how many amps do i need to feed (50) 100 amp single phase panels. Future condos

[Gartz]

Hello My question is we are trying to figure out how many 1 phase 100 amp panel can be fed from (2) existing 400 amp fused discos. The existing service is 120/240 3 phase delta. therefore we can only use 2 of the three legs hense single phase service. The building was old school being changed to condos. the builder wants (50) meter cans feeding (42) services for now and we want to run cable tray with ser. are there issues with using ser in that enviroment.

 

[Dennis Alwon]

What is the calculated load. You can have a hundred sub panels from a 400 amp service if the load is 400 amps or less

 

[cdslotz]

50x100 = 5000 amps

 

[Gartz]

The main question i have is how do i calculate my connected load for these 100 amp services.

 

[kwired]

I would be contacting POCO to see if we can get this changed to a 120/208 wye system.

400 A @ 240 single phase = 96 kVA High leg is likely almost useless to you for dwellings.

400 A @ 208 three phase = 144.1 kVA. Similar amount of total power you would get from a 600 amp single phase supply.

It is not a question of how many panels can be fed, it is a question of what is the total load calculation. If each panel has a small load on it then there can easily be more panels.

If your load calculation exceeds 96 kVA you have a problem with what is existing - especially if none of the load will be placed on the high leg.

If your load calculation is less than 144 kVA you may still have sufficient existing supply conductors, switchgear, etc. but the wrong system supplying it to be able to use it.

 

[Gartz]

Yes i agree this should be changed to 120/208 y to get most out of service. It is a very old service with (2) 100k cans and (2) 50k cans feeding existing service mains. i think that using art 220 i can get away with a 2000 amp service to feed (50) 100 amp 1 phase panels for multi family dwelling

 

[Dennis Alwon]

The only problem with the wye is that you have to make sure all the equipment is rated for 208V. There is stuff out there but not as common as 240V. I would also see if you can get it changed to a wye but in terms of calculations I can only say that the high leg-- if used, will only be good for the 240V equipment. In terms of calculations with a high leg I would basically ignore the high leg and calculate the load as single phase.

Is each apartment being fed with single phase or 3 phase. What type of equipment is being installed and how many circuits. I am not even sure you can feed a single phase panel with a high leg as one of 2 phases employed-- not sure the NEC says that but I have never seen it done

 

[augie47]

Once you settle on your service voltage, devote some time to 220.84.
Performing some wild guess numbers, on a 208/120 3 phase system you might squeak by wit (2) 400s. On a 240/120 single phase its going to be more like (2) 600s or larger but the devil is definitely in the details here.

 

[mbrooke]

Im willing to give a rough guess of 1000amps 3 phase wye minimum. 1,600 single phase.


Check with the poco and transformer about placing such a large load on only 2 legs. In some areas pocos do not allow a high current single phase service.


As for getting 208 on equipment I do not see it as a major issue since for residential appliances it usually means just reduced output. An all gas appartment wye is a no brainer.

 

[PEDRO ESCOVILLA]

take the floor plans for the future condos, look at the electrical prints, figure all appliances, receptacles, etc as per article 220, look in annex D , for examples on how to do load calcs, try to get as realistic a picture as you can for each unit ( not some pie in the sky number), and go from there. theres a lot you can do for derating based on the number of units, etc ( for feeders and service sizing) good luck