ptay wrote:black taj,I was just trying to figure out what you meant by neutral currents flowing on the ground wires. The green wire should have no AC current flowing on it, right? It's just there to trip the breaker. Right?Correct. What I mean by circulating neutral currents is this:Your water pipe (called the grounding electrode) is connected to the neutral in the service panel via a copper wire (called the grounding electrode conductor or GEC) The neutral is bonded to the electrode because the earth is a lousy conductor and would never generate enough current to trip a breaker in a ground fault condition. Want to test it? Take an isolated ground outlet, power it up like normal and tie the ground wire from the outlet to just a ground rod that isn't bonded. What you'll end up with is an arc welder. Now, since a good number of houses share the same method of grounding to the same electrode that is the water pipe. Since ALL the neutrals are bonded to the pipe, there is a certain amount of current flowing on that pipe. Sometimes it is due to faulty wiring in one house, but the cumulative effect is that there will be current on the pipe. This will backfeed onto your system simply because of the connection to the water pipe. As I mentioned, the chemical ground rods are really the only way to totally separate your system.

Pure L wrote:Lots of food for thought up in here. Thanks for the replies.So my detached garage (~25 from my house) has its own power box (containing six 20 amp circuits) running from the service panel in my house.Just make sure that the neutral is not bonded to ground in the garage panel. I'm wondering about something though.......Since both the house and the garage power boxes are grounded to their own respective grounding rods, will this be a problem? No. NEC requires the use of a second ground rod at any outbuilding containing anything larger than a single 20 A circuit. A ground rod's only function is dissipation of lightning strikes on the service mast.I remember reading somewhere that this (the double grounding) could indeed introduce EMI problems. Double grounding is when you bond the neutral in more than one place, giving the ground parallel pathsAny truth to that? Is this required by code? (It was an electrician who did this.)Also, is it advisable to do IGs for all of my outlets? Or just the ones I'll be using for audio-type stuff? As stated before, I believe in a non metallic raceway, isolated grounds are pointless. You could install them for your audio equipment and be perfectly fine. A suggestion was made earlier to run a star topology ground. There is a standard grounding system in commercial high rises that might make this installation more elegant. If you'd like, PM me and I can tell you how to install a Hogan groundHow about lights? Anything I should think about there?Electrically, the loudest thing there is are HID lighting and fluorescent ballasts. If it's not a pain, separate the lighting circuits from your power and you'll be fine.Many thanks.

If by double ground, you mean to bond the neutral at a sub panel, then yes that is a violation. There is no requirement to ground to the water pipe. The language calls it a grounding electrode. The water pipe is the most common here, but not where PVC pipe is used, or in well systems. You can achieve this in other ways (Ufer ground, chemical ground, high resistance grounding etc.)

black taj,I was just trying to figure out what you meant by neutral currents flowing on the ground wires. The green wire should have no AC current flowing on it, right? It's just there to trip the breaker. Right?

Black taj,Isn't illegal to double ground, and to not bond to the water pipes?

Lots of food for thought up in here. Thanks for the replies.So my detached garage (~25 from my house) has its own power box (containing six 20 amp circuits) running from the service panel in my house.I'm wondering about something though.......Since both the house and the garage power boxes are grounded to their own respective grounding rods, will this be a problem? I remember reading somewhere that this (the double grounding) could indeed introduce EMI problems. Any truth to that? Is this required by code? (It was an electrician who did this.)Also, is it advisable to do IGs for all of my outlets? Or just the ones I'll be using for audio-type stuff?How about lights? Anything I should think about there?Many thanks.

double post

I've been thinking about this wiring for studios a bit after having done so a few times. If I were to do it again I would simply wire the whole thing for 240V. Ideally I would have a dedicated feed to do this and use a star topology for ground and outlet circuits feed. Quite simply this takes all the load off the neutral (because there is none) and also reduces any leakage to the ground. Sort of a poor man's balanced power supply but without all the code problems and weirdness you get with a 120 balanced power supply. This might also help with any induced line noise from switched mode power supplies or whatever. Especially for a digital studio, this would be easy considering 95% of the computers and gear that has some digital processing either has a universal switched mode supply or an external wall wart that can be easily replaced with a 240V version. I guess the only annoying thing would be swapping all the AC plugs to 240V NEMA 6 and making (or finding) your own NEMA 6 power strips. Another option would be IEC power strips but there is no protection from plugging in a 120V device by mistake.For 120V gear just use a portable 240>120 (non-autotransformer) isolated winding type transformer to maintain the balance.

I would agree that it's an interesting idea. The neutral and ground is not your only source of noise. Your hots will carry noise just as well.I'm not sure what you mean by portable transformers. But to my knowledge, aside from autotransformers, line and load windings are not electrically connected. That is to say, they are not holding hands. The windings simply transfer power via magnetic fields generated.

If your 'star' pount is anywhere except in the dist. Panel you're inviting trouble.I don't know your location (Honk Kong or some thing ?) but something seems fishy about running all the 220/240 lines and stepping down. The added transformers will radiate magnetic fields ... And do so closer to your instruments and gear.I see what you mean by the power becoming balanced. But i would argue that return currents are the same whether there on a grounded conductor or a second hot. I wonder if you know of any other studios that have done this. Sort of an interesting idea.