Rafael: I am glad to hear that you had the work done professionally and to code. And most importantly, safely. I noticed in your second reply that you said in fact the feed wire went from the meter base to your subpanel and that your subpanel had a master disconnect. I will add that where this is okay to do, it is considered a less safe practice then running the feed wire from a 100 amp breaker that was located in the main panel itself. One reason is that if there was a series arc fault or hot-to-nuetral/ground fault in the feed wire (an example would be as a result of physical damage), it might not trip the subpanel disconnect. The obvious worst case is a fire. By tapping out of the main panel, you are protected not only by the subpanel disconect, but the main disconnect also. Additionally, you have the ability to shutoff the subpanel at the main panel (Think fire safety!). As configured, your subpanel feed wire is hot at all times, even with the subpanel disconnect off!
As for "audible" gains, I would be highly skeptical due to the fact that there is very little to be gained in the first place. Modern home electrical systems are designed to perform at an extremely high level. They are also very robust and designed to operate under extreme conditions. Residential grounding systems are capable of withstanding near full dead-faults. The Electrical Code (NEC) is a certified masterpiece of engineering.
"Dirty" power comes from the factory. Home appliances, computers, etc. create more crap on the NUETRAL leg NOT THE GROUND. The ground *normally* carries NOTHING (or next to nothing). And by next to nothing I mean millivolts or even microvolts. The entire purpose of the grounding system is to provide a low-impedance pathway to earth ground for fault current. That's it folks! Grounding systems weren't even in use eons ago! Remember 2-prong outlets? There was no "ground" present! "Cleaning" dirty outside or inside grounding electrode connectors does absolutely "zippo" to power quality. It simply lowers the impedance to earth ground of everything in the grounding system. Beneficial? Yes. But to all of you who have copper main water pipes as a primary or secondary ground, keep in mind that you have several meters of buried piping as your grounding electrode that isn't very "clean" and yet 99% of all homes I inspect have a grounding system impedance of less than ONE ohm. And to any of you considering unscrewing these connectors and cleaning them yourself, DONT! *If* there is *any* fault current on the grounding system and you grab hold when the connector is loose, you have inserted YOURSELF into the grounding system!!! And your chest cavity and heart are likely directly in-line with the ground! People have been electrocuted doing this!
Someone in here asked if isolation transformers are a solution. However, I believe that using isolation xforms as an integral part of the home electrical system is NOT permitted! I cannot find one bit of code in the NEC that relates the use of permanent iso-xforms for residential use. And you'll have to excuse me for looking as this is not the kind of stuff I come across on a daily basis. The only coding listed for iso's is for hospital applications. All residential information is for autotransformers. From a purely basic standpoint I can see why this would be against the code. The use of plug-in isolation transformers however is fine. But you are only supposed to use one appliance on each.
Sean made an excellent reply regarding the benefits of isolation. However, I think the best application is to simply purchase a manufactured component that uses isolation like the Panamax MAX units. It is a much more elegant solution then attempting to loop together multiple transformers. For maximum safety, you are supposed to spec all transformers to carry GREATER than the full maximum fault current.
The next best solution is to avoid sharing the neutrals between circuits. This is really the only benefit I can see to installing a dedicated circuit. An individually home run circuit to the main panel is going to have the "quietest" power possible in the house (without any further isolation or filtering). Period! The use of 10 gauge wiring doesn't hurt, but the difference in resistance between even 100ft. of 10ga. and 12ga. Romex is only about 0.8 ohms! For a typical 30 foot run, with a load current of even 10 amps the gain in supply voltage at the component is less than 1/4 volt! A gain? Yes. Minimal indeed. But for the additional cost, why not. But it does not increase current draw capability! 10ga. simply heats up a small increment less than 12ga. under the same current load.
That's my take on it. I hate to say it, but anything more exotic (Cryo-outlets, $5000 power cords, plutonium bricks) goes really beyond the bang-for-buck scale. The gains per dollar spent become microscopic.
Respectfully,
Mike
MASS lic. building inspector
IAEI Certified Electrical inspector
