Complex sentence: With negligible current in the neutral under normal conditions, engineers typically elect to under size the transformer; a short time rating is applied (i.e., the transformer can only carry full rated current for, say, 60 s).
Split into simpler sentences: With negligible current in the neutral under normal conditions, engineers typically elect to under size the transformer. A short time rating is applied (i.e., the transformer can only carry full rated current for, say, 60 s).