Note on sheath losses in single-core single-phase cables

The conditions which govern the eddy currents in the lead sheaths of a pair of single-core cables undergo a change a s the sheaths are moved from the position of intimate contact. The consequent changes in e.m.f. and eddy losses have been the subject of considerable discussion. The following notes record an attempt to settle the matter experimentally by tests on a cable with a Drysdale potentiometer. The conclusions reached are that while the sheath circuit e.m.f. appears to be proportional to log d/r, the change in the losses as this ratio passes through the value 2 is rendered indeterminate by other variables which cannot be separately measured.