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.