i have a series of pens that are used solely for consultant information. i also set up a DWG translator for each consultant that keeps their pen weights, but maps their colours to my 'consultants pens'.
if you ask your M&E consultant to send you his electrical
layout
not his electrical layout DRAWING
you will also (most likely) receive a DWG file with very few layers. this can then be attached as an xref to your archiCAD file in much the same way and autoCAD guy would attach it to other DWGs that make up the final output drawing.
no messing around 'cleaning up' consultant information, no copy this/paste that and a very very easy update when his information changes.
then, as the others have suggested, you change your pens to a grey colour
in plotmaker and the consultant pen set to black. job done.
it's worth spending a hour or so talking with your consultants, understanding how they work, how they build their drawings up by overlaying different information and then establishing a protocol for exchanging
that information rather than final drawing output.
hope that made sense. there's a lot more about this to be found in the forum here as well . . .
cheers
~/archiben
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