When a series protective element such as a transient blocking unit (TBU) is used in combination with a shunt protective element such as a gas discharge tube (GDT), firing of the GDT can cause a transient having the potential to damage the TBU. This problem can be alleviated by placing a TBU core in series between depletion mode transistors having their gates connected. With this arrangement, the GDT transient causes a transient in the TBU circuit that has the effect of switching the transistors around the TBU hard off, thereby protecting the TBU from the GDT transient.