Transformer laterals

[shortcircuit1]

Hello,

I am a little confused with the transformer lateral calculations.

Lets say you have a transformer with 200kVA and you are bringing in 2 laterals from the secondary to two termination cabinets.Each termination cabinet is connected to 6 gang sockets and feeding 6 apartments.Now the demand load for 6 apts is 150kVA. So each lateral that i bring from the transformer can handle only 100kVA?If thats the case then 100kVA@240,single phase would be 416A which wont be enough for apt load.So i need to bring in two laterals from the secondary of the transformer?
Main question is if we bring in 4 laterals from a 200kVA XFMR will the load be 50kVA per each lateral?

 

[MyCleveland]

Hello,

I am a little confused with the transformer lateral calculations.

Lets say you have a transformer with 200kVA and you are bringing in 2 laterals from the secondary to two termination cabinets.Each termination cabinet is connected to 6 gang sockets and feeding 6 apartments.Now the demand load for 6 apts is 150kVA. So each lateral that i bring from the transformer can handle only 100kVA?If thats the case then 100kVA@240,single phase would be 416A which wont be enough for apt load.So i need to bring in two laterals from the secondary of the transformer?
Main question is if we bring in 4 laterals from a 200kVA XFMR will the load be 50kVA per each lateral?

Utility company does the laterals here, so assuming this is customer responsibility for you.
First thought is your load calc is way off. Doubtful you have 150kVA demand for six apartments.

Share some details on how you arrived at the 150 number.

 

[shortcircuit1]

Utility company does the laterals here, so assuming this is customer responsibility for you.
First thought is your load calc is way off. Doubtful you have 150kVA demand for six apartments.

Share some details on how you arrived at the 150 number.

I just took an example. Havent done any calculations.

 

[shortcircuit1]

Utility company does the laterals here, so assuming this is customer responsibility for you.
First thought is your load calc is way off. Doubtful you have 150kVA demand for six apartments.

Share some details on how you arrived at the 150 number.

Utility company has given the maximum XFMR size and its 170kVA. So we have to decide how many laterals we need to serve like will one lateral from the transformer will be enough or two.

 

[Ingenieur]

what is the amp rating of the 6 gang meter rack?
what is each apt feed?
how close are the racks to each other?
how long is the lateral? oh or ug?

 

[shortcircuit1]

what is the amp rating of the 6 gang meter rack?
what is each apt feed?

150A.Not sure if i understand the second question.Feed for meter comes from the termination cabinet ahead of the meter and goes to disconnect and then goes to load center.

 

[MyCleveland]

Utility company has given the maximum XFMR size and its 170kVA. So we have to decide how many laterals we need to serve like will one lateral from the transformer will be enough or two.

Cannot size the lateral until you know your load....just guessing.

Do you have apartment sq footage, appliance list, laundry ??, range...electric or gas, HVAC type, electric hot water ?

 

[shortcircuit1]

Cannot size the lateral until you know your load....just guessing.

Do you have apartment sq footage, appliance list, laundry ??, range...electric or gas, HVAC type, electric hot water ?

Cleveland,

I have done calcs based on loads but just for my knowledge if you are taking two laterals out of the transformer(170kVA) does that mean each lateral is able to handle 85kVA?

 

[MyCleveland]

Cleveland,

I have done calcs based on loads but just for my knowledge if you are taking two laterals out of the transformer(170kVA) does that mean each lateral is able to handle 85kVA?

Your lateral would be sized for your load.
I cannot help on wire tables for open laterals....never spec'ed.
Again, I don't think your load is anywhere where near 170kVA or even half that for six apartments. That is the only reason I keep pushing on checking your calc.

I have to differ on the lateral wire size.

 

[MyCleveland]

Cleveland,

I have done calcs based on loads but just for my knowledge if you are taking two laterals out of the transformer(170kVA) does that mean each lateral is able to handle 85kVA?

I have to differ on overhead cable sizing, never spec'ed or needed to look up tables.

Still believe your load is no where near 170kVA.

 

[shortcircuit1]

I have to differ on overhead cable sizing, never spec'ed or needed to look up tables.

Still believe your load is no where near 170kVA.

Let me rephrase my question if you have two or three laterals from transformer will each lateral have 1/3 kVA of the transformer?

 

[Ingenieur]

150A.Not sure if i understand the second question.Feed for meter comes from the termination cabinet ahead of the meter and goes to disconnect and then goes to load center.

so each apt gets 150 feeder and main lugs are likely 800 or 1000

 

[Ingenieur]

Let me rephrase my question if you have two or three laterals from transformer will each lateral have 1/3 kVA of the transformer?

not that simple
need to size on load and demand

 

[Ingenieur]

Cleveland,

I have done calcs based on loads but just for my knowledge if you are taking two laterals out of the transformer(170kVA) does that mean each lateral is able to handle 85kVA?

no
it is based on load, not the supply
under heavy load the xfmr may supply 250 kva or more

 

[don_resqcapt19]

Utility company has given the maximum XFMR size and its 170kVA. So we have to decide how many laterals we need to serve like will one lateral from the transformer will be enough or two.

If the utility is not supplying those conductors, then they are "service conductors, underground" and are subject to the rules of the NEC. That you mean that you need to size these conductors based on the Article 220 load calculations for the building. (Note this assumes that the utility is saying that you need to install the underground conductors because the service point is the secondary terminals of their transformer.)

 

[don_resqcapt19]

The ampacity of service conductors sized per the rules in the NEC will likely be at least twice the secondary full load current of the utility transformer. The load calculations in Article 220 are unreasonably conservative. The utility will size the transformer based on decades of real world load information.