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This post is in responce to a recent post by Caelin Gabriel about secondary grounds where he indicated such grounds can be dangerous. I recently installed two 20 amp dedicated lines for my system, one from each phase of the main box, using 4x10AWG romex (2 hot, 1 neutral, 1 ground) into spec grade outlets. I used a seperate box for the breakers for those lines and grounded the lines to a seperate ground rod. The grounding wire is attached to the secondary box prior to being connected to the ground rod. The secondary box is bonded to the main box via a metal conduit and the main box is grounded to the water pipes in the house. Does the ground rod represent, as i hope, an additional grounding point or does is qualify as a secondary ground? If it is a secondary ground, what are the potential problems. everything sounds good but i'd hate to fry things. thanks
The ground needs to be tied at only one point to the neutral so that the ground does not carry current . The water pipe , neural and ground should only be meeting the main circuit breaker box. If you can pull a secound neutral for the room to the circuit box. In the case of USA/ Canada power distribution the 110v-125v 50/60 hz is unbalanced (single ended) . Current code provides and that recording studios use an isolation tranformer to provide balanced power, I.E. the neutral will no be tied to ground but about 60v or 1/2 voltage off ground. This then requies that the equipment be ground with a three prong plug.
Every electrical code that I am aware of specifies a SINGLE grounding point. Any ground rod that is not connected to the primary rod (connected with a large gauge wire) would constitute a secondary ground.Remember that the neutral is connected to the ground bus bar at the panel. And you have the outlets grounded to a secondary rod that may be at a different potential than the primary ground. If I understand the wiring of your system, this means that you could have a potential difference between the neutral and ground at your outlets. Connect a volt meter (AC) to the the neutral and ground of your outlets. Ideally, there should be a reading of ~.0 - .3 ac volts. If it is more than 1 volt, you have a problem. Even if the reading is good, you may still have a ground loop problem.
Ideally, you would want the grounds and neutrals (of ALL the outlets used in the system) to be at the same potential. When you have multiple power circuits with independent grounds, you dramatically increase the possibility of ground loops. Even small voltage differentials can affect the sound quality of the system. We have found that a ground loop "hum" is just the most severe form of the problem. Many systems have low level ground loops that do not cause an obvious hum but they DO obscure ambient musical information and cause the system to sound noisy, hazy or obscure. If you lift the ground with a cheater plug and the system sounds significantly better, you have the problem.
The solution is to ensure that there is a low impedance path to ground. You need good electrical connections with large gauge wires to a proper grounding point.
Installing a secondary ground usually does improve the sound quality because it reduces the impedance to ground - shorter ground runs. But let's be clear - a secondary ground is usually not a safety hazard: 99.9% of the time. There are two saftey issues. The first is the ability of the ground path to trip the breakers in a short condition. If the impedance to ground is too high, then the breaker may not trip. This is not very likely if the ground was installed properly. My primary concern is for people that live in lightning prone areas. By installing the secondary ground, you have created a pathway through your home for the lightning to pass in the event of a strike. That is not my idea of fun, even if a lightning strike is rare.
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Caelin Gabriel
Shunyata Research Inc.
Thanks for the help guys. The line was installed by an electrician but he does mostly industrial work and he may not be so up on houshold codes. I was hoping that the bonding of the two boxes would make the system act as if it has one ground (another electrician i work with had suggested this) but i understand how there could be a different potential between the neutral and the ground. I'll check the potential aout the outlets when i get home just to see how things are but i think i'll reroute the ground from the rod to the water pipes anyway. The system as a lightning rod idea soulds a little bleak...i live in the midwest and our thunderstorms can be quite entertaining at times. As to Seans question about the sound difference...I don't know. I recently did a total system replacement from a B&O reviever and CD to tube monoblocks, pre and CD. The wiring that was in my room by my rig didn't even have grounds on the outlets so i just ran the 2 lines to be sure i could feed the amps before i ever set up the system (talk about christmas morning hell .. a pile of VTL gear just sitting for 3 weeks until i could get the line installed). The installation was actually as straight forward as the other option offered. I just was out of room on the main panel so the buddy box was required for the additional circits The system sounds great as is ...no ground loop hum most of the time though on 2 or 3 occasions over the last few months one channel would get a hum if the system was left idling for a while...turn the amp off and then on again no hum and never any apparent hum while music was playing. I was wondering if that could be a loop problem (as opposed to an amp componant that wants to go south) but most ground loops i've fought while setting up PA gear in clubs tend to stick around until you reroute some part of the system.
A lightning strike involves 100 million or more volts. If lighnining strikes in the vicinity of one of your grounds then a voltage potential may develop between these two grounds. You've now got (gasp) a ground loop. Essentially current will flow between the grounds. Care to guess what the lowest impeadance path could be? Yup, right through your rig. You've perhaps eliminated the ground loops in your system, but have created a potentially more dangerous ground loop.Remember also that this catastrophe could also result in a fire. If the insurance inspectors discover your grounding scheme I would imagine it's possible that they'd void your fire insurance.
There's a better discussion out there than the one I've included below. It shows how lightning travels across the surface of the earth and its effects on grounds. I can't find it now, but if I do, I'll post it for you.
if your main panel was already grounded well to cold water pipes, and the city/town is still using metal piping from the mains to your house, i don't think that you really needed a second ground. Now if the ground from outside wasn't all that great, then perhaps this would lead to a improvement. Having a good ground is important for helping components reject RF, and junk on your ac if your using a PLC.
Heath
Could you give a brief detail of what kind of an imporvement you have got out of using a dedicated line? I'd really appreciate it. I'm kind of considering doing this but I'm wondering just "how much" of an improvement there is, I'm sure its different in each individual case of course.Thanks,
Sean Heisler
D e s i g n _P o r t f o l i o
My dedicated power line setup is a lot simpler than the first poster's and might be preferable for you as a newcomer to the esoteric world of mains tweakery.
When I moved in, I had an electrician wire 30Amp cooker cable to a unswitched Supersocket (a Deoxit-treated 13A double socket). I confess I still have the standard fusewire rather than a circuit breaker, but I work on the principle that circuit breakers are better until they operate, at which point they leave oxides all over the "burnt" contact points, rather than fuse wire which melts and is replaced.You'll probably have gathered that this is a UK installation on 240V 50Hz mains, not your weedy little 110V stuff, but the principle is the same.
I have found that the hi-fi system is now working properly whatever other appliances are on in the house and is substantially free of clicks and pops from fridge thermostats and CH timers.
My DAC is an excellent detector of mains transients, since its protection circuitry always clicked when any inaudible or audible transient hit the system. It is now silent.
The rewire was part of a general rewiring in the house, but it was not particularly expensive - about the same as a metre of reasonable interconnect and a hell of a lot better value!
Remember to treat all your contacts and wire clamps with contact cleaner and of course use the best mains cables you can afford.
An amplifier is simply a mains power supply modulated by a music signal, so the mains deserves the same TLC as the music.
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