High Leg Delta

tom baker said:
Not here hasn’t been available for 20 years
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I get utility people opening with statements like that.
I deal with it about 1-2 times a year.
I am confident I could get it one in your area and or any part of the US.
 
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tom baker said:
Not here hasn’t been available for 20 years, but in eastern WA it would be different
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tortuga said:
I get utility people opening with statements like that.
I deal with it about 1-2 times a year.
I am confident I could get it one in your area and or any part of the US.
Click to expand...
I inquired about one in Eastern WA near Spokane, for Inland power. They said they could but overhead only, and overhead obviously has size limitations.

Tortuga, I Admire your confidence, but I challenge you to get national grid to provide a high leg delta service. ;)
 
electrofelon said:
I inquired about one in Eastern WA near Spokane, for Inland power. They said they could but overhead only, and overhead obviously has size limitations.

Tortuga, I Admire your confidence, but I challenge you to get national grid to provide a high leg delta service. ;)
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Yeah, they do overhead only because they build it with two different size transformers. Padmounts, if they order them, are limited in unbalanced loads just like the dry types we use. They oversize the center tap transformer, so they don’t have that issue. It’s easy for them to do it that way too, because they are just using two or three 120/240 single phase transformers connected in a delta or open delta configuration. They don’t have to keep an odd transformer that way. Years ago our poco wouldn’t do pad mount 277/480 volt transformers because they had to keep a spare in the yard. They would use pole mounts in a ground enclosure.
 
The 208 is for a couple of single phase loads.

My question was about the validity of the high leg to neutral circuit. If someone where to power a load (say 25 Amps/208) from the a high leg panel(the panel is fed from a step down transformer), will the load operate normally? Just like if were connected to 120/208 3 phase where two hot conductors are powering it ?


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Almost all 208v loads work on 240v, especially 1ph loads.

Using the high-leg to neutral is hard on the transformer.

Will your 240v 3ph loads work as well on 208v 3ph?
 
alixenos said:
The 208 is for a couple of single phase loads.

My question was about the validity of the high leg to neutral circuit. If someone where to power a load (say 25 Amps/208) from the a high leg panel(the panel is fed from a step down transformer), will the load operate normally? Just like if were connected to 120/208 3 phase where two hot conductors are powering it ?


Sent from my iPhone using Tapatalk
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Im sure it would work just fine
 
tom baker said:
Not here hasn’t been available for 20 years, but in eastern WA it would be different
Click to expand...
Last year I took a road trip all up and down Northern California, Oregon and Washington, and I saw open delta out in the countryside everywhere just as I figured it might be. In places it would really be hard to replace with wye because of primary configuration.

Here in PG&E country it is not going away anytime soon.
 
Birken Vogt said:
Last year I took a road trip all up and down Northern California, Oregon and Washington, and I saw open delta out in the countryside everywhere just as I figured it might be. In places it would really be hard to replace with wye because of primary configuration.

Here in PG&E country it is not going away anytime soon.
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Just to be clear, I dont think anyone is saying that POCO is making you change to wye, some are just not offering them for new services anymore.
 
From the Dominion Power Blue Book:

120 CHARACTERISTICS OF ELECTRIC SERVICE

120.1 The Company normally provides the following secondary voltages:

• Single-phase: two-wire 120V. (See Section 350 for two-wire 120V line and two-wire 120V
load wiring, and Section 360 for three wire 240/120V line and two-wire 120V load wiring.)

• Single-phase: three-wire 240/120 or 208/120 volts nominal.

• Three-phase: four-wire 208/120 and 480/277 volts grounded wye.

• Three-phase: four-wire 240/120 open delta* volts nominal.

*The service size for this three-phase four-wire 240/120 volt open delta connection shall be
limited to a total of 200 amps per transformer bank. An open delta connection can create
current and voltage unbalances that could potentially damage the Customer’s equipment.
Certain types of equipment, such as motors and refrigeration compressors, are more suscep-
tible to damage with this type of connection. Upgrades of existing delta connections beyond
200 amps are classified as a non-standard voltage connection.

120.2 Requests for secondary voltages not listed above are considered non-standard voltages.
These must have prior approval from the Company’s Planning or Engineering Standards
departments, as well as approval by the Company’s Metering department.
 
alixenos said:
The 208 is for a couple of single phase loads.

My question was about the validity of the high leg to neutral circuit. If someone where to power a load (say 25 Amps/208) from the a high leg panel(the panel is fed from a step down transformer), will the load operate normally? Just like if were connected to 120/208 3 phase where two hot conductors are powering it ?
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What kind of load is it? resisitive ? Inductive?
Just add 208V*25A (5200VA) to each transformer winding it travels across.
I support the 240D/120 service but I'd never use that 208V in a equipment design.
If its confined into the equipment you might look at a AB or ABB din rail breaker, they are 'straight' rated 240V:
 
This question of supplying line to neutral loads from the high leg of a 120/240 3 phase 4 wire service seems to come up quite often. As discussed here, there are many reasons this should not be done. I've often thought that there shoud be code language to prevent this from even being considered.
As far as this type of service being obsolete, I would beg to differ. Many POCOs still offer this (sometimes as the only option for a given load and area) and in many applications, such as light commercial with limited 3 phase loads it is a good choice for both the customer and the POCO. Many POCOs, if they allow them, will only allow this where their distrubution is overhead because they don't want to use 2 pad mount xformers.
 
I don’t have the experience with this that some of the guys here have, but I remember hearing that, aside from the difficulty with finding a suitable breaker, there is the possibility of transformer overload, if there is an open delta configuration, and there was discussion last time this came up, and I can’t find it now, that the voltage will very often not be stable.

Im not exactly sure why, but hopefully one of the members who knows more about this than me can chime in.

As far as pure function, yes, you can run, say, a 208V single phase motor with a high leg and a grounded conductor. The motor doesn’t care if it’s hot and grounded or hot and hot.

Whether it will work in a facility with other loads on the transformer is what I don’t have the experience to really dive into.
 
LarryFine said:
From the Dominion Power Blue Book:

120 CHARACTERISTICS OF ELECTRIC SERVICE

120.1 The Company normally provides the following secondary voltages:

• Single-phase: two-wire 120V. (See Section 350 for two-wire 120V line and two-wire 120V
load wiring, and Section 360 for three wire 240/120V line and two-wire 120V load wiring.)

• Single-phase: three-wire 240/120 or 208/120 volts nominal.

• Three-phase: four-wire 208/120 and 480/277 volts grounded wye.

• Three-phase: four-wire 240/120 open delta* volts nominal.

*The service size for this three-phase four-wire 240/120 volt open delta connection shall be
limited to a total of 200 amps per transformer bank. An open delta connection can create
current and voltage unbalances that could potentially damage the Customer’s equipment.
Certain types of equipment, such as motors and refrigeration compressors, are more suscep-
tible to damage with this type of connection. Upgrades of existing delta connections beyond
200 amps are classified as a non-standard voltage connection.

120.2 Requests for secondary voltages not listed above are considered non-standard voltages.
These must have prior approval from the Company’s Planning or Engineering Standards
departments, as well as approval by the Company’s Metering department.
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ITs interesting, Seattle city light says the same thing where they only list "open delta" specifically, with apparently no option for a closed delta :unsure:
 
It’s economically better for the poco to use an open delta because it only takes two transformers, and two lines. Most of those type services are in rural areas, so stringing a third line can be costly. As others have said, irrigation pumps for fields and such are usually off the main drag. They are also used for small stores for three phase refrigeration and hvac loads.
 
Birken Vogt said:
Last year I took a road trip all up and down Northern California, Oregon and Washington, and I saw open delta out in the countryside everywhere just as I figured it might be. In places it would really be hard to replace with wye because of primary configuration.

Here in PG&E country it is not going away anytime soon.
Click to expand...
Pacific Graft & Extortion loves it for small 3Ø services.
 
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