A yard waste chipper-shredder machine includes a reversible electric motor to drive a roller at low speed and high torque. Following surgical sternotomy, a separator is implanted in the thorax between the facing sternum surfaces resulting from the surgical sternotomy. The first network detects termination of the call attempt. An outer protective sheath may be disposed about the endovascular graft while in a constrained state which must first be retracted or otherwise removed prior to release of the graft from a constrained state. The guard layer is biased so as to further inhibit current leakage during circuit operation.