Questions on my next project

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Old 09-09-19, 11:33 AM
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Questions on my next project

I plan on installing two 20-amp circuits to my outdoor shed which is roughly 125 feet from my home. I spoke with my local inspector and he stated I need to bury PVC conduit 18” deep and run THHN wires. We agreed I would run four 10-gauge wires (for voltage drop) in the conduit (2 hot, 1 common, 1 safety ground).

I do have a few questions on the project:

1. Is this wire acceptable for underground burial/ my situation?

2. It’s cheaper to buy 500 feet of a single color THHN wire (black for example). Does code require me to run distinct color-coded wires? Can I use the black wire for all 4 wires (2 hot, 1 common, 1 safety ground) and label them accordingly at the terminating ends (using electrical tape or liquid tape for example)?

3. Can I use simple PVC cement to connect the conduit pieces? Do I need to do anything else to prevent water from infiltrating the conduit?

4. Is there any best practice for how to bury the conduit? Or ways to prevent others from digging-up the line?

5. He did mention something about needing a ‘slip joint’ at the shed. Can anyone shed any light on what that means? I thought I would use something like this on the shed itself.

6. Ideally, I would like to run a low-voltage cable to the shed. Is there anything wrong with installing a second conduit in the trench, placing it directly on top of the first conduit?

7. Any other tips or advice anyone can give me?

Thanks so much for the help!
 
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Old 09-09-19, 11:58 AM
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1. THHN is not suitable for underground. However most wire is dual rated and likely it has the THWN rating needed.
2. Distinct colours are not required.
3.PVC cement is fine. Water will get in. You can't stop it.
4.You could install tape about half way down as you fill indicating buried conduit.
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5.That will turn the conduit into the shed. An expansion joint is a slip joint that allows the conduit to get longer and shorter if the building heaves up in the winter.
6. There should be no problem running a low voltage conduit in the same trench.
7 Use sweep elbow where where the conduit turn up out of the ground.
 
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Old 09-09-19, 12:09 PM
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The wiring sold at Depot.... Southwire THHN..... is dual rated for wet use.
 
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Old 09-09-19, 08:34 PM
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Rethinking my scenario, the 125 foot length is only to the house. To the panel, I need to add another 40 feet. Given the entire run, end-to-end would be around 165 feet, is 10 gauge sufficient? Would 8 (or 6) be better?

Inside the house, could I run a simple 10/3 cable from the panel to a square box…and then connect the cable wires to the individual THHN wires? Would that suffice?
 
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Old 09-09-19, 11:34 PM
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#10 for a 165' run at 20A should be fine unless you have some large loads or a voltage drop will be a problem. What are you planning on running in the shed ?
 
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Old 09-10-19, 04:17 AM
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Hi, I would check wire prices at electrical supply house before purchasing at the Big box store, maybe even pipe etc.
neutral conductor must be identified with white tape or some means.
Geo
 
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Old 09-10-19, 05:30 AM
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Neutral conductor must be white. In this case with individual wires you are not permitted to recolour a black to white.
 
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Old 09-10-19, 09:00 AM
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Power will mainly be used for lighting (CFLs inside and flood lights outside) and the occasional power tool (bench grinder, chop saw).

Currently, I run a 14 gauge extension cord (on a 20a circuit ) for my power tools while I build the shed and I haven't seen any degradation in performance.

I tried various voltage-drop calculators (online) and I receive varying results. Some even suggest 6 gauge wiring.
 
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Old 09-10-19, 11:52 AM
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If a #14 was supplying you with adequate power..... then stay with the #10's.
 
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Old 09-10-19, 06:49 PM
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I have read that every 125 ft, there is a voltage drop of 10% so I always oversize my wires to the next gauge thickness for long run of 125 feet or more. So if I have a 20 amp circuit with 20 amp outlets and so on, I run from the connection (outside my house and in garage for example) to the shed 125 feed use 10 gauge wire to account for voltage drop. The breaker and outlets are 20 amp, but the wire is 30 amp 10 gauge. I pigtail off the 10 gauge with 12 gauge wires to the 20 amp outlets. Just asking but if you are getting a permit, and an inspection, the inspector is ok with your doing your own work? If you do your own work, take pictures, and make sure your work by step is approved by the inspector.

https://www.calculator.net/voltage-drop-calculator.html

Of course 10 gauge is overkill unless you are planning to do something intensive like run a shallow well pump out of a stream to water your lawn, or if you have some other use such as a welder (but that would mean planning now for 220v.). The deal here is once you cover up the conduit, it covers up faster than it gets dug up (again). You do not say how big the shed is or what your electrical needs are other than a plug and lightbulb. Just curious, why do you need low voltage wiring? Anything low voltage around my house is hooked to transformers.
 
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Old 09-10-19, 07:10 PM
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Inspector is totally cool with me doing my own work.

My electric needs are for shed lights (both internal and external) and flood lights for the lawn. Secondary purpose is for running power tools. For example, I will be storing my lawn mower in the shed and would like to put my bench grinder in there so I can sharpen the blade after each cut.

Low voltage is for running an Ethernet wire so I can put a wireless access point in the shed. I'm trying to get full wireless coverage throughout my entire lawn. I also might hookup the shed door to my alarm system.

Does pigtailing to a lower gauge have any negative effects? Are you allowed to do that?
 
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Old 09-11-19, 12:23 AM
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Does pigtailing to a lower gauge have any negative effects? Are you allowed to do that?
Pigtailing is acceptable and does not have any negative effects due to the short length of the wire.

It can be hard to get #10 wire on devices.
 
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Old 09-13-19, 12:21 PM
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I’ve been contemplating running a switch inside my house for the shed lights.
If I were to do that, would I need to use a 10 gauge cable to the switch box or could I get away with 12 gauge? Same thing with wiring the lights inside the shed - 12 gauge or do I have to stick with 10?

The run would be:

1. Panel to square box (40 feet - 10 gauge)
2. Square box to switch box (10 feet - ?? gauge)
3. Switch box back to square box (10 feet - ?? gauge)
4. Square box to shed (130 feet - 10 gauge)
5. Lights (15 feet - ?? gauge)
6. Shed back to square box (130 feet - 10 gauge)
7. Square box back to panel (40 feet - 10 gauge)

Does this make sense?

This would only be used for lighting, nothing else.
 

Last edited by k19_1234; 09-13-19 at 12:23 PM. Reason: List was messed up.
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Old 09-13-19, 01:00 PM
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You could use #12 for the switch line since you are protecting the circuit at 20A.
You can use #12 inside the shed too.
If the #10 goes all the way to the breaker..... the wire needs to be tagged at the breaker as stating "20A only" as #10 is typically protected at 30A.
 
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Old 09-13-19, 01:36 PM
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Sorry if I missed this and it was said already, but individual conductors pulled in conduit that are #6 and smaller are not to be identified by re-marking. The hots need to be black or red, the neutral needs to be white, and the ground needs to be green or bare copper.
The slip joints are to allow movement of the PVC conduit from expansion and contraction due to cold and heat.
 
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Old 09-19-19, 10:07 AM
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Thanks everyone for the help, it’s much appreciated.

My shed sits on cinder-blocks and I successfully dug the trench underneath the shed. I cut open the plywood floor and now have access to the trench from the inside.
My plan is to use a buried sweep elbow, drill a hole in the floor and bring the conduit directly through the hole to the inside of the shed. I will put the slip joint on the conduit and run it directly into a junction box mounted to the studs of the shed walls. I’ll cover the hole with liquid insulation.

Is there anything wrong with such a setup or any reason why the inspector might complain?
 
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