Hello and thanks for any advice in advance.
My goal is to update a 220v 15 amp circuit in my garage to a 220v 30 amp circuit.
The 220 circuit I am trying to update runs through schd 40 pvc conduit with 2 other separate circuits.
The situation is as follows (I did none of the existing wiring – I recently purchased the house):
My Main panel is in the attached garage and built into the wall.
There are 3 circuits leaving the panel with NM cable running ~6 feet behind the drywall away from the main panel to a conduit body mounted on the drywall surface.
The conduit is schedule 40 pvc. It is 1" but steps down to 0.75 then to 0.5" (details below).
There are two 220 15amp circuits and one 110 15amp circuit
The three NM cables then run through conduit. It is 1.0" conduit in the area with the three NM cables.
The 110 NM terminates first
The first 220 NM terminates shortly after. It is 0.75" conduit in the area with 2 NM cables.
The second 220 NM terminates shortly after that. It is 0.5" conduit in the area with only 1 NM cable.
All three circuits are running 14 gauge nm cable through the entire length — from the panel to the conduit body, then continuing through the conduit to the receptacles.
I have a few questions:
My understanding is that THHN wire is more desirable to be run through conduit instead of NM.
When updating one of the 220 15 amp circuits to 220 30 amp, I plan to use THHN wire. I think it is likely best for me to update the other circuits to THHN as well. Agree?
My understanding that NEC updated for 2020 saying that all circuits in a garage must be GFCI protected – is this true? If so – I will use a GFCI breaker for the new 220 circuit when I replace it. The garage is dry and I'm not concerned with water contacting the outlets.
Can all 3 circuits share a ground that is large enough to tolerate the largest circuit (the 30 amp)?
My understanding is that I will have 6 conductors running through the conduit so must derate to 80%. This should make no difference for the 110 15 amp and 220 15 amp with 14 gauge THHN wire (25*0.8=20). But will make a difference for the 220 30 amp circuit as I cannot use 12 gauge THHN (30*0.8=24). So I will step up to 10 gauge THHN for the 30 amp circuit (40*0.8=32). If this is all correct, should I use 10 gauge ground? Or do I have to derate the ground as well?
As far as running new wire through the conduit – any advice? I understand attaching my new 10 gauge wire to the old 14 and pulling will not be easy – especially in the section where there are 3 cables. Should I pull the old NM cable with a pull cord attached to it, then use that pull cord to pull the new cable?