So I am coming out of my subpanel with 1/2 in metal conduit and using metal handy boxes with NEMA 5-20 for all the receptacles on my two indoor branch circuits. One is dedicated for a window unit AC. All wires are 12AWG stranded copper THHN/THWN.
The ac receptacle is protected with AFCI and GFCI because part of the unit is outdoors. The other receptacles are protected with AFCI only.
So six conductors in all come out. At a t-type conduit body we split off L1/N/G and go up to a handy box near the window. L2/N/G continue on to the wall receptacles.
A separate N ang G run to each circuit. I chose to use a separate G for the two circuits in case the G to one circuit somehow comes loose. No splices are planned anywhere in this setup. All receptacles use the better clamp-type screw connectors the hold the wire captive between two plates.
Is this safe? Am I violating the fill calculation for the conduit body? I used an online calculator assuming 6 conductors pass thru box, and it yielded 13.5 cubic inches … really? Is that much room really needed with no splices?
Best Answer
You said metal conduit--1/2" EMT & rigid can have nine #12 thhn/thwn wires max fill per NEC annex C conduit fill.
The area of the conduit body would only be needed only if a splice is made in that location, so the derate for more than 3 current-carrying conductors would be the next concern. 4-6 conductors require a 80% derating but the higher ampacity 90 degree table can be used for derating and you still meet code because the derated value is 24 amps.
So this is safe for a 20 amp circuit(s).