100 amps to attached garage

[mastertech]

my question for the morning is what size wire, and should i look at either copper or aluminum? the main panel is a SD homline and the sub panel is a SD qo. the run is right about 90 feet. I think i have the correct size in mind but only for copper, is aluminum a better option?

UPDATE: see below

 

[Handyman163]

I'll be doing the same thing as well soon. Is there a chart to reference with amperage, distance, and wire size?

Like what size wire for:100A feed for 50, 75, 100, 200 feet, etc?
60A feed for 50, 75, 100, 200?

I think a chart would be simple enough, but I did find this. You can plug in your values, and it will spit out wire size in Cu and Al.

It looks like 100A of 240V over 90 feet calls for 4ga Cu or 2ga Al with a 3% voltage drop.

http://www.alternate-energy.net/voltlosscalc03.html

 

[BioHazard]

Copper is always better than aluminum...however aluminum will still do the job just fine and cost less.

 

[Norcal]

Table 310.16 in the NEC is where the info is, NM cable (Romex) is sized from the 60 degree column, SER cable where the 2008 NEC has been adopted is also sized in the 60 degree column, but if still on the 2005 or earlier edition NEC can be sized in the 75 degree column. There are those who think that table 310.15(B)(6) is the justification to undersize the conductors, but the criteria is not met in a subpanel feed to do so.

 

[hidollartoys]

I just sized your application on that calculator against the 2005 code and the calculator did not meet the NEC requirement. Everyone should be careful of these "simply" solutions found on the internet.

 

[Aceman]

To answer your question, you'd need 1/0 AL SER. If your calculated load is less than 75 amps, you could run #2 AL SER and breaker it at 80 amps. #2 AL SER is very common, you may have trouble finding 1/0, you'll most likely need to go to a real electrical supply house to get it.

 

[sdowney717]

http://www.powerstream.com/Wire_Size.htm

I do think we used 2 gauge copper thhn in grey plastic conduit. 4 wires, 2 hot 1 neutral 1 ground to go 35 feet to a garage for 100 amp panel.
And we drove a ground rod.
It passed city inspection.
My dads barn has had 2 power issues since built 15 years ago. The wire is ALUMINUM buried in the ground and it corroded and failed in 2 spots. This last time I told him to put the repair above the ground to keep it dry. The first time it was fixed by electric contractor and it failed anyway in the ground. Maybe fixed more than twice. The utility company came out and told him about where the break was. They have some device that can see the power in the ground.

The outbuilding I wired myself was like this. No Aluminum in the ground for me.
It was black wire like this and bought at the HD. The whole thing in 2 inch grey conduit.
http://www.grainger.com/Grainger/items/5ZG89

Type Stranded, Building
Wire Gauge (AWG) 2
Wire Type THHN
Stranding 19
Voltage 600
Max. Amps 130
Temp. Rating (F) 194
Color Black
Nominal Outside Dia. (In.) 0.381
Jacket Nylon
Insulation PVC
Spool Length 500 Ft.
Standards UL,E34382

 

[Norcal]

http://www.powerstream.com/Wire_Size.htm

I do think we used 2 gauge copper thhn in grey plastic conduit. 4 wires, 2 hot 1 neutral 1 ground to go 35 feet to a garage for 100 amp panel.
And we drove a ground rod.
It passed city inspection.
My dads barn has had 2 power issues since built 15 years ago. The wire is ALUMINUM buried in the ground and it corroded and failed in 2 spots. This last time I told him to put the repair above the ground to keep it dry. The first time it was fixed by electric contractor and it failed anyway in the ground. Maybe fixed more than twice. The utility company came out and told him about where the break was. They have some device that can see the power in the ground.

The outbuilding I wired myself was like this. No Aluminum in the ground for me.
It was black wire like this and bought at the HD. The whole thing in 2 inch grey conduit.
http://www.grainger.com/Grainger/items/5ZG89

THHN is not for wet locations which is any conduit underground or outdoors as defined by the NEC, if you have dual rated THHN,THWN then all is well but if singly rated THHN then there is a issue......

There is absolutly nothing wrong w/ properly installed aluminum wiring, I personally dislike any direct buried wiring but it needs to be in sand or properly screened soil which the above was not, as any nick in the insulation of a aluminum conductor will cause the AL to turn into a toothpaste like substance. Conduit IMO is cheap insurance.

 

[sberry]

I have 1000's of feet of number 2 alum in the ground, never had a problem. Your power company uses it on underground.

 

[hidollartoys]

The OP's post indicated it is an ATTACHED garage and this is a sub-panel application. You guys should throughly read before offering advice.

 

[mastertech]

thanks for the replies, what i ended up doing was running 1-1-1-3 aluminum wire from the main to the sub panel and coated all terminations with noox-x an anti-oxidation paste. wire from the local electric supply was 1.27 a foot.

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[Gary S]

I just sized your application on that calculator against the 2005 code and the calculator did not meet the NEC requirement. Everyone should be careful of these "simply" solutions found on the internet.

I agree. Consult a licensed electrician in your area. I'm not an electrician, but I don't trust that calculator. I plugged in my setup and it came up with #6 copper. I installed #2 copper as recommended by a local electrician. Better safe than sorry later.