Copper or aluminum Feeder cable?

[tuip]

I'm building a detached garage and am planning a 100A branch circuit of the main panel. Build thread here http://www.garagejournal.com/forum/showthread.php?t=293079&showall=1


I have 1.5 inch conduit already between both buildings and am contemplating between 3-3-3-5 SER copper or aluminum.

It seems I can save a quick few hundred dollars between the 2. Any pro / cons to going with aluminum before I purchase? Would the aluminum equivalent be 2-2-2-4 ?

 

[pattenp]

If the conduit is below ground you can't use SER. #2 Al is good for 90A. How far is the run?

 

[tuip]

About 50-60ft from the main panel to the sub panel.

 

[tuip]

Just looked again at the code .. looks indeed the conduit is considered a wet location so SER is out. Presumably it would be either 2GA or 1GA Stranded THHN ?
Studied electric engineering .. but the electrical code differs per country so this should be a fun research project.

 

[pattenp]

For the full 100A use #1 Al RHH/RHW-2 in compacted conductors or #1 Al Simpull THHN/THWN-2. Those will fit fine in the 1.5" conduit. If you don't care about the cost then use #3 Cu THHN/THWN-2.

Oh and the equipment ground can be #8 Cu or #6 AL.



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[theoldwizard1]

MHF 2-2-2-4 is probably the "best bang for the buck". I think you can get 90A at 50-60'. Someone who understands the NEC charts better than I needs to check.

 

[tuip]

Looks like 1 AWG is the way to go .. off to ordering some stuff and start pulling wires soon. For the ground wire it looks like it would be non-bare 8 AWG cu ?

 

[930dreamer]

If you were closer I have a spool of 1/0 copper.

 

[pattenp]

Why use copper for the ground? If using #1 Al for the conductors then use #6 Al for the ground.

 

[tuip]

Thanks ... I'll keep that in mind.

 

[zmaxmotorsports]

For the full 100A use #1 Al RHH/RHW-2 in compacted conductors or #1 Al Simpull THHN/THWN-2. Those will fit fine in the 1.5" conduit. If you don't care about the cost then use #3 Cu THHN/THWN-2.

Oh and the equipment ground can be #8 Cu or #6 AL.



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#8 copper ground for a 100a service?

 

[sberry]

Studied electric engineering .. but the electrical code differs per country so this should be a fun research project

There will be no local code variations for this. Last I heard Chicago may have a couple things on methods. It would be interesying to know if there are any local amendments in Michigan? I dont know of any from my county.
8 depending on the conductor size. If it was sized up for distance and V drop the ground may have to be larger.

 

[wyliesdiesels]

#8 copper ground for a 100a service?

Yup!

But this isnt for a service, its a feeder!

 

[sberry]

Can use it to the rods on 100 too I believe but better electrodes piping and such should have a size up. Where the rods are auxiliary the ideal is to have the primary a size larger.

 

[zmaxmotorsports]

Yup!

I guess Im just stuck in the old days of using a #6 for a 100a and a #4 for 200a service,need to get the book out.

 

[Slowgsr]

I guess Im just stuck in the old days of using a #6 for a 100a and a #4 for 200a service,need to get the book out.

Up here #8 cu is legal for 100a ground yet it requires mechanical protection as #6 cu does not, reason why #8 isn't used (up here anyways)

And I use #3 cu for 200a. Or when I do a 75 or 112kva transformer

 

[Stuart in MN]

I guess Im just stuck in the old days of using a #6 for a 100a and a #4 for 200a service,need to get the book out.

There are two different ground conductor size charts in the NEC, 250.66 for the ground wire connection to the ground rod, and 250.122 for the ground wire used for grounding raceways and equipment.

Per 250.66 you'd use a #6 for 100 amp service (with copper), per 250.122 you'd use #8 for a 100 amp circuit (with copper.)

 

[wyliesdiesels]

Hold on a minute everyone. Were getting mixed up here and talking apples and oranges.

This thread is about a feeder NOT a service!

So were talking about an EGC(equipment grounding conductor) NOT the GEC(grounding electrode conductor) to electrodes.

The EGC and GEC are 2 different things. Dont wanna confuse them.

Can use it to the rods on 100 too I believe but better electrodes piping and such should have a size up. Where the rods are auxiliary the ideal is to have the primary a size larger.

Yes u can but requires conduit/physical protection.

I guess Im just stuck in the old days of using a #6 for a 100a and a #4 for 200a service,need to get the book out.

U need to read T250.122 which is for EGCs NOT GECs on main services.

For a 200a feeder, u would use a #6 cu or #4 AL EGC...

Up here #8 cu is legal for 100a ground yet it requires mechanical protection as #6 cu does not, reason why #8 isn't used (up here anyways)

And I use #3 cu for 200a. Or when I do a 75 or 112kva transformer

Yea #8 is code here for the GEC as well but requires physical protection.

But again, were talking about an EGC in a feeder NOT the GEC for a service.

*stuart beat me to it*

 

[tuip]

So either #1 CU and #6 CU for EGC or 1/0 AL and #4 AL for EGC. I grew up in the Netherlands and color codes and gauges are different according to their electrical code.

 

[pattenp]

To restate - 100A feed needs #3 Cu or #1 Al.

Per NEC 250.66
If the 100A feeder is #3 Cu the GEC can be no less than #8 Cu. If the 100A feeder is #1 Al then the GEC can be no less than #6 Al. But in any case the GEC does not have to be larger than #6 Cu or #4 Al if connected to rods, pipe or plates.

As for the EGC, it needs to be at least a #8 Cu or #6 Al.

 

[tuip]

Thanks One more question .. so #3 Cu can handle 100A .. I took some measurements today and it looks like I'm closer to about 90-100ft in lenght between the main and the subpanel. I'm getting mixed results on the calculators that are available. Some tell me #1 Cu for this run to prevent too much voltage drop .. others say I can stick with #3 ... what is it ?

 

[pattenp]

You are fine with #3 Cu up to about 140ft to keep the VD at no more than 3% at full load of 100A. Stick with #3 Cu.

 

[wyliesdiesels]

Thanks One more question .. so #3 Cu can handle 100A .. I took some measurements today and it looks like I'm closer to about 90-100ft in lenght between the main and the subpanel. I'm getting mixed results on the calculators that are available. Some tell me #1 Cu for this run to prevent too much voltage drop .. others say I can stick with #3 ... what is it ?

thats just the reason why i do VD calcs by hand. U never know what parameters online calculators use such as termination temperature ratings, max VD %, etc...

The calcs are easy to do by hand...