3 12-3 supplying kitchen

[domelectric]

What if I used one 12-3 for the two SA circuits, one 12-3 for the microwave and refrigerator, and one 12-3 for the D and D? Any input. You guys are great!

 

[LarryFine]

No objection, but two stipulations: pigtail neutrals so a receptacle removal cannot interrupt their continuity, and use a 2-pole breaker if you use a split-wired receptacle for the D and the D.

 

[necnotevenclose]

Okay for some reason I was thinking disposal not microwave (I deleted original post). So to correct my self I do think you can do that, but at a risk that while running the microwave the refrigerator may start to cycle which may cause the wire to overheat and or the breaker may trip. With the current trend that I have been seeing in kitchen appliances people are starting to use 0-degree refrigerators which have a larger draw. As for microwaves you never know if the installed microwave will be 750W or 1200W.

 

[iwire]

So to correct my self I do think you can do that, but at a risk that while running the microwave the refrigerator may start to cycle which may cause the wire to overheat and or the breaker may trip.

NEC...

one 12-3 for the microwave and refrigerator

As the OP said 12/3 not 12/2 I think we can assume there will be a 20 amp breaker suppling each.

 

[necnotevenclose]

NEC...

I'm just skeptical on circuiting microwaves and refrigerators to the same circuit. I wouldn't want my breaker that feeds my microwave taking out my refrigerator. During design I have always provided seperate branch circuits for my SA, microwaves, refrigerators, dishwashers and garbage disposals. I think it provides the customer with a better product. However, unless, it is for an apt complex or retirement home where mods may not be likely I would look at the loads and see if I could combine equipment together on the same circuit.

As the OP said 12/3 not 12/2 I think we can assume there will be a 20 amp breaker suppling each.

lets hope so.

 

[iwire]

I'm just skeptical on circuiting microwaves and refrigerators to the same circuit. I wouldn't want my breaker that feeds my microwave taking out my refrigerator

NEC I don't think your getting it.

12/3 NM has Black, Red, White and bare conductors.

Use black, white and bare for microwave on one 20 amp single pole breaker.

Use red, white and bare for the refrigerator on another single pole breaker.

An overload on on appliance will not effect the other appliance.

 

[Dennis Alwon]

The use of a multiwire circuit can be penny wise but may be pound foolish. If the utility loses a neutral or if the neutral gets disconnected in the panel say goodbye to the microwave.
I know this is a what if situation but it may be a reason to consider the cost difference. I believe I can pull 2- 12/2 cables for close to the same price as a 12/3. Pull the cables together to save labor so the cost difference between a 12/3 and 2 12/2 cables is not that great. (at least around here it is not).

 

[infinity]

I like the idea of using MWBC's. We use as many as possible. Saves time and money on pulling home runs and terminations.

 

[NoVA Comms Power]

The use of a multiwire circuit can be penny wise but may be pound foolish. If the utility loses a neutral ...

Aren't the potential consequences (no pun intended) of loosing the utility neutral the same; whether-or-not the branch circuit is MW?

 

[Dennis Alwon]

Aren't the potential consequences (no pun intended) of loosing the utility neutral the same; whether-or-not the branch circuit is MW?

That is correct. I guess losing the utility will affect either situation.

 

[iwire]

I guess losing the utility will affect either situation.

It sure will.

So as long as you have faith in your ability to terminate at a few points you should have no fear of 'loosing' a neutral.

Besides an open neutral does not always end the life of the equipment connected to it.

 

[LawnGuyLandSparky]

In many instances, like 200a 40-ckt panels, the prospect of installing up to 40 2-wire cables is frightening.

 

[George Stolz]

In residential, in terms of box fill, I found very few occasions where I found MWBCs handy. I used single gangs with 21 cu. in. of space - I don't see how 12/3 could be used for countertop GFIs, unless the 12/3 is looped from box to box, and the phases are used alternately, tying the other phase through for the next box.

Since the neutral would be required to be pigtailed, that adds (unaccounted for) fill to each box.

I suppose it could be considered a superior installation to have receptacles on different circuits surrounding each one, but it seems like it would be a PITA to install to me.

With the disposal/dishwasher, I would run a 14-3 HR, it was an easy habit.

In commercial, I find MWBCs to be a necessity. You get a lot more circuit per pipe with them than without them.

In many instances, like 200a 40-ckt panels, the prospect of installing up to 40 2-wire cables is frightening.

I don't recall having much of a problem with that, myself - but I would also route my homerun around to the bottom of the panel if necessary.

 

[roger]

When I was wiring houses we ran at least 90% of the home runs in three wire MWBC's, we would hit the first box and split to two wire circuitry from there.

It saved a good deal of time in a room such as the kitchen (as in this thread) or a large home with numerous circuits on the far end of the house.

Roger

 

[stickboy1375]

In residential, in terms of box fill, I found very few occasions where I found MWBCs handy. I used single gangs with 21 cu. in. of space - I don't see how 12/3 could be used for countertop GFIs, unless the 12/3 is looped from box to box, and the phases are used alternately, tying the other phase through for the next box.

with a 1gang mudring... come on George... You would seriously prefer to pull an extra wire to the kitchen?

 

[George Stolz]

Stick, that looks like three more items I didn't need to remember to stock in my van; 12/3, a nail-on fiberglass 4" box, and a fiberglass mud ring.

Yes, I never pulled a MWBC for counters, and never had a problem.

Yes, others do, and never have a problem.

To each their own.

There was a guy at our shop who'd go out of his way to pull MWBCs, and consistently had a problem with box fill. If I kept it simple I didn't have to think about box fill, so instead of standing and thinking I could be pulling the next home run.

If a person is smart enough to be able to use them effectively, I say go for it, I have no problem with them. I just didn't try to cultivate that habit, myself.

 

[Pierre C Belarge]

There was a guy at our shop who'd go out of his way to pull MWBCs, and consistently had a problem with box fill. If I kept it simple I didn't have to think about box fill, so instead of standing and thinking I could be pulling the next home run.
.

The MWBC did not cause his box fill problems, his lack of preparing for the box fill problems caused the problems.

 

[danickstr]

i thought bi-wired had to have a bar in the two breakers

 

[iwire]

i thought bi-wired had to have a bar in the two breakers

Currently in general no.

Under the future 2008 NEC yes.

 

[roger]

i thought bi-wired had to have a bar in the two breakers

Only if it lands on a common yoke, see 210.4(B), this may change in 2008 though.

Roger