Extending house circuits to sub panel

[underdog5004]

Hello,
I have a dual xw+ 5548 system, with batteries, in the shed out back. I plan to connect this to a transfer switch, which would then feed my house, through a subpanel. Currently, the circuit wires land in the main panel. I want to move them to a subpanel, about 15ft away.

I think the wires aren't long enough to reach the sub panel, so I was planning to run them into a junction box, or similar, to splice into a longer run that makes it to the sub panel.

I have 5 or 6 circuits to transfer, all 12-2 romex, 20a breakers.

My question is, is there a better way to extend the existing wires ,other than splicing in a junction box for the home run to the sub panel?

Thank you!

 

[BentleyJ]

Realistically, since wire can't be stretched so there are really only 3 solutions. Move the subpanel closer, replace the entire length of wire for those branch circuits or splice it in a J box.

With #12, you could use wire nuts or Wago type connectors. (I'm sure some on the forum may object to Wagos but they are rated for 30 to 32A)
If using wire nuts, recommend twisting the wire first with linemans pliers before installing the wire nut or if Wago maybe upgrade to the lever type.