Check the main service disconnect label for the amp rating
Look for a marking such as 100A, 100 Amp, or 100 Amps on the main breaker
Verify the service type on the panel label: 3-phase, 4-wire, or 3Ø
Inspect the meter socket and service equipment for the service rating label
Confirm the utility service drop or service lateral is three-phase
Check the panel bus rating and main lug or main breaker rating
Verify the feeder conductors are sized for 100 amp service
Confirm the disconnecting means is rated at 100 amps minimum
Check the electrical drawings or one-line diagram for service size and phase
Review the utility service order or account records for service classification
Measure line-to-line and line-to-neutral voltages with proper test equipment
Confirm the presence of three hot conductors
Verify the neutral conductor is present if the system is 4-wire
Check the nameplate on transformers or service equipment for phase and amp rating
Have a licensed electrician or utility representative verify the service rating
Compare the installed overcurrent protection to the service conductors and equipment ratings