Adding subpanel to new garage

[RMAR10]

I have a 200A panel within a couple feet of the outside meter on my house. I'm adding a screened in porch at the other end of the house connected to a breezeway connected to a new garage/shop. The new addition porch/breezeway/garage-shop will be all attached under roof connected to the house. From the existing panel to the panel I want in the garage/shop is about 60 to 70 feet. I already have a 200A panel and 120 feet of 3 conductor aluminum service wire. Can I double tap the existing panel lugs a couple feet to a ~100A breaker box, then run the service wire to the new panel? Any other ideas on getting to the new panel without adding a double lug meter, or having to trench from the existing panel around the house and into garage to the new panel? Add a 100A breaker to the existing panel and run service to the garage panel as a sub-panel? Any input helpful, thanks. Also, I live in the country in an unincorporated area so no strict code to deal with.

 

[Jadnashua]

You bought the wrong wire...any subpanel needs a 4-conductor cable with a separate ground wire (two hot, one neutral, and one ground lead). The ground and neutral are only supposed to be connected at the service entrance panel, and must remain separate everywhere else and that includes the subpanel. It is important to not have current running through the ground wire except during a fault situation.

 

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[RMAR10]

You bought the wrong wire...any subpanel needs a 4-conductor cable with a separate ground wire (two hot, one neutral, and one ground lead). The ground and neutral are only supposed to be connected at the service entrance panel, and must remain separate everywhere else and that includes the subpanel. It is important to not have current running through the ground wire except during a fault situation.

So I go the service wire for free and I already had an extra main panel to use as the subpanel. I'm now thinking of adding just a 100 breaker to my existing main (have about 5 slots open) to feed the sub panel.

Does this sound ok?

Here are some other questions:

1. I need separate ground and neutral busses in the sub?
2. Neutral isolated from the case?
3. Ground connected to the case?
4. No ground rods for the subpanel?
5. Circuits wired to separate the grounds and neutrals, unlike the main?

 

[Jadnashua]

You need a pro to confirm, but it is my understanding that on a subpanel, the ground and neutral busses must be isolated from each other and fed with their own wire from the main panel. A remote building requires its own ground rods...not sure if your situation qualifies or not for that with a breezeway interconnecting the main house to the other area.