Re: Commercial grade 20amp branch ckts
This kind of conflict is common when "The Geek Squad" (modern technology) and the real world mingle. When new ideas meet existing and often archaic codes, or even common practice, engineering specifications or just bad habits some design/install firms, engineers, or contractors can't seem to break.
Today's modern servers, switches and electronic equipment found in computer rooms and even desktop PCs and laptops have no need for an "isolated ground" either. Only the 70's era IBM-mainframes actually spec'd out that requirement. But the mere mention of the exaggerated, unlikely, if not impossible consequences of data & hardware losses are used by the unscrupulious beneficiaries every day, if not designed in from the getgo by sheer force of habit.
A similar situation arises in the residential arena- when a dedicated 15a circuit and receptacle is installed for a window shaker. (Or, heaven forbid, one 20a circuit is installed for TWO!) Be prepared for a fight when the inspector demands a single 20a circuit for a 4.5 - 6.5 amp portable room air conditioner. After all, window units are still 30" x 24" by 42" deep, are made of cast iron, and weigh as much as a refrigerator, right?!
Am I missing something? If not what section can I use to back myself up?
RUWired offered a sensible solution. If this receptacle was being installed for some unknown or future use, the EC might be more in the right to press for minimum 20a rated devices and circuits only. However; when the use and load is known, the ball is completely in your court and it's your call.
Don't be too suprised to find this "fight" all boils down to the fact that the E.C. simply doesn't stock, or doesn't wish to have to stock or aquire 15a rated twistlock receptacles.
BTW, as an FYI most of MCI's telco switch rooms call for 15a twistlock, UNLESS OTHERWISE stated. (#12 awg conductors were however, a NYC code requirement.) Same for MFN, MFS, Lightspeed, Lightpath, RCN, Time Warner, the former Global Crossings, Telergy... you've got plenty of backup.