I was going to say that there recently was a thread on this topic, but I think you are familiar with it
http://forums.mikeholt.com/showthread.php?t=108500
I appreciate your bringing up this topic again, because I thought through a post but never wrote it up. mdshunk brought up some good points about properly and reasonably selling to these customers.
As was suggested in that previous thread, I believe that fixing any issues with unbalanced _current_ would give better 'bang for the buck' and not only code legal, but possibly code required. I believe that a couple of amps flowing in a large loop is more likely to influence a human than a 120V conductor sitting right beside a 0V conductor. There are numerous wiring errors which can cause unbalanced current flows which lead to magnetic fields; correcting these errors will also lead to a safer and more code compliant wiring system. There are a few code acceptable installations that lead to large magnetic fields; correcting these is a design issue, but not one that will put you at odds with the code.
I agree that 'in theory', a properly installed technical power system could be safe in a home, but proper design of such a system is not trivial. For example, a standard 120V load becomes a 'line to line' load, and requires a double pole switch; switch loops become a nightmare. No more MWBCs. No more devices that require a grounded conductor for safety (no more 'screw shell' lamp holders). Many common appliances would not be suitable for installation on such a system. Code doesn't prohibit such a system in suitable locations, but places the 'conditions of supervision and maintenance' requirement that would make it nearly impossible to legally install in a home.
If I were an EC (I'm not) dealing with this customer (I'm not), I would proceed as follows:
I would not dismiss what the customer is feeling; "there are more things in Heaven and Earth than I can imagine in my philosophy"
I would try to educate them on the difference between current (causing magnetic fields) and voltage (causing electric fields) and try to steer them to correcting current issues before correcting voltage possibilities.
I would sell them the followings _staged_ approach.
1) Magnetic field survey. If there are a few easily corrected wiring errors causing magnetic fields, then repair these on a T+M basis. If there are extensive problems, then go immediately to step 2)
2) If solving unbalanced current issues doesn't provide relief, or if there were so many such issues as to make rewiring cheaper, then sell a complete rewiring job. This complete rewiring job would _not_ be a 'balanced power' system, rather it would be a standard code compliant system in _metallic_ wiring methods, intentionally designed to be easy to convert to balanced power. For example, no MWBCs are used _or_ MWBCs have low loading so that they can be converted to a single 120V circuit. No switch loops used, so that double pole switches could easily be installed in place of single pole switches. Large enough switch boxes, etc. All light fixtures selected to be safe on a balanced power system, no screw shells.
Essentially you are fixing all current balance issues, installing metallic shielding, and making the 'balanced power' installation 'drop in'.
3) If the customer pays for it, possibly concurrent with 2), get a lawyer and the AHJ involved to figure out the legal requirements for installing a balanced power system. Perhaps the 'conditions of supervision' requirement could be met if the customer has _prepaid_ for a service contract, so that they always call you to fix their system. You don't want the liability of a very non-standard system and a hack or handyman. I'm sure that such a system can be built safely, but there will be non-trivial legal hoops.
4) If 2) doesn't solve the problem, and 3) gets resolved, then install a transformer and switch things over to make the 'balanced power' system.
Additional issues to consider:
1) Currents not considered part of the electrical installation can lead to magnetic fields. For example, you may find current flow on metallic water pipes, even with the power off to the home. Perhaps this should be corrected before paying for balanced power.
2) Many appliances produce significant magnetic or electric fields, even on a balanced power supply. It may pay to substitute appliances before doing any wiring.
3) Residential single phase 120/240 service _is_ balanced; with clever installation you could maintain this balanced nearly to the point of use. Consider a room with some recessed cans. You could wire this so that you have equal numbers of 'opposite phase' cans, all using a single 14-2-2 cable (no shared neutral, two circuits).
4) It may be easier to provide a code compliant low voltage DC system for residential use. This would eliminate the 60Hz AC entirely.
-Jon
