star grounding question...

So how does star grounding apply to an A/C sub panel? What my electrician did is run a 40 amp 65' 8 gauge non-armored A/C cable from the main A/C panel to the sub panel. I then have 4 20 amp 7' runs of 10/2 romex to my A/C sockets. The only ground rod that I have is a 10' 5/8" commercial grade ground rod that goes to my main A/C panel. Should I have a separate ground rod for the sub panel or a separate ground wire from the sub panel to the main panel or some other configuration? The system sounds great, but maybe there's something that I can do to get a lower noise floor. I plan on using cryoed breakers and already have good A/C sockets. I also plan on using Virtual Dynamics A/C wire to replace the 8 and 10 gauge wire that I have presently. Thanks! Stan

Talon4
65' #8 awg wire, that's kinda small wire for the distance. I am just guessing but the electrician installed 8-3 with/ground nmc, romex, for your sub panel feed. 2 hots, 1 neutral, and bare ground. The bare ground is terminated on the neutral/ground bar in your main electrical panel, just where it should be. Your sub panel is 120/240 volt, 40 amp rating.
Star grounding, "Nsgarch" said it well.
Inside your sub panel there is a separate bar for grounding. This ground bar is where the electrician connected the bare grd wire from the #8-3 w/grd feeder. This grd bar is also were the branch circuit equipment grds connect to. A common ground point, star ground.
No separate ground rod for a sub panel.

Jim

Jea48-Yes, that sounds accurate. I watched the whole process. Also, my electrician said that 8 gauge was okay up to 180', after that 6 gauge is the way to go. So are you saying that it is already star grounded? Any ideas are welcome. Thanks! Stan

Yes, it is star grounded.

Jim

Stan, Like I said, you want to have a continuous ground from your new AC sockets > to your sub panel > to your main panel. If you put in a new ground rod 70' or more away from the one at the main panel, there could be a potential (voltage difference) between the two ground locations causing a current in the neutral leg -- you don't want that.

How does the 8AWG transition to the 10AWG -- through 4 breakers at the sub panel? I hope so! And do you have a 40A breaker (or fuse) at the main panel where the 8AWG takes off?

I think what people mean when they tell you to star ground your panel is slightly incorrect. I think what they really mean is to star wire it. That means that each duplex outlet in the wall should be wired directly back to the panel with a hot, neutral and ground wire, and not daisy-chained with other outlets like is done in cheap plug strips.

But electrical systems MUST BE GROUNDED (for fire insurance reasons if nothing else!) When you finally plug everything in, you will probably want to lift the ground pin on all the three prong plugs of all components except the one on the preamp, UNLESS -- you are A.) using all balanced interconnects, B.) a Balanced Power unit, or both.

If you have breakers at your sub panel (and I hope you do!) you can wire a little high speed diode between the equipment side of each breaker and ground. If there's a power surge or lightening strike, the diode will close, grounding and thus opening the breaker, before the surge can hurt your equipment (of course you'll have to replace the diode!) but it's a way of getting great protection without any sonic degradation -- which you do get from most power units that incorporate traditional surge protection circuits (the ones that can be reset :~)