I am installing a 400 amp electrical service ,it is going to be underground I need to line up my 3inch sweep in the foundation before they pour cement . Can you tell me how I should go about doing this so the 3 inch sweep will line up with my panel so I can install my panel after the framing is done .
Thanks fred

A sweep? How will it be orientated? Coming out the top or bottom of the panel and sweeping out through the wall?

So the sweep will be embedded into the concrete intended to sweep into the top/bottom of the panel?

I have to ask these questions as I never did it that way, perhaps that is the best for you, but, we never have an underground conduit drop into a panel straight away.

Are you going to have one 400A panel? That is an odd way of doing it for a residential service.
Are you the electrician?

The only real way to tell is to get the specs from the manufacturer's web site. Most have KO layouts for their panels.