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Hi,
I have situation, where service panel (2x200amp) got moved to the side of the house, where already had 2 x SER AL 4/0 4/0 4/0 2/0 wire at meter main going so 2 subpanels, now I have 2 x 2'' conduit from service entrance to the house (about 40'). Planing put 18x18 jbox to splice SER and feed from main. Looks like the only way to go is 2/0 copper (240'). can I downsize neutral to reduced cost (already have 4/0 AL half way ;) I'm using polaris conectors reated for AL/CU
Any other way to do it?

Thanks
Martin
 

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Interesting. I've taken to simply going along with the material costs because what can be saved is trivial compared to the beating we're taking on all wire. That said, I also keep the neutral the same size as the phase conductors because it is still the easiest way out when dealing with multiple jurisdictions.

I sure wouldn't like mixing aluminum and copper, but lugs rated for both and No-Alox (?) should make it work.

Good luck.
 

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You can downsizes your neutral as low as a #2 copper however I would want to see what the calculated load is before I would pass that install. Normally I downsize the neutral on resi work one size.

I would also be careful with the use of 4/0 alum in that install as well as 2/0. With the acceptance of the 2008 it is now pretty clear that in order to use t. 310.15(B)(6) the panel would have to power the entire load of the house. Around here we use 3/0 copper to each panel as required, IMO, by the NEC in your situation.
 
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