On Fri, Mar 12, 2010 at 5:16 PM, Peter J. Thomas <pj_thomas@comcast.net>wrote:
> On 3/11/2010 5:35 PM, Doug Braun wrote:
>
>> Hello,
>>
>> I want to install an electrical outlet (the standard 120V duplex type) in
>> a box where both phases (sic) are available. I have noticed that duplex
>> receptacles normally have both sockets connected together, but there are
>> little break-away tabs that would allow you to wire each socket
>> independently. So, i was thinking of hooking up the receptacle so that each
>> of the 120v phases was connected to a different socket (and of course the
>> neutral was common to both).
>>
>>
> Do not use a common neutral. Each outlet needs is own common return. If
> you use a 20A duplex break and 12 gauge 3 wire (4th wire bare ground) romex
> (rated 20A IIRC) and install 20A outlets, the two hot leads will be
> protected to 20A but a common return could be carrying 40A if you plug in 2
> 20A loads, twice the rating for 12 gauge.
12/3 is generally legal for a mulitwire set up like this; the two hots are
on different sides of ground (240 between them; 120 to ground), so there's
no (real; there's theoretical ways to do it that don't happen in the real
world) risk of overloading neutral. There are issues with GFCIs on
multi-wire circuits. if you need GFCI, you need to either use a GFCI
breaker designed for the purpose (expensive!) or split the run (into 12/2)
before the first outlet, then you can use a GFCI as the first outlet on each
side, or you can use a GFCI at each outlet.
(There may still be some cases where the NEC requires an oversized neutral.
I don't know of any, but I'm not a licensed electrician.)
--
David Scheidt
dmscheidt@gmail.com
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