SLD LVBC was replaced by the ISD BC 120/277 with differences.
The SLD could handle 1920 total watts at 120V. The ISD can only handle 1200 Watts at 120V and 1500 Watts at 277V. To offset the load difference, we add an PP20. The PP20 will take in 1920 Watts at 120V and 4400 Watts at 277V.