Surge suppressors, dataline and DC signal, are used to protect equipment from transient overvoltages present on data or DC signal lines. The suppressor may operate by absorbing the surge (the shunt type suppressor) or by blocking the surge from flowing (the series type suppressor) or by a combination of the two. The shunt type suppressor has a characteristic clamping voltage that is normally chosen to be around the maximum safe operating voltage of the circuit. To prevent equipment damage from both internal and external surges, point-of-use surge protection devices (SPDs) can be used.