A coupler for allowing electrical transmission of an alternating current signal through the wall of a hazardous area enclosure, comprising: a hollow coupler housing body having an elongated shape defining a first end and a second end; an electrical circuit inside said hollow coupler housing body wherein there is a space between the electrical circuit and the hollow coupler housing body; potting material encapsulating the electrical circuit and filling the space; a first electrical connector projecting out said first end and a second electrical connector projecting out said second end, said first and second electrical connectors being connected to each other through said electrical circuit; characterized in that said electrical circuit includes transmission line connections (60, 64), receiving line connections (62, 66), protective earth ground connection; current limiting resistors (70, 76); fuses, which provide for over-current protection in case of a fault; and Transient Voltage Suppression, TVS, diode arrays, connected together in parallel, having a capacitance not greater than four picofarads, wherein said Transient Voltage Suppression, TVS, diode arrays are connected between one of the transmission line connections (60, 64) or one of the receiving line connections (62, 66) and the protective earth ground connection; and wherein said Transient Voltage Suppression, TVS, diode arrays have a clamping voltage, such that the electrical circuit permits alternating current signals to pass through between the first and second electrical connectors but shunts to ground any signal greater than the clamping voltage of the Transient Voltage Suppression, TVS, diode arrays. a hollow coupler housing body having an elongated shape defining a first end and a second end; an electrical circuit inside said hollow coupler housing body wherein there is a space between the electrical circuit and the hollow coupler housing body; potting material encapsulating the electrical circuit and filling the space; a first electrical connector projecting out said first end and a second electrical connector projecting out said second end, said first and second electrical connectors being connected to each other through said electrical circuit; characterized in that said electrical circuit includes transmission line connections (60, 64), receiving line connections (62, 66), protective earth ground connection; current limiting resistors (70, 76); fuses, which provide for over-current protection in case of a fault; and Transient Voltage Suppression, TVS, diode arrays, connected together in parallel, having a capacitance not greater than four picofarads, wherein said Transient Voltage Suppression, TVS, diode arrays are connected between one of the transmission line connections (60, 64) or one of the receiving line connections (62, 66) and the protective earth ground connection; and wherein said Transient Voltage Suppression, TVS, diode arrays have a clamping voltage, such that the electrical circuit permits alternating current signals to pass through between the first and second electrical connectors but shunts to ground any signal greater than the clamping voltage of the Transient Voltage Suppression, TVS, diode arrays.