Originally Posted by frenchelectrican
The larger box size will depending on following factors :
1) numbers of conductors
3 = line line neutral, all same size
-3 from mainpanel (upgradeable to 6 in future)
-3 to 1st subpanel
-3 to 2nd subpanel
all 4g, need 60 amps, 75C, derated for 85 amps* 4-6 in same conduit (*.8), and high temperature [boiler room/hot summers] (*.94)=63.92amps
3) type of cable or conduit
1.25" EMT from main panel
1" EMT to 1st panel
4/3 AC cable to 2nd panel
4) depending on which way it will enter the junction box
Either main panel wire and 1st subpanel enter on the east of the box, 2nd subpanel enters on west side of box, OR main panel wire enters on the south of the box, and 1st subpanel enters on north, 2nd subpanel enters on west of the box.
In junction boxes the 3 4g wires (per splice) are spliced with split bolts, fusing tape, covered with electrical tape. Currently the 2 subpanels will share a double pole 60 amp breaker, but in the future if I get a service upgrade, I might upgrade for each subpanel to be on its own 60 amp breaker, and increase number of/amps of the circuits in the sub panels.
Main Panel/service is 100 amps, 2 hot wires from 3 phase power, 208v hot to hot, not sure what the upgraded amperage would be (underground fed, my neighbor's detached 1 family house is fed from my basement before the meter), but I'm not doing a service upgrade myself.