Branch circuit as the main disconnect

[Steve-O]

Hello, having a debate here..
100A residential main service panel where the service conductors are landed on a 70A branch circuit, bypassing the 100A main. The wiring isnt rated for 100A so I understand why they may have do this but I cant find any code referencing why this is wrong. TIA

 

[Dennis Alwon]

Minimum service for a residence is 100 amps...

230.79 Rating of Service Disconnecting Means. The service
disconnecting means shall have a rating not less than the calculated
load to be carried, determined in accordance with
Part III, IV, or V of Article 220, as applicable. In no case shall
the rating be lower than specified in 230.79(A), (B), (C), or
(D).
(A) One-Circuit Installations. For installations to supply only
limited loads of a single branch circuit, the service disconnecting
means shall have a rating of not less than 15 amperes.
(B) Two-Circuit Installations. For installations consisting of
not more than two 2-wire branch circuits, the service disconnecting
means shall have a rating of not less than 30 amperes.
(C) One-Family Dwellings. For a one-family dwelling, the service
disconnecting means shall have a rating of not less than
100 amperes, 3-wire.
(D) All Others. For all other installations, the service disconnecting
means shall have a rating of not less than 60 amperes.

Also

230.42(B) Specific Installations. In addition to the requirements of
230.42(A), the minimum ampacity for ungrounded conductors
for specific installations shall not be less than the rating of the
service disconnecting means specified in 230.79(A) through
(D).