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Old 08-05-2012, 12:40 AM   #1
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Outdoor wiring and box fill


I'm doing some outdoor wiring for my pergola (patio cover) and want to know if my plan is the best way to minimize box fill. The 14 ga wires are feed up from the post footer and inside 1/2" sch 40. I've got 3 wires (hot, common, ground) thhn coming up one of the posts and into a dbl gang switch box. I'll set them up into 3 runs once they come out of the switch box. I plan to pig tail them in the box, sending the first run of the 3 up to a receptacle a few feet away, the second run will go to one switch (lights) and the third run to the other switch (ceiling fan). So by wiring it this way, I'll have 3 wire nuts, 2 switches, several wires from the pig tails, and 9 wires exiting the box.

So is this the best way to wire this or is there a better way that would reduce the number of wires in the switch box? Also, is this box fill allowed or a violation? I don't plan to have this inspected, but I still want it to be up to code. I attached a diagram of what I'm doing to help with the visual.

Thanks for your help!
Kevin
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File Type: pdf Wiring Diagram.pdf (60.7 KB, 47 views)

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Old 08-05-2012, 05:14 AM   #2
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Outdoor wiring and box fill


Get a box of at least 26 cubic inches for the two switches, etc. This should not be difficult for a 2 gang box.

Note that all the ground wires together count one point and the switches each count 2 points. You have one set of hot and common coming as the feed and 3 sets of hot and neutral continuing on to lights, fan, and receptacle respectively. Total 13 points, 2 ci per point for 14 gauge wireing equals 26 ci.

Wire nuts count 0 points and short lengths (pigtails) wholly within the box count 0 points. However in some situations (such as with dimmer switches or ground fault circuit interrupter receptacles which are larger) you need a yet larger box to be able to stuff everything in.

You can have many wires coming into a box, you just need enough space.

(Rules are different outside the U.S.)

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Last edited by AllanJ; 08-05-2012 at 05:21 AM.
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Old 08-06-2012, 12:49 PM   #3
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Outdoor wiring and box fill


Thanks for the great info Allan.

Here's a follow up question, what boxes/conduit are best in wet/sun exposure conditions - plastic or aluminum? Or is it just personal preference?

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Get a box of at least 26 cubic inches for the two switches, etc. This should not be difficult for a 2 gang box.

Note that all the ground wires together count one point and the switches each count 2 points. You have one set of hot and common coming as the feed and 3 sets of hot and neutral continuing on to lights, fan, and receptacle respectively. Total 13 points, 2 ci per point for 14 gauge wireing equals 26 ci.

Wire nuts count 0 points and short lengths (pigtails) wholly within the box count 0 points. However in some situations (such as with dimmer switches or ground fault circuit interrupter receptacles which are larger) you need a yet larger box to be able to stuff everything in.

You can have many wires coming into a box, you just need enough space.

(Rules are different outside the U.S.)
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Old 08-06-2012, 01:03 PM   #4
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Outdoor wiring and box fill


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Originally Posted by blue sky View Post
Thanks for the great info Allan.

Here's a follow up question, what boxes/conduit are best in wet/sun exposure conditions - plastic or aluminum? Or is it just personal preference?

Either one will work but let me pass a quick tip drill a very small hole at the bottom of the junction box so that way the moisture will drain out of the box otherwise it will destory whatever it inside the junction box.

But for the conduit itself genrally plastic last longer than steel conduit.

Use the shed 80 come up from the ground but under the ground run you can stick to the shed 40 conduit but just beware the inside diamaiter will be different. you will have no issue pull that many conductors however pull all of them at the same time it easier to do this way than try to do single pulls.

Merci,
Marc
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Old 08-06-2012, 04:24 PM   #5
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Outdoor wiring and box fill


Marc, so are you saying that any humidity let in through the small hole wouldn't affect the wires in the box over time (corrosion, etc)?

I don't know if it's a good or bad practice, but I usually spread a thin bead of silicon over connection points to help seal from moisture.
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Old 08-06-2012, 05:02 PM   #6
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Outdoor wiring and box fill


Quote:
Originally Posted by blue sky View Post
Marc, so are you saying that any humidity let in through the small hole wouldn't affect the wires in the box over time (corrosion, etc)?

I don't know if it's a good or bad practice, but I usually spread a thin bead of silicon over connection points to help seal from moisture.
What I do is duct seal all the conduit entries and use thread sealant on the threaded KO seals... I dont drill weep holes, but most people do, but they don't use thread sealant either, I myself haven't had any issues with my method.

Best of luck.

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