ElectAid contains many calculations and lookup tables used everyday in the Electrical Design Industry. It is based on NEC 2011.
Calculations:
Voltage Drop
Cable Sizing
Transformer Amps
Conduit Fill
Amps from HP
Amps from KW
Amps from KVA
KW
KVA
HP
OHMs Law
Lookup Tables:
Motor Ampacities
Grounding Electrodes
Equipment Grounding
Conduit Fill
Cable Properties
Standard Breaker Sizes