First - I'm not asking for DIY help. I know better than mess with power (I'm an IT guy and I know my limits)!
At work, we have some 3 phase 208v power plugs that I'd like to use. However, the receptacles on these outlets are NEMA 14-30R. The computer equipment that I need to plug into these outlets are NEMA L21-20P. Can an electrician simply change the outlets? Or is these something physically different about the power?
Well, if the 14-30R's were properly installed, they will be on 30A circuits. The 14-30 configuration isn't intended for use on 3 phase, either. It is intended for single phase 125/250V, 30A with a grounding pin. If it is providing 208V 3 phase, there is either no neutral or no equipment ground available. The other possibility is that only 2 of the three phases are available.
The L21-20 is a 5-wire configuration, while the 14-30 has only 4 contacts. Assuming that all 3 phases and the neutral are present in the box, then the L21-20s should be able to be installed (the center pin needs to be grounded to the box), but the breakers protecting them will need to be replaced with 20A units. If only 2 phases or no neutral conductor are present in the box, your electrician will need to bring a new conductor from the panel, which could be relatively simple (if the run is in conduit) or extremely difficult, depending on the installation.
As with most questions, it isn't possible to give a really accurate answer without looking at what you have installed there.
On the schematic that I have it lists the outlet type as:
NEMA 14-30R for DATA RACK (208 V, 3 o)
the o above is actually an o with a line through it..that means 3 phase I think.
So, what do I need to clarify with the construction people? It is too late now to change any work being done on the project, as it is to be completed Sept. 1 (after 5-6 years of work). Should I just wait until after construction is complete and bring in my own electrician to tell me what is going on?
The label "208V 3 phase" would imply that there is no neutral conductor present., and the neutral blade on the 14-30 receptacle is being used for one of the hot phases. If the system had a neutral, it would be designated as "208Y/120V".
You need to have an electrician open up the outlet box, and see if there is a neutral conductor in the box. If there isn't, you will need to install one to use the L21-20 receptacles. I would advise having this done ASAP, as adding a conductor will be much easier during construction than after the sheetrock is up.