Surge protection devices including varistors

A surge protective device (SPD) unit comprising:

• a printed circuit board (PCB) assembly including a PCB including PCB contacts;
• and
• an SPD module mounted on the PCB and including:
• first, second and third terminals electrically engaging the PCB contacts to connect the SPD module to the PCB assembly;
• a node connected to the third terminal;
• a varistor stack assembly including:
• a first varistor;
• a second varistor;
• and
• a node electrode interposed between the first and second varistors;
• wherein the node electrode is electrically connected to the first and second varistors and includes the node;
• a first branch including:
• the first varistor connected between the first terminal and the node;
• and
• a first thermal disconnector mechanism configured to disconnect the first varistor from the first terminal or the node;
• and
• a second branch including:
• the second varistor connected between the second terminal and the node;
• and
• a second thermal disconnector mechanism configured to disconnect the second varistor from the second terminal or the node.