what size green wire 100 amp subpanel

[Raisedonadeere]

Running thwn #3 AWG 2 hots and 1 neutral 40 foot wire length in conduit underground to a subpanel in new garage. I have seen that the green?/ground wire can be smaller. I chased my tail for an hour trying to find it but I give up. what size green do I need to order and how does one search or determine the size.

One post I saw said #8 to go with the #3's but I was sure I saw #6 elswhere.

Sorry to ask stuff I should be able to find.

 

[alfredeneuman]

#8 copper or #6 aluminum

 

[wyliesdiesels]

Nec 250.122(b) is what youre looking for

 

[Raisedonadeere]

Thanks to both. I am getting nervous as a long tailed cat in a room full of rocking chairs over passing this electrical inspection.

 

[bjcouche]

The equipment grounding conductor is based on your breaker size, not your wire size. As stated earlier, 6awg aluminum or 8awg copper is good for a 100A breaker. For a 60A breaker 10awg copper is allowed.
There is a caveat to all this info though... If you are OVER sizing your hot wires for ANY reason, (like voltage drop), you are also required to over size your grounding conductor. Say for instance you had 2awg copper on an 60A breaker, that wire would be over sized for the 60A breaker, and thus you would have to size your grounding conductor larger than 10awg as well...
You listed 3awg but didn't indicate whether it was copper or aluminum or what your breaker was rated for...

I'm unsure of how many inspectors are going to know about these nuances, much less know how to calculate them. They're usually too busy making sure that the outlet you mounted on your ceiling for your garage door opener is tamper proof, and that it has a GFCI breaker in the panel...

Brian

 

[TractorJeff]

Plus he could down size his Neutral based on his Load schedule

 

[andyvh1959]

I too am into the electrical for the detached shop garage I have built. The 100 amp breaker panel for the new garage is about 50' total from the meter on the back of the house. So I'll run a buried line in conduit from the meter to the new garage main. I'll have 30 amp outlets in the garage for my air compressor and my MIG welder. But I don't plan to run those both at the same time. There'll be another connection for the in floor heating system/pump. I'll also install an outlet in the garage in case I ever (or someone else) wants to install a wall mounted air conditioner. right now I have one 5/8" ground rod down through the slab, but I've found I need a 2nd ground rod at least six feet from the original?

 

[Innovate1]

The pros here can confirm but for 80A and #2 AL you should be able to reduce the neutral 1 size to #3. It also depends on if the local AHJ allows reduced neutral. For ground #4 I think. Southwire also has a conduit fill calculator. I put in 3 strands of #2 + 1 of #4 since it didn't have a selection for #3. Minimum size is 1-1/4 but going up one size to 1-1/2 will make the pull easier.

 

[PCustoms]

The pros here can confirm but for 80A and #2 AL you should be able to reduce the neutral 1 size to #3. It also depends on if the local AHJ allows reduced neutral. For ground #4 I think. Southwire also has a conduit fill calculator. I put in 3 strands of #2 + 1 of #4 since it didn't have a selection for #3. Minimum size is 1-1/4 but going up one size to 1-1/2 will make the pull easier.

Think he's still looking for wire 4 years later?

 

[Innovate1]

Think he's still looking for wire 4 years later?

Probably not. Looks like I confused this with a more recent thread...

 

[mike93lx]

Probably not. Looks like I confused this with a more recent thread...

How dare you