Subpanel Configuration Check.

[jarvis60]

Hello everyone,
Looking to confirm/adjust my minimum wiring configuration for a subpanel (100 amp). The subpanel will be located in a detached garage and the wires will travel from the main to the subpanel via a pvc conduit (1 1/4) underground. The total distance is 40 feet or less. Beside unbounding/isolating the neutral bar and adding two ground rods, is the following configuration correct?

* Wires protected by 80 amp breaker at the main
* #4 cu for black
* #4 cu for red
* #4 cu for white
* #8 cu for ground/green

Do I need to step up to #3 cu for the 80 amp breaker? Does the #8 cu for the green wire meet the minimum requirements? Am I missing anything else?

Thank you.

 

[u2slow]

80A breaker is protecting the wire... so no need for #3 copper. Aluminum is usually the most affordable way to feed a building.

Codes vary a lot between Canada and USA, so your location matters. Up here we'd use direct-burial #2 aluminum cable, perhaps even a 90A breaker, and the grounding at the main service is sufficient.

 

[pattenp]

Your wire sizes are fine for 80A.

 

[jarvis60]

Thank you both for your comments. Much appreciated.

80A breaker is protecting the wire... so no need for #3 copper. Aluminum is usually the most affordable way to feed a building.

Codes vary a lot between Canada and USA, so your location matters. Up here we'd use direct-burial #2 aluminum cable, perhaps even a 90A breaker, and the grounding at the main service is sufficient.

As for the aluminum cable, my understanding is that you are referring to something like this found at wireandcableyourway (2-2-2-4-****-underground-secondary-distribution-cable) . However, given the size of the pvc pipe, it would not fit... correct?

 

[pattenp]

The **** 2-2-2-4 is USE cable and is not allowed to enter the structure. MHF is needed or XHHW-2. If my memory serves me 1.25" conduit is the very minimum size for 2-2-2-4 Al if using the XHHW-2. The MHF is thicker cable being direct bury.

 

[jarvis60]

Thank you for the clarification. I believe and someone correct me if I am wrong, but using XHHW-2 even if I switched the ground to an #8 cu would probably be hard to pull the wires.

 

[pattenp]

1.25" PVC conduit is good for five #2 Al XHHW-2. The pull is doable, lube will help. 40ft shouldn't be bad as long as you are not maxed to the 360 deg limit of turns between pull points. I'd go with three #2's of the XHHW-2 and one #6 of the XHHW-2 for the ground. The #6 will need to be green because of the color requirements for conductors smaller than #4.

The copper is great if you don't mind the cost.

 

[dcg9381]

Note, there are also Conduit-fill calculators that you can use to check this stuff out yourself:
https://www.southwire.com/calculator-conduit

I like to run a minimum of 2" electrical conduit for stuff like this, but as you've mentioned you use smaller conduit, especially if you're going to move to copper. There are some nice flexible transitions (Liquid Tight) in 1-1/4 size if you need to do something that isn't as easy as a 90 or 45.

You can vacuum a pull wire through conduit that's attached to a grocery plastic bag via a shop vac... How hard it will be depends on how many turns are in that conduit.

 

[jarvis60]

Yeah.. I saw the southwire conduit calculator, but honestly I did not trust I was doing it correctly or I was missing something since the number that I got back was like 27.72% fill using parameters like (Conduit: PVC Sch 40, Conduit Size: 1 1/4, Wire Type: Aluminum XHHW, Size: 2 STR, No. of wires: 4).
As for the pvc pipe size, that's unfortunate, I am leveraging what the previous owner put down, but thank you for your tips. I have (2) 90 in my path and based on your suggestions, I should be able to alleviate at least one of them.

Thanks.

 

[mobetta]

40' of copper vs aluminum isn't a terribly expensive upgrade to pay for, especially if your the one pulling it

 

[jarvis60]

Thank you for that. I was definitely getting all caught up with the price differential between copper and aluminum. Moving forward with copper.

 

[AP514]

+1 Copper for the win
just my thoughts on that..

 

[pattenp]

There is absolutely nothing wrong with using aluminum. Today's aluminum wire is not the aluminum wire of years ago.

 

[wyliesdiesels]

amazing how so many are still afraid of aluminum

http://www.southwire.ca/en/commercial/aluminum-building-wire-40-years-later.htm

 

[Vernon29RW]

I just pulled 4-4-4-6 copper through 1 1/4 pvc40 conduit for about 55 feet of length. Plenty of room in the conduit. My run consisted of 2) 90 degrees and 2) 45 degree bends. I did the grocery bag trick and worked like a charm. My dad fed the wire into the conduit and I pulled the string from the other end. We didn't struggle with it at all. Good luck with your install

 

[jarvis60]

Thank you for your comment. That is very encouraging Vernon29RW.

 

[jarvis60]

amazing how so many are still afraid of aluminum

http://www.southwire.ca/en/commercial/aluminum-building-wire-40-years-later.htm

I did not have much luck with the link you posted. Not sure if the link is broken or needs updating.

 

[wyliesdiesels]

I did not have much luck with the link you posted. Not sure if the link is broken or needs updating.

website is down

try later

https://www.isitdownrightnow.com/southwire.ca.html

 

[dcg9381]

amazing how so many are still afraid of aluminum

http://www.southwire.ca/en/commercial/aluminum-building-wire-40-years-later.htm

It's not that we are afraid of it, just in large ampacity, it gets to be a pain in the *** to work with. Other than that, just use anti-ox paste and torque it correctly.

Then again, in large ampacity, it's a lot cheaper than copper.

 

[wyliesdiesels]

It's not that we are afraid of it, just in large ampacity, it gets to be a pain in the *** to work with. Other than that, just use anti-ox paste and torque it correctly.

Then again, in large ampacity, it's a lot cheaper than copper.

no ox paste is not required unless called for by the manufacturer

 

[Norcal]

It's not that we are afraid of it, just in large ampacity, it gets to be a pain in the *** to work with. Other than that, just use anti-ox paste and torque it correctly.

Then again, in large ampacity, it's a lot cheaper than copper.

All connections need to be torqued per specs, sloppy connections on copper will cause just as much problems as with aluminum.

no ox paste is not required unless called for by the manufacturer

Agreed.