[JGibson]

I'd like to run my circuit layout by everyone for feedback. I am finishing my basement, including a bedroom, bathroom, and a large open room which includes a wetbar, home theater, and kids/craft area. The total finished area is about 775 sq. ft. We have 200 amp service and 3 open breaker slots, so my circuits are as follows:

- 15 amp AF circuit for bedroom light and outlets. Use 14/2 homerun, single AF breaker. Are there any special considerations when running an AF circuit?

- 20 amp GFCI circuit for bathroom outlet. Tap into existing GFCI in bath on first floor. Is 3.5 bathrooms (6 outlets protected by GFCI plug in master bath) on one 20 amp circuit acceptable?

- 20 amp GFCI circuit for 3 wet bar counter outlets. 20 amp dedicated circuit for refrigerator, use 12/3 homerun with tandem breaker.

- Four 15 amp circuits for general lighting. Use 14/3 homerun with tandem breakers. My question here is the best way to divide the lights and plugs in the common area. We have 26 lights (mostly 65W recess) and 14 outlets, for 10 fixtures per circuit. I am thinking one circuit will be all lights, while the other three will have both lights and plugs.

Thanks for any input you may have.

-John

[labman]

What do you mean by a tandem breaker? Do you mean the ones that fit into one slot giving 2 circuits from one buss contact? If so, bad choice for shared neutrals. I used to be totally opposed to shared neutrals, but have learned enough here to understand it is OK if the 2 circuits come off opposite legs of the feed. Feed them both off the same buss, and the neutral is carrying the sum of the 2 hot wires with no breaker to protect it.

Using just the right type of wire may save money for the guy that buys 500' coils and has about 6 types on his truck. If I was doing a job like that, I might buy one big coil of 12-3 with ground and run all the circuits with it. Well not on any 3 way light switches.

If you divide the lights on a couple of circuits, you are less likely to left completely in the dark.

I took what I learned here about shared neutrals and looked at my house. Not only is my stove wired that way, but my service entry only has one neutral for 2 hots. I am still not going to wire up separate circuits in my house that way.

[JGibson]

Yes, I meant dual pole/single slot breakers. The thing I noticed in the rest of the wiring (the house is only a year old) is that the electrician ran 3 wire for 2 circuits, and both circuits are not on the same dual pole breaker but on adjacent breakers. Below A and B are on 14/3, run to an outlet, then split there.

-----------------
| 15 |
----------
| 15 | A
-----------------

-----------------
| 15 | B
----------
| 15 |
-----------------

Thanks,
-John

[labman]

The buss bars that run down through through the box are constructed so that adjacent breakers feed off opposite incoming feeds. Usually at the top of the box, you have double pole breakers with the 2 levers linked together providing 240 volt service to stoves, A/C, water heater, etc. Thus, you can use a 3 wire cable for 2 circuits because if both circuits are drawing power, you sort of have both loads in series in a 240 volt circuit like the stove and so forth. It is not a short cut I would take, but meets code. On the other hand, there are breakers that fit in one slot and provide 2 circuits both off the same buss bar. The hot wires are in parallel, and if there is only one neutral, it carries the sum of the 2 loads as I said.

There have been a couple of questions here lately where I think people have bought that style breakers to wire up a 240 circuit, and it didn't work. They will power two 120 volt circuits, but wired up with 12-3, the single neutral can end up carrying 40 amps. Better not buy any wire or breakers until you hear from tkrussel.

[tkrussell]

Sure appears to be tandem breakers you have, with two switches in one space, and connect only to one hot leg. Connecting two circuits on one hot leg that share a neutral is prohibited, and as Labman mentioned, will cause the neuch to carry potential 40 amps with 2-20 amp circuits.

The wire will overheat and cause problems. The way the electrician did it, with one circuit on both hot legs, if both circuits carry their max of 20 amps, the neuch will carry zero amps,and is exactly what must be done.

Check with your state to know if the smoke detector should be on the AF circuit. It may or may not be allowed to be AF protected.

There is no limit to how many bath GFI's can be on one cirucit, common sense comes into play here depending on the amount of people that will use mseveral outlets at once.

Everything else looks great.

[JGibson]

Great, thanks. I'm still trying to understand what he did. What I'm seeing is a 14/3 and a 14/2 coming into an outlet box (single outlet for the hot water heater, a gas power vent). Two neutrals and a pigtail to the outlet are connected, the black from the 14/3 is connected to the black of the 14/2, and the red from the 14/3 goes to the outlet. The 14/3 comes from the breaker panel and the 14/2 continues on and is the existing basement light circuit. In the breaker box the lower switch on one tandem is labeled "water heater" and the upper switch on the tandem below it is labeled "basement" (A and B in my diagram in the earlier post). Based on what you're saying this could potentially overload the neutral.

There is one smoke detector in the basement and it's already on an AF. I was planning to run another 14/3 from it to the new detector in the bedroom.

Thanks a lot for your help!

[labman]

You are OK if the red wire and black wires come off adjacent breakers, each drawing power from a different buss. They go through the loads, and the current flows back the other hot wire. The neutral carries the difference. Where you get in trouble is using the breakers that use one connection to one buss to provide 2 circuits and connecting both to the same neutral.

[JGibson]

Perfect, so if I hook it up exactly as he did I'm good to go.

Thanks, you guys have been a great help!

[Borewyrm]

2 points

1) 4 wire isn't that expensive. Use that instead of 3 wire and your arc fault/ shared neutral worries are gone.

2) Invest in GFI's for each bath. You can use the same home run but jump the bathrooms using the Line Side of the GFI. Same the trouble of having to go to the master bath to test/reset

[Borewyrm]

3 points

1) 4 wire isn't that expensive. Use that instead of 3 wire and your arc fault/ shared neutral worries are gone.

2) Invest in GFI's for each bath. You can use the same home run but jump the bathrooms using the Line Side of the GFI. Same the trouble of having to go to the master bath to test/reset

3) When calculating circuit load, a normal high hat can be counted as half a point (fixture) due to its restricted nature. I just say this so you don't frazzel your brain if you have 2 or 3 "extra" cans on you circuit.