I'm in the process of rewiring my whole house. Currently, I have the raw wiring fed to the breaker. I know this needs to be put in conduit. How many size 12 with ground, can I have in any one conduit. They all run along one wall, can I just get some pvc and throw them all in and mount this to the wall?

 

Are you sure you need them to be run in conduit?
If so, you are permitted 6 thw in 3/4", 10 thw in 1", 19 thw in 1-1/4", 12 thhn in 3/4", 20 thhn in 1", 37 thhn in 1-1/4". The quantity is individual current caring conductors depending on insualtion type (as noted above). Are you running individual conductors or cables with multple wires in each?

 

Keep the number under 10 wires (not cables) per conduit if you want to avoid having to downsize the breaker due to ampacity derating. If you didn't fully understand that last sentence, please do more study before starting your rewire. Good luck.

 

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

 

NEC 310.15.B.2.A table says that if you install 3 current carrying conductors or less the ampacity of a conductor in a conduit can be rated at 100 %. That same table says 4 to 6 current carrying conductors in a conduit must be derated down by 20 %. That same table says 7 to 9 current carrying conductors in a conduit must be derated down in ampacity by 30%. That same table says 10 to 20 current carrying conductors in a conduit must be derated down in ampacity by 50 %. It gets worse from there.

Using that table if you install that 4th 12 awg copper current carrying conductor in that conduit that 20 amp rated wire now must be protected with a maximum of a 15 amp breaker. If you install that 7 th 12 awg copper conductor in a conduit you now are not allowed to install that 12 awg conductor anywhere in the home with voltage rated over 50 volts at all because it is not even 15 amp rated which is the smallest ampacity rating allowed in a dwellng for 120 volts or more.

The reason for the derating of ampacity is because these current carrying conductors are heating each other and unable to cool due to the close proximity of other current carrying conductors in that conduit.

Hope this helps

Wg

 

Thanks, that last paragraph more or less said it all. I do have 20 amp breakers, so I will keep it to 3 or less per conduit. Thanks

 

For the purpose of ampacity deratings and the like, is the neutral wire considered a "current carrying conductor"?

RW

 

Normally it's not but in 3 phase applications were there are lots of 3rd harmonics it is considered a load conductor. But since this is for diyer's working at home neutrals don't count. But they do count for pipe fill.

 

Article 310.15(B)(4) says that "a neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a)" (which is the ampacity adjustment table).

The above makes perfect sense since the sum of the current on all three conductors cannot exceed twice the capacity of an individual wire. So counting the two hot wires is enough.

But in a regular circuit (not a multiwire circuit), the grounded conductors carry just as much current as the hot wires, and they generate just as much heat. There's no excuse for not counting them.

Article 310.15(B)(4)(c) says you don't have to count the grounding conductor.

The NEC does not specifically define the term, "current-carrying conductor." However, except for the exception noted in 310.15, I think it's logical to assume that a conductor that carries current should be considered a current-carrying conductor.

 

Where to you live? Chicago? It just may be possible to use romex instead of conduit. What do you mean by "raw wiring to the circuit breaker?" We're here to help.

 

John your right about counting the neutral since most diyer's would run seperate nuetrals for each hot.

 

Doesn't the number of conductors also get impacted by the type of conduit. PVC is listed in a separate chart?

 

Mike134 you seem to be confusing neutrals and grounded legs. A white wire of a 120 volt receptacle with only one hot wire and one white retrun path is not a neutral conductor but it is a current carrying grounded leg.

A neutral carries the unbalanced load between two hot conductors. All white wires run with only one hot wire in that circuit is a current carry conductor and must be counted concerning 310.15.B.2.A.

You can not have a neutral wire unless it serves two hot wires.

By the way you are right about some three phase systems such as corner grounded delta systems. In the above mentioned three phase system the grounded coductor of the three phase power must be counted as a current carrying conductor.


Hope this helps

Wg

 

WG I'm not confused at all........In Chicago the grounded conductor is always called a neutral and is always white unless it's a 277/480 panel then it's gray. I think your splitting hairs about terminology.......Look at it this way if you open up a panel what gets connected to the neutral bar??? Neutral wires of course......

Mike

 

No.

 

Mike there is a definite difference between a grounded leg and a neutral although they both are allowed to be white and used to be allowed to be natural gray.

A white wire on a 120 volts can definitly be overloaded and can cause a melt down and house fires due to too much load on a circuit. A grounded leg whether white or gray is always a current carrrying conductor

A neutral if a true neutral can never be overloaded as long as the wiring design is a properly balanced system as required by the NEC.

Now to try to show you the difference and to provide proof that I am not just splitting hairs try the following experiment. Then later when you answer this puzzle then someone else can come in and tell you if you are right or not.

EXAMPLE PUZZLE NUMBER ONE;
If you have a normal 20 amp 240 volt branch circuit that you would normally find in a house and there is a neutral used to carry the unbalanced load and if line one hot condductor of this 20 amp 240 volt multiwire branch circuit is carrying 18 amps and the second hot wire of this same 20 amp 240 volt multiwire branch circuit is carrying 19 amps, how many amps can be read on the white NEUTRAL wire that is carrying the unbalanced load?

EXAMPLE PUZZLE NUMBER TWO;

If you have a normal 20 amp 240 volt branch circuit that you would normally find in a house and there is a neutral used to carry the unbalanced load and if line one hot condductor of this 20 amp 240 volt multiwire branch circuit is carrying a full capacity of amp at 20 amps and the second hot wire of this same 20 amp 240 volt multiwire branch circuit is carrying 0 amps, how many amps can be read on the white NEUTRAL wire that is carrying the unbalanced load?


EXAMPLE PUZZLE NUMBER THREE;

If you have a normal 20 amp 120 volt branch circuit that you would normally find in a house then there there has to be a GROUNDED LEG [NOT A NEUTRAL] used to carry the load of that single hot wire back to the neutral bar and if the hot conductor of this 20 amp 120 volt branch circuit is carrying 18 amps and becuase this is a 120 volt branch circuit there is no second hot wire, how many amps can be read on the white grounded wire that is completing the circuit back to the neutral bar?


EXAMPLE PUZZLE NUMBER FOUR;

BE AWARE THAT THIS EXAMPLE IS WHERE THE WHITE WIRE CAN BE OVERLOADED AND START FIRES DUE TO THE CONFUSION THAT ALL WHITE WIRES ARE NEUTRALS. THEY ARE NOT THE WHITE WIRE IS A GROUNDED LEG AND MUST BE SIZED THE SAME SIZE AS THE HOT CONDUCTOR OF A 120 VOLT CIRCUIT.

If you have two hot conductors with both hot conductors being on the same phase or feeder serving that panel. and you use a single white wire [THAT ONLY LOOKS LIKE A NEUTRAL BUT IS ACTUALLY A GROUNDED LEG] serving both hot conductors being power by the same line one of the feeder and if you had the first hot wire carrying 18 amps and you had the second hot wire carrying 19 amps how many amps will be carried on the white grounded leg that LOOKS LIKE A NEUTRAL?

This set of puzzles should show the importance of knowing the difference between the neutral carrying the unbalanced load and the grouded leg acting as a return path completing the circuit.

Remember that a 240 volt circuit with a neutral has two hot wires coming from the panel that measures 240 volts between the two hot wires.

Remember also that two 120 volt circuits being fed by the same line 1 feeding that panel measures 0 volts between the two hot conductors from that same line 1 feeder in that panel.

The misunderstanding that you have spoke of is exactly why I said the white wires that can not be intermixed in a house is intermixed very commonly causing havoc in the electrical designs and also fire hazards are created by that lack of understanding the important difference between a white grounded leg and a white neutral.

Let us know what you calculate the amp loads of those white wires in those 4 puzzles then we can get down to showing you the major IMPORTANT differences between a neutral and a grounded leg.

Remember for us to learn we almost always have to make mistakes, that others catch and then get into detail as to the proper way to have done it.

OLD SAYING

If you are not making mistakes you can not be doing anything. Believe me when I say that I have made way more than my fair share of mistakes. Just ask those that have been in this forum for a long time they can sure attest to me being good at making mistakes in my statements. I have come to believe my mouth must smell like a FOOT !

Good Luck

Wg

 

Hi all,

I don't want to hi-jack anyones thread, but I find myself on the verge of learning something great here. I am dying to hear the answer to the puzzles. no,no, I just cant' wait! Let me take a shot at one.

Puzzle 1. (er, uh, I have 2 candidate answers)
First: 37 amps will be on the 'neutral' wire. (18 + 19 = 37)
Second: 19 amps will be on the 'neutral' wire. Due to the wires being out-of-phase?



Patiently waiting for class to resume....

 

Lugnut, neither of your answers is correct. Think some more on it.

 

How about this? 37 / 2 = 18.5 amps

 

Not there yet. Keep thinking.

 

I'm stumped. Must be a trick question. How about 40 amps, just enought to not trip the breakers?

Another answer. 80 amps or so just before the breakers trip.

 

Nope. Think about the 180 degree phase difference that is the subject of another thread. What would you get if you added the waveform on the red wire to the waveform on the black wire? Also remember that a 12-gauge wire, even a 12-gauge white wire, is only rated to carry 20 amps. If it carries more than 20 amps, it's going to start a fire.

 

I hope I am wrong on this answer, but here goes.

19 - 18 = 1 amp

...something about 'negating 180 out of phase'...

 

1) 1 amp
2) 20amps
3) 18 amps
4) 37 amps

as long as you keep insisting white wires are not neutrals then you need to call hot wires what they really are........ungrounded conductors........boy this is going to get confusing on the job sites........"hey Tom pull more on the ungrounded conductor.......now take up the slack on the grounded conductor.....don't forget to leave a loop on the grounding conductor......I'll stick with hot, neutral and ground thank you.....

Mike

ps what do you call that big white wire in the panel coming from the meter that all those individual grounded conductors are connected to??

 

BTW sometimes your 240 20 amp circuit will be created using 2 single pole breakers and other times a 2 pole breaker is required.

 

While I'm waiting for the test scores, let me reflect on what I think I have learned about residential ground names from the past in this forum.

White wire - ground for a single circuit. Can also be Neutral, see below.
Common wire - Same as White wire.
Bare wire - ground wire for safety.
Green wire - same as bare wire.
Neutral wire - a shared ground for 2 or more different circuits.
Ground - a general term for a wire that leads to a earth ground. Could be white, bare, green, neutral, common.

Is that close enought for horse shoes?

P.S.
Mr Nelson, you mentioned fire hazzard for exceeding 20 amps on 12 gauge ground wire (I hope I quoted you right?) . So I was just wondering.... It that hazzard equal to the hazzard of exceeding 20 amps on a 12 gauge HOT wire? My focus here is that the ground wire will be 7 volts (or whatever) on the return path from a load. While the hot wire will be 110 volts. Does the lower voltage significantly mitigate the risk of fire?

 

Lugnut, you sure are a glutton for punishment!

• The white wire is not "ground" -- it's a grounded wire. There are huge differences between a ground, ground wire, grounded wire, and grounding wire. As long as we're trying to be precise.
• "Common" is another of those informal terms not used by the NEC. But I think most people would equate it to the neutral.
• A "bare" wire is simply a bare wire. Most applications for grounding allow a bare wire.
• A "green" wire is a wire covered with green insulation -- of course, the wire itself is not green. It is not allowed for any purpose except grounding.
• Officially, the term "ground" is used to refer to any connection to the earth. Note that officially the bare wire you see at your receptacles (i.e., the "grounding" conductor) is not a "ground".
• And while we're being picky, the term "wire" is little-used in the NEC. The preferred term is "conductor".

I'm kind of with Mike on most terminology. For purposes of discussion, we usually use hot, neutral and ground. However, if one ever hope to understand what one reads in the NEC, you need to know about the official terms. But if you don't plan to study the NEC itself, then feel free to use hot, neutral and ground.

The amount of heat produced by 20 amps through a 12-gauge wire is independent of the voltage. The heat is the same on an ungrounded conductor on a 120-volt circuit, an ungrounded conductor on a 240-volt circuit, a grounded conductor, or a neutral conductor. 20 amps is 20 amps. The heat produced is W=I*I*R. You can see that it only depends on the current (I) and the resistance of the wire (which is pretty much a constant). Of course, all other things being equal, the current does depend on the voltage, but still -- 20 amps is 20 amps.

Lugnut, are you going to keep after this issue until we publish the entire NEC on this thread?

 

John,

are you going to grade my test scores for WG??

Mike

 

Sorry John, I'm outta here.

 

Mike, I give you 100%. John.

 

Lugnut, I hope it wasn't something I said. You're pushing us all to think about this stuff. You are asking questions that need to be asked.

 

I'm sorry, that was a misspeak. I am using size 12 romex with ground. I live in Iowa.

 

Romex is UL approved to be used in a house without conduit.....check with your local inspector to see if they require conduit..if so then you don't use romex but either solid or stranded THHN wire........keep the number 6 and under and you don't have to worry about pipe size (can all be 1/2 thin wall wether it's 14 or 12 ga.>or derating plus it will be alot less confusing when you trim out

 

Sorry everyone I was called away and had to delay getting back to you on this neutral / grounded leg subject.

To help you understand the term ground try the following link that provides definitions of each term.

http://homewiring.tripod.com/termground.html

I agree with what John was saying on the definitions with the exception of the term common.

Common like John suggested is often referred as he said in generic terms however the term common is a connection in common with. Example of a common conductor can be the black screw of a three way switch. This common conductor is a hot conductor yet is declared as a common connection. The reason it is called a common connection is this black screw of the three way switch is in common with the other two screws depending on the position of the switch. At any given time the two brass screws are never in common with each other yet the black screw is always in common with one of the two brass screws.


Wg

 

EXAMPLE PUZZLE NUMBER ONE;
If you have a normal 20 amp 240 volt branch circuit that you would normally find in a house and there is a neutral used to carry the unbalanced load and if line one hot condductor of this 20 amp 240 volt multiwire branch circuit is carrying 18 amps and the second hot wire of this same 20 amp 240 volt multiwire branch circuit is carrying 19 amps, how many amps can be read on the white NEUTRAL wire that is carrying the unbalanced load?

ANSWER; 1 AMP BEING THE UNBALANCED LOAD BETWEEN THE TWO HOT CONDUCTORS IN A MULTIWIRE CIRCUIT HAVING TWO HOT CONDUCTORS OF OPPOSITE PHASES. THE TWO OPPOSITE PHASE COUNTER ACT EACH OTHER SAME AS A 220 VOLT CIRCUIT WITHOUT A NEUTRAL WIRE HAVING THE LOAD TOTALLY 220 VOLT. IN THE ABOVE PUZZEL YOU HAVE AN UNBALANCED LOAD SHOWING A 120 VOLT LOAD. THEREFORE THE NEUTRAL CARRIES ONLY THE LOAD THAT IS NOT MET BY THE TWO OPPOSITE HOT LEGS AS JOHN EXPLAINED.

EXAMPLE PUZZLE NUMBER TWO;

If you have a normal 20 amp 240 volt branch circuit that you would normally find in a house and there is a neutral used to carry the unbalanced load and if line one hot condductor of this 20 amp 240 volt multiwire branch circuit is carrying a full capacity of amp at 20 amps and the second hot wire of this same 20 amp 240 volt multiwire branch circuit is carrying 0 amps, how many amps can be read on the white NEUTRAL wire that is carrying the unbalanced load?


ANSWER;

20 AMPS ON THE NEUTRAL IS CONSIDERED AS THE LOAD ON THE NEUTRAL BECAUSE THERE IS NO LOAD ON THE SECOND OPPOSING HOT LEG OF THE MULTIWIRE CIRCUIT.


EXAMPLE PUZZLE NUMBER THREE;

If you have a normal 20 amp 120 volt branch circuit that you would normally find in a house then there there has to be a GROUNDED LEG [NOT A NEUTRAL] used to carry the load of that single hot wire back to the neutral bar and if the hot conductor of this 20 amp 120 volt branch circuit is carrying 18 amps and becuase this is a 120 volt branch circuit there is no second hot wire, how many amps can be read on the white grounded wire that is completing the circuit back to the neutral bar?

ANSWER;


THE WHITE GROUNDED LEG WOULD HAVE TO BE SIZED TO CARRY THE SAME AS THE HOT LEG BEING 18 AMPS THEREFORE THE WHITE WIRE MUST BE SIZE 20 AMP ALSO.


EXAMPLE PUZZLE NUMBER FOUR;

BE AWARE THAT THIS EXAMPLE IS WHERE THE WHITE WIRE CAN BE OVERLOADED AND START FIRES DUE TO THE CONFUSION THAT ALL WHITE WIRES ARE NEUTRALS. THEY ARE NOT THE WHITE WIRE IS A GROUNDED LEG AND MUST BE SIZED THE SAME SIZE AS THE HOT CONDUCTOR OF A 120 VOLT CIRCUIT.

If you have two hot conductors with both hot conductors being on the same phase or feeder serving that panel. and you use a single white wire [THAT ONLY LOOKS LIKE A NEUTRAL BUT IS ACTUALLY A GROUNDED LEG] serving both hot conductors being power by the same line one of the feeder and if you had the first hot wire carrying 18 amps and you had the second hot wire carrying 19 amps how many amps will be carried on the white grounded leg that LOOKS LIKE A NEUTRAL?

ANSWER;


37 AMPS MUST BE CONSIDERED AS BEING CARRIED ON THE WHITE WIRE BEING A GROUNDED LEG. THIS WIRING STYLE IS A VIOLATION OF THE NEC BECUASE YOU CAN HAVE A MELT DOWN HAVING ENOUGH AMPS ON THAT WHITE WIRE TO ALMOST BE TWICE ITS CAPABILITY TO CARRY THE LOAD. YOU WOULD HAVE TO CONSIDER THIS WHITE GROUNDED LEG TO BE A 20 AMP RATED GROUNDED CONDUCTOR THAT IS CONSIDERED TO BE CARRYING 37 AMPS WAY OVER ITS AMPACITY.


This set of puzzles and the accomanying answers should now show the importance of knowing the difference between the neutral carrying the unbalanced load and the grouded leg acting as a return path completing the circuit. Fires and life and limb depend on you knowing the difference between the neutral conductor and the grounded leg.

Remember the white wire to a receptacle is a grounded leg. The white wire of two hot conductors of opposing phases is considered a neutral. There is definitly a big difference between the two that can cause fire and injury and maybe even death if not known.

The above discussion is the reason that often times John and myself and Sparky and many others that reply advise that multiwire circuits are not for the DIYer to use but only for the advanced electricians that know the difference between a neutral and a grounded leg.

This difference between a neutral and grounded leg can more easily be seen in a commercial motor load design having three phase [three hot conductor] while 120 volt and single phase 240 volt is installed while using only one or two of the hot conductors. In this case if you don't balance the laod properly as the NEC requires then you can overload even a neutral conductor very easily.

This is also why i worry about the rules in Chicago and other places that require conduit in homes. Home owner's are not oftenknowlegable enough to understand what we are saying in this post yet the conduit design most commonly promote multiwire circuits. If a grounded leg is used as a neutral fires can be almost a certain result. I have always had a concern in this conduit rule be used with home owners without the knowledge to know the difference between neutral and grounded leg in conduit system wiring style.

Confusion is very very common thinking that a white wire is always a neutral inviting overloading a grounded leg in a 2, 3, 4 gang switch box with all the white wires wire nutted together. Makes for dwellings to be very messy in wiring design causing the odd readings between white and non-loaded bares.

Hope this helps

Wg

 

Just thought that I would clarify one thing left unsaid to my knowledge, however it may have been said and I missed it.

When calculating ampacity derations only current carrying conductors are counted in the number of current carrrying conductors in a raceway as per 310.15.B.2.A.

White or gray nuetrals that carry only the unbalanced load is not counted in the above chart for ampacity deration

White or gray grounded legs that act as a return path of a single hot conductor of a branch circuit must be counted in the deration calculation using table 310.15.B.2.A.

Hope this helps

Wg

 

WG I have to disagree with your example #2

A "normal" 240 volt circuit with one leg loaded at 20 amps and the other at zero doesn't happen in any situation I can think of other than a split wired recepticle located in a kitchen for example<SP>. A more correct discription would be 2- 120 volt circuits sharing a neutral one obtained from the A phase the other from the B phase .

 

Mike, back we go to the technical and precise language of the NEC. When you have "2- 120 volt circuits sharing a neutral ", the NEC considers that to be one circuit, not two. Of course, in our normal imprecise language, most of us speak of that as two circuits, since it acts a whole lot like two circuits. But it really is simply one 240-volt circuit as Wg said.

 

I have to disagree John because if I took a wiggy and measured across the load I'd only come up with 120 volts on either circuit. Only when you don't connect the neutral into the circuit and only use the hots do you have a true 240 volt circuit. For example a dryer runs at 240 and it's elements are UL labeled at 240 volts and they do not connect to the neutral/grouned conductor however the light bulb and perhaps the drum motor run at 120 volts and are UL labeled at 120 volts and require connection to the neutral.

Think we'll ever stop splitting hairs??

 

Well, this is one of those hair-splitting discussions, isn't it? We wouldn't want to go on like this on every thread, but once in a while isn't too bad.

I guess my only reply is that the NEC doesn't necessarily conform to what you or I might think is logical. The fact that a multiwire circuit seems like two 120-volt circuits rather than one 240-volt circuit doesn't change a single word of the code.

The NEC definition of a multiwire branch circuit in article 100 is "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." Note the use of the singular in all uses of the word "circuit". However, just to keep things confusing, in 210.4(A), the NEC says that "a multiwire branch circuit shall be permitted to be considered as multiple circuits." Go figure. I think the bottom line is that we are all correct, even though we are all saying different things.