Isotel premium surge suppressors work harder, last longer and protect better than any other surge suppression device in the world. Isotel model provides protection for both AC and telephone lines. Dual RJ11 modular jacks protects one modem/fax line. Instantaneous surge response, handles up to 120,000 amp spikes, stopping overvoltages before they cause damage to your sensitive electronic equipment. Also provides superior filtering of electromagnetic and radio frequency interference over the widest range of line noise frequencies. Heavy-duty extruded aluminum housing is security against heat built-up from lightning strikes and circuit overloads. Outlet configuration allows for the best use of all outlets even when using transformers. Joule Rating: Isotel 4 Ultra - 1350 Joules, Isotel 6 & 8 Ultra - 1500 Joules.