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Old 08-02-2011, 05:33 PM   #1
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Small design review please


Greetings,

As a part of my bathroom remodel, I'm doing some electrical work.

In a 2-gang box, I need to install a timer switch for a fan and a triple rocker switch for three light circuits. These parts will fit, including wires. But I have to minimize the number of wires entering the box, so I came up with the schematic shown. This is more than a schematic, it is intended to show physical connectivity and wire routes. For example, there would be jumpers inside the box that connect one terminal of each rocker switch to electrical "hot."

All romex cables have a non-insulated ground wire which is not shown. All such wires will be connected to ground at the attic box and to the frame of the 2-gang box in the bathroom or to the fan or light fixture.

My understanding is that the maximum number of connections that can be made in a box is a function of the volume (e.g., in cubic inches) of the box. If I subtract the volume (cubic inches) taken up by the timer from the volume of the 2-gang box, I may have too many connections.

Could someone quote me the rule on connections and box volume? I'll do the calculations.

Would anyone care to comment on this design in general? I don't usually see connections like this, but the need to reduce wires entering the box has resulted in this plan.

Note that a given romex cable in this design will not necessarily carry a load current _and_ its associated return current. I understand that wires in metallic conduit must carry load current and return current, but I think this is to minimize induced current in the metalic conduit itself, which is not an issue with romex.

Thanks,

Tom
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Old 08-02-2011, 09:45 PM   #2
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Small design review please


Why not install a short piece of conduit, and install all your conductors in that?

You would need a total of 7 conductors:

Black (hot)
White (neutral)
Red (fan switched)
Black (Light #1)
Red (Light #2)
Blue (Light #3)
Green (ground)

If you insist on using romex, you could use two pieces of 3-conductor cables.
Re-label the white in the 2nd piece blue for your light #3 switch leg.

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Old 08-02-2011, 10:33 PM   #3
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Small design review please


Thanks, I like the idea. Saves on ground wires for sure!


The conduit is a good idea. Can I use flex? 3/4 inch ok for the number of conductors?

I'll have to get some black and some white 14 awg wire. Then I use heat shrink or other identifier on the black wires?

Thanks again,

Tom
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Old 08-02-2011, 10:37 PM   #4
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Small design review please


If the wires are not in a cable assembly you would need to use the correct colors, not re-identified, unless you are just keeping the switch legs identified.
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Old 08-02-2011, 11:14 PM   #5
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Small design review please


They would all fit into a piece of " flex. But if you want to indulge yourself, go ahead and use the 3/4"
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Old 08-03-2011, 01:19 AM   #6
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Small design review please


I can get the wire by the foot at HD so I can get the proper colors.
Also, I found that I can use a single, straight, rigid conduit from box to attic.

Great solution - thanks again.

Tom

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