Another 200 to 100 panel question

[joekan]

First post!! I'm coming off my 200 amp panel and going to heat up my MIL apartment that is being built. This apartment will be attached to my house and it's about 70 feet from panel to panel. I've already ran 2" pvc buried over to the new site. I'm going to be pulling in service entry cable.
Can someone please tell me what size copper and aluminum I will need?
I'm thinking the alu. will be 3 1oughts and #6 ground, but I think my 2" will be too small. If that be the case, I'll pull copper.
Thanks so much for the help,
Joe

 

[matt151617]

You can't use service entry cable in conduit. Get mobile home feeder, #2 AL. Make sure it's 4 wire. Protect at 90 amps. No need to pay a lot for copper.

 

[pattenp]

You can only use the Mobile Home Feeder (MHF) if the conduit is also to the panels. The MHF needs to be in conduit inside of a structure. The SER can be placed in conduit but not under ground. SER is for above ground use in wet or dry locations.

 

[joekan]

So I can use #2 alum.? Then what size would be my ground?
I have to use service entry b/c when it comes into the 200amp. I have to run it in open air to get to the panel. Any other way?
Thanks!

 

[matt151617]

If you run SER open air you would have to transition in a box to mobile home feeder where it goes underground.

 

[pattenp]

Do you want a full 100 amps? #2 Al is good to 90 amps. If you what a full 100 amps you'll need to use #1 Al. The problem is MHF is a four conductor cable and does not come in #1. You will need to buy individual aluminum THHN/THWN wire for the run under ground. You'll need #1 Hot - #1 Hot - #1 Neutral - #6 Ground. For the open air portion in the house and apt you can use 1-1-1-3 SER.

 

[Aceman]

If it's a totally seperate dwelling unit that only shares a common wall with the main house, I'd run it by my inspector and see if he'd let me use 310.15(B)7 and run #2 AL for 100amps. #2 is much easier to find.