Can you apply 220.82 optional method for single phase 120/240V 1ph 3-wire high leg delta

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
The incoming service for the multifamily dwelling (12 units) building is 120/240V 3ph 4wire high leg delta. The building has a 40HP 3PH elevator. The voltage between phase B and neutral is 208V. Are you able to supply some of the units with "A-B-N" or "B-C-N" from the high leg delta service like what is usually done with 120/208V 3ph 4 wire wye service? If yes, can you calculate the load per 220.82 for the "A-B-N" or "B-C-N" feeder for each unit? Since only A or C phase can be used for the 120V loads in "A-B-N" or "B-C-N" feeder, the loads won't be balanced between A and B or B and C. Is it still reasonable to apply 220.82 when calculate the load and size the feeder? But 220.82 doesn't say you can't apply it to 120/240V 3-wire service with high leg delta. 220.82 doesn't say you are able to use this method only when you are able to balance the loads between phases.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
I believe you are on the right track however if this is a new building I would strongly suggest that the power company change this out to a 3 phase wye and not a delta configuration. Someone will need to be very careful to not place any 120v circuits on that high leg.
 
Location
Tulsa
Occupation
Electrician
Sorry, use the high leg for one phase feeding the single phase panel in a mfd. 208 to ground Or 208 to grounded conductor since it not a neutral.

As I read it it say single 120/240 or 208 y/120 set of 3 wire so on and so on
Not 120/208/240
May learn something new.
 

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
I believe you are on the right track however if this is a new building I would strongly suggest that the power company change this out to a 3 phase wye and not a delta configuration. Someone will need to be very careful to not place any 120v circuits on that high leg.
Sigh... That's the problem. The utility company says they don't have 120/208V 3ph 4wire wye available for this building. Or something like it will be extremely expensive if you do want to pull the 3ph wye service. I will double check with them.

Did you see some one use a 240V delta 3ph 3W to 120/208V 3ph 4W wye transformer and then supply the units meter bank from the transformer secondary? I find online there is 240V delta 3ph 3W to 120/208V 3ph 4W wye transformer.
 

jim dungar

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Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Just use the A and C phases for your individual unit's 120/240 single phase loads. The unbalance can be addressed by the utility, as it is a common issue with these services.

Only use the B phase for your three phase loads and any large 240V 'house' loads.
 
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zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
I'm ready 2014 by the way. Mine does not have " high leg delta" in 220.82
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The 220.82 only says the total connected load served by a single 120/240V set of 3-wire service or feeder conductors with ampacity of 100 or greater. In my opinion, It doesn't forbid the 120/240V 3-wire feeder coming off from 3ph 4W high leg delta. But I think there will be issue if we apply 220.82 to 120/240V 3-wire feeder from 3ph 4W high leg delta since not able to balance the loads.

Do you guys think 220.5 (A) is talking about this? I think it talks about using nominal voltage in computing.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
View attachment 2557871
The 220.82 only says the total connected load served by a single 120/240V set of 3-wire service or feeder conductors with ampacity of 100 or greater. In my opinion, It doesn't forbid the 120/240V 3-wire feeder coming off from 3ph 4W high leg delta. But I think there will be issue if we apply 220.82 to 120/240V 3-wire feeder from 3ph 4W high leg delta since not able to balance the loads.

Do you guys think 220.5 (A) is talking about this? I think it talks about using nominal voltage in computing.


I disagree. It states that section applies to a single 120/240 or 208Y . This means a delta cannot be used but that section is for a single dwelling not multi-family

220.5 is just about nominal voltages
 

jim dungar

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Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
View attachment 2557871
The 220.82 only says the total connected load served by a single 120/240V set of 3-wire service or feeder conductors with ampacity of 100 or greater. In my opinion, It doesn't forbid the 120/240V 3-wire feeder coming off from 3ph 4W high leg delta. But I think there will be issue if we apply 220.82 to 120/240V 3-wire feeder from 3ph 4W high leg delta since not able to balance the loads.

Do you guys think 220.5 (A) is talking about this? I think it talks about using nominal voltage in computing.
This section applies if you only bring A and C phase (120/240V 3W) to each dwelling unit.
 

zemingduan

Member
Location
Philadelphia,PA
Occupation
Electrical Designer
I disagree. It states that section applies to a single 120/240 or 208Y . This means a delta cannot be used but that section is for a single dwelling not multi-family

220.5 is just about nominal voltages
Could any one explain to me does the 120/240V here only refer to the 120/240V 1ph 3W wye? Or it can also refer to 120/240V 1ph 3w from high leg delta? Shall it be written as something like 240Y/120V if it only refers to 1ph 3W wye? Do I miss some rules?
 
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Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Why 208v> It is still 240v between phases. 3ph 4 wire Delta is all you need to know. Somehow on the plans you need to communicate that the high leg should not be run to the apartments.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I think the point here is : Does the 120/240V here only refer to the 120/240V 1ph 3W wye? Or it can also refer to 120/240V 1ph 3w from high leg delta?
The 120/240V does not refer to a wye, it refers to the common single phase service voltages provided to most residences. As Jim points out, with a high-leg delta A-N-C should be used to provide the "nominal voltage" of 120/240 specified in 220.5(A). Often the utility will have a larger transformer for A-N-C than the other legs if the three-phase loads are relatively small compared to the single phase ones, especially if the transformers are overhead. I'm in agreement with Dennis's comments too.

If you had a 3-wire B-A-N feeder like you mentioned, with 100A of 240V loads across A-B of the high-leg delta and 100A of 120V loads across A-N, then there would be 173A drawn from the A phase feeder conductor due to the 60° between legs of the delta. Doesn't sound like a good idea.
 
Location
Tulsa
Occupation
Electrician
I believe they use 208y so as not to use the high leg which is 208 to ground/ grounded. Other wise it's 120/240 for single phase and single from from three phase delta.

Imagine to load calc on the phase to grounded at 120v if the high leg is the other phase in the single phase load center. For the 240 single phase circuits if high leg is used in this case would it require delta breakers since the slash rating is 120/240.
Back at the service the line to line and grounded would not change for all 120 volts circuit. Since it's mid point grounded between two of the three phases and not neutral between all three.
As mention one big pot and one small one.
At this point I would do an old six wire and problem solved. Size to 120/240 single phase.
Just my thoughts on it.
Still may learn something here if allowed.
I may run some numbers in the next few days to compare.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
The incoming service for the multifamily dwelling (12 units) building is 120/240V 3ph 4wire high leg delta. The building has a 40HP 3PH elevator. The voltage between phase B and neutral is 208V. Are you able to supply some of the units with "A-B-N" or "B-C-N" from the high leg delta service like what is usually done with 120/208V 3ph 4 wire wye service? If yes, can you calculate the load per 220.82 for the "A-B-N" or "B-C-N" feeder for each unit? Since only A or C phase can be used for the 120V loads in "A-B-N" or "B-C-N" feeder, the loads won't be balanced between A and B or B and C. Is it still reasonable to apply 220.82 when calculate the load and size the feeder? But 220.82 doesn't say you can't apply it to 120/240V 3-wire service with high leg delta. 220.82 doesn't say you are able to use this method only when you are able to balance the loads between phases.
You don't run the high leg to the units. You just treat all the units as standard single phase. The house panel gets the 3 phase delta 4 wire just to run the elevator. All the other house loads just go on A and C. . Typically a 3 phase main for the house and single phase meter bank with a single phase main for the apartment loads. The POCO will build xformer bank with one smaller xfrmer for the house panel third leg. This arrangement is fairly common in many small apartment buildings that have an elevator.
I'm guessing the POCO won't give a wye service because they likely don't have the 3rd primary phase nearby.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Could any one explain to me does the 120/240V here only refer to the 120/240V 1ph 3W wye? Or it can also refer to 120/240V 1ph 3w from high leg delta? Shall it be written as something like 240Y/120V if it only refers to 1ph 3W wye? Do I miss some rules?
There is no such system as a 120/240 wye or a 240Y/120 systems, they go against the laws of physics.

Yes, you can get 120/240 1P3W by using only two legs a 240V high leg delta. There is nothing special or unique about this single phase. They are often built from individual transformer which are sized to address a severe unbalanced loading.

It is not uncommon to find 240/120V high leg systems where a single 3-phase panel is used for the large house loads and standard 1-phase panels for the individual units.
 
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