A guided wave radar level gauge for determining the filling level of product in a tank, said gauge comprising: a housing with a grounded housing wall providing explosion proof protection, an explosion proof first signal passage in said housing wall, said first signal passage configured to be connected to an external power supply, an explosion proof second signal passage in said housing wall, said second signal passage providing an intrinsically safe output, a transmission line probe connected to said IS output, said probe being adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product, wherein said housing encloses: radar level gauge circuitry (14, 15, 16, 17) which is incompatible with intrinsic safety requirements, a microwave unit connected to the IS output, said microwave unit configured to generate and transmit a microwave transmit signal S T and receive a microwave return signal S R reflected from the tank, and a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components, characterized by an electrical barrier connected between the RLG circuitry and the microwave unit, said electrical barrier preventing energy or voltages incompatible with IS requirements from reaching said microwave unit, said electrical barrier having a barrier ground potential which is independent from the grounded housing wall. a housing with a grounded housing wall providing explosion proof protection, an explosion proof first signal passage in said housing wall, said first signal passage configured to be connected to an external power supply, an explosion proof second signal passage in said housing wall, said second signal passage providing an intrinsically safe output, a transmission line probe connected to said IS output, said probe being adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product, wherein said housing encloses: radar level gauge circuitry (14, 15, 16, 17) which is incompatible with intrinsic safety requirements, a microwave unit connected to the IS output, said microwave unit configured to generate and transmit a microwave transmit signal S T and receive a microwave return signal S R reflected from the tank, and a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components, characterized by an electrical barrier connected between the RLG circuitry and the microwave unit, said electrical barrier preventing energy or voltages incompatible with IS requirements from reaching said microwave unit, said electrical barrier having a barrier ground potential which is independent from the grounded housing wall. radar level gauge circuitry (14, 15, 16, 17) which is incompatible with intrinsic safety requirements, a microwave unit connected to the IS output, said microwave unit configured to generate and transmit a microwave transmit signal S T and receive a microwave return signal S R reflected from the tank, and a set of blocking capacitors connected between the microwave unit and the IS output, which blocking capacitors serve to block any DC components, characterized by an electrical barrier connected between the RLG circuitry and the microwave unit, said electrical barrier preventing energy or voltages incompatible with IS requirements from reaching said microwave unit, said electrical barrier having a barrier ground potential which is independent from the grounded housing wall.