[Enanosky44]

We are doing renovation in some buildings and updating the services.... How do you calculate or how you know what gauge of wire, you will use.... For example:
1 building has 5 existing meters, so we need 5 new meters.... On some o the meters there is a label which says 120/240volt 3 phase delta... Somebody ask me what does that mean... And I couldn't answer...
Where do I get a good book or info a out it...

 

[Mich drew]

Id call an electrician if I were you.

 

[BBQ]

You would start with load calculations in article 220.

You would also contact the power company to see what the short circuit current is.

 

[Enanosky44]

I'm the helper, that's why I ask my boss to put me in a place where I will learn.... And I think I will... I guess is a matter of time... But it frustrate you sometimes.... Is there any other book or video or website? I just son wanna be there with my face looking all blank....

 

[Ultrafault]

Great, good on you i have been slackjawed for years, it may be chronic.
Get a code book.
Are you taking classes along with your apprenticeship?
If not
Get:
Electrical Wiring Residential: 17th Edition
Electrical Wiring Commercial: 17th Edition
Electrical Wiring Industrial: 17th Edition
and either Tom Henry or Mike Holt exam prep.
Know those books back and forward and you will then know almost nothing and be ready to learn.

The answers to your questions are: 120/240 3 phase is known a high leg delta.
As you see the x0 or neutral is tapped from the middle of the transformer winding much like a split phase 120/240 single phase. The b phase or high leg has 208 volt potential to ground and is phased with an orange color.

There are only 3 phase systems that supply 120v to ground for gen rec loads. This one and 208/120y

The second question requires more leg work. As bbq said you must first do a load calc via article 220. Then for residential dwelling only the wire size can be obtained from 310.15(B)7 .

Don't let these guys scare you we get alot of homeowners on this site and they try to run them off. you will find we all love to preach to apprentices.