Anatomy of wiring through my house's sill

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Old 05-24-17, 06:46 PM
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Anatomy of wiring through my house's sill

Hi All,
I'm working on the planning phase for running power from my basement to my backyard shed. I am new to town and want to impress/befriend my inspector so I'm hoping to get some verification of my plan which is a compilation of several different online diy tutorials, which may have provided more confusion than clarity.

1. My main question is around running the cable (in this case, 12-2 UF protected by a 20 amp GFCI breaker) through the sill of my house to the outside world. Once I've drilled a hole through the sill, can the UF cable go through it bare or does it have to be in conduit? Directly on the opposite (outside) wall I plan on lining up knockout on the back of a 1 gang metal outdoor electrical box. In that box, do I need to separate the UF cable and make a new connection, or if I'm running the same cable, can I skip the box and continue into the conduit run? (In some how-tos it is stated that the reason for the box is to have access to the connections outdoors, I think that assumes a standard 12 gauge cable inside is being connected to the UF cable outside.) Essentially, what should this look like?

2. I've read in certain books/articles that there is a limit to the number of turns a cable can take. Is this just in one run? In other words, if I put an outlet in between where it comes out of the sill, and goes into the shed, will that "reset" the sum of angles I'm allowed?

3. Just want to confirm that for UF cable, GFCI protected, in 1/2" non-metallic (PVC) conduit, my trench only needs to be 12"? Table 300.5 is a little hard to read. It almost looks like I don't need the conduit underground if the UF cable is GFCI protected.

Your help is much appreciated and will go a long way to getting on the good side of my inspector who is already notorious for not liking homeowners doing their own work.
 
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Old 05-24-17, 07:35 PM
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can the UF cable go through it bare or does it have to be in conduit?
Yes it can and you don't need conduit.

do I need to separate the UF cable and make a new connection, or if I'm running the same cable, can I skip the box and continue into the conduit run
You can continue, but if you will not make use of the junction box why not just use a pull elbow or LB fitting? Use them will require installing conduit through the wall, but I think that will look cleaner.

You may also choose to run 12-2 NM-B up to the exterior junction box, then splice UF or THWN from that point. THWN will be easier to work with than UF.

there is a limit to the number of turns a cable can take
There are no limit to the number of turns a cable can take. However, there are limit to the number of turns in conduit before needing a pull access (junction box, pull elbow, LB fitting, etc..). I don't remember the limit, but the reason is if there are too many turns or the run is too long, it is hard or impossible to pull wire through. Having access to the cable or wire in the middle, allows pulling them in multiple shots. They don't need to be cut. Just feed through.

Just want to confirm that for UF cable, GFCI protected, in 1/2" non-metallic (PVC) conduit, my trench only needs to be 12"?
Yes, but I'd recommend deeper if possible.
 
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Old 05-24-17, 07:47 PM
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Question 1: If you use UF no box but it does need to be protected by PVC conduit till it enters the ground so you can use a pull elbow outside and a short piece of PVC into the ground. If you use UF cable it is best to direct bury. It can be hard to pull in conduit.

Question 2:
there is a limit to the number of turns a cable can take.
That refers to conduit not cable.

Question 3:
Just want to confirm that for UF cable, GFCI protected, in 1/2" non-metallic (PVC) conduit, my trench only needs to be 12"?
Yes, but I wouldn't run it in conduit. Just use for a protective sleeve where it enters and leaves the ground.

If you want to use conduit use individual conductors such as THWN in conduit. In this case you could use a box outside at the house. Run NM-b inside and into the back of the box and then convert to THWN.

While you can use cable in conduit all the way it is harder to pull and there is no need if the conduit is continuous all the way. Use 1" conduit and you will be future proofed should you ever need more power at the garage.

You will also need a disconnect at the shed. A 20 amp light switch is okay for this.
 
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Old 05-24-17, 08:00 PM
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If you use UF cable it is best to direct bury.
It can be (and it is what it is meant to be), but I don't think that is the best. Especially if it will be buried at 12".
Chances are one day someone will put a shovel in the ground and damage the cable.

Conduit and THWN is the best solution for me.
 
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Old 05-24-17, 09:50 PM
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I have the habit of answering as I read and didn't see the 12" till after I wrote that. I agree at 12" conduit is better (though not required).
 
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Old 05-25-17, 10:28 AM
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And non-metallic 1/2" PVC conduit would be sufficient in the event of a shovel? (Of course a layer of sand and warning tape will be on top of it)
 

Last edited by samd1223; 05-25-17 at 10:31 AM. Reason: Adding 1/2" PVC
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Old 05-25-17, 10:44 AM
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If you use individual conductors yes. If you persist in using UF I'd suggest at least " to make pulling easier.
And non-metallic 1/2" PVC conduit would be sufficient in the event of a shovel?
Maybe?
 
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Old 05-25-17, 12:47 PM
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Standard schedule 40 PVC is just fine against the standard array of household human-powered yard tools. It does not provide much resistance to power equipment. You can always go schedule 80 PVC for additional protection, but it may be a special order item in smaller sizes.
 
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Old 05-25-17, 06:54 PM
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And non-metallic 1/2" PVC conduit would be sufficient in the event of a shovel? (Of course a layer of sand and warning tape will be on top of it)
It is very unlikely you will be able to breake 1/2" PVC conduit with a "human powered" shovel. Unlike plumbing PVC, conduit PVC is softer and it is harder to crack/break. You will see what I mean if you try bending one or take a hammer to it.

What good will sand and warning tape do at 12"? Shovel can go that deep when you just stick it in the ground and step on it.
 
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Old 05-26-17, 07:25 AM
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I would up the conduit size to 3/4"/ Running UF through 1/2" PVC will not be fun.
 
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Old 05-26-17, 11:50 AM
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Agreed that a clean sand backfill is a waste of time when using conduit, but the warning tape is required by code.
 
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Old 05-26-17, 03:03 PM
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There are no limit to the number of turns a cable can take. However, there are limit to the number of turns in conduit before needing a pull access (junction box, pull elbow, LB fitting, etc..). I don't remember the limit
There can be no more than 360 degrees of total change in direction between pull access points. So at minimum a pull point would be required after 4x90's, or 3x90's and 2x45's, or 2x90's and 4x45's, etc (don't forget that offsets DO count towards that 360!). You can always put more, because it makes for much easier pulling. But there can't be less than that.
 
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Old 05-30-17, 07:37 AM
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No UF in PVC conduit?

Hi all,
Thank you very much for your help. After pulling UF wire through the conduit I was very pleased to be done. It was a HUGE pain. I went to my inspector to just run a few questions by him, and he told me I can't run UF in PVC conduit. "It's a different kind of wiring." He said I needed to use individual conductor wire instead. What do you guys think?

Thanks,
Sam
 
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Old 05-30-17, 08:04 AM
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Your inspector needs to read the codebook . It is even required to protect cables against physical damage.
 
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