Open delta question

tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
240v said:
I'm sorry guys this probably has nothing to do with what you're discussing
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You should start a new thread, sounds like a normal ungrounded delta.
Back to the OP:
electrofelon said:
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. On top of all that, I just not sure I have the energy right now to deal with Seattle City light 🥺
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I think you have a good case for the POCO making it a closed delta.
When do it with reluctant utilities here the customer pays for the transformer upgrade.
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
240v said:
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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That confirms it for me.
It’s a corner grounded delta 240 bank.
It’s either intentionally grounded at the utility bank OR it’s unintentionally grounded somewhere after the point of delivery
 
2

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
LarryFine said:
Read post #29.
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So I'm still not following are my readings normal or do I have a problem. Everything I've watched about Delta and Y and single and 3 phase mention getting other voltage either it being 480v 208v there just seems to be other voltages that can be achieved anyway is there anything I need to be concerned about with this type of system
Hv&Lv said:
That confirms it for me.
It’s a corner grounded delta 240 bank.
It’s either intentionally grounded at the utility bank OR it’s unintentionally grounded somewhere after the point of delivery
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Ok thank you so much. Am I going to have issues with it or what I described is normal and it's business as usual. I'm wondering why I was told this is a ungrounded system if it's actually corner grounded or maybe I'm just not understanding the whole grounding thing. When I think of a ground I expect to see a ground wire or would it just be grounded at the main cause in the control panels I see the ground wires and neutrals connected to the panel wall which I didn't think you were supposed to connect neutral and ground except at your breaker box. So I need to read up on a corner grounded Delta 240v bank
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
240v said:
So I'm still not following are my readings normal or do I have a problem. Everything I've watched about Delta and Y and single and 3 phase mention getting other voltage either it being 480v 208v there just seems to be other voltages that can be achieved anyway is there anything I need to be concerned about with this type of system

Ok thank you so much. Am I going to have issues with it or what I described is normal and it's business as usual. I'm wondering why I was told this is a ungrounded system if it's actually corner grounded or maybe I'm just not understanding the whole grounding thing. When I think of a ground I expect to see a ground wire or would it just be grounded at the main cause in the control panels I see the ground wires and neutrals connected to the panel wall which I didn't think you were supposed to connect neutral and ground except at your breaker box. So I need to read up on a corner grounded Delta 240v bank
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On an ungrounded delta, one phase can fault to ground and nothing happens. the second phase faulting though will trip something..If it is TRULY ungrounded at the transformer bank, then its faulted or an electrician many years ago grounded one phase of it.
 
2

240v

Member
Location
Cincinnati Ohio
Occupation
Maintenance electrician
mtnelect said:
Why not install the customary three transformers instead ?
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I don't know out of my pay range but this place still has most equipment running on cabinets of relays and stuff and from what I understand cause of the chemical and gas procedures this system is less likely to experience interruption due to a fault. I honestly don't know why they don't run 480v it's more efficient easier on equipment cheaper. It is a small business only around 30 people for all 3 shifts but if you can help with a argument why we should switch to 3 transformers or 480v then I'm all ears but I don't think they will cause of down time and the way it is now is grandfathered in and they think it's ok the way it is but it's a nightmare I don't know how half the stuff is even working but it's what I have to work with I'm just struggling to understand it. In the end it's a three wire system and I'll treat it as such and I'll try to learn as much as I can about it
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
tortuga said:
You should start a new thread, sounds like a normal ungrounded delta.
Back to the OP:

I think you have a good case for the POCO making it a closed delta.
When do it with reluctant utilities here the customer pays for the transformer upgrade.
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I agree. 240 please start a new thread if you wish to continue your discussion.
 
M

MTW

Senior Member
Location
SE Michigan
@240v Here is a video for you that covers the basics of different types system's grounding, to give you a better understanding of all the different types from a basic perception level, covers the code issues and the reasons why or why not.
It;s not an exhaustive source of information but gives you the basic's of the different types of systems.


And I agree, you need to start your own thread, for clarity for yourself and others who may come across it later, as well as not to clutter the discussion that was preceding your arrival at this thread. You will learn better, keeping your questions to one thread on one forum, and this is the place to be for the learning curve your faced with at the present.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
240v said:
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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What are your voltages to ground?

It sounds like your system started out as ungrounded but over the years it has had L1 get a poor connection to ground, thus becoming a corner grounded system.

What is a concern is the conductor you are calling 'neutral'. Are you sure this is not actually an intentionally grounded conductor via an electrode like a ground rod?

Corner grounded systems need special breakers. Fuses cannot be used on the grounded conductor.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
mtnelect said:
Why not install the customary three transformers instead ?
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tortuga said:
Fellon said the POCO was not offering a full delta for some reason.
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Correct Seattle city light does not say they offer closed delta in their spec book. I have not yet investigated whether they make exceptions. I suspect if it came down to it they would just make it a larger open delta, maybe a 167 and 100
 
B

Birken Vogt

Senior Member
Location
Grass Valley, Ca
Did it get addressed in the thread, if you load the lighting pot to 416 amps and the power pot to 208 amps, how much current is flowing on the corner that they share in common?
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
ptonsparky said:
Someone should correct me if I'm wrong, but I believe about 550.
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Yes, if the 208 and 416 amps are both at the same phase shift with respect to their voltages, e.g. both resistive.

550 = 208 x sqrt(7). Use the law of cosines for a 60 phase difference.

Cheers, Wayne
 
kwired

kwired

Electron manager
Location
NE Nebraska
LarryFine said:
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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You might be correct, though NEC would require the grounded conductor to be identified with white or gray all the way through the system.

What he may really have is possibly the conductors marked blue should be marked white and the conductors marked white (that are on load side of the service disconnect) should be marked green.

Many get confused when the grounded conductor is not a neutral conductor for some reason. It is kind of a rare situation so that doesn't help.
 
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