COMMUNITY FORUM

budlightdeuce

06:32PM | 10/15/02
Member Since: 10/14/02
1 lifetime posts
Bvelectrical
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
76 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).]

tdhorne

10:06AM | 10/16/02
Member Since: 09/01/02
26 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.
--
Tom

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.

motor-T

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.

Mark

Click_to_reply_button
Inspiration_banner

INSPIRATION GALLERY



Post a reply as Anonymous

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

Reply_choose_button

captcha
type the code from the image

Anonymous

Post_new_button or Login_button
Register

Carefully using a ladder or binoculars, check the roof for any raised shingles. If there are any signs of damage or wear, ... It turns out that many bath and kitchen cleansers contain chemicals that are dangerous to the skin and eyes, and often pro... So often we paint tiny nooks white to make them appear larger, but opting for a dark, dramatic wall color like this one—Be... Chocolate-colored walls and large window frames allow the exposed wood beams to take center stage in this small screened p... If you're not crazy about the idea of commingling plants and pool, this modern variation may be more to your liking. The s... Yes, a freestanding garage can become its own tiny house. Artist Michelle de la Vega has all the comforts of a modern resi... There’s nothing like a new set of cabinet hardware to refresh a room. The possibilities are endless: Go modern, rustic, or... Pursue what's known as the stack effect. To achieve it, open the windows on both the upper and lower floors, and as warm a... Like no other floor type, a checkerboard design works wonders to underscore the retro kitchen theme. Vinyl flooring, ceram... Twine lanterns add pops of crafty—but sophisticated—flair to any outdoor setting. Wrap glue-soaked twine around a balloon ... When securely fastened to a tree or the ceiling of a porch, a pallet and some cushioning make the ideal place to lounge. V... Incorporate nature into your lighting scheme by securing a dead tree in a concrete mold and draping your pendant lamp from... For the cost of a can of exterior paint , you can totally transform your porch. Paint the floor a hue that complements yo... In this urban apartment, a standard-issue patio became a serene and green perch by replacing the typical concrete with gro... If you put the washing machine in the mudroom, you can stop the kids from walking through the house in dirty, grass-staine...
Follow_banner_a
Newsletter_icon Google_plus Facebook Twitter Pinterest Youtube Rss_icon
 
webapp1