Main vs. sub panel for dedicated lines


I am building a second home on my property. Will have a dedicated audio room. I will be routing 2 or 3 dedicated lines for my audio system. The high current devices for the home will be run off the main panel. I will install a sub panel supplied by the main to accommodate power for 2 bedrooms and a 1/2 bathroom.  

Question, should I run my dedicated lines off the main or the sub panel? I could move some of the high current devices to the sub panel if needed.

Thanks in advance for advice. 
mesch

Showing 9 responses by jea48

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.


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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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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lowrider574,352 posts

06-02-2021
10:37am


@jea48
@mesch
I have a new service panel and a subpanel. When the sub was installed, a second ground rod was added. Two different electricians installed the panels, both said two ground rods were required to meet PA code.
@lowrider57

Two rods yes. Both should be for the main electrical service panel.
(Reason for two as I described in my post above.)

If you would, go out side where the two ground rods are located and look if you see only one bare ground wire going into the house and not two ground wires.

The correct installation, the two rods shall be a minimum of 6ft apart from one another. The two rods are connected together with a ground wire that is then extended into the house and connects to the service entrance neutral conductor buss bar. The neutral bus bar is bonded/connected to the panel metal enclosure.
The two rods are counted as one Grounding Electrode, (NEC).
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For a sub panel in an out building, separate building, a ground rod (Grounding Electrode) is required. The ground rod is connected to the equipment ground bar in the sub panel creating a grounding electrode system for the separate building.

For a sub panel located in the same building as the main electrical service panel the separate earth connection ground is not required. If not required why would anyone want it? The separate earth connection can/does cause more harm than good. In fact the separate earth connection can/will add noise to the branch circuit equipment grounding conductors connected to the earth connected ground rod.

This guy has helped over the years in writing parts of the National Electrical Code, (NEC).
Auxiliary Grounding Electrode. (NEC 250.54)
https://www.youtube.com/watch?v=gg4wBI7bWgI
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Can each rod individually be connected to ground in the main panel?
Sure. Especially for your situation. Both rods ground wires would connect to the service entrance neutral conductor neutral bar.
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lowrider574,353 posts   

06-03-2021  
 3:04pm


Question: why are two ground rods used?

Hi @lowrider57

From one of my above posts:
06-02-2021
8:24am

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.

I am curious what’s going on with the two ground rods in the basement. Sure would like to know. 3 ft apart? Not 6 ft apart? Are the two rods connected together by a bare #6 solid copper wire?

How about the old ground rod that was used for the old service? Did the electrician use it for the new main electrical service as one rod and the new rod(s) in the basement for the other? Curiosity killed the Cat.....

Best regards
Jim.
millercarbon9,434 posts

06-03-2021
11:27pm

I would also recommend grounding the ground to ground, and then grounding the Earth to ground. You never can be too sure, so I would ground all the grounds to all the pipes as well. Because, like, they go into the ground.

Yeah, I know what you’re thinking. There he goes being a a-hole again. But no, this actually is code now. The difference between all this BS everyone is so intent on doing, and what actually works, is so obvious if you could hear it that would be the end of that. But you can’t. It is way too much work. You never in your life will do it to compare and know. That’s why I did it. To know. Then comes the reason I hardly ever bother posting on the subject, https://youtu.be/9FnO3igOkOk?t=39

MC, finally a post of yours that makes sense. :)

Broken down into simple English.
To earth ground a sub panel or not to earth ground a sub panel that is the question......
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MC,
I was looking at your system thread and read this:
Stewart Marcantoni taught me it all begins at the wall. The System begins with 4 ga wire at the panel. This 4 ga brings 240v power to a step-down transformer located just beneath the system. Now at 120v, it is only about 5 ft from the Medusa power center. The step-down transformer and Medusa are both grounded to the same ground rod the same 5 feet from the system. Power wire is all cryogenically treated.

@ millercarbon ,

I have some questions if you don’t mind.

What size, (breaker handle rating), is the 2 pole breaker, at the main electrical panel, that feeds the primary winding of the isolation power transformer?

What size, VA rating, is the isolation power transformer?
Does the secondary have overcurrent protection? Are connected circuit(s) wiring protected?

Is the secondary, one winding, or two windings? In other words can the secondary be wired for 240/120V out or 120V out only?

Is the ground rod used to earth ground the new separately derived power system? Is one of the 120V secondary winding leads intentionally grounded making it the neutral, The Grounded Conductor?

Is the neutral conductor bonded to the transformer metal case/metal enclosure/ transformer Iron core? Are circuit EGC(s) (Equipment Grounding Conductor)(s) connected to this star equipment grounding point?

Is the ground rod bonded to the main electrical service "System Ground"/"Grounding Electrode System" with a minimum #6awg copper wire?

OR,
Are you floating the 120V secondary? (No reference to ground from either lead/leg of the 120V secondary of the xfmr? An Ungrounded Power System....
The ground rod is only connected to the 120V EGC(s) connected loads.
Ground rod is not connected to the main electrical service Grounding Electrode System.

FWIW
Fact.
Mother Earth does not possess some magical mystical power that sucks nasties from audio equipment.

Grounding myths from somebody that knows something about grounding.

Henry W Ott
Quote:

Grounding Myths

"Electromagnetic Compatibility Engineering" by Henry Ott

3.1.7 Grounding Myths

More myths exist relating to the field of grounding than any other area of electrical engineering. The more common of these are as follows:

1. The earth is a low-impedance path for ground current. False, the impedance of the earth is orders of magnitude greater than the impedance of a copper conductor.

2. The earth is an equipotential. False, this is clearly not true by the result of (1 above).

3. The impedance of a conductor is determined by its resistance. False, what happened to the concept of inductive reactance?

4. To operate with low noise, a circuit or system must be connected to an earth ground. False, because airplanes, satellites, cars and battery powered laptop computers all operate fine without a ground connection. As a mater of fact, an earth ground is more likely to be the cause of noise problem. More electronic system noise problems are resolved by removing (or isolating) a circuit from earth ground than by connecting it to earth ground.

5. To reduce noise, an electronic system should be connected to a separate “quiet ground” by using a separate, isolated ground rod. False, in addition to being untrue, this approach is dangerous and violates the requirements of the NEC (electrical code/rules).

6. An earth ground is unidirectional, with current only flowing into the ground. False, because current must flow in loops, any current that flows into the ground must also flow out of the ground somewhere else.

7. An isolated AC power receptacle is not grounded. False, the term “isolated” refers only to the method by which a receptacle is grounded, not if it is grounded.

8. A system designer can name ground conductors by the type of the current that they should carry (i.e., signal, power, lightning, digital, analog, quiet, noisy, etc.), and the electrons will comply and only flow in the appropriately designated conductors. Obviously false."

Henry W. Ott

Who is Henry W Ott?
http://www.hottconsultants.com/bio.html

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