The LSIG in the feeder or service provides protection for the downstream equipment as there is no isolation transformer in a transformerless UPS. A downstream fault will pick up the LSIG in the feeder or service source, thus limiting the need for additional LSIG as fault protection on the UPS output.

What is LSIG protection?

G = Ground Fault (equipment ground fault protection) Therefore, LSIG = Long-time + Short-time + Instantaneous + Equipment Ground-fault Protection.

What is LSI trip function?

long-time pickup — The current level at which a circuit breaker's long-time delay function begins timing. ... LSI — A combination of adjustable trip functions including long-time ampere rating, long-time delay, short-time pickup, short-time delay and defeatable instantaneous pickup.