Telecom Transformers HALO Electronics Telecom Transformers are for use with 56 and 64Kbps, T1/E1, E3/ DS3 and E4 applications and UL/EN60950 recognized. Their patented SMD construction provides high reliability SMD isolation modules for all leading Line Interface Units (LIUs). Isolation modules are available in Functional, Supplemental and Reinforced insulation to meet the most stringent safety requirements.