An optical sensor assembly for measuring current and voltage in a current carrying cable, the optical sensor assembly comprising: a base unit having a top end and a bottom end; an optical current sensor mounted in the top end of the base unit, the optical current sensor comprising a polarized light input, a reflective prism, and a light output operably connected to a light detector, the polarized light input being configured for transmitting a beam of polarized electromagnetic radiation into the reflective prism, and out the light output; at least one hook for hanging the base unit from the current carrying cable; a concentrator housing having a first end and a second end; a pivot of the second end of the concentrator housing pivotally attaching the concentrator housing with the top end of the base unit such that the concentrator housing is configured to move between an open position and a closed position so as to position a magnetic concentrator around the current carrying cable; a locking element for removably securing the first end of the concentrator housing to the base unit in the closed position; the magnetic concentrator having a first end and a second end that together define an airgap therebetween, the magnetic concentrator being mounted on the concentrator housing such that the magnetic concentrator fits around the current carrying cable when the base unit is hung from the current carrying cable by the at least one hook and when the concentrator housing is moved to the closed position, and further such that the reflective prism of the base unit is operably positioned in the airgap of the magnetic concentrator when the concentrator housing is in the closed position; wherein the optical sensor assembly is configured such that a plane of polarization of the beam of polarized electromagnetic radiation within the reflective prism is rotated by the magnetic field in the airgap, the rotation being proportional to the strength of the magnetic field in the airgap and measurable by the light detector for determining the current in the current carrying cable; and a voltage sensor operably positioned on the base unit for measuring the voltage of the current carrying cable. a base unit having a top end and a bottom end; an optical current sensor mounted in the top end of the base unit, the optical current sensor comprising a polarized light input, a reflective prism, and a light output operably connected to a light detector, the polarized light input being configured for transmitting a beam of polarized electromagnetic radiation into the reflective prism, and out the light output; at least one hook for hanging the base unit from the current carrying cable; a concentrator housing having a first end and a second end; a pivot of the second end of the concentrator housing pivotally attaching the concentrator housing with the top end of the base unit such that the concentrator housing is configured to move between an open position and a closed position so as to position a magnetic concentrator around the current carrying cable; a locking element for removably securing the first end of the concentrator housing to the base unit in the closed position; the magnetic concentrator having a first end and a second end that together define an airgap therebetween, the magnetic concentrator being mounted on the concentrator housing such that the magnetic concentrator fits around the current carrying cable when the base unit is hung from the current carrying cable by the at least one hook and when the concentrator housing is moved to the closed position, and further such that the reflective prism of the base unit is operably positioned in the airgap of the magnetic concentrator when the concentrator housing is in the closed position; wherein the optical sensor assembly is configured such that a plane of polarization of the beam of polarized electromagnetic radiation within the reflective prism is rotated by the magnetic field in the airgap, the rotation being proportional to the strength of the magnetic field in the airgap and measurable by the light detector for determining the current in the current carrying cable; and a voltage sensor operably positioned on the base unit for measuring the voltage of the current carrying cable.