North, I've had to do this and I believe they consider them intermittent.
It is regulated by ANSI 17.1.
Like any submittal, you have to ask the elevator contractor for his load ratings and include them in your own as an appliance.
If the contractor has not been selected yet, you can usually find one who will quote you load data. How tall, etc. is all they require. If the bldg is short enough you may have to 'guess' if they want to go hydraulic and you may find you'll have to adjust your calc after the elevator contractor is selected.
Most property owners use the same elevator company over and over.
Back to your question, the definition of intermittent is expected to last for 5 minutes or less, and most elevators never run for a continuous 5 minute period without stopping at a floor.
They design the equipment for continuous use however.
See NEC Article 620 and the Annex D Example D9 Feeder Ampacity Determination for Generator Field Control, and Example D10 Feeder Ampacity Determination for Adjustable Speed Drive Control
See 620.13 and 620.61 in the 2002 NEC.
NEC Article 100 defines a continuous load as one that operates for 3 hours or more.
Duty, Continuous. Operation at a substantially constant load for an indefinitely long time. Duty, Intermittent. Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest. Duty, Periodic. Intermittent operation in which the load conditions are regularly recurrent. Duty, Short-Time. Operation at a substantially constant load for a short and definite, specified time. Duty, Varying. Operation at loads, and for intervals of time, both of which may be subject to wide variation.