Design Principles for Lighting Circuit Runs?

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  #1  
Old 08-25-06, 11:12 AM
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Design Principles for Lighting Circuit Runs?

In drawing up a complete new wiring layout for my house, I'm finding that the most complicated circuits by far are the lighting circuits. I've decided to completely separate the lighting and receptacle circuits, and so each of my lighting circuits spans several rooms. Most of those rooms typically involve multiple lights controlled by multiple switches, and many have at least one three way switch setup.

The electrical books I have are good at explaining individual switch and light combinations, but less good at suggesting how multiple combinations should be joined together on one circuit.

I have a pretty good understanding of electricity in general, so I can certainly come up with a circuit layout that does the job, but I'm trying to minimize the number of boxes that have more than two cables coming into them. So I was wondering - are there any general guidelines that you experts out there use when laying out complicated lighting circuits?

For example, is it best to have a primary cable run carrying power through all the lighting ceiling boxes in sequence, and then run switch loops out to the switches as necessary? Or is it better to do all my branching at the switches - where the boxes are often bigger? Or is every situation unique?...

Any hints and tips much appreciated!

Cheers,

Sy
 
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Old 08-25-06, 11:22 AM
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I use the lazy man's approach. First I look at what the customer wants. Meaning what lights controlled by what switch. Then I get my material and go to the room.

Since I am a very lazy man. I do as little work as possible to satisfy the customer and still make the lights work the way they want.

Everything is considered including how many holes I have to drill, how many wires would need to run around a corner in a wall. etc.

I also don't spare the four conductor cable. It can save a ton of labor.
 
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Old 08-25-06, 02:21 PM
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Originally Posted by jwhite
I also don't spare the four conductor cable. It can save a ton of labor.
When you say 4 conductor, that's just regular 3 wire plus ground, right? That does seem to be an essential tool for passing power on further down the run beyond switches or switched outlets.

Still, I find myself having to consider box fill capacities more carefully than I would like, e.g. with a 20 cubic inch plastic ceiling box and 12 AWG wires, I only have 8 volumes available. So if I have three 12/2 cables entering the box, it seems I'm already over the limit (6 volumes for the conductors in the three cables, one for the equipment ground, and two more for the fixture wires, equals 9 volumes). Or do the fixture wires not count?

Cheers,

Sy
 
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Old 08-25-06, 04:27 PM
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Talking

Think about this:
If you have a problem with the circuit or circuits that feed the lighting branches, do you really want to have to work through all of the fixtures in the ceiling?
This is an antiquated wiring method that was very popular with homes that were run in conduit instead of cable. Everything and I mean everything would be fed from the ceiling boxes. Makes it easy to install but when it comes to troubelshooting, you have to remove fixtures to check the connections and then reinstall the fixture.
Most of the time you will find it easier to run the feed to the switch box and then run a "switch leg" to the lights.
Just my two cents worth
 
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Old 08-25-06, 04:38 PM
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By "4 conductor" I believe that jwhite means four plus a ground. This is either 14-4 or 14-2-2 (could also be 12 gage).

Use of this wire can be very helpful in carrying an unswitched hot wire and neutral in certain instances involving three way switches.
 
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Old 08-25-06, 09:56 PM
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It depends on the layout of the house if daisychaining power through the fixtures or the switches suits, although electrically daisychaining through the switches is less complex.

In my on-slab addition, I found through fixtures was fine.

With a basement or open walls, at the switch is preferred.
 
  #7  
Old 08-25-06, 10:17 PM
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Interested to hear about the 4 conductor cable - hadn't seen that before. I know exactly what you mean about the issue of passing an unswitched hot to the end of a three-way switch setup so that's an interesting solution.

Many thanks for the other comments as well.

Cheers,

Sy
 
  #8  
Old 08-26-06, 03:37 AM
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Why not use #14 for lighting. It will cost you a couple more breakers for the whole house and help will all the box fill problems. The cost of 14 vs 12 wire will offset most of the cost of the breaker and extra length for homeruns.

Depending on the type of the light fixture, the conopy adds to the box fill. Yes I count the fixture wires, as they usually do leave the box, but they are also usualy #16 or #18 guage wire.
 
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Old 08-26-06, 10:29 AM
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"EACH of my liting circuits spans several rooms" ???

This could be construed as 5 liting-circuits for 35 rooms.

But First; is this a design for a house-under-constuction? If this is an existing structure, you have a formidable re-wiring project.

Please verify the type project as to a new/old house--thanks!!!
 
  #10  
Old 08-26-06, 11:34 AM
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Since I'm separating out my lighting circuits from everything else, I did toy with the idea of using #14 wire for those circuits. But after reading various people's thoughts on the matter I guess I came to the conclusion that #12 is the way of the future for everything... Is this wrong? Are there any drawbacks to using #14 for pure lighting circuits?

In answer to PATTBAA's question: this is a (fairly extensive) remodel, but the walls and ceilings are currently open on the entire floor that I'm working on. The existing circuits are pretty inadequate: ungrounded conductors, many things that don't conform to code, dimming lights whenever I turn on appliances, etc. It's a two story house and I'm just working on the first floor for now. I'm planning two pure lighting circuts for this floor - it's about 1000 sq ft.

Cheers,

Sy
 
  #11  
Old 08-26-06, 12:15 PM
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#12 is required in some areas. Kitchen, diningroom, breakfast nook, pantry, laundry, and bath GFI recs. Any place else where the appliance requires 20 amps.

#14 is fine for the rest of the house. I have heard people say things like "I only used 12 wire in my house" most of the time the person saying it was trying to brag to his friends, but actually knew very little about electrical work.

As for the 1000 sq feet. code minimum is a joke. at 3 va per sq foot that means 3000 va or 25 total amps of load for all the lights on that floor, and all of the recepticls not mentiond in my first paragraph above. That is right two 15 amp circuits would easily cover it all "legally"

I like the idea of seperate lighting and rec circuits, because lights rarely trip a breaker, and you can still see to fix the problem. Even if the lights do trup the breaker, you will have a spot to plug in the drop light while you see to fix the problem.

Since I do very little work on spec houses, I can afford the luxury of not building to code minimums. I would say off hand that two circuits is fine for the lighting on this floor, but it still depends on what you plann for lights. For lighting I like to add the actuall wattage of the lamps that will be installed and load no circuit beyond 60 percent. This leaves just a bit of room for the next guy to add one bulb or so without overloading the circuit.

Next I would put dedicated 15 amp recs for anything I know is better off with it.. TV/entertainment center, Computer room. Then I fill in with a rule of thumb that has no basis in code or fact just was taught to me as a good idea. No more than 7 recs on any other 15 amp circuit.

I use a 20 amp circuit to feed the outside outlets. One circuit and I wrapp the house with it to cover them all. If you plan alot of outdoor activity on your deck, you may want one circuit 20 amp just for that.

I didn't start this post with details of the required outlet circuits, but I did mention them there, and they are really the starting point for your layout.
 
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