Plug the Breaker Buddy in to two separate outlets and if the green light comes on you are on separate circuits. Helps avoid tripping breakers on dual cord machines or when using accessories like an (RX20) or separate electric heater. No light means on same breaker. Dimly lit means different breakers but same phase (does not always work) Fully lit means different breakers on different phases. Great for multi-corded carpet cleaning machine, carpet cleaning heaters, power wands, running large dehumidifiers. Compare to current or past OEM associations: 1623-2718 AX68 Square housing (photo to the right) AX49 Round housing (thumbnail image) Clean Storm 20131106 (Water resistant box below) 121273 SBMWAX-49 HYDR-PTS-AX68 The factory does not let you pick the size or shape or color of the housing, Latest design is to the right in a square housing. The function is the same. All sales final / returns not accepted on this part