So I'm currently waiting on a few HVAC parts to be shipped, so I'm sort of at a standstill. There are a few minor things I'll be doing in the meantime, but I can't get any major work done until I get the first part of the HVAC started... and that's putting holes in the exterior to run the ductwork.
Good news though. I heard back from Rod on my HVAC design, and his response was... "The HVAC is looking pretty good", and "There is nothing in your HVAC design that concerns me". This was a HUGE relief. Once all the parts get here, I'm really confident I can get this done right.
I do have some electrical concerns though. I have a pretty good understanding of the electrical, but I was hoping maybe someone could help clarify some of the details, as well as see if I'm missing something really important. I've read 2 books on electrical wiring, plus the section in Rod's book, plus several papers on isolated ground systems, so I feel like I'm in good shape.
Ok, my house has a 200 amp main panel. There is a grounding rod right there at the panel connected with 4AWG stranded wire, and driven deep into the ground. There is a 2nd grounding rod at the front of the house that is bonded to the water pipes. Currently, there is a sub panel in the garage (studio), that is supplied by a 40 amp breaker being fed underground via conduit with four 10AWG conductors (2 hot, 1 neutral, 1 ground) from the main panel. I want to replace the 40amp breaker with a 60amp breaker, and swap the 10AWG conductors with 6AWG conductors.
Question 1: is this OK? And does the size of the ground conductor matter? Should it also be 6AWG, or can it be smaller?
Inside the studio, There will be just 1 penetration in the wall where I bring in the power conductors. Everything will be surface mounted (sub panel, outlets, switches, lighting, etc). I plan on having one phase of the panel be ONLY for studio/audio equipment, and all of those outlets will be isolated ground receptacles. They will be run in EMT conduit, so the conduit acts as the safety ground, and the hot, neutral, and isolated ground conductors will be run inside the conduit together, and will all be home runs back to the sub panel. The other phase of the sub panel will be for everything else, i.e. lights, hvac, standard plugs, etc.
As for the isolated grounds, I understand each isolated ground conductor needs to be sent to a separate ground bus bar that is not connected to the ground bus or neutral bus in the sub panel. They also need to be connected back to the ground bus at the main service entrance.
Question 2: Can I install a 2nd small panel in the studio to house the isolated ground bus bar, then send a single isolated ground conductor back to the main service entrance via the underground conduit to connect to the main ground/neutral bars in the main panel? So I will essentially have 5 conductors in the underground conduit from the house to the studio, instead of 4? And if so, what size should that ground conductor be?
Question 3: Am I correct that I do NOT need another ground rod outside the garage/studio? As long as the isolated grounds are bonded to the main service ground/neutral bar (which is bonded to the grounding rod at the service entrance), i'm good?
This sketch should illustrate everything.
Edit: Oh! back in post #9 on the first page of this build thread, Stuart mentioned putting a filter on the air intake (From outside to inside), and the return air register to keep the ducts and silencers as clean as possible. Sure having to clean these every once in a while is a chore, but I'd much rather that than the alternative. I've been researching filters, and can't seem to find something that would work. Is there a specific type of filter I should be looking for?