# Why does a double fed receptacle trip the breaker (actual science behind it)



## McClary’s Electrical (Feb 21, 2009)

Breakfasteatre said:


> split recepticles
> 
> recently i had a friend ask me why when he replaced receptacles in his moms kitchen, that when he turned the power back on, the breaker tripped.
> 
> ...


You are bucking phases. It's a 240 volt dead short.


----------



## Shockdoc (Mar 4, 2010)

That is first grade stuff. Reminds of how i had to replace a three wire feed because some idiot buried a splice and fed a 3 wire with two 2 wires today.


----------



## electricalperson (Jan 11, 2008)

i forgot to break a tab on a switched receptacle before back when i was new. all that happened was the switch did not control the receptacle because it was fed from the same circuit. back fed the switch.


----------



## macmikeman (Jan 23, 2007)

I know the code allows the practice of multiple circuits on single yolk devices, but I always thought it was a stupid way to wire in general. I know, I know,- no difference from that and a 240 volt receptacle outlet, or it is common practice in some arena's and all that, I get it. I just always considered it a lame way to go thats all. Lamer than backstabbing or using crimp tubes, or putting in receptacles ground up, or using blue carlon boxes, or dozens of other things kicked about frequently on this and the other sites... Its just me, but I don't make it my habit.


----------



## Dennis Alwon (May 9, 2009)

If the receptacle was a multiwire branch circuit it would be a dead short across phases. If the circuits were on the same phase then nothing would happen unless they had gfci protection.


----------



## Dennis Alwon (May 9, 2009)

Shockdoc said:


> That is first grade stuff.


 Hey Doc, this is not helpful and you had to begin somewhere. Try and be helpful not hurtful. Thanks


----------



## Chris1971 (Dec 27, 2010)

Dennis Alwon said:


> Hey Doc, this is not helpful and you had to begin somewhere. Try and be helpful not hurtful. Thanks



Quit being so hurtful.


----------



## retiredsparktech (Mar 8, 2011)

Dennis Alwon said:


> If the receptacle was a multiwire branch circuit it would be a dead short across phases. If the circuits were on the same phase then nothing would happen unless they had gfci protection.


 You can't do it that way because you are sharing a neutral. The code requires that you use a double braker for this application.


----------



## retiredsparktech (Mar 8, 2011)

retiredsparktech said:


> You can't do it that way because you are sharing a neutral. The code requires that you use a double braker for this application.


 Shoot, meant double pole breaker, common trip.


----------



## 480sparky (Sep 20, 2007)

Shockdoc said:


> That is first grade stuff. ...........


Not me. I learned this in kindergarten, and I understand it's being taught in preschools and daycare centers now. I've also heard there's legislation being proposed to introduce this to newborns in hospital maternity wards.

Maybe some time in the future scientists will be able to alter the parents DNA so a child is genetically born with such knowledge.


----------



## McClary’s Electrical (Feb 21, 2009)

retiredsparktech said:


> Shoot, meant double pole breaker, common trip.


 

Good point, but that just started in '08. They're everywhere without them, and many places are still on '05 code.


----------



## McClary’s Electrical (Feb 21, 2009)

Breakfast eater PM'd me and want this discussion to become more technical and scientific. Obviosly this could get rather in depth but this is a summary if someone wants to add to it.


When electricity is generated it is generated in a circular motion of rotation. There are poles in the generator that create the magnetic field. The poles are positioned around the rotation of the generator. Each pole is a phase. An electrical meter measures the difference in potential in two points. So your two points in the first measurement(one side of the split receptacle) would be phase to ground and give you 120 volts. The second meaure (on the other side of the split receptacle) would be phase to ground also and again give you 120 volts phase to ground. The meter has read you the difference of potential between phase and ground in those two locations. Now take your meter and read phase to phase. The difference in potential is no longer phase to ground, but phase to phase. Each phase in a 120/208 3 phase service is generated 120 degrees apart from the opposing phase. So the difference in potential from phase to phase becomes 208 rather than the 120 you see phase to ground. Think of a compass on paper. Start in the center, 120 degrees to one point, then the opposire direction to the same 120 degrees away. Now measure between the two. That will show the difference in potential when those two phase short.


----------



## RobTownfold64 (Mar 17, 2011)

retiredsparktech said:


> Shoot, meant double pole breaker, common trip.


It doesn't have to be a 2 pole breaker or common trip. Separate breakers with a handle tie is all that is required.


----------



## oliquir (Jan 13, 2011)

macmikeman said:


> I know the code allows the practice of multiple circuits on single yolk devices, but I always thought it was a stupid way to wire in general. I know, I know,- no difference from that and a 240 volt receptacle outlet, or it is common practice in some arena's and all that, I get it. I just always considered it a lame way to go thats all. Lamer than backstabbing or using crimp tubes, or putting in receptacles ground up, or using blue carlon boxes, or dozens of other things kicked about frequently on this and the other sites... Its just me, but I don't make it my habit.


maybe it is stupid in US but in canada we had to do that in kitchens before the CEC accepted the 20A receptacle


----------



## macmikeman (Jan 23, 2007)

oliquir said:


> maybe it is stupid in US but in canada we had to do that in kitchens before the CEC accepted the 20A receptacle


Then as a native I would have to say double stupid...:laughing:


----------



## crosport (Apr 4, 2010)

macmikeman said:


> Then as a native I would have to say double stupid...:laughing:


 What?You can't see the advantage of a split recept.Not a difficult concept to grasp.


----------



## Dennis Alwon (May 9, 2009)

retiredsparktech said:


> You can't do it that way because you are sharing a neutral. The code requires that you use a double braker for this application.


Sure but the op is not asking about code. He was asking about double fed which isn't legal anyway. :thumbsup:


----------



## oldtimer (Jun 10, 2010)

Dennis Alwon said:


> Sure but the op is not asking about code. He was asking about double fed which isn't legal anyway. :thumbsup:


 Suppose the outlet was double fed, from two breakers off the same bus.

Not only is it not legal or logical, it can be dangerous. Think about it!


----------



## Dennis Alwon (May 9, 2009)

oldtimer said:


> Suppose the outlet was double fed, from two breakers off the same bus.
> 
> Not only is it not legal or logical, it can be dangerous. Think about it!


I don't want to think about it I have seen it a few times.


----------

