An optical waveguide sheet 50 is fastened to an inward facing access door 4 of the load center 2. When the door is closed, the optical waveguide sheet is positioned so that one portion is juxtaposed with the circuit breaker 10A in the load center, to enable the optical waveguide sheet to receive an optical signal 70A characterizing current in the circuit breaker. The optical waveguide sheet 50 is further positioned so that another portion is juxtaposed with an optical window 48 of an aggregator. The optical waveguide sheet is configured to internally reflect the optical signal 70A within its body and to conduct the internally reflected optical signal from the circuit breaker to the optical window of the aggregator. The aggregator may provide information characterizing current usage to an alarm, a measurement device, the smart grid, or a storage device for later use.