Splicing branch conductors from main panel to sub panel fed by solar inverter

[Bigcountry]

My question is:
i have a sub panel we are feeding from an inverter that has an ATS built in. The main panel is a few feet away from the sub panel.
When splicing the branch circuits I can leave the neutrals and grounds or grounded and grounding conductors on the main panel and just take a #6 to the sub panel that will basically be the grounded neutral for all the neutrals. Sub panel is only a 30amp service.
Or
Do I have to splice all the neutrals and take them to the sub panel.

i would assume the same for the grounding wires. Either one larger wire or take all individual.

The way I read nec 300.3 I have to take all of them to the sub panel.

Also can I splice these wires in the main panel or do I have to pull them out and splice in a jbox outside the main panel.

 

[jaggedben]

A neutral for a branch circuit must originate in the same enclosure as the overcurrent protection for the branch circuit, or in an adjacent (i.e. attached) junction box. You cannot run neutrals from the main service panel out to circuits that have their circuit breakers in the sub, even if the main and sub are only a 'few feet away'.

Equipment grounding allows for some exceptions, but basically the same rule applies, especially with new construction.

Some clarifications might also help...
-Is the subpanel a critical loads panel?
-What brand is the inverter, and/or do you know if its ATS switches the neutral?

If the ATS switches the neutral then you could have a particularly dangerous and non-functional situation if the neutrals for the sub circuits are tied into the main.

As far as splicing in the main panel, that depends on how many wires there are, which code cycle you are on, and how your AHJ feels about 312.8. I've experienced a few AHJs who prohibit splices in panels in spite of that section. If you have too many wires you might have to pull them out to a j-box to meet space requirements, regardless.