14 or 12 gauge wire in remodel ?

16 years ago

This is a questions for the electricians. When installing new wiring say in a basement remodel or even new construction, do you use 14 gauge anymore or strictly 12 gauge in your outlets and lighting wire?

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mike__b

12 years ago

I ran across this thread while searching for some info about14 and 12 gauge wire, and I was surprised by the different opinions. I'm not an electrician, though I've wired AC and DC circuits since I was a kid. A small bit of basic electromagnetism will help solve some of the things discussed here, I'll make a few points with regard to these wires...

First, the power dissipated in a length or wire is directly proportional to the current squared and its total resistance. Resistance in a wire is directly proportional to the resistivity of the material its made of, the length of wire and inversely proportional to the cross sectional area of the wire. The resistivity of copper is roughly 1.68*10^-8 ohm-meters.

From the description above and due to the conservation of charge and current, I would state that regardless of the load of distance of wire, each foot length of X gauge wire with N amps of current dissipates the same power irregardless of the total length of the wire. So the power used due to the resistance in the wire per unit length is the same no matter how much load is hooked to the wire.

Using the resistance of a wire, you only need Ohms Law to calculate all the other properties described in this thread.

Using a base of 46 meters (roughly 151 ft, SI units are need for easy calculations), I'll show some calculations of voltage drop, etc.

resistivity of copper (rho), p - 1.68*10^-8 ohm-meters
length, L - 46 m
cross sectional area of 14 ga, A - 2.08*10^-6 m^2

Note that when you multiply the first two and divide by area, the meter units cancel and you are left with only ohms, resistance.

voltage drop for 14 ga over 46 meters at 15 amps:
Resistance, R = (pL)/A = .372 ohms
Voltage drop (Ohm's Law) = R * I, at I = 15 amps, V drop = 5.57 V

voltage drop for 12 ga over 46 meters at 15 amps:
Resistance = .233 ohms
Voltage drop = 3.50 V

voltage drop for 12 ga over 46 meters at 20 amps:
Resistance = .233 ohms
Voltage drop = 4.67 V

So there it is. Relative to its accepted current limit, 12 gauge has less voltage drop. But 14 ga still is within the NEC standards of You can use some algebra on the formulas above and solve for a maximum length based on a 6 volt drop.

6 = (pLI)/A => Max length L = 6A/pI

Max length for 14 gauge @ 15 amps: 49.52 m => 162.4 ft
Max length for 12 gauge @ 15 amps: 78.81 m => 258.5 ft
Max length for 12 gauge @ 20 amps: 59.11 m => 193.9 ft

Note: these are based off pure copper resistivity, any impurity in the copper used in wiring would likely cause more resistance.

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Comments (22)

normel
16 years ago
Both. 14 for lighting, 12 for receptacles.
bigbird_1
16 years ago
In Canada we still use 14ga for everything 120V except kitchen GFCI'd countertop plugs, which are of course 20A/12ga. Bathroom recepts can still be GFCI 15a, but 20A is recommended.
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For regular appliance and lighting circuits: 14 ga wire needs a 15A breaker, 12 ga wire needs a 20A breaker. The reason electric baseboard heat is different is that it is a continuous constant load, no dips or peaks. In Canada, because we can use the full value of the circuit for this type of heating (not the 80% of circuit capacity rule), we multiply 240 volts X 15 amps and we get 3600 watts. If we run the full 3600 watts as allowed, it may trip the 15A breaker. That's why we are allowed to use a 20A breaker in this case. "Not touching" means not physically contacting the water pipe. Are you calling electric baseboard heat "strip heat"? Regardless, nominal household voltage is considered 120V, not 110. Each hot bus bar in the panel supplies 120V. There are 2 of these hot bus bars. By installing a double pole breaker, which is a breaker that has 2 joined handles on it, into the panel so that each stab of this breaker inserts into a different bus, you will get two separate 120V feeds for a total of 240V. To insure 240V from separate buses, the breaker must be inserted so that there is a plastic divider in the panel that literally splits the double breaker in half. One stab of the breaker goes above this divider, the other stab goes below. Most baseboard heat is 240V, so you would use a double pole breaker. The cable to the breaker would be 14/2 or 12/2, or even 10/2, depending on the watts of the heater/s. Each wire of the cable, white and black would connect to one of the two lugs of the double breaker. It doesn't matter which wire goes to which lug. The white wire should be marked with black felt or tape to indicate that it is indeed a hot wire. Any pro or DIY'er would see a white wire connected to a breaker and know that it's part of a 240V circuit. Note that no neutral wire is used or required for a straight 240V circuit. The ground wire is still required.
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davidandkasie
16 years ago
eveerythign in my house is 12. i sort of wish the lights were 14, but they built it with 12 and that can be a pain when you are changing out fixtures.
billhart
16 years ago
Just don't put #14 on a circuit fed from a 20A breaker-that requires #12.

A circuit on a 15A breaker can be #14 and as pointed out it is easier to work with. If you have long runs it is beneficial to use #12 on the 15A circuits as there will be less voltage drop (dimming lights when other loads change).

It is highly advisable to use 20A (#12) circuits for bathrooms and to keep each bathroom on its own circuit because of the big loads hair care appliances can take.
joed
16 years ago
If it is a 15 amp circuit it gets #14.
If it is a 20 amp circuit it gets #12.
What the circuit is used for determines the amps required.
gilshultz
16 years ago
The rule is relative simple, use 14 for lighting and 12 for plugs and do not mix them. That keeps the dimming etc at a minimum when large loads start. The breakers protect the wire not the loads so use a 20A for #12 and a 15A for #14. Don't forget to connect all the grounds properly, they protect you. Unless your run is over 150' and has a large load increasing the wire size has virtually no effect, it just costs money, for example 150' of Romex (300' wire) @ 15A will drop 11.5V on #14 and 7.2V on #12, the delta is only 4.3V.
billhart
16 years ago
Even with #12 the 7.2 V is 6% of your power going to waste and possible problems starting motors. At the assumed distance of 150 ft, which is longer than most runs in the average house, #14 would be a bad idea for heavy loads and #12 still doesn't quite meet the suggested guideline of 5% drop.
bigbird_1
16 years ago
"The rule is relative simple, use 14 for lighting and 12 for plugs and do not mix them."

What rule is that? It certainly isn't the NEC or CEC.
petey_racer
16 years ago
I think a better way to put it would have been: "My rule is relatively simple..."
texasredhead
16 years ago
I may have mentioned that I did a service call to the home of a friend that was having a GFCI problem. The home is new and quite large and nice. The individual who wired the home did everything with 12ga on 20 amp circuits. IMO, this is just fine, however, I think 12 ga is a little overkill on light circuits. We even use 14ga 15 amp circuits on some receptacles such as bedrooms where there is little demand. By code, we use 12ga 20 amp circuits on all receptacles in kitchens and dining rooms and others where we think necessary such as garage circuits and GFCI circuits in bathrooms. Why not use all 12 ga? Think we all enjoy wrestling 12 ga wire.
arichard21
16 years ago
14 for bedrooms is what I do, and I also agree for things like lights and smoke detectors. It is a bit easier to work with...

BUT...

I have noticed a trend of guys going all 12awg even in places where it is not needed. They all say the same things... "the what ifs", as in preparing for the future.
matt_m
15 years ago
I am using 12 gauge for everything in my addition -- lights and receptacles. We're going to be in this house for the long haul, and I figured in the future I might want to tap into some power for outside lights, or whatever. And even if I don't grab power from a receptacle in the future, I like the thought of a bigger wire taking care of a relatively light load of electricity. Yeah, it's a real pain in the rear trying to pigtail that crap in a box, but I'm happier with it than if I had used 14 gauge.
petey_racer
15 years ago
Well, as Americans we all know the "bigger is always better" mentality is all around us.
We also know this theory is quite flawed and we are paying the price for it now.
bigbird_1
15 years ago
"I figured in the future I might want to tap into some power for outside lights, or whatever. "

Be careful of the code there. My local code says that outside lights or recepts must be on dedicated outside only cc'ts. I can't tap off inside cc'ts.
tjdabomb70
15 years ago
12 gauge for everything, fer crying out loud.
stallaep_rogers_com
13 years ago
Guys,, just want say how much I've appreciated this thread. I looked exhaustively for a pros and cons to using 12 AWG vs 14 AWG for all circuits (including standard 15 Amp ones). I was always taught that 14 was for 15 Amp, and 12 was for 20 Amp, but lately I've read about using 12/2, especially for longer runs to compensate for line loss. I'm not so worried about the added cost or even the added difficulty of pulling 12/2, but like most of you, I just hate working with it inside boxes or making pigtails.

I'm building my dream home and just starting on the electrical rough in, so this couldn't have come at a better time. I could see using 12/2 for long runs, and by that I mean typically 70 to 100 feet, but only for receptacles, not lighting.

I live in Ontario Canada, so our electrical code isn't exactly the same as your NEC. If anything, we're usually a little behind the curve (e.g., we still only require AFCIs in new bedrooms where as your NEC requires them in almost every room of a house).

I'm thinking I should probably run 12/2 on 15 Amp breakers on these longer runs, 12/2 on 20 Amp breakers for appliances like fridge, freezer, washer, dishwasher and to all the oulets in my workshop.

Finally, the only point I didn't see mentioned when people argue the "future use" card, is that in our modern society, the trend seems to be moving toward higher efficiency, so I don't think devices of the future should be drawing as much power as they have in recent years. Hopefully these improvements in efficiency should make up for higher usage...

Any thoughts?
bleon2009_gmail_com
13 years ago
I agree devices are getting more efficient in the way they use energy. However, we are using many more devices than in the past and the new devices are often using more power than earlier models (again, even if they use the added power more efficiently). An example is my wife's stand mixer. The new model is quieter and does not get very hot (efficient use of electricity); but uses about 50% more amps than the old mixer.

I err on the side of more circuits and/or 20 AWG circuits for future requirements.
Linda West
6 years ago
Better to have bigger wire on a smaller breaker than the other way around. Connecting #14 wire to runs that go back to your breaker panel that is set up with all 20 amp breakers would not be a good idea. Play it safe and go with #12.
mtvhike
6 years ago
Linda, connecting #14 wire to a 20A breaker is a violation of the code. When I wired my old house, I used #14 wire/15A breakers for lighting and #12/20A for receptacles. When my new house was built, the electrician used #12/20A for everything (other than high-power devices).
James VerWeire
5 years ago
Mtvhike..Linda Didn't say to use 14 gauge.
Ron Natalie
5 years ago
It is highly advisable to use 20A (#12) circuits for bathrooms

Not only advisable, required by the code if you're somewhere that uses the NEC. Kitchen Small Appliance circuits, bathroom receptacles, laundry receptacles all need to be 20A circuits.

14 or 12 gauge wire in remodel ?

mike__b

Comments (22)

normel

bigbird_1

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