Current on a 12 gauge wire

[ray66v]

And you CAN use a GFI recep. on a MWBC.

I stand corrected.

True. But, with limitations. No pass through.

 

[ray66v]

Curious how much money such a circuit might save. That's the reason for doing it am I right? Or is there improved function of some kind? Don't see why a KISS circuit couldn't be used why the complexity.

It saves wire. Reduces congestion in areas where cables are running, like by the service panel. Saves installation time. Reduces the time to wire the panel. And, can reduce the amount of fill in a box.

If the price of 12/4 ever comes down, it would be nice. Then, sharing a neutral isn't necessary.

 

[downsizingnow48]

I'm trying to understand the savings in quantitative terms. Maybe $400 materials? And 4 hours of electrician time @ $100/hr? So savings in the range of $1000? Cost of construction @ $100-$150 per sq ft = $200-$300k for a 2000 sq ft home. So a very rough estimate of savings might be 0.5% of the cost of construction? I am thinking of the trade-off between saving the electrician some time and materials up front, against maybe 5 decades of dealing with the somewhat inconvenient and possibly dangerous consequences identified by commenters.

 

[ray66v]

I'm trying to understand the savings in quantitative terms. Maybe $400 materials? And 4 hours of electrician time @ $100/hr? So savings in the range of $1000? Cost of construction @ $100-$150 per sq ft = $200-$300k for a 2000 sq ft home. So a very rough estimate of savings might be 0.5% of the cost of construction? I am thinking of the trade-off between saving the electrician some time and materials up front, against maybe 5 decades of dealing with the somewhat inconvenient and possibly dangerous consequences identified by commenters.

How much does a builder save when they use staples, instead of nails?

I would consider that a bigger concern.

Small savings do all add up.

 

[ultrarunner]

It's like pros that still use 14 ga for 15 amp circuits.

When I wired my homes there was no 14 ga anywhere... the savings in wire meant nothing to me having lived in a home where two bathrooms shared a 15 amp circuit... the circuit breaker always tripped whenever I had company due to the limitations of a 15 amp circuit in a place where blow dryers, etc. are commonly used.

On my last project bringing power to a shed I went with 3 wire on a double 20 amp breaker to provide options... 220v or two 20 amp circuits or a combination...

At the hospital we have at least one of these receptacles in each OR (Same but Hospital Grade)

Leviton 5842-I 2 Amp, 125/25 Volt, Narrow Body Duplex Receptacle, Straight Blade, Commercial Grade, Self Grounding, Dual Voltage, Ivory - Electric Plugs - Amazon.com

 

[ray66v]

It's like pros that still use 14 ga for 15 amp circuits.

Knowing the electricity demands today, I can't see anyone who has a conscience, using 14 gauge for any new construction.

They used a lot of 14 gauge around here in the 80's. Most of it was installed with push in connections on the switches, and receptacles.

After 30+ years of use, the connection is often so bad, you can pull the wire out of the back, without much difficulty.

 

[buickanddeere]

Each circuit needs its own neutral.

Wrong, neutral can be shared when the two single phase supply breakers are on line 1 and line 2.

 

[buickanddeere]

Dishwasher and water heater will use two live lines, white insulated neutral and bare ground. If hard wired or plugged into a receptacle behind the closed door of a cabinet no AFCI or GFCI is required because the loads have a connection to ground that holds the touchable parts to earth potential incase of fault.
The other 12/3 circuit can be supplied from an ordinary two pole 20 amp breaker . Both island duplex receptacles will have to be a combination 20amp AFCI/GFCI T-Slot .

 

[buickanddeere]

Less chance for problems if every circuit has it's own neutral. No shared neutral circuits. BTW, almost all circuits are designed to run at 80% max current. 15 amp breaker = 12 amps, 20 amp breaker = 16 amps.

a 12/3 run from the panel only requires one cable vs two cables if running a pair of 12/2 to carry the same load.

 

[teejk]

Knowing the electricity demands today, I can't see anyone who has a conscience, using 14 gauge for any new construction.

They used a lot of 14 gauge around here in the 80's. Most of it was installed with push in connections on the switches, and receptacles.

After 30+ years of use, the connection is often so bad, you can pull the wire out of the back, without much difficulty.

Code has evolved to the point where you cannot mix lighting circuits with outlets (GFCI, arc fault, etc.). Given we now have dedicated lighting circuits, 14ga wire on 15a breakers is fine...as LED continues to evolve, even that will be over-kill.

 

[buickanddeere]

Light circuits should be separate from receptacle circuits in home, business and industry.
The fridge should be on it's own dedicated circuit with it's own ordinary breaker , the only other shared load a recessed single receptacle for an electric wall clock which is a good idea as it will indicate a tripped breaker. Receptacle for fridge if behind fridge and obstructed from access can be a plain non tamper proof, no AFCI and no GFCI .

 

[ray66v]

Even on dedicated lighting circuits, I can't see 14 gauge. Yes, it's theoretically enough.

I have also seen them tapped into. It's just not worth the few dollars it saves.

Last time I checked, it's also not allowed in some locations here.

 

[downsizingnow48]

So, with respect to cost there appears to be some savings but, at least to my mind, minor in relation to the cost of building a single family residence. And minor in relation to living with the identified quirks of shared neutral for decades.

Now there is the second question about function. The discussion has identified several functional downsides. Are there any functional advantages to shared neutral?

Just because something can be done, does not mean it should be done.

 

[buckeyefarmer]

Wrong, neutral can be shared when the two single phase supply breakers are on line 1 and line 2.

Shared neutral for some circumstances has been discussed. It's not clear the ops case meets this since op says he requires dedicated dishwasher circuit. Some might argue it is still dedicated with a dual breaker, I'm not sure, and too indifferent to get my code book out. I know I wouldn't install it that way, nor would I allow it in my house. Maybe Canadian code allows?

Light circuits should be separate from receptacle circuits in home, business and industry.
The fridge should be on it's own dedicated circuit with it's own ordinary breaker , the only other shared load a recessed single receptacle for an electric wall clock which is a good idea as it will indicate a tripped breaker. Receptacle for fridge if behind fridge and obstructed from access can be a plain non tamper proof, no AFCI and no GFCI .

 

[3Ts]

I've looked at the electrical installation in more detail - the distance from the main breaker panel is about 30'. There are NO bonded 20 amp breakers in the main panel (no 240v 20a) The 12/3 wire goes somewhere but the red wire never shows up in the main breaker panel so now I'm wondering if there are other things on the circuit as well. I also found a 10 gauge wire on a 240v 40a breaker. I'm going to have to have a serious discussion with the builder (not the electrician) after this weekend!

 

[ultrarunner]

Modern wire insulation does allow for higher ratings...

Her in my city I have to go by city code...

14 ga = 15 amp

12 ga = 20 amp

10 ga = 30 amp (Except my city requires 8 ga for 30 amp electric dryer)

Plus, we do make allowances for original permitted work that remains serviceable and unaltered...

I would be concerned about sharing a neutral without a bonded breaker because of the potential problems in that only one side trips or someone reshuffles the breakers and both end up on the same leg...

Reminds me of another case I helped with... new owners of an older home had his brother in law add a circuit for a disposal... well they soon noticed the large through wall AC did not work... you guessed it... the AC did not have a double breaker or a tied breaker so the brother in law put both sides on the same leg when her reshuffled the breakers to make room in the panel for the new disposal circuit...

 

[buickanddeere]

So, with respect to cost there appears to be some savings but, at least to my mind, minor in relation to the cost of building a single family residence. And minor in relation to living with the identified quirks of shared neutral for decades.

Now there is the second question about function. The discussion has identified several functional downsides. Are there any functional advantages to shared neutral?

Just because something can be done, does not mean it should be done.

With two sets of 12/2 and 1500 watts on each there will be four wires carrying current and making heat in that conduit the wires were illegally pulled through with the water. With 12/3 with 1500W on each line there will only be two wires carrying current.

 

[ultrarunner]

But is it "Illegal" if their is no applicable code or authority of jurisdiction?

I use to go through this all the time as many of the structures pre-date code... as in still having gas piping for gas lamps, lead drain pipes, windows of the size that do not meet egress requirements or beautiful Stained or Beveled glass doors that are not laminated or tempered...

In my own home there are many things that do not meet modern code and I am under no obligation to change them.

 

[teejk]

Even on dedicated lighting circuits, I can't see 14 gauge. Yes, it's theoretically enough.

I have also seen them tapped into. It's just not worth the few dollars it saves.

Last time I checked, it's also not allowed in some locations here.

14ga is a bit easier to deal with.

 

[ultrarunner]

14 is a joy to deal with and around here the load on existing light circuits is a fraction of what it once was...

150W GE reading bulb replaced with a 9.5W LED... or 3ea 100W bulbs replaced by 3ea 9.5W LED....