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Discussion Starter · #1 ·
Hi,

I’m going to install a sub panel in my detached garage and I would like to make sure everyone agrees I’m doing this the correct way and asking for any ideas for improvement. I’ve recently trenched from the house to the garage and installed 1” PVC Schedule 40 conduit.

My main panel has 200A service. In the main panel, the neutral and ground are bonded. I’m planning on using a 50A dual pole breaker to feed the sub panel.

I’m planning on using 10’ – 15’ of #6/3 NM from the breaker to a junction box in the crawlspace. In the junction box, I will connect the Romex 6/3 to four strands of #6 THHN\THWN. I will use split bolt connectors to connect the strands. I’m not coming out of the service panel with the stranded #6 because I do not have any available 1” punch out holes in the main panel box that I can connect conduit to, however, there is an available punch-out that will fit a 6/3. The THHN\THWN will exit the junction box in the 1” Schedule 40 conduit. There will be about 60’ of stranded cable from the junction box to the sub-panel.

Inside the sub-panel I will connect the black and red stranded cables to the hot lugs. I will connect the white stranded cable to the neutral lug \ bar. I will install an accessory ground bus bar and connect the green stranded cable. I will NOT connect the green screw to bond the metal case to the neutral bar. I will install a #6 ground wire and connect to two ground rods that I will install outside the garage. The ground rods will be connected in series to the same ground wire.

Please let me know if you believe I’m missing something or if my design fails for any reason.

Thank you
 

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You can use large wire nuts to connect the wires.
 
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You will need a means of disconnect at the outbuildings.
 
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Very Stable Genius
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Since I'm in Canada, this may not be useful, but here's a few thoughts anyways.

-#8 gnd to go with the 3 X #6's.
-If there's a 3/4" KO available: run 3/4 from the panel to box in the crawl space then 1" PVC from there as planned - pull T90 all the way between
the panels using the crawl space box as pull box instead of JB.
-In Canada there'd be no need for grounding electrodes

Again, this would work up here, YMMV.
 

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Discussion Starter · #6 ·
Thank you all for your replies, I greatly appreciate the info.

You can use large wire nuts to connect the wires.
I understand that Ill need to reverse-tape the split bolts then regular-tape them so they don't get super sticky.

Would you please help me understand any pros \ cons for split bolt vs wire nut?


You will need a means of disconnect at the outbuildings.
I should have stated this in my OP but I did not.

The sub-panel will only have 6 spots for branch circuits. I 'think' a panel of this size will not require a separate shutoff breaker. With that said adding another 50A breaker will only add $10 for the breaker and a few extra for a different panel so it's not a big deal at all. You used the word 'need'. Would you please elaborate?



Since I'm in Canada, this may not be useful, but here's a few thoughts anyways.

-#8 gnd to go with the 3 X #6's.
-If there's a 3/4" KO available: run 3/4 from the panel to box in the crawl space then 1" PVC from there as planned - pull T90 all the way between
the panels using the crawl space box as pull box instead of JB.
-In Canada there'd be no need for grounding electrodes

Again, this would work up here, YMMV.

I've already purchased four strands of #6, so unless there is an issue I hope not to be spending more on wire.

There may be a 3/4" KO & this may be a good option! So on one side of the JB 1" conduit to the garage and on the other side 3/4" conduit to the main panel, right?
I purchased Southwire THHN \ THWN but for the life of me I cannot see if it says T90 on it...


The local code here is: the sub-panel has to be 5' off the ground & there can't be any exposed Romex, in the garage.
Exposed romex? Do you mean any NM cable will need to be behind drywall? Any exposed cable will need to be BX or MC ?





Again, thank you all very much for your replies!
 

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Very Stable Genius
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I've already purchased four strands of #6, so unless there is an issue I hope not to be spending more on wire.

There may be a 3/4" KO & this may be a good option! So on one side of the JB 1" conduit to the garage and on the other side 3/4" conduit to the main panel, right? Right.
I purchased Southwire THHN \ THWN but for the life of me I cannot see if it says T90 on it...
Don't want to say that the NEC will allow 4 x #6's in one 3/4 pipe. By using 3 x #6's and a #8 it's more likely to be compliant. Other option would be to use 3/4 EMT for the main panel to pull box. This way the EMT is the Gnd so you only need the 3 #6's in that section of pipe.
T90 is short form for THHN-90/THWN-75....at least with guys I've worked
with.
 

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Guapo
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In NYC, no exposed cables are allowed. The surrounding suburbs may allow BX, I'm not sure. Check your local codes. I wouldn't call the building dept. because they make force you to get a permit.
 

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Discussion Starter · #9 ·
Don't want to say that the NEC will allow 4 x #6's in one 3/4 pipe. By using 3 x #6's and a #8 it's more likely to be compliant. Other option would be to use 3/4 EMT for the main panel to pull box. This way the EMT is the Gnd so you only need the 3 #6's in that section of pipe.
T90 is short form for THHN-90/THWN-75....at least with guys I've worked
with.

CodeMatters,

Thanks!
This conduit fill chart shows that I can put 4 strands of #6 in 3/4" Sch 40 PVC.

THHN-90, like 90*C and THWN-75 like 75*C, correct?

I was thinking you were referring to the Southwire SIMpull. I know I purchased Southwire but I don't know if its SIMpull or not.
 

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Discussion Starter · #10 ·
In NYC, no exposed cables are allowed. The surrounding suburbs may allow BX, I'm not sure. Check your local codes. I wouldn't call the building dept. because they make force you to get a permit.
Would BX be considered exposed? Thank you!
 

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er... I aren't a Newbie.
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DadinPA,

As you said, make sure you have the neutral and ground separated in the sub-panel (as it is strict code). Also, you may need to ground the sub-panel to the outside ground, just make sure to check the code on that.
 

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Discussion Starter · #14 ·
DadinPA,

As you said, make sure you have the neutral and ground separated in the sub-panel (as it is strict code). Also, you may need to ground the sub-panel to the outside ground, just make sure to check the code on that.

CNT, thank you for the comment.
Would you please explain the technical reasons that some codes require outside ground and some do not?
 

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Discussion Starter · #15 ·
Wire nuts are easier and less costly.
Thank you very much. Yes wire nuts are definitely less costly. The split bolts were $4 each... Since I have already purchased them is there any other reason?

When I purchased the split bolts I didn't see wire nuts that large but I can look again.

Would you also please comment on the size of the sub panel?
The sub-panel will only have 6 spots for branch circuits. I 'think' a panel of this size will not require a separate shutoff breaker. With that said adding another 50A breaker will only add $10 for the breaker and a few extra for a different panel so it's not a big deal at all. You used the word 'need'. Would you please elaborate?

Thanks again, I greatly appreciate and look forward to your reply.
 

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A "Handy Husband"
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Split bolts are a PIA to insulate properly.

NEC 110.14 (B) "...shall be covered with insulation equivalent to that of the conductors or with an insulating device identified for the purpose."

This means insulated with rubber tape or equivalent and over-wrapped with electrical tape (friction tape in the old days). Vinyl electrical tape alone does not meet the requirements. Large blue wire nuts is the way to go.
 

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Very Stable Genius
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I use the "big blue marrettes" but would probably use the ones in the
attached pic (with heat shrink) if the price weren't ridiculous up here.
Not willing to spend nearly $30 to connect 4 conductors.
 

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Would you please explain the technical reasons that some codes require outside ground and some do not?
Don't sweat the technical reasons.

The NEC doesn't require the ground rods for a subpanel in a residential building or attached garage.

If the subpanel is in a detached building or structure, it needs grounding.
 
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