securing electrical equipmen

huangyhg

securing electrical equipment
i have a project with a lot of switchgear equipment that is normally welded to plate inserts in a concrete slab and don't have the method of securing them.  levelling is an issue and there is little clearance for anything but thin shims.  the tolerances are pretty tight and almost unrealistic.
i was planning to cast level insert plates that were depressed about 1/4" below the finished floor with the intent that the shims be welded to the insert plates and the equipment welded to the shims.  this will permit thicker shim plates that can be welded.  i'm not a big advocate of welding 20ga material.  the shims would be of variable thickness and be approx 1/4"-3/8" thick (vary) and that they would be adjusted after the concrete has reached an age of 2 or 3 months; i don't know how to adjust the slab for longer term creep yet, if it's an issue (doubly reinforced? or whatever).  the shims could be machined to a proper thickness if necessary and the elevations could be optically/laser determined.  there are about 60 of these shim locations.
has anyone had a similar problem and any suggestions about how to improve/tackle the above?  
dik
your solution for initially levelling the equipment sounds reasonable, but i don't see how that will maintain the equipment perfectly level on a suspended floor.  if you weld the equipment down, it will deflect with the floor.  how critical is it for the switchgear to be level?  surely there must be some tolerance.
dik - as you stated, the requirements for leveling switch gear are very strict. in electric generating stations the thin "sheet metal" shims that you mentioned are typically used, since the gear has to be leveled in all directions yet in full contact at each support. i suggest that you discuss your approach with the electrical engineers, they (and the switchgear manufacturers) will likely have the final decision on what is done in the field (regardless of the design).
imho, your approach will not be viewed favorably, no matter what it's (structural) merits. the time needed to custom machine plates with the correct thickness will be considered an unreasonable delay (and, in this case, i would agree with the ee's that it is).
any other suggestions.  other than indicating that there is a problem in providing a level mounting surface, they have been of little help.  you'd think that they would have 'levelling bolts' that could be constantly leveled if required.
if they want the equipment to be absolutely level and located on a suspended floor, they will have to have an active levelling system as you suggest.