it is very common to start with a larger than required (for the breaker) and then downsizing the wire when reaching a point that the larger wire is no longer needed.
It happens when the wire is derated to account for voltage drop.

there are many instances where that would be permitted by code, but if it's just a general purpose branch circuit on a 20 amp breaker then no, you can't do that. if it's on a 15 amp breaker it's fine.

The breaker MUST be sized to the smallest size wire on the circuit. In your example the breaker would need to be 15 amp since the is #14 wire on the circuit.

That should be obvious Joed. But I can just see someone looking in the panel, seeing # 12 wire, and going OHHHH.... I can switch this to 20A! I'll bet even the pros would think about why it's only 15A instead of 20A.

that is why the #12 should be marked at the panel that the circuit contains #14 as well.

"that is why the #12 should be marked at the panel that the circuit contains #14 as well."

I'm not familiar with that Code provision. Chapter and verse, please?

Article 408.4 Circuit Directory
"All circuits and circuit modifications shall be legibly identified as to purpose or use on a circuit directory located on the face or inside of the panel door... " (2002NEC)

I believe using a 15A breaker on 12AWG wire would fall under circuit modifications.

In residential work you shouldn't mix wire sizes in the same circuit (other than appliance whips / pigtails). I think most inspectors would have a problem with it regardless of calculated voltage drop. I know that the ones in my town do.

solarpowered, the chapter and verse would be those of good old fashioned common sense, remember i said SHOULD be, not MUST be. although normel pointed out one that could be interpreted to mean it must.

I do not interpret the NEC as agreeing with most of the posts on this thread. Typing is very slow for me, so read the code for yourself. Article 240.4(D). The permissible applications listed in 240.4(E) and 240.4(G) do not to me seem to fit the proposal originally stated on this thread. There is lots of bad information posted on various forums.

Just about the time when I thought I had heard it all........ I have never heard of down sizing wire gauge in the middle of a circuit. It's not a pratice allowed in Dallas, let alone done.

i have mixed in extreme cases... like when we moved out main panel. i had to extend a few ccts, and didnt have any 14/2 on hand, but had alot of 12/2. it is CLEARLY marked at the panel that it is a 15 amp cct and contains 14 awg wiring on the cct.

bus driver; not sure what you are saying. We are not talking of tap conductors or the conductor being undersized for a particular breaker rating. As long as the breaker is sized for the smallest portion of the circuit (with the excpetion of tap conductors ) you can change the size whenever you feel like it.

Texasredhead; can you cite a code section that would dissallow the practice?

davidlaferney: I believe the inspectors either have a reason that you are not understanding (or maybe the situation itself) or they are mistaken as to the requirements of the code

jmorrow; you are simply wrong.

I do like and support the idea of making notation in the panel. Normals cite could be used by an inspector to require such. Yes, too many people look at a wire size and figure they are safe to upsize the breaker to the max allowable on that wire size, sometimes mistakenly. This would help prevent this practice.

I am not an expert, but it doesn't appear to me that this practice is prohibited by code. However, I think (stress : personal opinion) that it is not a good or workmanlike practice. It will be more straightforward to use the same size of wire throughout the circuit.

dozer,

i am most certainly not wrong. there are many situations where that would be permitted by code. you are just ignorantly assuming that the original poster was refering to a general purpose branch circuit. not enough information was given to even suggest that notion. i can think of a situation where you could downsize to #14 protected by a 100amp breaker, but i guess that info isn't included in the "electrical wiring for dummies" book you obviously learned from. maybe you should write a letter to georgia's secretary of state and ask her to revoke my master electricians license. and as for the panel labeling thing, a modification to a circuit would mean that whatever equipment or devices the branch circuit extension controlled must be labeled. no electrician would ever change a breaker size just because it could be bigger. harry homeowner may, but that is none of the nec's concern. what's to stop ol' harry from putting a 60 amp breaker on a piece of 12 so "it will have more power" (

give me code that states it is wrong. I cannot think of ANY offhand where it would be illegal.

read the first post again. He gives no clues that it is anything other than a general question about a typical circuit. It is obvious it is concerning a general circuit.

as far as you being right, no, you are still wrong. if I am wrong, supply code to qualify your answer..
quit huffing and puffing and prove me wrong.

davidr; this type of thing is done all the time in commercial applications where wiring runs can be hundreds of feet long. It is done to reduce voltage drop. Actually there is no code requiremnt to upsize the wire since voltage drop considerations are only a suggestion and not a mandate. There is nothing unworkmanlike about it. it provides no benefit to oversize the wire any more than neccessary. After that, you are throwing away money.

Also, around here in commercial work it is common to run up to 10 (without multiwire circuits) or 20 (with multiwire circuits) 20A receptacle circuits in a single pipe by using #10 wire in the pipe, which derates to 20A with 20 or fewer CCCs. Once you start branching out from the homeruns, you can drop to #12.

jmorrow; I could not find an active license for you in Georgia. The closest I could find was this license that lapsed in 2002.

https://secure.sos.state.ga.us/myverification/Details.aspx?agency_id=1&license_id=715362&;

anything more current or active?

240.D doesn't apply to the OP at all. It addresses minimum OCPD's for wire sizes. All it says is you can't put a 20A breaker on 14 guage wire, etc. You can run 12 guage wire for a 15A circuit all day long. Also, I not convinced that that it would constitute "circuit modification", but that would be up to the local AHJ.

You are required by code to derate conductors based on raceway or cable fill and ambient temprature. Table 310.15(B)(2)(a) gives the adjustment factors for derating for number of conductors, and Tables 310.16 through 310.20 show correction factors for ambient temp. Depending on what wiring method is being used, and how it is implemented, it
becomes necessary to use larger conductors to meet code requirements. This does not change the load characteristics of the circuit or the size of the overcurrent protective device, only the wire size. Once again, since you are required to do this by code, I wouldn't call it a circuit modification.

pfmatrix is wrong, but the person who he is arguing with is wrong as well when they say its okay to use 12 and 14 guage wire if the downstream load does not exceed 15A. It's okay to use 12 and 14 guage wire if the OCPD is 15 amps. If the downstream load exceeds 15 amps, the OCPD will open.

This is a quote from the original post: "Other guy says that its perfectly ok to start out as 12 and drop to 14 at a junction box as long as the load down stream from there is not drawing over the 14 gauge wires AMP capabilites." No explanation, no qualifiers. Based on only that statement, I know of no inspector that would accept such an installation. We have been offered examples from the commercial and industrial installations of similar applications to the one described. But many of the readers here are novices here who struggle for understanding if more than two conductors are involved. Never would I do this in a residence. I have certain personal standards that exceed the code and this is one of them.

I agree with davidr. A pratice may be allowed by code but that does not make it a good pratice. Very simply, we use 12/2 for 20 amp circuits and 14/2 for 15 amp circuits all the way on both.

bus driver,

can you please explain to me exactly why its not a good idea to do that?

heres an example:

lets say i am wiring a big bedroom. i would prefer not to use 12 awg in the room itself, as 14 is easier to work with. but i want to have the capibilities to upgrade later so i use 12 awg from panel to the first outlet in the room -- them 14 awg the rest.place that in a 15 amp breaker.

then, 15 years down the road when said bedroom gets remodeled, i want to upgrade to a 20 amp cct, because the kids are now teenagers with tv's, dvd players, video games, computers, cell phones, etc. ALL i have to change is the wiring in the room itself, and not the home run back to the box. change out the breaker to a 20 amp and done.

i am but a novice DIY'er who has read a few books and has a BASIC understanding on electricity. this is one topic i am now completly confused about.

okay, i also remembered seeing this thread a while back whwew a similar question was asked, and bigbird (is he still around??) states that there is no issues with 2 different wire sizes on a given cct, so long as the breaker is sized for the SMALLEST awg wire on the cct...
http://ths.gardenweb.com/forums/load/wiring/msg0406581717130.html

Here is a link that might be useful: another thread similar to this one.

heres an example:

lets say i am wiring a big bedroom. i would prefer not to use 12 awg in the room itself, as 14 is easier to work with. but i want to have the capibilities to upgrade later so i use 12 awg from panel to the first outlet in the room -- them 14 awg the rest.place that in a 15 amp breaker.

then, 15 years down the road ......

Radioguy
If you sell the house instead are you going to rewire before you sell?

Regards
Chris

chris, you make a very good point.

but i what i see going on here is there hasnt been a SPECIFIC reason why you cant/shouldnt mix wire sizes on a given cct, other than its bad practice.

heres a better example.

i am currently building a shed/workshop. at the moment, i will only have the need for 1 cct out there. but if i run a 12 awg out to it, thats all i will be able to have.

if i were to run 8 awg from the main panel out to the shed, then downgrade it to 12 awg to wire outlets and lights. but i still have the option of using that 8 awg to add a 40 amp sub panel down the road if i decide to upreade the shop.

what about in that case?

14 is easier to work with? This has come up time and time again including a discussion about wiring an entire house in 12ga. In our operation it falls to me to install most of the receptacles and switches. We simply do not switch wire sizes in mid-circuit just to make my job easier.

It sounds to me Texas like you and your company have strict standards you abide by. That's commendable. But just because it's your company policy to not change wire size doesn't mean it can't be done, right? It sounds like your policy is a "best practice" and not necessarily code. I'm not trying to argue with you in the least. Just trying to find the truth to this situation.

texasredhead, when you are a DIY'er with limited amout of time each day to work on a project, anything that makes the job a little bit easier is a godsend.

so before this gets too much out of control... and ignoring all my "examples",.

IS IT A VIOLATION OF THE NATIONAL ELECTRIC CODE TO USE A LARGER SIZE WIRE ON A SMALLER BREAKER???

No it is not.

Notice that the original post did not say that the argumentative friend said to protect the circuit at 15 amperes. In fact, the implication is that it would be protected at 20 amperes.

Tell you what, go ahead and install in your house a circuit in which the wire size is reduced at some junction box downstream. Any pro who happens to see it later will declare that it was installed by an amateur!

If voltage drop is a concern, I install the larger conductors for the entire run to keep voltage drop to the minimum.

If voltage drop is a concern, I install the larger conductors for the entire run to keep voltage drop to the minimum.

Dozer's and Solar's comments puzzled me at first. If it's a long run, and you want to reduce voltage drop, why wouldn't you want to use the larger size all the way to the end?

But after some thought I can see an instance in which the practice of upsizing for only part of the run would make sense - where it was the greatest part of the length and enough to reduce the voltage drop as required.

An example would be a detatched garage 100 ft from the house. You are installing a 20a circuit for a couple of receptacles and lighting. A 100' run of 12-2 at 120v would have over 6% voltage drop at 20a. So, you might upsize to #10 for the buried portion, changing to #12 in the garage itself to make the wiring easier.

Personally, I think I'd still carry the #10 on through, but that's me. I can see how some folks would want to use the more "cooperative" #12 wherever possible.

But getting back to the original question, there's no indication that this circuit was to be protected at 15 amps instead of 20 amps. So, I would have to say that, in my understanding of the code, I don't know of any circumstances in which one could still be code compliant while changing to #14 at a j-box.

I do very little because it "makes the job easier" in this type of situation. I upsize and downsize wire because it is required to reduce the resistance to reduce voltage drop. When I downsize the wire at a point further down the line, it is to save the customer money and reduce the price quote. That is how you get jobs

If the upsized wire is on something like a gen purpose recep circuit, it is difficult to figure out where one might reduce the wire size but in circuits such as lighting with a known load, it can be calculated and utilized.
It offers no benefits to continue the larger wire beyonf the point it no longer serves the voltage drop purpose.

as far as bus driver picking the OP's first post apart; I believe you are reading too much into the question. He did speak as to why the he believed it to be a problem:

I think that this would be wrong because someone could put a 20 AMP breaker on this ciruit and part way the wire size would only be rated for 15 amps.

While he did not specifically state that this circuit was on a 15 amp breaker, he did explain that a mistake could be made and upsize the breaker to 20 amp. It does not take much to figure out what he was asking.

"as far as bus driver picking the OP's first post apart" Is this an objection to attention to detail?
"Other guy says that its perfectly ok to start out as 12 and drop to 14 at a junction box as long as the load down stream from there is not drawing over the 14 gauge wires AMP capabilites." How have I read too much into this?

not that sentence BD but it is followed with:

I think that this would be wrong because someone could put a 20 AMP breaker on this ciruit and part way the wire size would only be rated for 15 amps.

Now I may be reading into it myself but what that says to me is that they realize a 20 amp breaker would be oversized so that means they originally have a smaller breaker on it. Since a 15 is the next step down and would be legal (or any smaller breaker for that matter), I surmised that OP started with a 15 amp breaker. I simply feel that in some folks desire to tear apart others, they are trying to make this a bigger issue than what it is and what was intended.

Now here is where I admit my mistake. I don;t know what I read last night but my statement to jmorrow in my second post was incorrect. I reread his post and obviously it is correct. I really do not know what I saw in that that struck me as wrong but as it is written, I see nothing wrong with it.
That doesn't negate the fact he seems to be a bigger jerk than I am as shown in his follow up post but that does not make him incorrect.

My apologies for that to jmorrow.

Wow, coming back to look at my original post I realize now that in my effort to keep the post short I may have left out too much info to get replies without so much differances of opinion. Thing is we where moving a machine at work about 20 feet that was wired from the panel to its own internal fuse block with number 12 red wire. We had no number 12 red instock so he ask me to wire from the junction box above where the machine had set to its new location using the smaller number 14. The ciruit is actually on a 10 AMP breaker. Neither of us are electricans, just experienced maintenace mechanics. My example of someone putting a 20 AMP breaker on this ciruit in the future was based on a situation I had at my house. When I bought the house I had the service upgraded. The electrican that did the work put in the new panel and put in the breakers based on the wire coming into the panel or perhaps based on the current breakers present. Sometime later while doing some home remodeling I found 14 gauge wires tied into 12 gauge wires that where orginal to the house but some previous remodeler taped into. So in that case my house had 14 gauge wire protected by 20 AMP breakers. I changed the breakers to 15 AMP. Thus I assmumed and thought I had read somewhere that was a big no no. I can see the reasons for running bigger wire for long runs and dropping to smaller but If I'm reading all the post right so far the ciruit would only be allowed to have a breaker with the smaller wire size in mind.

If I'm reading all the post right so far the ciruit would only be allowed to have a breaker with the smaller wire size in mind.

with very few specific exceptions, none that would generally apply to a home, that is correct.

i am not sparky, so the above is based on what i have learned here.

The first post mentioned the different ideas/beliefs from two different people. My earlier remarks focused on one idea/belief from one person at a time. That fact seems to have escaped one of my detractors. Now to the original poster. these new facts change the perspective considerably. Should you ever need a lawyer, give him/her all the facts up front. And I do consider an electrician as capable of being a professional as is a lawyer.

It’s allowed where it’s derating for heat, example running 20 amp circuits 10 awg wire in 1 inch emt, after reach junction box you. you split circuits into 3 pipes 1/2 inch. you could run 12awg wire. it’s code legal.

Hello, I'd like to add something that's maybe a bit off the original question, hoping someone can give me advice. In short: (I'm also not an electrician / professional)

I run an extension cord to my car shelter for the block heater and since it is about 70 feet away I chose 12 gauge. But the short piece under the hood is definitely not 12 gauge. (probably 16 gauge)

My question: is the whole effort for nothing because of the changed wire gauge?

Can it cause any problems or being a hazard?

Thanks

I don't think this applies to extension cords, which frequently have wire sizes less than the ampacity into which the cord is plugged.

Thank you for the reply.

Please excuse my ignorance but could you please just confirm or not confirm if:

- if I loose power because of smaller gauge at the end of the line ?

(meaning - will the block heater get less power because of the 2 feet of 16 gauge after 60-70 feet of 12 gauge?)

- if it is a hazard?

Thanks

That's a different question. How much current does the block heater use? The simple answer is "yes, it will lose power, but is that significant?" Have you tried it? if so, does the 16GA wire get warm?

Ok guys

15 amps 14 awg

20 amps 12 awg

30 amps 10 awg

40 amps 8 awg

50 amps 6 awg

read the label it will tell you the amerage for example if it says your pulling lets say ten amps your good right under 15 if its over that 15 amp rating it will burn the wire and most likely start a fire…best i can do hope this makes sense to you guy with the block heater