14 or 12 gauge

[Dennis93]

I'm running exterior accent lights. 8 of them at 50w a piece = 400 watts. Divided by 110 volts = 3.23 amps. Now my upstairs is hooked up to a 15 amp circuit for all the lights. Should I just tap into that, or do I have to run a new wire and put a new breaker in?
I have room in my panel, just wondering if I need to go through all that trouble.

Also, if I use 12 gauge from what I learned I can go to a 20 amp breaker. However, none of the NEC charts I found tell me how far I can run a particular gauge of wire before it becomes too long and I need to go one gauge up. I'd run this from my garage to the main attic of my house, about 100 ft, plus add about another 100 ft for all the branches. Just wondering if any of you all had the luck of coming across the chart that tells you how far you can go before you have to get a lower gauge wire to get the same amps?

If I ran 12 gauge wire just for peace of mind, and then tapped into a 15 amp breaker, would I be doing any harm? Just wasting money? I ask because I only ran 14 gauge to my shed, and tapped it into a 15 amp, but when my well pump runs, that wire gets stupid hot, so wouldn't mind getting a lower gauge wire if it was less likely to get hot. But then I was thinking if I added thickness to the wire I would just be increasing resistance, and thereby making it hotter? I realize it sounds contrary to what is common, so tell me if my logic is flawed or not.

Thanks a lot!

 

[DesertSparky57]

Hot hot wiring is never good.

Buy an Ammeter. Read the book that comes with it and use it on your well pump wiring. Warm can be acceptable in certain instances, singe your skin to the wire is never ever ever acceptable. High amperage where you shouldn't have it is a sign of two or three things, none of which are desirable in a circuit. The pump is being overworked if its pulling more amps then it should be. This means either the work load is too big or the motor is too small. Electric motors are also a wear item, many don't think so, but it's true. Excessive work load for extended time equals shortened lifespan of your motor, very simple equation. Another often overlooked cause of high amperage is connections. **** quality wire nuts, which are forbidden to be used on a motor btw, don't last and once you get corrosion it snowballs over time all on its own leading to the same as above, shortened lifespan of your components.

The ammeter will also tell you if you have "room" to tap the circuit you wish to make install of your lights easier. An ammeter is quite possibly an electricians most desirable tool, other than a voltmeter.

Your logic on wire sizing is both a little wrong and a little right. Lets simplify it and say that wire size will never decrease the amount of load you need to supply, but can be so large as to become part of your load. But we are talking long distance here, and big wire. In your house, since it seems like you are the type to add stuff, 12awg on a 15A breaker might not be such a bad idea. It's much easier to swap a breaker when you want more lights than it is to re-pull a circuit all the way across your house somewhere.

But seriously, buy an ammeter and investigate this 'stupid hot' wire. Please. Electricity can burn your house flat. That would ****!

And sorry for the long post, I just came home from work, swapped a few burnt up overworked motors out actually...

 

[Speedy Petey]

In a situation like this there is NO reason to use #12 on an existing 15A circuit. It's more expensive and much harder to work with with many lights and boxes.
A new circuits it's your call, but I almost never put residential lighting on #12. Box fill can be a real issue many times and some recessed lighting junction boxes are pain fully small to work in.

Also, for a new circuit in the average home there is also NO reason to use a 15A breaker for #12. The whole "you can 'upgrade' later" philosophy makes NO sense. It is NOT an upgrade to put #12 on a 20A. It is standard issue, so just use a 20A from the start.

 

[mdd1986]

I'm running exterior accent lights. 8 of them at 50w a piece = 400 watts. Divided by 110 volts = 3.23 amps. Now my upstairs is hooked up to a 15 amp circuit for all the lights. Should I just tap into that, or do I have to run a new wire and put a new breaker in?
I have room in my panel, just wondering if I need to go through all that trouble.

Also, if I use 12 gauge from what I learned I can go to a 20 amp breaker. However, none of the NEC charts I found tell me how far I can run a particular gauge of wire before it becomes too long and I need to go one gauge up. I'd run this from my garage to the main attic of my house, about 100 ft, plus add about another 100 ft for all the branches. Just wondering if any of you all had the luck of coming across the chart that tells you how far you can go before you have to get a lower gauge wire to get the same amps?

If I ran 12 gauge wire just for peace of mind, and then tapped into a 15 amp breaker, would I be doing any harm? Just wasting money? I ask because I only ran 14 gauge to my shed, and tapped it into a 15 amp, but when my well pump runs, that wire gets stupid hot, so wouldn't mind getting a lower gauge wire if it was less likely to get hot. But then I was thinking if I added thickness to the wire I would just be increasing resistance, and thereby making it hotter? I realize it sounds contrary to what is common, so tell me if my logic is flawed or not.

Thanks a lot!

I think what you are looking for is a voltage drop chart or voltage drop calculator. The way it works is the longer the run, the larger the voltage drop. Many times you will upsize to the conductor for voltage drop rather than coordination with a trip setting of a circuit breaker. This is not usually common in residential applications.

If you google voltage drop calculator there are few that are pretty good you can use.

You can also verify if the conductor size you are using for your well pump is indeed undersized. If its a long run, it could require #12s or possibly #10s. But as posted earlier. Conductors should never feel hot to the touch.

 

[Dennis93]

Yes, I googled it and I have a pretty high voltage drop. So my question is, then if only getting a bigger gauge to account for voltage drop, do I still keep a 15 amp on a 12 then? Or can I run a 20 amp then even though it is a long run ~200 ft.

Also, could I account for voltage drop by running 12 all the way to where I need it to a junction box, and then branch off from there with 14 to each individual light. The branches would be less than 30 ft at the max. I ask this because the junction boxes for the lights are real small and 14 would be a lot easier to splice. I realize I'd only be able to put a 15 amp on it then, but would it eliminate voltage drop if I used 12 and then went to 14?

 

[mdd1986]

Yes, I googled it and I have a pretty high voltage drop. So my question is, then if only getting a bigger gauge to account for voltage drop, do I still keep a 15 amp on a 12 then? Or can I run a 20 amp then even though it is a long run ~200 ft.

Also, could I account for voltage drop by running 12 all the way to where I need it to a junction box, and then branch off from there with 14 to each individual light. The branches would be less than 30 ft at the max. I ask this because the junction boxes for the lights are real small and 14 would be a lot easier to splice. I realize I'd only be able to put a 15 amp on it then, but would it eliminate voltage drop if I used 12 and then went to 14?

I have never done it that way before. Im not sure if that makes alot of sense. I think if you have a 200 foot run and your maxing out #14s (well over 5% vd) then i would just give it its own circuit at that point. You can run a 20amp circuit breaker with the #12s if you desire but a 15amp should do the trick as long as the load calls for a 15 amp breaker.

Also if you did it the other way with splicing #12s with #14s you would have to use a 15 amp circuit breaker and wouldnt be able to use a 20 amp circuit breaker. You cant use #14s on a 20 amp circuit breaker.

 

[nehog]

... I'd run this from my garage to the main attic of my house, about 100 ft, plus add about another 100 ft for all the branches. ...

If that garage already has power (sub-panel, for example) you can't run a second power line from the house to it.

 

[Dennis93]

No, the house main breaker/panel is in the attached garage.
Just by the time I run it from the panel to the other end of the house in the attic its ~200 or so feet. I just did 14 from the box all the way to the junction box in the attic. Now thinking if its enough worry to go buy 12 gauge to wire or just let voltage drop do it's thing. I'm only looking to run 3.2 amps total anyway.

Does anyone know, that if you have to get a lower amperage breaker if you account for voltage drop? For example, if I am running 14 all the way but there is significant voltage drop, it just means I'll have less amps at the end right? It doesn't mean that I can't put a 15 and need to go down to like a 10 if they even make them does it.

I guess my question is, if I run a 12 gauge for say a 1000 ft, there will be significant voltage drop, but would I still be ok to put a 20 amp breaker on it?

 

[MrMark]

When voltage drop is a concern you upsize the wire but keep the breaker the same as you originally designed the circuit for. So, if you need a 15 amp circuit, based on your design, and it is an overly long run, you would upsize to 12 gauge wire but keep the breaker the same, here 15 amps. The reason for this is that voltage drop is figured based on current flow X wire resistance.