number of electrical wires in conduit

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  #41  
Old 03-10-02, 08:55 PM
Wgoodrich
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The key thing that is hazards to the point of being a life safety issue is that DIYers that do not know what a neutral is thinks and does connect two 120 volt breakers from the same line 1 or same line 2 using the single white wire as there return path. When this is done the two breakers do not counter each other and adds the total load on each breaker to the one single white wire which is a grounded leg because there is no two phases present. This is highly dangerous and is strictly against the NEC.

The NEC is word the way it is in an attempt to prohibit the use of one white grounded leg to serve two breakers that are in phase with each other thus adding the total amp capacity of the two beakers combined onto the white grounded leg. This is why a grounded leg must be counted as a current carrying conducitor concerning 310.15.B.2

A neutral conductor carries the unbalanced load between two hot conductors that measure a voltage between the two hot conductors. Therefor the two hot conductors counter each other and the neutral can have zero load on that neutral if the two hot conductors that read voltage between those two hot conductors are balanced. The neutral only would carry that load that is unbalanced between the two hot conductors that measure voltage between them.

If the above is not known the white grounded leg can be way overloaded and will overheat and will start fires.

Very important splitting of hairs.

I know the term neutral is a common terminology when talking electricity used both for a neutral and a grounded leg. However the difference in electrical design is very dependant on designing a neutral or designing a grounded leg is paramount.

Never connect two hot conductors in phase with each other to only one white conductor that is required to serve two different breakers on the same phase. You will not only be inviting a fire you are asking for a fire. The white wire carrying the two hot conductors of the same phase on two different breakers can and will add load to that white wire beyond its ampacity. That white grounded leg serving two hot conductors of the same phase on two different breakers will not be carrying any unbalanced load of those two breakers, but that white grounded leg will be carrying the total load of both breakers added together. This grounded leg is not subtracted from each breaker's load as a neutral conductor would experience.

Hope this helps

Wg
 
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  #42  
Old 12-15-04, 01:57 PM
jsforrest
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So, in the end...??

Sorry, I got a little lost in the debate here and was having trouble wading through the posts....Can I just ask a simple question?

I am running short sections of conduit from my outdoor circuit breaker box to the under-house crawl space. These are only about 4 feet in total length. They will terminate in junction boxes, where I will make connections to romex.

Lets assume I use standard DIY wiring, running a black, white, and green 12 guage line for each circuit I am adding. How many circuites can I place in a conduit without having to install smaller breakers? I have all 20 amps in the box now.
 
  #43  
Old 12-15-04, 02:17 PM
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Four......
 
  #44  
Old 12-15-04, 03:34 PM
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I just wanted to give a to this thread! Thanks guys (and gals if any here) for the good lesson. Oh, and, I scored a 100% on the quiz if you're willing to take me at scouts honor.


It was explained to me by a couple of electricians how to do a multiwire circuit (one 12-3 to feed dishwasher and garbage disposal with their own breakers). I was cautioned to be sure to put the two breakers on separate phases. In the end, I decided not to go the multwire route because it would be too easy for someone to go behind me in the box and move one of the breakers (say to make room for a 220 breaker), placing both on the same phase. For that matter, it would be easy for me to do that. I decided for my own sanity not to mess with them, even though the concept makes perfect sense.

I had thought in the past that a multiwire circuit would be the perfect way to wire a kitchen...let the top half of each duplex recepticle be on one, the bottom on the other, share the neutral. I realize now that wouldn't work, because of GFCI protection...the shared neutral would not allow for the use of GFCI breakers or outlets, as it would carry unbalanced loads, thus tripping the GFCI's automatically. Am I thinking right?
 
  #45  
Old 12-15-04, 04:57 PM
jsforrest
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Originally Posted by John Nelson
Four......

Thanks John!
 
  #46  
Old 12-16-04, 02:28 PM
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Originally Posted by girlbuilder
Thanks for your reply. No I didn't understand that last sentence. Why would the breaker need to be derated is there are more than 3-3 wire cables in the conduit? Most of the rewire is done and I did pay attention to amperage and the other rules about wiring that I was aware of, but this is new to me.
Thanks, girlbuilder
You should not be running cables in conduit. You should be running individual conductors.
 
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