Sizing of a Multi Family Service

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ealle006

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Location
Plattsburgh, NY
Occupation
Electrician
I want to clear up some confusion I have regarding a multi family service. I am going to be installing (2) 2 gang meter modules for a 3 unit apartment building with a basement panel with storage. Currently, there are (2) 100 amp panels and (1) 200 amp panel for the apartments. I will be installing (1) 200 amp and (3) 100 amp main breakers outside within the meter modules. My total calculated load came to 330A. If I give myself wiggle room for future upgrades and go with a 400A service rating, I can use 600kcmil AL conductors as part of the riser. I am also going to install a main Disconnect before the meters. My confusion comes from the sizing of the service entrance conductors and the total potential current draw from the service (200+100+100+100 amps) of main breakers. Are the 600kcmil AL service entrance wires allowed to be unprotected or must I use 400A fuses in the main disconnect to protect those wires? Downstream of the main disconnect, must the conductors that feed each of the two meter modules (one will have 200A worth of breakers, the other will have 300A worth of breakers), be sized based on the total OCPD of the meter modules themselves or the calculated load? Is a fusible disconnect required in this situation to protected the service wires?
 
Welcome to the forum!
A sketch would help. It can be challenging to attach sketch or photo..,,I find it easier to do screen shot and attach that
 
I will be additional using SER cable, 4/0 for the 200 amp breaker and #2 for the 100 amp breakers. All wires sizes are in AL conductors except the GEC. Grounds and Neutrals isolated at the meter modules and bonded at the main service disconnect.Multi Family Service.png
 
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