I have a 30 amp UPS on a 15 amp (might have a 20 amp breaker) circuit. Been this way for about 4 years. ... This will work fine assuming the load never goes above 80% of the 15/20 amp load.

Appropriate for a two-pole 20-amp breaker or a single-pole 30-amp breaker. 8-gauge or 6-gauge wire . Used for 40-, 50- and 60-amp two-pole breakers; large appliances.