ground connection on dedicated line?

Lewinski,

Using separate grounding rods is a violation of the National Electrical Code and also a great way to commit suicide.
If you can afford it, have the electrician use steel (NOT aluminum) BX armored cable (instead of Romex) and steel boxes, whichever way you decide to go. If you're having the outlets installed, running the 3 wire plus ground cable with isolated ground outlets can't possibly hurt, might help (esp. if you use the BX) and won't cost all that much more.
If you wish to discuss this further, you may e-mail me.

How is it a way to commit suicide?

All electrical codes that I know of specifically state that every electrical service must be grounded at the source (utility) transformer and that all equipment grounds must terminate at that point. In other words, there can only be one point that ALL grounding conductors or grounding paths terminate, and that point is usually the house water main or ground rod. The water main/ground rod is connected directly to the neutral bus of the main service panel which in turn is connected to the utility transformer ground.

This does two things: first, any surges, static or spikes from lightning are dissipated. The utility transformer completes the circuit from the house ground to the transformer ground which permits the energy to be dissipated into the earth. If you place a second ground rod at any circuit as Elescher states above, then what could happen is that the energy from a lighting surge will be short-circuit to the second ground rod (away from the utility transformer) and the surge will backfeed into that receptacle, frying anything connected to it.

Second: if you place a seperate ground rod at a receptacle and there's a fault on the equipment, the circuit breaker may not trip. The ground rod will have a resistance, say, of 25 ohms. A 120 volt fault will cause a current of 5 amps to flow (120V/25ohms) - not enough to trip a 20-amp circuit breaker but enough to be dangerous to the touch. If you touch the equipment with one hand, not a problem. But with two hands, the space between your hands is a conductor and you will get a jolt. That's why most sensible amp technicians never put both hands inside a live amp chassis.

Bottom line: add the extra ground at your own risk. Illegal and a tad dangerous.

Audiophile's and there zeal to avoid noise forget about the safety aspect of a ground wire. Your equipment needs the ground (the bare copper wire) connected at the receptacle and directly back at the main breaker panel on the ground bus so you have a return path to trip the circuit breaker in the event your component has a short between the hot lead and the casework. Of course you must leave the ground prong on your equipment cable intact also...no cheater plugs.

I'm planning to install two 20A dedicated lines for my system and I'm wondering if the isolated ground on the receptacles should be connected to the general house ground, or to an independent ground. Any light you can shed on this would be appreciated.

Thanks much,
Lewinskih01

>>>>>>>>>>>

If you are going to install your branch circuits with NM-B, (example Romex trade name), there is no need for for IG, (isolated ground), type recept/s. If you already have them that's fine too. At any rate just because a rececpt is an IG type it should never have its IG ground connected to an isolated ground rod that is not connected to the ground bar in the electrical panel the branch circuit/s is fed from. That was never the intent of NEC for the use of an IG recept.....

Why some think the earth is some mystical magical power that makes an audio system sounds better is beyond me.....

The main purpose of the equipment ground is to provide a low resistive path for any ground-fault current to flow back to the source. If the ground-fault current is high enough it will cause the overcurrent device, breaker or fuse, to open. The current flow is interrupted. The equipment ground has done what it was supposed to do.

As for audio equipment, that uses an equipment ground, the proper AC polarity orientation of the primary winding of the power transformer can affect the sound of a piece of equipment. Not because of the earth, jmho, but rather the relationship of the hot, neutral, and equipment ground of a 120V grounded power system.

The power that enters your home is fed from a utility transformer with an output voltage of 120/240V single phase. The secondary winding of the transformer is center tapped in the middle of the winding. The center tap is the neutral. NEC, (National Electrical Code), states that the electrical systems in a dwelling shall be a grounded AC power system. Simple terms the neutral shall be connected to the earth.

The neutral becomes the Grounded conductor. To keep it simple lets look a 120V dedicated branch circuit.
One Hot conductor, (The Ungrounded Conductor).
One neutral conductor, (The Grounded Conductor)
and one equipment grounding conductor. (The Grounding Conductor).

Think of a grounded AC 120V power system as having a high side, (the hot conductor) and a
Low side, (the neutral conductor).

The equipment grounding conductor is at 0V potential with respect to the neutral. That is because back at the Main electrical service panel both the neutral and equipment grounding conductor wires are connected to the same neutral/ground bar. *Just a note here, the main electrical service panel is the only panel or location where the neutral and equipment grounding conductor can be tied to a common point. But in all instances in some manner all equipment grounds eventually tie back to the main service panel neutral/ground bar.

NEC states that all the conductors of a branch circuit shall be installed in the same raceway, or cable, and terminated in the same panel the branch circuit is fed from. That includes the equipment grounding conductor.....

NEC 250.4
(A) Grounded Systems.
(1) Electrical System Grounding.
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line sures, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth earth during normal operation.

NEC 250.4 (A)
(5) Effective Ground-Fault Current Path.
Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low impedance circuit facilitating the operation of the overcurrent device. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered an effective ground-fault current path.

Now lets look at an isolated earth ground rod that is not connected back to the neutral/ground bar of the main service panel in any manner.

Instead of the equipment ground of the recept connected to the neutral/ground bar of the main service panel it is instead connected to an isolated ground rod.

Well first off NEC clearly states the earth shall not be used as an effective ground-fault current path to return to the source.

Ever heard of someone hunting fish worms with a rod stuck in the earth and connecting a hot 120V wire to it? It will bring the fish worms to the surface of the ground.....

Well the isolated ground rod will do the same thing in the event of a ground-fault condition. And if the fault is severe enough a large amount of current may flow. Flow where you may ask? The ground-fault will take any path it can find. One thing about current it will always take the least resistive path. It may re inter your home through your grounding electrode system to your main electrical service panel. Or your neighbors house may be closer.

Problem is the earth is a lousy conductor, and good chance the resistance of the earth in series with the fault will cause a voltage drop and not enough current will flow to cause the overcurrent device to trip open.....

Remember what I said about an isolated ground rod is great for hunting fish worms, and any ground-fault current will always take the least resistive path? There has been animals and people killed from stray voltage.
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In 2005 NEC added a section in article 250 for those who want to use a Supplementary ground rod.

NEC 2005 250.54 Supplementary Grounding Electrodes.
Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or
250.53(C) or the resistance requirements of 250.56, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).

In simple English, As long as the branch circuit equipment grounding conductor is connected to the equipment ground bar in the electrical panel the branch circuit is fed from, NEC allows a Supplementary ground rod to also connect to the equipment grounding conductor at the recept rough in box.