all 480v. I'm just not familiar with this type of system and want to know if I should worry about it at all and just treat it like any other 3 wire system I was just wondering if there was anything I needed to know about this configuration when wiring motor starters controls and stuff and why don't I get 480v between the two 240v lines shouldn't the two voltages combine or does that have something to do with being in or out of phase. Sorry I sound like a idiot but I've only been doing the industrial side for a couple years and this is the first job I was hired as a electrician and to make matters worse I'm the only one on a 3 man maintenance team that has any electrical background at all I would just feel better knowing what kind of system I'm dealing with so I can further educate myself so I can be a valuable member of the team. Thank you.
 
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