Main vs. sub panel for dedicated lines

Each panel will have an 8’ ground rod, check with electrician for code.

If the sub panel is located in the same building as the main service panel a ground rod is not required for the sub panel. Yes per the NEC a driven ground rod can be connected to the equipment ground bar in the sub panel. (2017 NEC 250.54) I would not recommend it though.

If the sub panel is located in another building, such as a detached garage, then a new grounding electrode is required and bonded to the equipment ground bar/ panel enclosure/feeder equipment grounding conductor. (Feeder neutral conductor is never bonded to ground in a sub panel. Neutral conductor/ bar shall be isolated from ground/ panel enclosure.)

Minimum required number of driven ground rods for the main service panel technically is one, * IF *, the ground rod to soil resistance is 25 ohms or less.
How can the electrician know for sure if it is 25 ohms or less? With testing equipment that is made to test it. If an electrical inspector sees only one ground he will ask to see a print out of the test. It is cheaper by far for the electrician to just drive two ground rods and be done with it.

mesch, makes absolutely do difference. In order to isolate your system from everything else your would have to have the power company install a separate high voltage transformer on your lawn and run a second main from that to run the system, just a bit absurd from a financial standpoint.
For good equipment it does not matter. I have a three phase workshop in my bottom floor. I can run the phase converted, stop and start machinery and you can hear the tiniest click in the system. All of this is running off the same main. The power company did make me get my own transformer but this was to isolate my neighbors from me, not me from myself.

Just to add to why a sub panel(s) may be needed.


For one because a 42 circuit main panel (If main breaker is in the panel 40 spaces/circuits for branch circuits) isn’t enough spaces/circuits for all the circuits need for the home. I have a sub panel for just that reason. It is mounted beside the main panel.
(42 circuit used to be the max for an electrical panel. That was changed a few NEC code cycles back. There is not any limit now to the number of spaces/circuits in a panel enclosure.)


Sometimes a sub panel is used because of the distances lengths of home run branch circuits. Not for just branch circuit voltage drop. Considered is material and labor, it is cheaper to install a sub panel than run several branch circuit home runs back to one panel. And again one panel was not big enough.

Another reason for more than one panel is the size of the electrical service.
Two main disconnects are located on the outside of the house by the electric meter, (Often in a common enclosure with the meter socket). Each main breaker will feed a sub panel. They both might be side by side or separated from one another for splitting up branch circuit home runs.

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Lowrider57, I will use 10 ga and 20 amp breakers for each line. Or I will use 12 ga and 15 amp breaker for the digital one. I will use high grade 20amp receptacles for each line.

Jea48 hit on the reason for the sub panel. I need more circuits. And also the fact that I may not need the sub connected to ground rod. I think I have been told that this depends on the distance between panels, if too close there can be problems. The distance between the two panels will be less than 15'. I will ask my electrician regarding need for this and do as he says.

gs5556, No circuit will require a length of Romex longer than 50' so voltage drop should not be a concern.

Mijostyn, yes I thought that it would likely make no difference, however since I need(want) a sub panel  I thought I could isolate high current circuits from those supplying outlets, lights, and the audio system in the addition. 

Thanks all!

And also the fact that I may not need the sub connected to ground rod.

Like I said I would not recommend it. It will not improve the sound of your audio system. In fact it may degrade the sound. Lightning loves an auxiliary grounding electrode though. Lightning strike travels through the earth, enters the aux ground rod travels up through the ground wire to the equipment ground bar on its way to the main electrical and on its’ merry way back to earth. Suppose it stops and looks around inside the sub panel on its’ way back to earth?

The earth does not possess some magical mystical power that sucks nasties from audio equipment.

Adding an additional ground rod to the main electrical service Grounding Electrode System may lower the grounding electrode to soil resistance. IEEE recommends 5 ohms or less.

FYI the main reason for connecting the electrical service to the earth is for lightning protection. You can have as many ground rods installed for the main electrical service as you like as long as they are all tied, connected together, and connect to one point at the electrical service equipment. No matter how many electrodes there are they are counted as one.

The distance between the two panels will be less than 15’.

How big/size, ampere handle rating, will the two pole breaker in the main electrical panel be that will feed the sub panel? Feeder wire size?

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