400 amp service 3 ph 120/240 b ph high leg
- Thread starter Teddy714
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Sounds Kosher, as long as your POCO approves.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Our POCO no longer installs hi leg services
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Any idea why?
ptonsparky
Tom
- Occupation
- EC - retired
A WAG. They have three primary phases available every where?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Probably everything new is now pad mount, and they don’t want to keep those in the yard because they are not used much anymore. I know of lots of delta’s where all three phases are present. Mostly small industrial parks now where equipment is 240.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I believe it's inefficient electrically, and the main reason it ever existed has diminished over the years.
kwired
Electron manager
- Location
- NE Nebraska
Put up to six mains if you want, that been the rule for a very long time.
Starting with 2020 NEC however they must all be in separate units or separate sections of a switchboard.
Liability and ease of installations.
There are many of these high leg banks connected wrong between the metering requiring it on the right side and the breaker panel requiring it in the middle. I see it often..
Adding to that there is the possibility of the POCO connecting it wrong on an overhead service when it gets torn down, it has happened before.
A lot of linemen don’t understand it, whether it’s a two pot or a three pot installation.
Many POCOs (mainly IOUs) have simply went to 120/208 or 277/480. You want something different, you do the conversion..
I wish the CEO here would do that.
We have open delta in two and three pot configurations, single transformers feeding 480 for lighting,
two transformer 120/208, three transformers feeding both 120/208 and 120/240 split phase, and even have one spare transformer for one tower that runs a special voltage around 515
corner grounded deltas, and center grounded 480 deltas
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Actually it’s more efficient, less voltage drop due to higher voltage, smaller transformers can be used for the same load. The reason it’s not used as much anymore is only 2 out of 3 phases can be used for 120 volt loads. Most industrial now start with 480 volt services, as costs to install those have dropped.
kwired
Electron manager
- Location
- NE Nebraska
Here rural POCO's typically still offer 120/240 high leg delta, mostly only for pole mounted sources on new installs, they typically don't want to put more than 50kVA (individual units) in a bank on a single pole though. Upgrading something existing with padmount is more of a case by case thing.
There is a lot of limited load 480 volt services (mostly center pivot irrigation systems with other power sources for pumping water) on the system and they still install many two pot 480 volt open delta for those services for those even if all three primary phases are on the same pole. Demand on these services is not really all that much. When watering you only have 1/3 to 1/2 hp motors that run maybe 2 or 3 motors at one time and even then only for a few seconds at a time.
That’s for voltage regulation
Large loading across two coils results in uneven voltages.
- Location
- Illinois
- Occupation
- retired electrician
Can you expand on that? If you have a 25kVA load, you need 25kVA of transformer.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
The amperage is lower in the windings, With a wye, the voltage shifts, with a delta, the amperage shifts. I will have to dig up the diagram showing that. It may also be in an Ugly’s book.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I wonder what the cost threshold is for a PoCo to replace a high-leg with a wye-connected service if the customer wants that. On the one hand, it's installed-base and you don't mess with something that's working. OTOH if the PoCo actively doesn't want to support high-leg services and the customer is willing to pay their costs to change, when does the PoCo say "OK, we'll change it at no charge to you."
From the PoCo side-
the service conductors might or might not change
the feeding transformers might change (but not if there's enough wye capacity already)
various record need to be changed & inspections happen
does the metering change at all?
From the PoCo side-
the service conductors might or might not change
the feeding transformers might change (but not if there's enough wye capacity already)
various record need to be changed & inspections happen
does the metering change at all?
??
Not sure what your trying to say here..
These banks are only for large single phase and SMALL three phase loads.
you overload one of these with three phase motors your voltages will be all over the place. Too much voltage imbalance causes increase of negative sequence currents.
Motors heat up and burn out quicker.
The bank is little more than a cost savings scheme for a POCO to not install a third transformer to serve nothing more than say a couple of 5-10HP motors.
once you get to about 35-50HP motors the delta needs to be closed up.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Yes, I was talking about closed delta’s. Yeah, as you said, open delta’s are used for small three phase loads with the majority of loads being single phase.
kwired
Electron manager
- Location
- NE Nebraska
They typically don't want more than 50 kVA units in three transformer banks either.
The still install single 75 and 100's on a pole for a single phase service though.
Pretty sure this aspect is a little more about weight and size of pole vs cost to build something that will handle it starts to even out or even become less cost to install a padmount transformer.
No, it isn’t. Look at #16
I just did a 300kVA 240 delta, with a local utility.
Side note on terminology I think we should use 'open delta' if we mean open delta and take 'delta' to mean closed delta.
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