Short Subpanel Run - Conductors and Conduit Questions

[BD55]

I'm putting in a 100a subpanel in my shop. For power run from house to subpanel (~20'), I'm planning on running hot, hot, neutral 3 awg 75C THHN and 6 awg solid or stranded ground in 2" buried pvc conduit (glued before pulling wire). I'm finding mixed information on whether THHN is acceptable for this use, and have searched the forum for similar topics, but I suspect I'm on track but wanted some additional thoughts. My breaker and panels are 75C rated, and THHN is rated to 75C in wet/oil/coolant, right?

 

[Proflyer]

I'm NOT an electrician, but a buddy is and is helping me with mine. I ran 4/0 from the house on a 125amp breaker to the shop and used 4/0 aluminum SER inside the house (all 4 wires in a sheathing), and then outside to the shop I ran 4/0 URD cable which is direct bury. I used a pvc elbow (45*) from the ground to the 2" sch80 PVC pipe that goes into the junction box on the house, and the disconnect on the shop wall outside. You need sch80 for above ground but can use sch40 for the elbow and underground. Rented a trencher and put in a 30" deep trench. My run from the house to the shop is 100' (inside house is 75'), and I plan on putting solar on the shop that'll back-feed to the house, thus the 4/0. I think you can do 2/0, especially for that short of a run, but I wanted more wire than needed so I could back-feed the solar without issue of too much voltage drop. From what I understand, and working with this 4/0, running it all in conduit is a pain in the ****...the stuff does not flex a whole lot. Also mine is 4 conductor...I think it's hot, hot, neutral and ground...but again I'm not into sparky stuff so not sure, just did what buddy said to do.

 

[captaindiode]

Most, but not all, THHN is dual rated THWN. Underground, I believe THWN is required.

 

[Norcal]

A note, in conduit anything over 10 AWG must be stranded, & a grounding conductor smaller then 4 AWG used as a grounding conductor must have green insulation, THHN is for dry locations only, the good news is most THHN is dual rated as THWN for wet locations.

 

[BD55]

Thanks for the responses - I'll scratch the solid/bare ground and get green insulated stranded 6 awg. If I'm understanding the comments, most THHN is dual rated for wet locations, so I need to verify the wiring I get has that dual rating in order to use within underground conduit?

 

[mike93lx]

You also need two ground rods.

 

[mike93lx]

Thanks for the responses - I'll scratch the solid/bare ground and get green insulated stranded 6 awg. If I'm understanding the comments, most THHN is dual rated for wet locations, so I need to verify the wiring I get has that dual rating in order to use within underground conduit?

Yes, absolutely need to. I would be surprised if you buy some that isn't dual rated

 

[Innovate1]

I didn't see any mention of aluminum or copper for the wire but guessing for #3 at that current it must be copper. #1 AL is good for 100A and no issues with voltage drop for that short run. A lot cheaper than copper. I used XHHW from wireandcableyourway.com. 4/0 for 125A service posted by someone else is massively oversized even for a long run - must have some left over cable from a job or something.

 

[Proflyer]

I didn't see any mention of aluminum or copper for the wire but guessing for #3 at that current it must be copper. #1 AL is good for 100A and no issues with voltage drop for that short run. A lot cheaper than copper. I used XHHW from wireandcableyourway.com. 4/0 for 125A service posted by someone else is massively oversized even for a long run - must have some left over cable from a job or something.

Oversized for sure, but adding solar panels to the shop roof instead of the house, so we went huge for that. Not only is it hard to work with, but it's $$$...stuff was darn near $10/ft. Do NOT do that unless you need it!

 

[BD55]

You also need two ground rods.

Thanks - grounding is covered using a Ufer.

Yes, absolutely need to. I would be surprised if you buy some that isn't dual rated

Good to know - thanks

 

[BD55]

I didn't see any mention of aluminum or copper for the wire but guessing for #3 at that current it must be copper. #1 AL is good for 100A and no issues with voltage drop for that short run. A lot cheaper than copper. I used XHHW from wireandcableyourway.com. 4/0 for 125A service posted by someone else is massively oversized even for a long run - must have some left over cable from a job or something.

Sorry, should have mentioned, yes, copper. It's a short run and some tighter quarters to get into the main panel, so I'm just going to go with the smaller gauge copper. Thanks for the input