ground connection on dedicated line?

Lewinski,

I, too, vote "yes" on separate lines for analog and digital.

I recommend steel BX (rather than aluminum or copper) because only a ferrous material will block magnetic fields. You should not need the 18" spacing with steel BX (and as Tobias said, it's great for keeping the squirrels from snacking on your wires--copper is soft as well as pricey).

Thanks again guys. You've been very helpful.

Jea48: thanks for spending the time to explain it like that. My second post was submitted before your response was posted. Plus the tip and link regarding polarity are great. I hadn't thought or heard about that.

Regarding BX, I spoke to a couple of local wire manufacturers and they recommend copper armor. Any reactions? I read threads were people mentioned the benefits of running a dedicated line for analog devices and another dedicated line for cd players and other digital devices. They also recommend keeping both lines 18 inches apart to avoid noise induction from one to the other. I need to make both runs inside the same pipe (concrete building). Would the armor prevent noise from the digital-dedicated line to be induced onto the other, and do you believe that noise would be material to sound reproduction?

I apologize to keep asking more questions, but I'm tempted by the great replies.

Regards,
Horacio

Lewinski,

Markphd is correct but his response might need clarification. Romex is one brand a type of insulated cable assembly generally containing, within its outer insulating sheath, 2 or 3 insulated conductors and an uninsulated ground conductor.
BX is a brand of steel or aluminum armored flexible conduit with insulated wires inside. In addition to protecting the conductors contained within, the armor serves as a ground conductor.
In the US, Romex and BX are used as generic terms, just like most of us call cellophane tape "Scotch tape" no matter what brand it is.

Out here in the sticks we like to use BX in the walls, in case we get squirrels.

Just connect the dedicated circuit ground back to the main panel.

A quick call to your local municipality will tell you whether you can do otherwise legally. Keep in mind that local electrical codes may add to national codes.

Romex is a brand name but it's often used as a generic name for your basic, standard house wire. BX cable is simply wire in a flexible metal sheathing. It's typically used in garages or inside a house when the wire is not buried in the wall, but is surface mounted. This is often done in older heritage homes that are retrofitted with electricity. Rather than rip up wall or ceiling plaster, surface mounted electrical cables and metal receptacle boxes are used. BX is a flexible metal conduit. Alternatively, rigid metal conduit is used.

I should mention I'm not in the US. So maybe not illegal here. Point taken, though: one ground. What should the resistance be to be considered a good ground?

As for the US, as measured at the receptacle the resistance measured from the neutral to the equipment ground shall not exceed more than one ohm.......

Thanks guys. Very insightful. It also seems I touched a hot spot for some, and that's fine. It's all well-intended feedback.

I should mention I'm not in the US. So maybe not illegal here. Point taken, though: one ground. What should the resistance be to be considered a good ground?

Alrau1: because I'm not in the US, can you please shed some light on what BX armored cable is, and what Romex is? I'm aware of copper and aluminum shielding, but not sure what BX stands for.

Thanks again

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.
====================

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.

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.

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.

How is it a way to commit suicide?

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.

Elescher, I keep seeing recommendations like yours and then I keep seeing others state that this is a violation of electrical code in the U.S. I know one can physically do what you describe, but is this in compliance with code?

Anyone?
.

An isolated ground requires using separate isolated grounding rod(s). Basically what you need to do is disconnect the existing ground lead from your receptacles, and then run a 2 guage (or thick as possible) copper braided wire from the receptacle ground to your newly installed grounding rods...totally isolated from your main house ground. A must for anyone willing to take the extra steps to get the best performance from their system. Doing this will only make your system sound better.

Lewinskih01, from all that I've read in this forum and elsewhere, you should connect the ground from your dedicated circuit directly back to your service panel bus bar. There is a lot of discussion about separate ground rods for separately grounding your circuit, but from what I read, the electrical code in the US requires all grounds to be bonded to a single location. For most of us in our home environments, this is the bus bar in the service panel. If you can manage it, it's good to use one circuit for each rectacle, with a continuous run of wire back to the service panel.

There was a very succinct post from an Audiogon member about using "isolated grounds" but I can't find it now. Here is a post from another forum that makes the same points:

In a home environment, an isolated ground is completely uneccessary. A dedicated circuit installed to your HT system makes that statement even more true.

An isolated ground system is required in a commercial building because they have many miles of cable and heavy equipments such as motors and air chillers etc, that can create a rather noisy ground system that wouldn't be very compatable with any sensitive equipment that was plugged in the wall. As a result, they keep this "dirty" ground isolated to the buildings metal conduit system and run a separate safety ground to the third prong of the buildings wall receptacles.

This requires that "three wire cable" is run instead of standard electrical "two wire" cable. The cable uses an insulated hot wire, insulated neutral wire and an insulated ground wire plus the standard bare ground wire. The receptacles used don't have continuity between the third prong and the metal case to keep these two grounds isolated. These two grounds are kept separated and are tied to different ground points. Ultimately the two ground systems are then bonded together. This keeps the third prong isolated from the dirty signiture of the case ground in the building.

If you are running a dedicated two wire circuit in your home with a standard safety wire, what would adding the extra isolated ground wire gain you? Nothing. In a dedicated circuit the case ground is not being passed on through other multiple case connections, nor is there any parallel conduit interference. The safety wire in your dedicated circuit takes a direct path to the service panel without any other interference or connections. This is the lowest impedance point to ground.

Simply run standard 12 gauge two wire NMD cable you can purchase at Home Depot for your dedicated 20 amp circuit(s). It's a nice idea to purchase the better industrial grade receptacles rather than the 99 cent kind, but the isolated ground type won't gain you anything in this situation.

Generally if you're concerned about EMI/RFI interference, you would use simple local filtering to remove it. Most of these line conditioners they sell contain a good EMI/RFI filter.
http://www.hometheaterforum.com/htf/archive/index.php/t-62832.html

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