in fig4 b a failure indicating device may be connected to the indicator terminal 428 the current sense resistors 471 or current sense capacitors 481 and the thermal sense resistors 472 or thermal sense capacitors 482 are configured to provide a distinguishing indication between current limiter components 430 open circuit and thermal protector components 450 open circuit the current limiter components 430 may be a single strand of silver wire multiple strands of silver wire silver ribbon perforated silver ribbon copper ribbon or perforated copper ribbon a fuse tube may also enclose the current limiter component 430 as shown in fig5 b in order to increase the current limiting capability of the current limiter component 430 the thermal protector components 450 are a low melting point alloy wires such as lead antimony alloy wire or lead indium alloy wire the thermal protector 450 may also be a commercially available thermal cutout device a power distribution network connects to the first input terminal 420 and the second input terminal 422 of the surge protection device 40 fig4 c shows an enclosed module 44 of a multiple circuit surge protection device 40 the structure 40 shown in fig4 a is positioned within a housing 490 and the housing 490 is filled with sand 492 sand 492 is used to position the thermal protector components 450 and to thermally couple these components to the metal oxide varistors 460 the sand 492 and the bridge 440 provide isolation between the current limiter component 430 and the other components including the thermal protector devices 450 and the metal oxide varistors 460 sand 492 is also required to enable interruption by the current limiter component 430 of high fault currents.