Well I have to join in rejecting the idea that multi wire branch circuits are inherently problematic. I won't argue about the audio circuits because my experience does not include extensive audio system work. The housing industry is very competitive and every legitimate avenue to control cost must be explored. My present work is in home wiring repair and extension. I will pull a three wire plus ground cable if I even suspect that there will be a need for another circuit in the same part of the building. I undertook to wire a dedicated outlet for a sump pump as a "Christmas in April" project. I looked around the sump pumps location and there was the laundry equipment tied into a general lighting circuit. I pulled a three wire cable to the four square that contained the laundry equipment receptacle and ran the sump pump receptacle outlet from there. A very slight increase in cost and a marked improvement in the whole homes wiring plant. Since the laundry appliances are not left unattended for days at a time I used a GFCI receptacle for them but the sump pump is on a single 20 ampere receptacle.
I pull three wire cables to bathrooms now to solve the monster hair dryer problem. Not only does the basin outlet end up resupplied but so does the thousand watt plus unit heater that so many bath rooms have.
Multi wire branch circuits are also handy to supply existing out buildings. One car garages and small sheds often need just a little more but a feeder, grounding electrode system, and building panel is a budget buster.
[RANT MODE ON] It ties right into a sore subject. Anyone that cannot work safely with a multi wire branch circuit has no business doing electrical work. I am not opposed to home owner DIY work but if you can't take the time to understand enough about wiring to make a multi wire branch circuit just another useful technique then you haven't done enough studying yet. Invest the time to learn or hire someone who has done so. A person who gets hurt because they opened the neutral of a multi wire branch circuit is the definition of an UNQUALIFIED PERSON. [/RANT]
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Ton H
