06:32PM | 10/15/02
Member Since: 10/14/02
1 lifetime posts
Why is it u cannt put a 3 wire(ie a 14-3 homerun)on the same phase? Nobody seems to be able to give me a stright answer.

Electrical Inspector

01:19AM | 10/16/02
Member Since: 09/27/02
73 lifetime posts
note this pictoral here budlightdeuce;

see how the top AC waveform alternates.

now imagine the 'white' or 'nuetral' of your 3 wire as the line in the middle, it will see the 'return' current of both 'phases', but they will cancel each other out.

i.e- if your 3 wire were to be served via 2 breakers on the red & black, and said breakers were of phase A & B , each pulled 10 amps, no current on the nuetral.

If A pulled 10 amps, and B pulled 5 amps, there would be only 5 amps 'return' on the nuetral.

should the breakers have been both A phase, the nuetral would 'return 20 amps, and 15 amps in the above examples.

i hope this helps, others may imbelish....

[This message has been edited by Electrical Inspector (edited October 16, 2002).]


10:06AM | 10/16/02
Member Since: 09/01/02
25 lifetime posts
You may find the NEC definition of this kind of circuit instructive. As long as there is a voltage between the two ungrounded conductors as well as an equal voltage between each of the ungrounded conductors and the grounded conductor then the current on the grounded conductor will be the difference between the currents on each ungrounded conductor. If the two ungrounded conductors are supplied from the same voltage source so that there is not a voltage between them then the current in the grounded conductor does not cancel but adds instead. Since each ungrounded conductor is protected at it's ampacity and the grounded conductor, which is the same size and has the same ampacity, does not have any over current protective device (OCPD) it can be overloaded, fail, and cause a fire.

The three wire version of this circuit was invented by the edison electric company and was used with Direct Current. This is why the three wire version of the circuit is called an "Edison Circuit" to this day. The original edison circuits were supplied by series wound generators and balancer sets. These three wire "Edison Circuits" were later converted to AC by center tapping single phase step down transformers. The four wire version was developed by Tesla and is only used with three phase Alternating Current.

DC Edison circuits are still used in modern practice to supply emergency lighting panels in some buildings. Under normal power the three wire feeders to the emergency lighting panels are supplied from a single phase AC supply. When the AC supply is lost and the transfer equipment drops out onto the DC supply a 220 to 240 volt battery array that is center tapped to limit the voltage to ground to half the end to end voltage carries the load.

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.


01:45PM | 10/17/02
Member Since: 09/27/02
9 lifetime posts
Using your question, of a 14-3 on the same phase, the short answer is it would seriously overload the neutral. Worst case would be 15 amps on each leg there would be 30 amps returning on the neutral.


Click to reply button
Inspiration banner


Post a reply as Anonymous

Photo must be in JPG, GIF or PNG format and less than 5MB.

Reply choose button


Post new button or Login button

To test the boundaries of small-footprint living, interior designer Jessica Helgerson moved her family to a 540-square-foo... Filling an underutilized area beneath the stairs is a smart way to save space. Doing so with a stash of wood, however, is ... The Audubon Society inspired wallpaper in this Adirondack-styled mudroom will get you in the outdoor mood. Grab your coat ... Chalkboard paint opens up endless possibilities for customizing your dresser time and time again. Use chalk to label the c... A fireplace in the bathroom creates the ultimate setting for relaxation. Homeowners often choose electric or gas over wood... This roomy boot tray made from punched metal stands up to all the elements. Station it in your mudroom or at your back doo... There’s nothing like a new set of cabinet hardware to refresh a room. The possibilities are endless: Go modern, rustic, or... FLOR tiles are an affordable way to customize a carpeted floor covering for any space. Make anything from runners to wall-... Chalkboard paint features prominently in this elegant yet unpretentious headboard design. Add a new message daily to reflec... Salvaged boards in varying widths and colors make up the dramatic accent wall in this attic space. The high-gloss white of... The indecisive homeowner need not fret over choosing one (or even two) cabinet colors. The kitchen cabinets in this artist... Incorporate nature into your lighting scheme by securing a dead tree in a concrete mold and draping your pendant lamp from... Simple and striking, a couple of pieces of "lovingly used" furniture creates a special kind of charm. A weathered chair fo... First dress up your metal shelves with a coat of paint in an accent color that complements your kitchen decor. Then arrang... Dark wood shelving and a matching upholstered bench keep this closet sleek and refined. The large window brightens the sub...
Follow banner a
Newsletter icon Flipboard glossy Facebook Twitter Pinterest Youtube Rss icon