Wire and conduit selection for 100A feed to sub panel?

[Zaxxn]

Hi all!

SO many threads about this subject on here, but nothing that mirrors what I am planning to do exactly, so before pulling the trigger and spending hundreds of dollars I figured I run it by the experts here.

Situation: Main panel in the basement at the opposite end of the house from the attached new construction shop. Have about 60' through the basement to the conduit that runs from there over and out of the slab of the attached shop building (another 20' total).

Plan: Run 3-3-3-6 Cu XHHW-2 through 1 1/4" NMLT conduit through the basement and then into the conduit out into the shop.

Anyone see anything wrong with this product selection? Should I step down to a 90A breaker feeding the sub panel with this wire choice and length of run?


Extra credit question: Currently I only have 100A service to the house, and the 200A upgrade is still over a month away. Could I place the 100A or 90A breaker into the main panel (plenty of room) anyways right now already (obviously knowing that if I am stupid, I potentially could trip the main with other house loads and garage loads, but there is really nothing in the shop aside from lighting and a gas burner yet), or should I get a smaller breaker for the meantime and then upgrade to a 100A or 90A when the service upgrade is complete?


Thanks so much for all your help already in advance!
--Zax

 

[pattenp]

You're fine with #3Cu at that distance for 100A. You can use #2 Al XHHW-2 through 1.25in. conduit for 90A and save some $$.

Check your panel info tag to see if the stabs are rated to take up to a100A breaker, if so then you can put in a 100A breaker.

 

[mike93lx]

Go aluminum unless you hate money.

You can absolutely use a smaller breaker for now, as long as the wire will fit, but I would just put a 90a in and be done, assuming the panel can accept it.

 

[sberry]

The 2 alum will go thru a straight 1 1/4 pipe but its a problem with turns and LB, its the main reason they have 1.5

 

[wyliesdiesels]

I would use bigger conduit and go with #2 al.

Also, if you do use #3 cu, the EGC/ground wire can be #8...

Make sure the neutral bus in the subpanel is isolated.

 

[dcg9381]

I did it with:
100' Aluminum URD **** 2-2-2-4 Cable Direct Burial Quadruplex Secondary Wire

Currently $132 per 100' at Amazon.

I cased it in 2" PVC conduit, but 1.25 or 1.5 would be fine....

Some discussion of this being only "90A" rated, but wire specs indicate otherwise. I do have it on a 90A breaker.

 

[teamextreme]

Have about 60' through the basement to the conduit that runs from there over and out of the slab of the attached shop building (another 20' total).

Plan: Run 3-3-3-6 Cu XHHW-2 through 1 1/4" NMLT conduit through the basement and then into the conduit out into the shop.

You're planning on pulling 60ft of #3 through sealtite? Have fun with that, I think it will be a ***** to pull thru. (I'm assuming NMLT=Non Metalic Liquid Tite) Unless you are going through joists or something like that, there's no way I'd run sealtite. Plus it's WAY more expensive. And even if there are lots of obstructions, I'd run some flavor of cable/romex instead.

FYI, I ran the exact setup to my shop (just not ST), #3 Cu through 1.25" PVC and it pulled/worked just fine.

 

[theoldwizard1]

You're fine with #3Cu at that distance for 100A. You can use #2 Al XHHW-2 through 1.25in. conduit for 90A and save some $$.

You will save more if you use 2-2-2-4 MHF (4 conductors, each basically XHHW-2).

 

[pattenp]

I did it with:
100' Aluminum URD **** 2-2-2-4 Cable Direct Burial Quadruplex Secondary Wire

Currently $132 per 100' at Amazon.

I cased it in 2" PVC conduit, but 1.25 or 1.5 would be fine....

Some discussion of this being only "90A" rated, but wire specs indicate otherwise. I do have it on a 90A breaker.

URD **** is only approved to be installed outside of the structure. It does not have fire resistant rated insulation so is not to enter a structure. What amps the specs say vs. what's allowed by the NEC is apples and oranges.

 

[pattenp]

You will save more if you use 2-2-2-4 MHF (4 conductors, each basically XHHW-2).

MHF is not basically XHHW, it's RTH/RHH/USE. The insulation is thicker being direct bury and will be tougher to pull trough 1.25in. conduit. The XHHW may cost a few pennies more per foot but will be easier to pull. I'm assuming the conduit in slab of shop is also 1.25in.

 

[Zaxxn]

MHF is not basically XHHW, it's RTH/RHH/USE. The insulation is thicker being direct bury and will be tougher to pull trough 1.25in. conduit. The XHHW may cost a few pennies more per foot but will be easier to pull. I'm assuming the conduit in slab of shop is also 1.25in.

As always, SO much awesome information on this forum!!!

Yes, pattenp, that's the thing, the conduit in the slab is 1.25. It's not terribly long, about 14' to a 90 (the long sweep kind) and then up to the slab. I wanted to go with a 90A and MHF but was worried I couldn't accommodate that in the 1.25 conduit in the slab? Will it work?

And if I do use MHF, would I then not need conduit through the basement?


Thanks again already in advance,
--Zax

 

[wyliesdiesels]

1 1/4" would be the minimum but may be tight.

MHF needs to be inside conduit inside structures since it has no overall jacket!

 

[pattenp]

The #2 MHF will fit in 1.25in conduit and needs to be in conduit where above ground including inside. You could use SER in basement and transition to MHF in conduit via a large junction box. Get 2-2-4-6 MHF if possible for an easier fit.

 

[Zaxxn]

Ok, that sounds good if I can get the 2-2-4-6 somewhere local. But then again, not sure if it's a mistake, but the web sites I see list the OD of 2-2-2-4 and 2-2-4-6 AL MHF as almost the same even if it doesn't make sense? Good difference in price to the XHHW though! And I can run it just in some schedule 40 conduit through the basement then instead of going with some NMLT flex stuff?

 

[pattenp]

Yes, you can use Sch40 PVC through the basement. I see the manufacturer shows the OD as the same but from my actual use of both sizes the 2-2-4-6 seams smaller. Maybe it's an optical illusion. All said, I have put 2-2-2-4 MHF in 1.25in conduit, just use some lube to make it easier to pull.

 

[Zaxxn]

Ok, sounds great! Thanks! I am also pretty sure even HD stocks 2-2-2-4, so that would make things real easy!

 

[pattenp]

In my area HD carries 2-2-4-6 and Lowes carries 2-2-2-4.

 

[Farmallboy15]

Or you could call your local electric supply house and have it cut to the exact length you want at half the cost per foot compared to Lowes/HD. Anything #6 and over I went to the supply house, it was literally half the price of Lowes...

 

[theoldwizard1]

2-2-4-6 MHF seems "odd" to me ! I understand the "logic" behind it (you are not likely to run "full" loads on L1 and L2 at the same time and 240V loads don't use the neutral at all) but it still seems "odd".

Check prices at Wire and Cable Your Way

 

[dcg9381]

I just did this.
$130 for 100 feet of:
100' Aluminum URD **** 2-2-2-4 Cable Direct Burial Quadruplex Secondary Wire
(Available on Amazon).

Some indications that this is only good for 90A in conduit, but that runs contrary to the wire rating itself.. I have it on a 90A breaker.

It's fine in 1.25" conduit. 2" is better.

 

[Bert_]

2-2-4-6 MHF seems "odd" to me ! I understand the "logic" behind it (you are not likely to run "full" loads on L1 and L2 at the same time and 240V loads don't use the neutral at all) but it still seems "odd".

Check prices at Wire and Cable Your Way

120v loads on opposite phases will also make the neutral current cancel. Even if you tried it would be very hard to overload a neutral that is reduced the common two sizes.

On bigger services with mostly line to line loads I often run a half size neutral.


If you running conduit the whole way save yourself some work and just order xhhw. Pulls so much better.

 

[wyliesdiesels]

I just did this.
$130 for 100 feet of:
100' Aluminum URD **** 2-2-2-4 Cable Direct Burial Quadruplex Secondary Wire
(Available on Amazon).

Some indications that this is only good for 90A in conduit, but that runs contrary to the wire rating itself.. I have it on a 90A breaker.

It's fine in 1.25" conduit. 2" is better.

This type of wire is not permitted inside structures.

And if you look at table 310.15(B)(16), you will see that it is indeed rated for 90a regardless of conduit. So im not sure what youre referring to.

 

[pattenp]

This type of wire is not permitted inside structures.

And if you look at table 310.15(B)(16), you will see that it is indeed rated for 90a regardless of conduit. So im not sure what youre referring to.

dcg9381 posted the same back in #6 and I responded as you did. He's not saying if he used the URD inside or not, I assumed also inside.

 

[wyliesdiesels]

dcg9381 posted the same back in #6 and I responded as you did. He's not saying if he used the URD inside or not, I assumed also inside.

yeah i figured maybe he missed your reply so i figured another reply to his might get his attention.

 

[dcg9381]

And if you look at table 310.15(B)(16), you will see that it is indeed rated for 90a regardless of conduit. So im not sure what youre referring to.

I think you are saying that NEC rules here and that they set allowable "ampacity", correct?

I'm not arguing - just inquiring.

Wire manufacturer specs say otherwise (cite pending), so my take away is that that it the wire can handle 100A in conduit, but NEC code requires 90A max breaker.

Do you agree?

 

[dcg9381]

URD **** is only approved to be installed outside of the structure. It does not have fire resistant rated insulation so is not to enter a structure.

I agree with this also. Technically, if you need it to go to an interior main, it needs to be brought to an outdoor panel, spliced to interior-approved wire, then brought to an interior sub-panel.

If I did bring it to an interior main, my though was "I'll never get caught" and my structure is non-residential.

 

[alfredeneuman]

my structure is non-residential.

Where does it say the structure must be residential?
It's true for any structure

 

[wyliesdiesels]

I think you are saying that NEC rules here and that they set allowable "ampacity", correct?

I'm not arguing - just inquiring.

Wire manufacturer specs say otherwise (cite pending), so my take away is that that it the wire can handle 100A in conduit, but NEC code requires 90A max breaker.

Do you agree?

Only partially agreeing.

Yes the NEC ampacity table is the code that installs must abide by.

But where are you getting this info that the ampacity is higher in conduit or that the wire manfu. says ampacity is higher?

 

[wyliesdiesels]

I agree with this also. Technically, if you need it to go to an interior main, it needs to be brought to an outdoor panel, spliced to interior-approved wire, then brought to an interior sub-panel.

If I did bring it to an interior main, my though was "I'll never get caught" and my structure is non-residential.

The insulation is not rated for use inside ANY structure PERIOD! There is no designation for residential...

 

[dcg9381]

Understood and totally agree.
If I reversed the side of the steel panel the main was on, it'd be 100% compliant..

 

[mike93lx]

Understood and totally agree.
If I reversed the side of the steel panel the main was on, it'd be 100% compliant..

Sounds like you are trying to justify a bad install. You aren't going to get support from many here on that.

It's your perogative to do it wrong, just don't expect people to agree

 

[3rdgendslmech]

I ran dual rated #2 Al xhhw and a #4 ground through 1.5 PVC conduit. It's very do able with a helper. I went through 2 90 degree sweeps a LB into the panel at the barn and 2 LBs piggy backed at the house panel. As long as you use lube and a decent pull rope you're good. Also when you lay your conduit, you want to pull from the "bell" end of conduit...less chance for hanging up.

 

[bjcouche]

If it were me, I'd go with the 2-2-2-4 or 2-2-4-6 aluminum, but I wouldn't go with the MHF. The MHF comes TWISTED together, designed for direct burial. MHF CAN be pulled through conduit, especially if the conduit is oversized, however, it is difficult to pull through 90 degree curves because the cable being twisted together wants to bend like one single cable, not 4 individual ones.
The electrical distributors by me carry THHN/THWN-2 in aluminum. It comes as a compact conductor and pre lubed. Four individual conductors will pull way easier than four twisted ones. You can't use THWN-2 for direct burial, but if you are placing it inside conduit you're good.
Brian

 

[Junkyard Jim]

I have sort of the same issue as the OP. I can run under the house from one side to the other and then go underground to the barn. I am planning to run through conduit even under the house for safety’s sake. I found this online and would like to know what everyone thinks of it. I haven’t bought it or even brought it up to my electrical adviser yet. What do you think?

https://www.wireandcableyourway.com/2-2-2-4-aluminum-mobile-home-feeder-cable.html

 

[bjcouche]

I think you can buy the exact same stuff from your local Home depot, Lowes, Menards, etc. and you don't have to pay the shipping.
Brian

 

[Junkyard Jim]

I think you can buy the exact same stuff from your local Home depot, Lowes, Menards, etc. and you don't have to pay the shipping.
Brian

I priced it out with shipping and I can have it dropped at my door for about a hundred dollars less than driving thirty minutes to town to pick it up. I was more wondering ifpeople thought it would be good to use in the application me and the OP are considering. Thanks

 

[bjcouche]

MHF (Mobile Home Feeder) rated USE2/RHH/RHW-2, from different manufacturers or suppliers is basically all the same. I was previously suggesting the the OP that I would use individual conductors instead of a twisted bundle like MHF is. The OP's conduit is 1.25" and four wires twisted together are harder to pull through 90's than 4 individual conductors. In the link you posted, from wire and cable your way, they also sell XHHW-2 individual wire.
Brian

 

[Junkyard Jim]

Thanks Brian. The light came on about the difference in single strand and twisted together.

 

[pv74]

Sched 40/80 conduit fill:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=SCH_40_80_PVC_Conduit_Fil_VES

Liquid Tight conduit fill:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=LIQUIDTITE_CONDUIT_FILL_VES

Wire Size:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=wiresize_calculator_VES


I would go with #4 copper, that is what the wire size calculator tells me for 80' @ 100 Amps. In fact, the size calculator goes out to 115' with #4 copper. Sounds like enough of a margin for error to me.

If you are not comfortable wiring a large sub panel, make a deal an electrician that you trust to run the panel to your shop and install the ground rods properly. Run the branch wiring yourself. That's what I did. In the long run, the cost to have this done correctly is minimal and you have the piece of mind that it was done right.

 

[teamextreme]

Sched 40/80 conduit fill:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=SCH_40_80_PVC_Conduit_Fil_VES

Liquid Tight conduit fill:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=LIQUIDTITE_CONDUIT_FILL_VES

Wire Size:
https://www.vikingelectric.com/c/BusinessPagesView?storeId=13801&catalogId=10251&page=wiresize_calculator_VES


I would go with #4 copper, that is what the wire size calculator tells me for 80' @ 100 Amps. In fact, the size calculator goes out to 115' with #4 copper. Sounds like enough of a margin for error to me.

If you are not comfortable wiring a large sub panel, make a deal an electrician that you trust to run the panel to your shop and install the ground rods properly. Run the branch wiring yourself. That's what I did. In the long run, the cost to have this done correctly is minimal and you have the piece of mind that it was done right.

I wouldn't trust that calculator as far as I can throw my laptop. First off, #4 is not acceptable for 100A, you need #3. Even looking at the 90 degree column in table 310-16, #4 is only rated at 95 amps. No clue where that calculator is coming up with those numbers. Second, why is there a voltage selection for an ampacity calculator. I entered 100A and 20ft but had the voltage at 120v, and it spit out #8! I changed it to 100ft and it changed to #1. WTF?