- Occupation
- Licensed Electrician
If you mean two hots and a neutral then yes.
3 phase 120/208
- Thread starter mannyb
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MAC702
Senior Member
- Location
- Clark County, NV
Don't know. I've never seen that configuration, either, but was just responding the the OP asking about 230/460.
JFletcher
Senior Member
- Location
- Williamsburg, VA
I believe he was writing that a 230V motor rating is for a 240V system voltage, and 460V motors for 480V. in other words, a motor rated for 230/460 will work on a 240V or 480V system, not that there is a 240/480V system.
But I have heard of single phase 240/480. Basically a double voltage 120/240 system. Maybe it was kwired who has mentioned them as used on irrigation pumps/farm use.
A high leg 3ph 240/480 system would have 416V B phase to neutral. Never seen one of those either tho I'm sure there are some around the country for odd/old applications.
High leg deltas are pretty common here in older applications, tho I have not seen any of them in newer apps (newer being mid-80s to today). Never seen a pad mount high leg, they're all old trash cans up on the poles.
What is odd to me is that most of the high leg deltas I can point to exist where 3ph is readily available. I was under the impression high leg deltas are mainly installed where 3ph isnt present, but here it seems to be a matter of adding one transformer to the pole vs 2.
jumper
Senior Member
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Sorry, I meant feeding an open delta, not coming off a high leg open delta.
Feeding the primary side not coming off the secondary.
MAC702
Senior Member
- Location
- Clark County, NV
That makes sense. I remember thinking of that at the time, but drew a total blank about it today, thinking about the voltage system and not the motor itself.
- Occupation
- Licensed Electrician
Now I'm confused. Two hots and a neutral on the primary side of a open delta, yes.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
What neutral on the primary?
https://4.bp.blogspot.com/-yN-8wIZA...pen+delta+or+V+connection+of+transformer.jpeg
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- Occupation
- Licensed Electrician
Yes, they are common for farm irrigation. Use 480V to feed a roto phase that feeds a pivot or a pump or both.
There's different reasons for that. I would think the primary ones being they started as an open delta before the area was upgraded to three phase and the fact that wye systems were not always preferred like they are now.
- Occupation
- Licensed Electrician
I thought you had to have three wires on the primary side of an open delta, just not necessarily three hots.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
:thumbsup:
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
So I understand that one only needs two hots and a neuter for an open delta, but I dont see the logic in a POCO running two phases and neuter. Why not just run three phases? I guess if they want to make it a MGN is that it?
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
I did not know that. I knew you only needed two trannies, but not about using a noodle for the third conductor on the primary.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
I am guessing that the premise is that POCO has 1 phase and a neutral feeding a tranny existing.
Add one phase conductor and one tranny and you have an open delta 3 phase.
I am a bit fuzzy on how exactly this works, but I only work off the secondary side so I ain’t gonna worry too much.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Stumbled across Seattle City Light's construction document for open deltas.
http://www.seattle.gov/light/engstd/docs2/0125.02.pdf
It appears they feed them with two hots and neutral, even if they have all 4 wires. They have some good jargon too: "Teaser" and "Lighter" for the transformers
http://www.seattle.gov/light/engstd/docs2/0125.02.pdf
It appears they feed them with two hots and neutral, even if they have all 4 wires. They have some good jargon too: "Teaser" and "Lighter" for the transformers
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
You are looking at the secondary connections. That document is a little unclear because they show two primary connections, not the third, then they discuss the neutral in context with the secondary. SCL is one of the few places that will derive a 240/120 3 phase 4 wire service from an open delta bank. I had one at my shop in Seattle, it confused people a lot, even me, because it’s somewhat rare. But there STILL must be 3 primary phases. The open delta just saves them the cost of one transformer.Stumbled across Seattle City Light's construction document for open deltas.
http://www.seattle.gov/light/engstd/docs2/0125.02.pdf
It appears they feed them with two hots and neutral, even if they have all 4 wires. They have some good jargon too: "Teaser" and "Lighter" for the transformers
As to 240/120 3 phase 4 wire services in general, utilities that still offer it will often limit the 120V loading to 5% of the total load, because it is inherently unbalanced. The intent of that service is for customers with MOSTLY 3 phase loads who need a SMALL amount of 120V lights and receptacles, NOT the other way around. If most of the loads are single phase with a few 3 phase, they will want you to accept 208Y120 and balance the loads. MOST 230V motors 5 HP and under are designed to allow for 208V input, but if not, use buck-boost transformers for them.
MAC702
Senior Member
- Location
- Clark County, NV
Are you saying most will be labeled as such, or most that are labeled 230 are still okay on 208?
Most of the motors I install in HVAC equipment are so designed, but it says 200-230 on the label.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Okay, I got some people saying that the open delta is fed with two phases and a noodle.
Another just said it is three phases.
Anyone know exactly which is correct?
We all agree that it is only two trannies.
Another just said it is three phases.
Anyone know exactly which is correct?
We all agree that it is only two trannies.
mivey
Senior Member
Open delta to delta requires three phases.
Open wye to delta requires two phases and a neutral.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
I am not an expert on this stuff, but how can you make three phase out of single phase? Split phase by inversion, sure, but 120 degree phase separation? How?
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