Where is this requirement or limitation stated in this website?:
Originally Posted by
donf
This site is set up for DIY users doing residential work. Not commercial installations.
While usually single family dwellings can be done by a homeowner, and everything beyond a this must be done by a qualified tradesman, I do not see why any question about anything other than a residential application is not allowed.
Please provide backup for your statement.
This is incorrect:
Originally Posted by
donf
For example, if this were a residence, then you would use a #4/3 AWG copper with a 70 Amp breaker (sized for continuous use), 240/120 single phase connection.
Per NEC 2008 edition Table 310.15 (B) 6 - #4 copper can be used for a 100 amp residential feeder.
This statement illustrates some lack of knowledge and experience in the trade:
Originally Posted by
donf
However, I believe that Commercial uses three phase not single phase.
Various two pole single phase electrical equipment, to include circuit breakers, panelboards, and disconnects are made up to 1200 amps single phase, and certainly are not limited to residential applications.
In an effort to answer the original question, while #6 copper is the minimum size conductor allowed for a 60 amp feeder, consideration must be taken for the load and distance. If the max load is 48 amps at 120 volts, the max wire size to allow for no more than 3 % voltage drop would be #3 copper wire.
This is a design issue, not a code issue, and a qualified electrician and/or engineer needs to be consulted to size this feeder.