When to use 15A vs. 20A circuits (and #14 vs #12 wire)?

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We are about to install several new circuits as we upgrade the electrical systems in this very old house.
- For "normal" rooms (i.e. not kitchen, bathroom, garage, workshop, or outdoors), should one go with standard 15A circuits or should one put in 20A "just in case"?
- Even if you just put in 15A breakers and receptacles now, does it pay to pull through #12 wire just in case you ever later want to upgrade?
- How big is the difference in price for wiring (per foot) and for circuit breakers?
Thanks, Jeff
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if he's giving you that option do go 20a wire&brkrs,,, probably well under a buck per foot extra. brkr is same price

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I believe 20A breakers cost nearly enough the same as 15A ones and 12AWG wire is only a little more expensive than 14AWG. I strongly recommend to not cheap out. I believe that current code for new construction permits 15A capability as opposed to 20A only for lines dedicated to specific loads. As in no outlets, or one outlet (which should be for a specific load that does not draw more than 15A) plus no other loads. I could be off a little, but I believe 15A is a "cheap out" permitted in a few specific instances.
However, I have yet to hear of a code requirement to upgrade existing 15A circuits that were installed when code permitted them. Just have the breakerbox/fusebox have adequate labeling that the circuits in question are 15A circuits - especially if there are fuses rather than breakers.
Local building codes may have exceptions - please know the requirements if you sell your house.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Around here it is #12 and 20 amp breakers for all outlets, #14 and 15 amp breakers for "typical" lighting. The differance in price is little. Greg
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I would also do it this way.
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The only reason to use 14 (other than saving a couple dollars of course) is that it is a little easier to work with; and that only matter if you have a particularly difficult installation.
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Jeffrey J. Kosowsky wrote:

#12 cable costs almost twice as much as #14, but it's such a small part of the total cost it's the wrong place to try to save money. Use 20A breakers and #12 wire for any branch circuit that has even one receptacle.
You can use #14 cable and 15A breakers for the lighting circuits to save a little money and make it easier to wire.
BTW, those 39 duplex receptacles are false economy for any outlets that you will actually use very often -- they wear out, so pay an extra dollar and use heavy-duty 15A receptacles. I think they call them "spec grade". You really don't need 20A receptacles for anything residential (except maybe a dedicated circuit for a big window air conditioner.)
Just my opinions, Bob
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zxcvbob wrote:

I just checked Lowe's and they are $21.50 for 14 and $30.50 for 12, more like 50% more rather than 100%.
Matt
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Matt Whiting wrote:

It was $15 and $25 last time I bought any...
All the more reason to use #12 -- the savings is not that much to pay for the added capacity.
Bob
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Cost difference: Minimal. It's only the wire, and that is a small fraction of total cost.
Someone who has a little spare time should go through the calculation of the resistive loss of 14-gauge versus 12-gauge wire (which is quadratic in current, so mostly matters for heavily loaded circuits). I vaguely remember calculating that before we built the house, and concluding that assuming constant energy usage (motors with constant load or constant brightness demand from illumination), it would save about 3% of the electricity to use 12-gauge wire, if a circuit is highly loaded (something like 80% of breaker rating).
I would always go with 12-gauge wiring for receptacle circuits. Otherwise, you'll more easily get into a situation where a breaker trips because you plugged in a space heater, or are using a blow dryer for some craft project while the toaster is going, or something like that. Also reduces annoying flickering of lights when big appliances turn off and on.
On the other hand, I would usually go with 14-gauge wiring for lighting circuits, just because the stuff is easier to work with (easier to make up boxes, easier to wire neatly, and don't have to use such large boxes).
Matter-of-fact, I would always wire receptacle circuits on a separate breaker from lighting circuits. Like that you can work on one of them and use the other one to have lights. Say your kid breaks the receptacle in his room on a winter evening, and you have to fix it before bedtime (because the baby monitor has to be plugged into it). Or you are working on installing a new light fixture on a dark afternoon. This is easy to do if each room can be illuminated from two different circuits (with a portable plug-in worklight for the second case), without having to resort to extension cords.
So this is exactly what we did when we built the house: All receptacle circuits are 12-gauge with 20A breakers. The lighting circuits are mostly 14-gauge with 15A breakers. In some cases, I actually used 12-gauge wire for parts of lighting circuits with "big" lights (like the 200W exterior floodlights), just to make sure resistive losses are minimal.
Along the same lines: When wiring a shop area, go one size larger on the wires (even if that means having to wire the tablesaw outlet with 8 gauge wire, which is really nasty to work with). If you ever upgrade your tools (buy a larger welder, or a 5HP tablesaw) you'll be glad you did. And, whenever stringing wire for a pure 220V outlet (for example for a dryer or a motor), use 4-wire cable (which is confusingly called something like 10-3) and run a neutral wire. If you ever have to change the circuit for something entirely different, you'll be glad you don't have to replace the wire in the wall. For example, we changed a laundry room into an office area, and turned the 220V 30A dryer outlet there into a dedicated computer circuit, reusing the existing 10-3 wire for a single 20A circuit (removed the dryer outlet, put a regular 120V outlet in, removed the 30A two-pole breaker, and used just the black and white wires with a regular 20A breaker).
Some other posters suggested using spec-grade receptacles. Excellent idea. I don't know what the difference between spec-grade and commercial grade is (or if there is any), but I find working with reasonable quality hardware (like good commercial receptacles) much more pleasant.
In a related post, snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

I completely agree on the sentiment. But to my knowledge, the national code (NEC) does still allow 15A circuits for all manners of uses. Matter-of-fact, I know of nothing in the code that would prevent someone from running very odd things (like 6A or 10A circuits for lighting), as long as the load calculation for these circuits are OK. Regular 120V 15A outlets (the usual ones) can only be put on 15A and 20A circuits, and kitchens and bathrooms require a certain number of dedicated 20A circuits. But, as far as I know, it is still legal to use 15A circuits for lighting (which I think is a good idea), and for receptacles (which I happen to think is a bad idea).
Has that changed recently?
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few cents per foot. Breakers prob. identical price. Also; if you have a situation where you may need more capacity than a 20 amp circuit can handle, this might typically be a kitchen area, a suggestion. Instead of two wire (White?Black plus ground) #12 install three wire (White/Black/Red plus ground) #12. This will allow all the outlets on that run or perhaps just one or two important ones to be 'split'. That is each outlet can be wired so that the upper half of a duplex connected to one leg of the supply and the lower half to the other leg of the supply thus doubling the capacity of the circuit. The additional cost of the third conductor will be small. The only other cost will be that of a two-pole breaker in place of a single pole breaker.
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If I was a developer building 50 new homes, I would want to cut expenses anywhere possible and install 14 ga. wire/15 amp everywhere unless 12 ga./20 amp was required by code. A few dollars saved times 50 homes can add up to a big savings and more profit!
If I was a developer building my *own* home, all 120 V outlets and lighting would be 20 amp with 12 ga. wire.
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Electrical contractors save $$ by using the 14 ga backstabs (these things suck) on the outlets. No more 12 ga ones made.
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Eric Ryder wrote:

There *are* 12 gauge ones made in "spec grade" (Ten gauge, actually.) I really like them. You stab the wire in the back and then tighten the side screw to clamp it in place. It's almost as fast as the old spring-loaded stab connectors, but it's reversible and it's at least as secure as the side screw terminals. But they cost over $1 per device.
Bob
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Bill wrote:

This is true with the typical ignorant home buyer, but folks like me wouldn't buy your house so your profit would be negative! :-) And when I saw the panel full of 15A breakers, I'd know you were a second or third tier builder and wonder what other corners you had cut.
Matt
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What is the % of homes wired with 15a circuits as the norm as allowed by code, usually within developments by builders, (all apparently owned by "ignoramases") as opposed to the % of the fantasy "spec grade" home you live in or would only consider?

Wow, a top-of-the-line "1st tier custom homebuilder." We're dancing with the electrical construction Gods now... Excuse me while I get back to wiring the new World Trade Center.
Which by the way, has 15a lighting circuits.
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HA HA Budys Here wrote:

Well, yeah, at 277V. I'm not sure that means anything.
Best regards, Bob
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I would be more concerned if they were all 20s. That is the cheap way to get your 3va per square foot. Less circuits are required.
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On Wed, 27 Oct 2004 18:21:02 -0400, Matt Whiting

Most new homes come with a panel full of 15A breakers...plus a bunch of 20A...and some 30s, 50's, etc.
Most new homes sell.
Have a nice one...
Trent
Budweiser: Helping ugly people have sex since 1876!
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Bill wrote:

Well then, you wouldn't be much of a business man or promoter. Look at all they hype you could get if you said all the wiring was 12 gauge and heavier than the normal house. The extra few buck per house, would be worth a lot of money in advertising.
I also would select (have for add ons) 12 gauge wire for my house, but there is no reason to put in all 20 amp breakers. Certainly there is no reason for most lighting circuits. How often would one have more than 1800 watts of lighting on a circuit; that eighteen 100 watt lights. A better alternative is more circuits.
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