Derating neutral wire

[anbm]

Went to job site today, and saw a main service swbd (5,000A MLO, 240/120/1, has five feeder breakers) (The swbd was installed probably around 1980)
serving high-rise condominium.

Incoming feeder underground to swbd: (13) sets of 2#750MCM-AL, 3/0 Neutral-AL. It appears the neutral wire is de-rated, is it allowed per code?
If so, what is the rule?

 

[infinity]

The neutral is sized according to the load calculation so it can be smaller than the phase conductors. There is a minimum neutral size for a grounded system.

 

[anbm]

The neutral is sized according to the load calculation so it can be smaller than the phase conductors. There is a minimum neutral size for a grounded system.

Dig into the code book, 230.42(C) refers to 250.24(C1)(1) or (2), it appears neutral wire can be smaller than hot wires... but I am not sure if this rule only applies to 3-phase system or doesn't matter.

 

[packersparky]

Dig into the code book, 230.42(C) refers to 250.24(C1)(1) or (2), it appears neutral wire can be smaller than hot wires... but I am not sure if this rule only applies to 3-phase system or doesn't matter.

Look at 220.61 and table 250.102(C)(1).

 

[infinity]

Dig into the code book, 230.42(C) refers to 250.24(C1)(1) or (2), it appears neutral wire can be smaller than hot wires... but I am not sure if this rule only applies to 3-phase system or doesn't matter.

Reduced service conductors neutrals are permitted on both 1Ø and 3Ø systems. Packer gave you the code sections.