Breaker rating versus wire size

Hi! I've been reading a lot of information regarding breaker size and wire gage, and have the following question:

If my breaker size is rated for 15 amps, and I use 12 gage solid wire, will this cause a problem? The circut would be used for receptable outlets (TV, stereo, lamps, etc.), and switches (ceiling lights, mainly). Or, should I ONLY use the correct wire size, which, in this case, would be 14 guage? I live in the city of Los Angeles.

Thanks, for your response!

 

14 Gauge is cheaper. 12 Gauge wont do any better. If you have already run the 12, just buy a 20 amp breaker instead. The breaker is sized to protect the wire,,,not what it,s connected to. A fused disconnect secured within reach of the equipment is sometimes used like for a condensing unit, with the maximum size fuse to the equipment as written on the equipment(not to exceed the Circuit breaker) and you have the protection.
For house wiring standard appliances, use the proper size CB for the wire run.

 

I agree with everything that hvac01453 said.

Nevertheless, I'd still use 12-gauge wire as my minimum. Why? (1) 12-gauge offers you the option to go to a 20-amp breaker, either now or when you might need it later. (2) 12-gauge will cause less voltage drop in the wire. (3) Less chance of flickering lights with 12-gauge. (4) You can buy just one wire size for almost all of your cabling needs.

What are the downsides to 12-gauge? (1) 12-gauge is more expensive, but that's not significant for most DIY projects, (2) 12-gauge is harder to run, but again it's not very significant for DIY projects, (3) 12-gauge takes up more space in the box -- even with the largest single-gang box available, you normally can't put more than three 12/2 cables into one box.

None of these are huge factors. Use 14-gauge on 15-amp circuits if you prefer. But 12-gauge wire on 15-amp circuits is not a problem. No big deal either way.

 

Thanks for the advice!

I have been reading a Home Depot book on wiring basics, and it said that I should match the wire AWG to the CB size, else there could be problems. It also said that recpts should also match to the CB size as well. But, it seems to me that a 15 AMP CB should work okay with a 12 AWG. Does it really matter if the recpt does not match to the CB size? Also, if I use a 20 AMP CB (which I think I'll do), does that mean the maximum amount of wattage is 2400 (120v X 20a)? If so, then as long as I don't exceed the maximum amount of wattage, then the circut won't overload, but could I still overload the service main, depending on the load carried by the other circuts?

Thanks!

 

I think what the book is trying to avoid is the use of larger breakers on smaller wire not the other way around. It is not good to put (also not allowed) #14 wire on a 20 amp breaker but #12 on a 15 amp is OK. The best part of running the #12 right from the start if need be it is easier to install a 20 amp breaker latter on if needed then run another circuit because the 15 amp one is overloaded.

 

You may use either 15-amp or 20-amp receptacles on a circuit protected by a 20-amp breaker. Going from a 15-amp to a 20-amp receptacle is not necessarily a quality improvement, but going from a 35-cent receptacle to a $2 receptacle is.

In general, it is not a good idea to plan to use more than about 80% of that 2400 watts. In most cases, it is not a rule of code to limit yourself thusly (contrary to popular opinion that the 80% rule applies to everything), but it is still a good rule of thumb.

It's always possible to overload the main, but that is a complicated calculation. The calculation is not affected by whether you use a 15-amp or a 20-amp breaker. In general, you usually don't need to worry about that when adding 15 and 20 amp 120-volt circuits. It's the big things like new air conditioning that overload the main.

 

if you remodeling plans include buying 12 AND 14gauge wire, do it all in 12 gauge it is CHEAPER to buy one 250' roll of 12 gauge than to buy a 100' roll of 14 gauge AND a 100' roll of 12 gauge.
Yes 200 ft of wire is MORE EXPENSIVE than 250' of of 12 gauge.
Price of wire rapidly drops when larger quanities are purchased.
If you plan on doing much electrical work in the future buy a 250' roll and save the rest for later.
They really sting you on 25' rolls sometimes charging 3-4 times per foot.
It's not unusual for electricians to buy 1000' spools of wire at an even cheaper cost.

 

Many thanks for your helpful comments! I decided to go with a 15 amp breaker and 20 AWG. As 54regcap pointed out, it's cheaper to go with 12 AWG, especially with a larger roll, than to buy 14 and 12 AWG. I have other projects I can use the wire for, so thanks a good thought.

Basically, I want to use the new circut to power the outdoor Christmas stuff we put up over the years, and we seem to add more decorations every year!

I sure like this BB! I've looked at other ones that offer home improvement help and ideas, but this one, I think, is the best one! Lots of interesting topics and really helpful advice!

John -- my service panel currently has a separate breaker for the A/C, microwave, oven, a gas furnace, wash/dryer, and central vac system. I have room for more breakers, and actually have a few breakers that are not wired. Should I be concerned about not overloading the panel? The main breaker is 100 amps, with two bus bars, so I assume I am wired for 200 amps. Should I attempt to calculate what my panel can handle? I've seen the formula, and you're right it is rather complicated. Any more thoughts you have a greatly welcomed!

 

It never hurts to have more circuits with less actual load on each one.
You actually have a 100A service but that is really enough for most residential applications.
As long at the TOTAL LOAD doesn't exceed 100A (24,000W) you are good to go
I personally could get by with a 30A (I actually have 100A) service since I have NO 240V applainces (all the big applainces are gas)
The biggest load is the 10,000 BTU window A/C in the living room @ 1000W
7200W total would be plenty to power my house.