A 400amp main disconnect will need to be added outside a Building. Existing is a 400 amp main circuit breaker panel in the utility room. The Arc flash rating turned out to be a Cat. 4 for the Panel.(you have to wear a space suit) so by installing a Disconnect between the Panel and the transformer, the engineer says it will go to a category 2. This is fed from a pad mount transformer with the metering mounted on the outside. Can the feeders from the transformer be spliced in the disconnect if not long enough, to go to the line side of the switch? Or will we have to install a 2'x2' junction box. Existing, is the 4" LB going to the back of the Main Panel.
Sorry about the long story - Thanks, SJT

IMHO, run this past the local AHJ first. Also you may have to run it by the local POCO. 'Line' side may be POCO jurisdiction. Using barrel crimps should be acceptable.

I'm sorry I only have my 2008 NEC with me, ( we are still on that code) but would 230.33 be of use in this case?

harold:
230.33 refers you to 110.14 regarding splicing methodology, and refers to 300.xx articles which I understand are not applicable in the OP.

I mentioned the local POCO, and AHJ for a few reasons. Here (PS) crimp splices are acceptable on a case by case basis, as they are by me, and most other AHJs. Extending an existing lateral feeder to terminate at the line side of a disconnect switch, in lieu of replacement of that feeder can be acceptable. Crimp splice; feeder in acceptable condition, and sufficient 'space' within the disco.

I only had the "splice in the disco" come up once and I agreed to the irreversible crimp splice, simply because any alternative was very burdensome on the installer and I did not see any particular hazard. We were literally talking about a foot of wire.

Thanks for the inputs,
I think I'll go with the barrel crimps, if the wires are not long enough.
SJT