kwired
Electron manager
- Location
- NE Nebraska
Some details involving "high leg" were already brought up.
If you have 120/240 volts and you do have a three phase system - you will have a high leg, it is impossible to have all three legs have 120 volts to one point unless you have a wye system that only has 208 volts between all "phase" conductors. You can have a 240 volt wye system but voltage to neutral will be about 139 volts.
So if you have a high leg system you may want to look more carefully at your load calculations. All your 120 volt load is limited to just phase A and C assuming B is high leg. If you only have HVAC loads that are using the high leg you may just want to do load calcs assuming a 120/240 single phase service - less HVAC loads to come up with general lighting and other loads demand then add what ever is needed for the HVAC loads. Basically you are designing a system that will not be balanced.
240 volt breakers vs. 120/240 volt in a 2 pole typical "miniature" or "loadcenter" breaker are not popular, likely are not even in stock in most supply houses, and if you do order them are expensive. If supplying just heating or cooling equipment with the high leg you may find other options less costly and/or less confusing for people that try to do electrical work behind you. You will have nearly every third space in the panel unused because it is the high leg. Having a three phase AC unit is sometimes a reason to have a high leg system - but there is only one load that uses the third leg - in those cases install a single phase main panel for all other loads and install a single fused switch or single breaker as a second "main" to feed the AC or even small three phase panel if there is additional three phase loads is often a good design idea.