is the common ground connector necessary?
My guess is that it is necessary if you have metallic boxes, which seems to be part of code in the USA. Here in Chile we use plastic boxes and PVC conduit, so we obviously don't need that, but if you have metal boxes then I sure can see why you would want to ground that separately. That would be your last line of defense if anything comes lose or arcs inside the box. For example, if your live conductor comes lose and contacts the box, then the ground conductor on that receptacle wont do a thing to help you, and the box (plus the metal screws and faceplate attached to it) would be live! Not a good situation. So you need that "common ground" line to deal with that kind of situation.
However, that common ground should ONLY go to the ground bus in the distribution panel, and should NOT also be jumpered (bridged) to the receptacle ground in each box. If you did that,m you would create a potential ground loop, which is what you are trying to avoid....
He suggested that we take that 30 amp run and connected it straight to the mini-split and run a separate 30 amp line for everything else in the studio.
Yup! Smart move! Makes a lot of sense. You should also split that second 30 amp line into another two circuits: one for lighting and non-technical power, the other ONLY for your equipment. Keep things as separate as you possibly can.
He said that would minimize the chance of getting a dip in power when the mini-split powers on, but wouldn't everything running from the main panel dip (including the separate 30 amp line for the studio)?
Not if it is wired correctly. Those two circuits would both be coming directly from the main bus in the panel, and that main bus can handle the entire 100 amp load. The bus has very low resistance, so there will be practically no voltage drop between taps on it, even for large load changes. But a piece of wire is different. It has much higher resistance (relatively speaking), so any change in load (current flow) will cause a large change in voltage drop along that piece of wire. That's what you see as a "dip". So each circuit that comes off the main bus only sees the "dips" associated with its own circuit.
Your electrician is speaking words of wisdom. He is right.
He also pointed out that there isn't a separate grounding rod for the garage and we would need to put one in for my isolated grounding.
Yep! And maybe more than one, depending on the physical properties of the actual "ground" (="dirt") in your area. Where I live, I always specify four rods, each driven one meter into the ground, on the corners of a one-meter square, and connected together with heavy gauge copper. A single conductor runs from that grid to the panel, and that is the separate ground for the technical circuits. Check with your electrician, and your local code, to see what they say about getting a very good, low resistance ground. But are you going to install an isolation transformer for your technical power? If not, then be careful how you wire your grounds! You don't want to create a new ground loop between the existing house ground and your new technical ground...
- Stuart -
(such as in their pre-loaded face plates). So for panel mounts I'd definitely be going with Neutrik - but there's the question of the worth of gold connectors there as well.....
Yes I would lower it.