Delta calc

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Toros

Senior Member
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Tujunga, CA
Hi
do i need to run a full delta calc to determine the service size for a new built 18 unit apartment bldg where only the elevator is 3- phase
any other short cut
easier way??

thank you
 
Well there are several ways to do it... but it's mainly going to depend on the service(s) configuration. The 3? and 1? can be entirely separate services (or service entrances).


  • 240/120V 3? 4W
  • 208/120V 3? 4W
  • 120/240V 1? 3W
  • 120/208V 1? 3W
  • other
???
 
Smart $ said:
Well there are several ways to do it... but it's mainly going to depend on the service(s) configuration. The 3? and 1? can be entirely separate services (or service entrances).


  • 240/120V 3? 4W
  • 208/120V 3? 4W
  • 120/240V 1? 3W
  • 120/208V 1? 3W
  • other
???
Click to expand...

There will be only one drop, one service , my Friend which is 800A pull-120/240v, 3-ph,, 4-wire, delta
 
Toros said:
There will be only one drop, one service , my Friend which is 800A pull-120/240v, 3-ph,, 4-wire, delta
Click to expand...
You'll end up wasting money if you only have one service entrance.

Even with one drop, one service (NEC), you can do two or more service entrances. One 240/120 3? 4W for the elevator (perhaps house load, too), and one or more 120/240 1? 3W for the rest.

Your calc's would likely only be for each service entrance, while the drop would be on the POCO.

Where will the meter(s) be located in this service?
 
Last edited:
Smart $ said:
You'll end up wasting money if you only have one service entrance.

Even with one drop, one service (NEC), you can do two or more service entrances. One 240/120 3? 4W for the elevator (perhaps house load, too), and one or more 120/240 1? 3W for the rest.

Your calc's would likely only be for each service entrance, while the drop would be on the POCO.

Where will the meter(s) be located in this service?
Click to expand...

Would you explain me more Mr. Smart and associates What to do???? I have new-built , 18-unit apatment, propsed a new 1200A, 3ph, 120/240v, 4wire delta (fed from overhead pole) in los Angeles . Meters are attaced to the main disc.-pull box. are you recommanding that I have to present two calcs, one for 3-phase which is 3-ph. elevator only and one 1-phase load calc for the rest of the building, frankly add both of them for determining final load demand????. Building And Safetey here (to approve the plans) wants red leg delta calc to determine service of pull box based on obtained largest leg Thanks
 
Toros said:
Would you explain me more Mr. Smart and associates What to do???? I have new-built , 18-unit apatment, propsed a new 1200A, 3ph, 120/240v, 4wire delta (fed from overhead pole) in los Angeles . Meters are attaced to the main disc.-pull box. are you recommanding that I have to present two calcs, one for 3-phase which is 3-ph. elevator only and one 1-phase load calc for the rest of the building, frankly add both of them for determining final load demand????. Building And Safetey here (to approve the plans) wants red leg delta calc to determine service of pull box based on obtained largest leg Thanks
Click to expand...
What I'm saying is you can't calculate the load in VA, then determine ungrounded conductor ampacity with 3? calculation. You have to take the apartments' load in VA and divide by 240V, then take the elevator load in VA and divide by 240V?sqrt(3), then add the result of these two calculations to determine the minimum ampacity of A and C lines. The B (high leg) will just be the result of the elevator load calculation (quite likely this value will be substantially lower, for the sake of discussion, let's say 200A). This will satisfy the calculations.

From there we have to get into the practical application of wiring and equipment. Let's say the A and C lines require 1200A wiring and equipment. If you have one service disconnecting means, it will have to be 3? and rated 1200A. That means your service conductor ampacity for the high leg will have to be 1200A as well (possibly feeder too), even though it will only draw less than 200A.

You could install a fused disconnect and use a smaller fuse for the high leg. This would permit you to use smaller wire for the high leg... but fusing is not my area of expertise. I am not certain if you can get a 200A fuse that fits in a 1200A disconnect. If not, perhaps they make reducing adapter... don't know.

Anyway, consider two service entrances: one 3?, one 1?. You'll likely have to go with a 1200A 1? disconnect because of conventional sizing, but you could go with only a 200A disconnect (and wiring) for the 3?. Price out a 1200A 3? disconnect vs. a 1200A 1? plus a 200A 3? and associated wiring...
 
I doubt the utility will be willing to provide a 1200A 240/120 volt Delta service for an apartment building. Normally the building would be fed with a 208/120 wye service and the apartment would be connected to alternating phases. What you are proposing makes no sense.
 
curt swartz said:
I doubt the utility will be willing to provide a 1200A 240/120 volt Delta service for an apartment building. Normally the building would be fed with a 208/120 wye service and the apartment would be connected to alternating phases. What you are proposing makes no sense.
Click to expand...

Sorry that I posted wrong info. about over head feed 1200A 3ph. delta service this service is latheral, under ground from utility vault located in the midle of street.
 
Toros said:
Sorry that I posted wrong info. about over head feed 1200A 3ph. delta service this service is latheral, under ground from utility vault located in the midle of street.
Click to expand...
Where's the service point located? If line side terminals of service disconnect(s), then you have no service entrance conductors. Anywhere prior to that and you do and will affect sizing of service entrance conductors.

Everything else will be as noted in my last post.
 
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