Subpanel Sizing & Feeder Wire Calculator
Determine subpanel electrical feeder wire gauge (copper vs aluminum), 2-pole main breaker size, conduit dimensions, and detached building grounding requirements.
Calculated Results
Frequently Asked Questions
Why must subpanels have a separate neutral and ground wire (4-wire system)?
In a main electrical service panel, neutral and ground are bonded together. In all subpanels, the National Electrical Code (NEC 250.32) requires that neutral and equipment grounding conductors remain completely isolated. The neutral bonding screw/strap must be removed so normal return current does not energize metal conduit or panel cabinets.
What wire size is needed for a 60A and 100A subpanel?
For 60A: #6 AWG copper (or #4 AWG aluminum). For 100A: #3 AWG copper (or #1 AWG / #2 AWG aluminum). For detached structures, Mobile Home Feeder (MHF) quadruple aluminum is the most economical code-compliant wire.
Do detached garage subpanels require new ground rods?
Yes. NEC Article 250.32 mandates that any detached building served by a feeder must have its own grounding electrode system (typically two 8-foot copper ground rods driven into the earth spaced at least 6 feet apart).
What conduit size is required for running subpanel feeder wires?
Per NEC Chapter 9 conduit fill rules (40% maximum fill for 3+ conductors): #6 to #4 AWG wire requires a minimum 1-inch to 1-1/4-inch Schedule 40 or 80 PVC conduit; #1 or 1/0 AWG wire for 100A requires 1-1/2-inch or 2-inch conduit.