High Leg Delta

electrofelon said:
Right and like I said in that thread, we usually don't even know which is the open phase, I've never worried about it, never seen a problem. Just to me these issues seem like something we are concerned about on forums, but in practice it's not an issue and no one ever worries about.
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Yeah here if the customer fails to notify the utility of any changes in load over 5kw and overloads a transformer they are responsible.
Its pretty rare like most accidents I agree with that,
but I should mention I have seen probably a half dozen situations where a commercial / industrial customer overloaded a transformer bank to failure. Most were 480/277 but some were 240 open delta.
The utility did charge then sue the customer for the cost of the emergency transformer replacement.
Customers insurance looks to EE's insurance for subrogation 'errors and omissions' of design.
 
wwhitney said:
That would be the high leg (B), and the open phase on a high leg open delta will certainly involve that high leg, but it may not be obvious which other leg (A or C) is on the open phase.

Cheers, Wayne
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Oh, you must mean which of the A and C phases is not connected to B through a transformer coil. I see that now.
 
tortuga said:
Yeah here if the customer fails to notify the utility of any changes in load over 5kw and overloads a transformer they are responsible.
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In 5 kW cumulatively or in a single load/appliance? That could be like four space heaters for an office in winter time or even one EV plugging in temporarily to charge. If the load is only through standard 120 V outlets or existing circuits, are they still on the hook?
 
hillbilly1 said:
That’s what I said. Delta 480 systems are not that common anymore.
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Some places they are non existent - as a POCO supplied source anyway. The few corner grounded ones I am aware of are not on the POCO system that I live in and do most my work in, but most of them I know of are in one that is nearby and I do a fair amount of work there as well. They won't install a new corner ground service but still have some old ones around. 480 delta with high leg is common around here though, and other than an occasional older system is always an open delta arrangement serving a limited load. Like a center pivot irrigation system but not the well - those often only need maybe 10kVA at the most, and often only for short time when they do.
 
kwired said:
Some places they are non existent - as a POCO supplied source anyway. The few corner grounded ones I am aware of are not on the POCO system that I live in and do most my work in, but most of them I know of are in one that is nearby and I do a fair amount of work there as well. They won't install a new corner ground service but still have some old ones around. 480 delta with high leg is common around here though, and other than an occasional older system is always an open delta arrangement serving a limited load. Like a center pivot irrigation system but not the well - those often only need maybe 10kVA at the most, and often only for short time when they do.
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Do they have a lot of places around you where the distribution lines only have two phases and a neuter? As I mentioned Seattle City light has tons of open deltas, but I don't think I have ever seen the only two phases and a neutral situation.
 
ggunn said:
Wouldn't the open phase be the one that is 208V to neutral? Several times I have encountered a service like this when applying with the POCO to install a PV system where they wanted me to install it single phase on A and C.
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High leg yes, an ungrounded or corner ground system can be more difficult to determine which two lines are the open end of the delta. Though thinking about it, seems to make sense that they likely would ground the closed corner of the delta to lessen impedance to grounded conductor if anything in a condition where a primary line were opened
 
electrofelon said:
Do they have a lot of places around you where the distribution lines only have two phases and a neuter? As I mentioned Seattle City light has tons of open deltas, but I don't think I have ever seen the only two phases and a neutral situation.
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In rural Oregon yes
 
electrofelon said:
Do they have a lot of places around you where the distribution lines only have two phases and a neuter? As I mentioned Seattle City light has tons of open deltas, but I don't think I have ever seen the only two phases and a neutral situation.
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PG&E typically runs no neutrals so primaries are connected open delta with 3 hots feeding, open delta still by far the most common in rural.

Up in farther north or east California, Oregon, Washington, Idaho, Nevada they all use primary neutrals, any rural service will most likely be an open delta fed with 2 phases.

I don't much leave the wide open spaces of the West so I don't know how they do it elsewhere.
 
There are numerous high-leg open-delta services around here, with Richmond being an older city.

They actually started as 3ph conversions to existing 1ph services for new 3ph loads like refrigeration.

For more info, look up "delta circuit breakers."
 
LarryFine said:
There are numerous high-leg open-delta services around here, with Richmond being an older city.

They actually started as 3ph conversions to existing 1ph services for new 3ph loads like refrigeration.

For more info, look up "delta circuit breakers."
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Yep, delta circuit breakers were a thing decades ago. Been banned now for decades.
 
ggunn said:
What is the difference between a delta circuit breaker and a three pole breaker?
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A delta circuit breaker, now prohibited by the NEC, had an extra pole and corresponding set of line and load terminals. Which let you install a 3 pole breaker in a 2 bus panelboard. Useful when you have only one 3 phase load and are retrofitting a single phase installation with a 3 phase service.

Cheers, Wayne
 
ggunn said:
What is the difference between a delta circuit breaker and a three pole breaker?
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Here is a photo of one & I still have it as a curiosity.

The Elusive Delta Circuit Breaker

QuoteI bought this on eBay. I had seen them in old catalogs, but never laid eyes on one. Use prohibited by NEC section 384-16 (e)beginning with the 1978 edition. The date on the box is May 27 1963, so it's almost as old as I am. NORCAL (edited to post clearer images)...
www.electrical-contractor.net www.electrical-contractor.net
 
ggunn said:
What is the difference between a delta circuit breaker and a three pole breaker?
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it's a 3p breaker with a fourth body attached as the way to get the third line to the line side of the third pole.

Follow the "high leg" which passes behind the pencil point:

1710348819319.jpeg

 
Hello guys
While everyone's on the subject of hi leg delta ...and not to change the subject but....
Any reason why we can use a single phase circuit (2 hot, 1 eq ground) to power our ductless splits at a restaurant renovation with a dated distribution system that were doing
One leg would be the 210 volt hi leg and the other would be A or C
We have space issues with our existing loadcenters so using this configuration would be helpful
There is no need for a neutral and they are rated for 240 volts

Thanks in advance

Bob Majowicz
 
majik009 said:
Hello guys
While everyone's on the subject of hi leg delta ...and not to change the subject but....
Any reason why we can use a single phase circuit (2 hot, 1 eq ground) to power our ductless splits at a restaurant renovation with a dated distribution system that were doing
One leg would be the 210 volt hi leg and the other would be A or C
We have space issues with our existing loadcenters so using this configuration would be helpful
There is no need for a neutral and they are rated for 240 volts

Thanks in advance

Bob Majowicz
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From what I understand it would be better if it's a closed Delta vs Open.
 
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