I need to run a sub panel service wire in conduit from my main panel to my subpanel in my garage. I was told that you should not run an aluminum servive wire in conduit. Is this correct?

 

The idea that a pre made cable cannot be installed in a conduit is urban legend. The trick is how to properly size the conduit.

However, if your conduit is running underground, then you need to use underground rated wires or cables.

If the conductors are made of copper or aluminum does not matter, except that the aluminum wires will have to be larger to carry the same amperage.

If you post more details about what you are trying to do, we can be of more help.

 

The 200 amp main panel in my house is connected to a 100 amp subpanel in my garage with conduit underground. The distance is 125 feet. I have not yet purchased the wire.

 

What size(diameter) and type of conduit do you have. That will determine what size wires will fit into it.

 

Keep in mind that depending on the amperage that will be used at the detached building, 125 foot is a long way, and one should consider voltage drop.

I know that VD is not a code requirement, but it is still a very good idea.

 

Inch and a quarter gray conduit. I'm not sure the type. I am going to be running lights and outlets for power tools. Nothing heavy and no welder.

 

A 100 amp feeder (you said service in your OP but this is not a service it is a feeder) needs to be either no 4 copper or no 2 aluminum.

Next we need to know if you will be using a three or four wire feed. Since this is a detached bldg you can use a three wire feed under certain conditions. (I do not reccomend it)

If there are not now, or you never intend to have any other metalic paths between the two buildings you can use a three wire feeder. A phone, CATV, water, gas, or anything else run in metal or that uses metal to transfer its medium, like a speaker system, would be another metalic path.

I did not run out all of the calculations, I only used the quick referance charts, but I think you need to use copper to make conduit fill. Even if the aluminum would fit, it would not be worth the extra effort pulling the wire.

Since you are not going to have alot of load at the out building, you could use a 60 amp breaker at the house, and much smaller wire to feed the other building.

What size/type of cable were you planning to use to start?

 

Do you want to know what size of wire I plan on using to run to the outlets and lights? I apologize for the confusion.

 

How many amps do you plan to feed the outbuilding with from the main panel?

Then, What size wire are you planning to use to feed this sub panel?

 

Let me clarify. I have a 200amp service in my house and will be running underground wire in conduit for a 60 AMP subpanel in my garage. I planned on using a 60amp breaker to feed the sub with #6 copper wire. Will this work?

 

You are correct for a 60A feeder. Use #6 THWN copper wire for the hots (black,black) and neutral (white), use #10 green or bare copper for the ground. You could also use #6 UF-B cable, but it can be a bear to pull through conduit.

 

That worked. Thanks!

 

Have run run the cable yet? #6 matches the overcurrent protection, but doesn't take voltage drop into account. 125' of #6 cable has an impedance of around 0.06-0.09 Ohms (depending on power factor), so you're looking at a voltage drop of 3-5V for this cable alone if you ever fully load that panel, and probably 6-8V or so total voltage drop to the receptacle. NEC mandates a maximum 3% voltage drop- if you haven't installed it yet, I'd recommend pulling in #4 instead, which will also fit in 1 1/2" PVC, but would be harder to pull.

In practice, with a lightly loaded panel, you probably won't have any issues with #6.

 

"NEC mandates a maximum 3% voltage drop"

Can you site that article and section number?

The only thing I have ever found in the NEC regarding voltage drop is a fine print note that says it is a good idea. And another note that IF you increase the wire size of the hots for voltage drop, you need to also increase the size of the ground.

 

NEC cites 3% several times- 210.19(A), 215.2(A)(3), 230.31(C), 310.15(A)(1).

It's good practice to treat FPN as requirements, and not recommendations. Nobody wants 90VAC receptacles Technically though, yeah, they're not binding requirements.