What size electrical box to rough in for the following:

[Kathy]

Hi,

Most of you know I already have a project thread going over in the Construction forum. You can read it here at Kathy's Barn Conversion.

My specific question right now concerns electrical wiring. I am roughing in the 14/2 gauge wire for lights thru my barn. I am unsure of what size blue plastic box I am supposed to get based on my needs. I know depth is also a factor as well as width. I've already done the electrical outlets with yellow 12/2 wire and that was simple enough. But lighting involves both a switch and a light fixture and I'm needing some help here.

The first location will have two switches for two different light fixtures. It will also hold the feed line from the panel and another line daisy chaining or jumping out to the next box in the series. That's a total of 4 wires there, correct? 4 wires and two switches inside. What size box?

The second location will be the same except add a third switch for a third light fixture. 3 switches, the panel feed line, and the line that will jump out to the next location. A total of 5 wires if I'm correct. What size box now?

The third location will be the same as the second (which is 3 light switches for 3 light fixtures) but now I will also add 14/3 wire about 8 feet over for a second set of switches that can also shut off all 3 light fixtures.
This is where I am haziest. Will I need 3 lines of 14/3 (one for each new switch) or just one feed of 14/3 to go to the other location of switches? Based on that answer, how many wires are we talking about for the size of the box?

To be completely honest, there will be two locations in the middle of all that that will simply hold one light fixture with one switch so I'm sure a standard box will work for that which is why I didn't make a point of asking. A simple one switch/one fixture setup is 3 wires, right? The feed line, the line to the fixture itself, and the line that will continue on and jump out to the next fixture.

So, can someone verify all this and advise the size and depth of blue plastic boxes I am to buy for this?

Thanks in advance.

[len-morgan]

Kathy,

I hate to be the bearer of bad news but I thing the reason no one has jumped on this is becuase the correct answer is: Don't do any of this. Hire an electrician. I know, I know, they're expensive, and after all, it's just putting down a little wire right? Well, not really. While shoddy construction COULD kill you, you have a carpenter at least making sure it's strong enough.

Electrical work is not like the framing construction part of the project in that it doesn't reallly effect accoustics too much. Except where leakage is concerned. You want to put putty pads around every location where the wiring will puncture your drywall. That means fixture boxes, outlet boxes, and switch boxes.

As to the size. it's a simple answer: The places where there need to be 3 switches need to be big eough to hold three switches. You might not be able to find that (I think 1, 2 and 4 are what's commonly available).

You should be able to get an electrician to draw you up a little plan that shows you what size/conductor count of wire to pull for your set up. Especially if he knows that he's going to get the business hooking up the ends to the main electrical box.

The fact that you want to have lighting fixtures that can be operated from more than one switch REALLY complicates the wiring. If you really want to do it this way, I'd personally recomend that you use something like the X-10 system so you end up with smart switches and you can set up (in software) which switches control which fixtures.

To reiterate: Don't do the electrical work yourself. We don't want this to be the "Kathy LaBonte MEMORIAL Recording studio."

len

[Kathy]

Kathy,

I hate to be the bearer of bad news but I thing the reason no one has jumped on this is becuase the correct answer is: Don't do any of this. Hire an electrician

You should be able to get an electrician to draw you up a little plan that shows you what size/conductor count of wire to pull for your set up. Especially if he knows that he's going to get the business hooking up the ends to the main electrical box.

Hi Len,

Thanks for answering.

I'm sorry, I wasn't very clear. I should have revealed that I already DO have an electrician. The guy who has wired this entire house when it was being built is the one who will be hooking up the wires when it's time. He has already come out once last fall to add 6 more outlets to the empty barn on the existing house circuit BEFORE we started doing any construction. I talked to him at that time about more power and he said he would put in a subpanel right in the barn.

Fast forward to recent times and I have been on the phone with him 3 times to get the info I need. He told me exactly what kind of Romex to buy myself and run. I have 250 feet of the yellow 12/2 for the outlets. He explained how to jump out each electrical box so that I could have 4 - 6 outlets on one circuit and just have one home run lead back at the location of where the subpanel will be (I'm not doing any of the star grounding stuff).

I did the outlets and that went fine. I used the existing holes he had made in the ceiling joists when necessary. I used standard blue boxes and left the wire hanging inside of them with about 12 inches of length to play with.

I also wanted a 30 amp circuit for my RV so I can run the air conditioning in the summer when it's parked in the driveway. I bought the 10/3 orange wire and put in 2 locations for that (one right next to the driveway door).

He then told me to buy the 14/2 for a circuit of lighting.

All I'm doing is leaving the wire ends in the approximate location with one lead wire going back to the location of the subpanel. I'm not hooking up anything.

In fact, when it comes to having the subpanel put in this spring, he told me to save money I could dig the trench myself from the house bulkhead to the barn. Once the ground is soft enough I will do that. Then he will come to lay in the cable, put in the panel, and hook up the outlets and lights where I have put them.

So, I'm not doing this entirely alone and I already have the electrician for the job who has advised me what to do to this point.

My question was really about the confusion I felt after putting in the outlets and realizing that lights were a little different because you aren't just dealing with one item (the outlet itself) but this time a light switch AND the light fixture. I wasn't sure how to run the cable for that AND what size box to get for the double and triple switches. I know I can just get a triple switch box but it is the depth that I am concerned about. I read that most DIY'ers make the mistake on depth when choosing a box.

Anyways, I've decided not to put ANY of the boxes in myself. He can do that. I will just leave the white 14/2 line hanging in each location that I need switches for lights. Then he can put the boxes in.

Oh, and I also ran a seperate 12/2 line for a circuit that will hold the mini split.

To reiterate: Don't do the electrical work yourself. We don't want this to be the "Kathy LaBonte MEMORIAL Recording studio."

len

Don't worry. I wouldn't even try. I just want to lay out the wire to the right locations so I can finish insulating and move forward.

[rod gervais]

Kathy,

it's actually pretty easy.

14 Awg. = 2 Cu. In. per conductor, 12 Awg. = 2.25 Cu. In. per conductor, 10 Awg. = 2.5 Cu. In. per conductor, 8 Awg. = 3 Cu. In. per conductor, 6 Awg. = 5 Cu. In. per conductor.

If you are using all conductors of the same size in your box, then you count the number of current carrying conductors [all colors including white but not counting green or bare] entering your box.

Devices count as 2 conductors for each device. Count the number of devices {switches or receptacles}. Multiply the total number of devices times 2. The answer from multiplying the total number of devices by the 2 is the total number of current carrying conductors you must add to your total number of current carrying conductor list.

OK- so in the case of a 3 gang box, with a single feeder and 3 light switches - using 14/2.

That would be 8 conductors (for the cable) plus 6 conductors for the switches, for a total of 11 conductors at 2 cubic inches per conductor - or a total of 22 cubic inches.

A standard 3 gang plastic 2 1/2" deep is 44 cubic inches - so you are more than safe usiing that. If you have options as far as depth goes - simply extrapolate for the cubic inches within the box (although the size in volume is usually printed on them).

Rod

[Kathy]

OK- so in the case of a 3 gang box, with a single feeder and 3 light switches - using 14/2.

That would be 8 conductors (for the cable) plus 6 conductors for the switches, for a total of 11 conductors at 2 cubic inches per conductor - or a total of 22 cubic inches.

Wouldn't that be 14 instead of 11 (six + eight)? If so, it would still end up being only 28 cubic inches so that standard box is still big enough.

So, the light fixtures themselves or should I say the wire that goes to them from the switch, is already figured into this equation somehow. That extra wire is what was/is confusing me.

One more thing (if I may push my luck with you): Let's take that same 3 gang box with 3 light switches and now make it capable of being turned on and off at a second alternate location 10 feet away from the original triple switch. All three light fixtures.

I know I use 14/3 to travel to the new location. But do I use just ONE feed of 14/3 or 3 feeds of 14/3? And how does that affect the box size now?

[len-morgan]

Are you talking about ONE remote switch to control three lighting circuits? If so, you would run the feed line (that goes back to the panel) into the "remote" box, and then the "output of that would go to the 3 gang box INSTEAD of the feed line you have have now.

In other words, you would use the remote box as a master cut off that feeds power to the 3 gang box which then turns on the individual lighting fixtures. You have to remember with this set up though that if the remote box is off, none of the lights operate.

len

[Kathy]

Are you talking about ONE remote switch to control three lighting circuits? If so, you would run the feed line (that goes back to the panel) into the "remote" box, and then the "output of that would go to the 3 gang box INSTEAD of the feed line you have have now.

In other words, you would use the remote box as a master cut off that feeds power to the 3 gang box which then turns on the individual lighting fixtures. You have to remember with this set up though that if the remote box is off, none of the lights operate.

len

No, I don't think that's what I mean.

I simply want another triple light switch at the other end of the room that can also turn on any of the 3 lights I choose as well.

Like for instance, in my house I have an overhead kitchen light you can turn on when you walk in thru the back door porch. But you can also turn that light on with another switch when you exit the kitchen to head into the living room. There are two switches that turn that same kitchen light on and off from 2 different wall locations.

Actually, the barn has the same thing. The overhead light is turned on when you walk in from the driveway entry. But you can also turn it on from the house entry. I can see the wiring here because there is no drywall in the barn and it's just one line of 14/3 from the main light switch to the second light switch.

My question is how to do that if you have more than one light fixture and switch involved. My belief is that it would take 3 runs of the 14/3 to the second location of switches but I just want to make sure.

[len-morgan]

I was afraid that was what you wanted. That is a much more compicated wiring diagram and I'll have to leave that to the professionals. Sorry.

len

[rod gervais]

Are you talking about ONE remote switch to control three lighting circuits? If so, you would run the feed line (that goes back to the panel) into the "remote" box, and then the "output of that would go to the 3 gang box INSTEAD of the feed line you have have now.

In other words, you would use the remote box as a master cut off that feeds power to the 3 gang box which then turns on the individual lighting fixtures. You have to remember with this set up though that if the remote box is off, none of the lights operate.

len

No, I don't think that's what I mean.

I simply want another triple light switch at the other end of the room that can also turn on any of the 3 lights I choose as well.

Like for instance, in my house I have an overhead kitchen light you can turn on when you walk in thru the back door porch. But you can also turn that light on with another switch when you exit the kitchen to head into the living room. There are two switches that turn that same kitchen light on and off from 2 different wall locations.

Actually, the barn has the same thing. The overhead light is turned on when you walk in from the driveway entry. But you can also turn it on from the house entry. I can see the wiring here because there is no drywall in the barn and it's just one line of 14/3 from the main light switch to the second light switch.

My question is how to do that if you have more than one light fixture and switch involved. My belief is that it would take 3 runs of the 14/3 to the second location of switches but I just want to make sure.

It would take 3 runs of the 14/3 to each switch from the lights - so now it would be 3 feeds with 3 legs each (power feeds directly to the light) - so 9 legs - plus the 3 switches for 6 more legs - for a total of 15 legs - a total of 30 cubic inches - so you are still fine with the standard 2 1/2" deep 3 gang box.

By the way - you're right - I got sloppy with my math above - the correct number was 14 legs.........

Rod