Current-carrying service conductors must be:
- At least 8 AWG if copper, 6 AWG if aluminum [230.23(B)].
- Of sufficient ampacity to carry the load as calculated per Article 220 [230.23(A)].
- Of adequate mechanical strength [230.23(A)].
That last requirement seems redundant. If you’re using conductors of sufficient ampacity and permissible type, they will have adequate mechanical strength.
Important: Do a thorough job of determining what load this service is going to supply. If you get that wrong, you could have the expensive problem of an undersized service
You may deliberately oversize the service to allow for expansion, but you shouldn’t spend that extra money out of error.
Some common errors in load determination:
- Incorrect characterization. Identify high-harmonic and low power factor (e.g., high inductance) loads; derate accordingly. If you can’t prove it’s noncontinuous, classify it as continuous rather than the other way around.
- Omission of specific loads. If you’re doing general load calculations by square foot, you must additionally calculate certain specific loads.
- Assumptions about intended use. The building must serve the occupants, not the other way around. In addition to the other load calculations, account for loads particular to the intended use. A manufacturing facility with aluminum melting pots and plastic extruders will have a heavier load than a typical office space.
